Arterial Spin Labelling

Radiographic Anatomy of Shoulder Joint

Radiographic Anatomy of Shoulder Joint:

Clavicle: The clavicle is a long bone having a shaft, and two ends. The shaft shows gentle S-shaped curve.

The lateral or acromial end of the clavicle bears a smooth facet which articulates with the acromion of the scapula to form the acromion-clavicular joint.

The medial or sternal end of the clavicle articulates with the manibrium sterni, and also with the first costal cartilage.

Conoid tubercle: This prominence lies near the acromial end of the clavicle.

Scapula: The greater part of the scapula consists of a flat triangular plate of bone called the body. The upper part of the body is broad, representing the base of the triangle. The inferior end is pointed and represents the apex. The body has anterior (or costal)) and posterior (or dorsal) surfaces.

Spine of Scapula: The upper part of the posterior surface gives off a large projection called the spine. The part of the posterior surface above the spine forms the supraspinous fossa, and the area below the spine forms the infraspinous fossa.

Humerus: It is a long bone. It has a cylindrical central part called the shaft, and enlarged upper and lower ends.

Humeral head: It is rounded and forms the shoulder joint along with the glenoid cavity of scapula.

Anatomic neck: The slightly constricted area directly below and lateral to the head is the anatomic neck which appears as a line of demarcation between the rounded head and the adjoining greater and lesser tubercles.

Lesser tubercle: It is the process or the prominence directly below the anatomic neck on the anterior surface.

Greater tubercle: The larger lateral process is the greater tubercle, to which the pectoralis major and supraspinatus muscles attach.

Intertubercular (bicipital) groove: It is the deep groove between these two tubercles (tuberosities).

Surgical neck: It is the tapered area below the head and tubercles, and distal to the surgical neck is the long body (shaft) of the humerus.

Deltoid tuberosity: It is the roughened raised triangular elevation along the anterolateral surface of the body (shaft) to which the deltoid muscle is attached.

Shoulder joint: This ball and socket joint is formed by the glenoid cavity of the scapula and the head of the humerus.

Glenoid cavity: It is a shallow, concave, oval fossa, directed anterolaterally and slightly superiorly- that is considerably smaller than the ball (head of the humerus) for which it serves as a socket.

Coracoid process: It is a beak-like process, superior to the glenoid cavity and projects anterolaterally.

Technical aspects of Chest Radiography:

Technical aspects of Chest Radiography:

Centring: 

If the film is well centred, the medial end of the clavicles are equidistant from the vertebral spinous processes at the T4/5 level. Small degrees of rotation distort the mediastinal borders, and the lung nearest the film appears less translucent. Thoracic deformities, especially a scoliosis negate the value of conventional centering. The orientation of the aortic arch, gastric bubble and heart should be determined to confirm normal situs and that the side markers are correct.

Suggested scheme for viewing the PA film:

1.       Request form : Name, age, date, sex, clinical information

2.       Technical : Adequate inspiration, centring, patient position/rotation, side markers, exposure/adequate penetration, collimation

3.       Trachea : Position, outline

4.       Heart and mediastinum : Size, shape, displacement

5.       Diaphragms : Outline, shape, relative position

6.       Pleural spaces : Position of horizontal fissure, costophrenic and cardiophrenic angles

7.       Lungs : Local, generalized abnormality, comparison of the translucency and vascular markings of the lungs

8.       Hidden areas : Apices, posterior sulcus, mediastinum, hila, bones

9.       Hila : Density, position, shape

10.   Below diaphragms: Gas shadoes, calcification

11.   Soft tissues : Mastectomy, gas, densities, etc.

12.   Bones : Destructive lesions etc.

Penetration:

With a low KV film the vertebral bodies and disc spaces should be just visible down to the T8/9 level through the cardiac shadow. Underpenetration increases the likelihood of missing an abnormality overlain by another structure. Overpenetration results in loss of visibility of a low density lesions such as early consolidation, although a bright light may reveal the abnormality.

Degree of inspiration: On full inspiration, the anterior ends of the diaphragm although the degree of inspiration achieved varies with patient build. On expiration the heart shadows is larger and there is basal opacity due to crowding of the normal vascular markings. Pulmonary diseases such as fibrosing alveolitis are associated with reduced pulmonary compliance, which may result in reduced inflation with elevation of the diaphragms.

The trachea:

The trachea should be examined for narrowing, displacement and intraluminal lesions. It is midline in its upper one part, then deviates slightly to the right around the aortic knuckle. On expiration, deviation to the right becomes marked. In addition there is shorerring on expiration so that an endotracheal tube situated just above the carina on inspiration may occlude the main bronchus on expiration.

Its caliber should be even, with translucency of the tracheal air column decreasing caudally. Normal maximum coronal diameter is 25 mm for males and 21 mm for females. The right tracheal margin where the trachea is in contact with the lung, can be traced from the clavicles down to the right main bronchus. This border is the right paratracheal stripe and is seen in 60% of patients, normally measuring less than 5 mm. widening of the stripe occurs most commonly with mediastinal lymphadenopathy but also with tracheal malignancy, mediastinal tumours, mediastinitis and pleural effusions. A left paratracheal line is not visualized because the left border of the trachea lies adjacent to the great vessels and not the lung.

The azygos vein lies in the angle between the right main bronchus and trachea. On the erect film it should be less than 10 mm in diameter. Its size decreases with the Valsalva manoeuvre and on inspiration. Enlargement occurs in the supine position but also with enlarged subcarinal nodes, pregnancy, portal hypertension, IVC, and SVC obstruction, right heart failure and constrictive pericarditis.

Widening of the carina occurs on inspiration. The normal angle is 60-75⁰. Pathological causes of widening include an enlarged left atrium and enlarged carinal nodes.

The mediastinum and heart:

The central dense shadow seen on the PA chest film comprises the mediastinum, heart, spine and sternum. With good centering, two thirds of the cardiac shadow lies to the left midline and one-third to the right, although this is quite variable in normal subjects. The transverse cardiac diameter (normal for females less than 14.5 cm and for males less than 15.5 cm) and the cardiothoracic ratio are assessed. The normal cardiothoracic ratio is less than 50% on a PA film. Measurement in isolation is of less value than when previous figures are available. An increase in excess of 1.5 cm in the transverse diameter on comparable serial films is significant. However, the heart shadow is enlarged with a short FFD, on expiration, in the supine and AP projections and when the diaphragms are elevated. The normal AP value is less than 60%.

All borders of the heart and mediastinum are clearly defined except where the heart sits on the left hemidiaphragm. The right superior mediastinal shadow is formed by the SVC and innominate vessels, a dilated aorta may contribute to this border. On the left side the superior mediastinal border is less sharp. It is formed by the subclavian artery above the aortic knuckle.

Various junction lines may be visualized. These are formed by the pleura being outlined by the adjacent air-filled lung. The anterior junction line is formed by the lungs meeting anterior to the ascending aorta. It is only 1 mm thick and overlying the tracheal transluceny, runs downward from below the suprasternal notch, slightly curving from right to left. The posterior junction line, where the lungs meet posteriorly behind the oesophagus, is a straight or curved line convex to the left some 2 mm wide and extending from the lung apices to the aortic knuckle or below. The azygo-oesophageal interface is the shape of an inverted hockey stick and runs from the diaphragm on the left midline up and to the right extending to the tracheobronchial angle where the aygos vein drains into the IVC. The curved pleuro-oesophageal stripe, formed by the lung and right wall of the oesophagus, extends from the lung apex to the azygos but is only visualized if the oesophagus contains air. The left wall of the oesophagus is not normally seen.

In young women, the pulmonary trunk is frequently very prominent.

In babies and young children, the normal thymus is a triangular sail-shaped structure with well-defined borders projecting from one or both sides of the mediastinum. Both borders may be wavy in outline, the ‘wave sign of Mulvey’, as a consequence of indentation by the costal cartilages. The right border is straighter than the left, which may be rounded. Thymic size decreases on inspiration and in response to stress and illness. The thymus is absent in DiGeorge’s syndrome. Enlargement may occur following recovery from an illness. A large thymus is more commonly seen in boys.

Adjacent to the vertebral bodies run the paraspinal lines. On the left this is normally less than 10 mm wide; on the right less than 3 mm. The left paraspinal line is wider due to the descending thoracic aorta. Enlargement  occurs with osteophytes, a tortuous aorta, vertebral, and adjacent soft-tissue masses, a paravertebral haematoma, and a dilated azygous system.

A search should be made for abnormal densities, fluid levels, mediastinal emphysema and calcification. Spinal abnormalities may accompany mediastinal masses; for example, hemivertebrae are associated with neuroenteric cysts.

The diaphragm:

In most patients the right hemidiaphragm is higher than the left. This is due to the heart depressing the left side and not to the liver pushing up the right hemidiaphragm: in dextrocardia with normal abdominal situs the right hemidiaphragm is the lowest. The hemidiaphragms may lie at the same level, and in a small percentage of the population the left side is the higher: Felson (1973) reports an incidence of 3%. This is more likely to occur if the stomach or splenic flexure is distended with gas. A difference greater than 3 cm in height is considered significant.

On inspiration the domes of the diaphragms are at the level of the sixth rib anteriorly and at or below the tenth rib posteriorly. In the supine position, the diaphragm is higher. Both domes have gently curbes which steepen toward the posterior angles. The upper borders are clearly seen except on the left side where the heart is in contact with the diaphragm, and in the cardiophrenic angles when there are prominent fat pads. Otherwise loss of outline indicates that the adjacent tissue does not contain air, for example in consolidation or pleural disease.

Free intraperitoneal gas outlines the undersurface of the diaphragm and shows it to be normally 2-3 mm thick.

The fissures: 

The main fissures: 

These fissures separate the lobes of the lung but are usually incomplete allowing collateral air drift to occur between adjacent lobes. They are visualized when the x-ray beam is tangential. The horizontal fissure is seen, often incompletely on the PA film running from the hilum to the region of the sixth rib in the axillary line, and may be straight or have a slight downward curve. Occasionally it has a double appearance.

All fissures are clearly seen on the lateral film. The horizontal fissure runs anteriorly and often slightly downward. Both oblique fissures commence posteriorly at the level of T4 or T5, passing through the hilum. The left is steeper and finishes 5 cm behind the anterior costophrenic  angle, whereas the right ends just behind the angle.

Accessory fissures:

The azygos fissure is comma shaped with a triangular base peripherally and is nearly always right sided. It forms in the apex of the lung and consists of paired folds of parietal and visceral pleura plus the azygos vein which has failed to migrate normally. Enlargement occurs in the supine position. At postmortem the incidence is 1% but radiologically it is 0.4%.When left sided, the fissure contains an accessory hemi-azygos vein.

The superior accessory fissure separates the apical from the basal segments of the lower lobes. It is commoner on the right side and has an incidence of 5% at postmortem. On the PA film it resembles the horizontal fissure but on the lateral film it can be differentiated as it runs posteriorly from the hilum.

The inferior accessory fissure appears as an oblique line running cranially from the cardiophrenic angle toward the hilum and separating the medial basal from the other basal segments. It is commoner on the right side and has an incidence of 5-8% on the chest film.

The left sided horizontal fissure separates the lingual from the other upper lobe segments. This is rare but in one study was found in 8% of postmortem specimens.

The costophrenic angles:

The normal costophrenic  angles are acute and well-defined but become obliterated when the diaphragms are flat. Frequently the cardiophrenic angles contain low-density ill-defined opacity caused by fat pads.

The lungs:

By comparing the lungs, areas of abnormal translucency or uneven distribution of lung markings are more easily detected. The size of the upper and lower zone vessels is assessed.

An abnormal opacity should be closely studied to ensure that it is not a composite opacity formed by superimposed normal structures such as vessels, bones or costal cartilage. The extent and location of the opacity is determined and specific features such as calcification or cavitation noted. A general survey is made to look for further. A general survey is made to look for further lesions and displacement of the normal landmarks.

The hidden areas:

The apices:

On the PA film the apices arc partially obscured by ribs, costal cartilage, clavicles and soft tissues. Visualization is very limited on the lateral view.

Mediastinum and hila:

Central lesions may be obscured by these structures or appear as a superimposed density. The abnormality is usually detectable on the lateral film.

Diaphragms:

The posterior and lateral basal segments of the lower lobes and the posterior sulcus are partially obscured by the downward curve of the posterior diaphragm. Visualization is further diminished if the film is not taken on full inspiration.

Bones:

Costal cartilage or bone may obscure a lung lesion. In addition, determining whether a density is pulmonary or bony when overlying a rib may be difficult; AP, expiratory and oblique films may be helpful and preclude the need to proceed to CT.

The hila:

In 97% of subjects the left hilum is higher than the right and in 3% they are at the same level. The hila should be of equal density and similar size with clearly defined concave lateral borders where the superior pulmonary vein meets the basal pulmonary artery.  However, there is a wide range of normal appearances. Any opacity which is not obviously vascular must be regarded with a high index of suspicion and investigated further. Old films for comparison are helpful in this situation.

Of all the structures in the hilum only the pulmonary arteries and upper lobe veins contribute significantly to the hilar shadows on the plain radiograph. Normal lymph nodes are not seen. Air can be identified within the proximal bronchi but normal bronchial wall are only seen end on. The anterior segment bronchus of the upper lobe is seen as a ring adjacent to the upper hilum and is seen on the right side in 45% of cases and the left side in 50%. Normally, there is less than 5 mm of soft tissue lateral to this bronchus. Thickening of the soft tissues suggests the presence of abnormal malignancy such as malignancy.

The inferior pulmonary ligament:

This is a double layer of pleura extending caudally from the lower margin of the inferior pulmonary vein in the hilum as a sheet which may or may not be attached to the diaphragm and which attaches the lower lobe to the mediastinum. It is rarely identified on a simple radiograph but is frequently seen at CT.

The pulmonary vessels:

The left pulmonary artery lies above the left main bronchus before passing posteriorly, whereas on the right side the artery is anterior to the bronchus resulting in the right hilum being the lower. Hilar size is very variable. The maximum diameter of the descending branch of the pulmonary artery measured 1 cm medial and 1 cm lateral to the hilar point is 16 mm for males and 15 mm for females.

The upper lobe veins lies lateral to the arteries, which are separated from the mediastinum by approximately 1 cm of lung tissue. At the first intercostal space the normal vessels should not exceed 3 mm in diameter. The lower lobe vessles are larger than those of the upper lobes in the erect position, perfusion and aeration of the upper zones being reduced. In the supine position, the vessels equalize. In the right paracardiac region, the vessels are invariably prominent.

The peripheral lung markings are mainly vascular, veins and arteries having no distinguishing characteristics. There should be an even distribution throughout the lung fields.

Centrally the arteries and veins have different features. The arteries accompany the bronchi, lying posterosuperior, whereas veins do not follow the bronchi but drain via the interlobular septa eventually forming superior and basal veins which converge on the left atrium.

This confluence of veins may be seen as a rounded structure to the right of midline superimposed on the heart, sometimes, simulating an enlarged left atrium. It is visible in 5% of PA films according to Felson. Pulmonary veins have fewer branches than arteries and are straighter, larger and less well-defined.

The bronchial vessels:

These are normally not visualized on the plain chest film. They arise from the ventral surface of the descending aorta at the T5/6 level. Their anatomy is variable. Usually there are two branches on the left and one on the right which often shares a common origin with an intercostal artery. On entering the hila the bronchial arteries accompany the bronchi. The veins drain into the pulmonary veins and to a lesser extent the azygos system.

Enlarged bronchial arteries appear as multiple small nodules around the hilum and as short lines in the proximal lung fields. Enlargement may occur with cyanotic heart disease, and focal enlargement with a local pulmonary lesion. Occasionally enlarged arteries indent the oesophagus.

Causes of enlarged bronchial arteries:

a.       General-cyanotic congenital heart disease, e.g. pulmonary atresia, severe Fallot’s tetralogy

b.      Local bronchiectasis, bronchial carcinoma

The pulmonary segments and bronchi:

The pulmonary segments are served by segmental bronchi and arteries but unlike the lobes are not separated by pleura. Normal bronchi are not visualized in the peripheral lung fields.

The right main bronchus is shorter, steeper and wider than the left, bifurcating earlier. The upper lobe bronchus arises 2.5 cm below the carina and is higher than the left upper lobe bronchus which arises after 5 cm. The bronchi divide between six and 20 times before becoming bronchioles with the terminal bronchioles measuring  0.2 mm in diameter. Each receives two to three respiratory bronchioles which connect with between two and 11 alveolar ducts. Each duct receives between 2 to 6 alveolar sacs which are connected to alveoli. The acinus, generally considered to be the functioning lung unit, is that portion of the lung arising from the terminal bronchiole. When filled with fluid,  it is seen on a radiograph as a 5-6 mm shadow, and this comprises the basic unit seen in acinar (alveolar/air space) shadowing.

The primary lobule arises from the last respiratory bronchiole. The secondary lobule is between 1.0 and 2.5 cm in size and is the smallest discrete unit of lung tissue surrounded by connective tissue septa. When thickened these septa become Kerley B lines.

Other connections exist between the air spaces allowing collateral air drift. These are the pores of kohn, 3-13 µm in size, which connect the alveoli, and the canals of Lambery (30 µm) which exist between bronchioles and alveoli.

The lymphatic system:

The lymphatics remove interstitial fluid and foreign particles. They run in the interlobular septa, connecting with subpleural lymphatics and draining via the deep lymphatics to the hilum, with valves controlling the direction of flow. Normal lymphatics are not seen but thickening of the lymphatics and surrounding connective tissue produces Kerley lines, which may be transient or persistent. Thickened connective tissues are the main contributors to the substance of these lines.

The lymph nodes:

The intrapulmonary lymphatics drain directly to the bronchopulmonary nodes and this group is the first to be involved by spread from a tumour. A small number of intrapulmonary nodes are present and can occasionally be seen at CT but never on the plain film. The node groups and their drainage are well described. Extensive intercommunications exist between the groups but the pattern of nodal involvement can sometimes indicate the site of the primary tumour. Mediastinal nodes may be involved by tumours both above and below the diaphragm.

1.       The anterior mediastinal nodes in the region of the aortic arch drain the thymus and right heart.

2.       The intrapulmonary nodes lie along the main bronchi.

3.       The middle mediastinal nodes drain the lungs, bronchi, left heart, the lower trachea and visceral pleura. There are four groups:

a.       Bronchopulmonary (hilar) nodes which enlarged appear as lobulated hilar masses.

b.      Carinal nodes

c.       Tracheobronchial nodes which lie adjacent to the azygos vein on the right side and near the recurrent laryngeal nerve on the left side.

d.      Paratracheal nodes are more numerous on the right side. There is significant cross drainage from left to right.

4.       The posterior mediastinal nodes drain the posterior diaphragm and lower oesophagus. They lie around the lower descending aorta and oesophagus

5.       The parietal nodes consist of anterior and posterior groups situated behind the sternum and posteriorly in the intercostal region draining the soft tissues and parietal pleura.

Below the diaphragm:

The lower lobes extend below the diaphragmatic outlines on the PA film. An erect chest film is preferred to an erect abdominal film for the diagnosis of a pneumoperitoneum. A search should be made for other abnormal gas shadows such as dilated bowel, abscesses, a displaced gastric bubble and intramural gas as well as calcified lesions. Interposition of colon between live and diaphragm Chilaiditi’s syndrome is a common and often transient finding particularly in the aged, the obvious haustral pattern distinguishing it from free gas. Subdiaphramatic fat in the obese may be confused with free gas on a single film.

Soft tissues:

A general survey of the soft tissues includes the chest wall, shoulders, and lower neck. It is important to confirm the presence or absence of breast shadows. The breat may partially obscure the lung bases. Nipple shadows are variable in position, often asymmetrical, and frequently only one shadow is seen. Care is necessary to avoid misinterpretation as a neoplasm or vice-versa. Nipple shadows are often well-defined laterally and may have a lucent halo. Repeat films with nipple markers are necessary if there is any doubt. Skin folds are often seen running vertically, particularly in the old and in babies. When overlying the lungs they can be confused with a pneumothorax. However, a skin fold if followed usually extends outside the lung field. The anterior axillary fold is a curving linear shadow extending from the axilla onto the lung fields and frequently causing ill-defined shadowing which must be differentiated from consolidation.

At the apices the opacity of the sternocleidomastoid muscles curving down and slightly outward may simuate a cavity or bulla. The floor of the supraclavicular fossa often resembles a fluid level. A deep sternoclavicular fossa, commonly present in the elderly, appears as a translucency overlying the trachea and simulating a gas-filled diverticulum.

Subpleural thickening seen peripherally is often due to subpleural fat or prominent intercostal muscles rather than to pleural pathology.

Companion shadows are formed by the soft tissues adjacent to bony structures, are 2-3 mm thick, and are frequently seen running parallel to the upper borders of the clavicles and the inferior borders of the lower ribs.

 

Apical pleural thickening, “the apical cap” has a reported incidence of 7% and occurs most commonly on the left side.

The bones:

All the bones should be surveyed. On occasions identification of an abnormality in association with pulmonary pathology may help to narrow the differential diagnosis. Sometimes a normal bony structure appears to be a lung lesion and further films such as oblique, lateral, inspiratory and expiratory or CT may be necessary.

The sternum:

The ossification centers are very variable in number, shape, position and growth rate. Usually there are single centers in the manubrium and xiphoid with three or four centers in the body. Parasternal ossicles and in infants, the ossification centers may be confused with lung masses.

The clavicles:

The rhomboid fossa is an irregular notch at the site of attachment of the costoclavicular ligament. It lies up to 3 cm from the medial end of the clavicle inferiorly and has a well-corticated margin. It is unilateral in 6% of cases and should not be mistaken for a destructive lesion. Superior companion shadows are a usual finding. The medial epiphyses fuse at 25 years and on occasions may appear as lung nodules.

The scapulae:

On the lateral film, the inferior angle overlies the lungs and can simulate a lung mass. The spine of the scapula on the PA film casts a linear shadow which at first glance may seem to be pleural.

The ribs:

Companion shadows are common on the upper ribs. Pathological rib notching as seen with aortic coarctation should not be confused with the normal notch on the inferior surface just lateral to the tubercle. The contours of the ribs are evaluated for destruction. However, the inferior borders of the middle and lower ribs are usually indistinct.

The first costal cartilage calcifies early and is often very dense, partly obscuring the upper zone. Costal cartilage calcification is rare before the age of 20. Central homogeneous or spotty calcification occurs in females whereas there is curvilinear marginal calcification in males. On the lateral film, the anterior end of the rib with its cartilage lying behind the sternum should not be confused with a mass.

The spine:

Routine evaluation is made for bone and disc destruction and spinal deformity. A scoliosis often results in apparent mediastinal widening and oblique films may be necessary to fully visualize both lung fields. The ends of the transverse processes on the PA film may look like a lung nodule.

In the neonate the vertebral bodies have a sandwich appearance due to large venous sinuses. Residual grooves may persist in the adult.

Viewing the lateral film:

Routinely the left side is adjacent to the film because more of the left lung than the right is obscured on the PA view, but if there is a specific lesion the side of interest is positioned adjacent to the film. A routine similar to that used for the PA film should be employed.

The clear spaces:

There are two clear spaces; these correspond to the sites where the lungs meet behind the sternum and the heart. Loss of translucency  of these areas indicate local pathology. Obliteration of the retrosternal space occurs with anteriormediastinal masses such as a thymomas, aneurysms of the ascending aorta and nodal masses. Normally this space is less than 3 cm deep maximum, widening occurs with emphysema.

Vertebral translucency:

The vertebral bodies become progressively more translucent caudally. Loss of this translucency may be the only sign of posterior basal consolidation.

Diaphragm outline:

Both diaphragms are visible through out their length except the left anteriorly where it merges with the heart. A small segment of the right hemidiaphragm is effaced by the IVC. The posterior costophrenic angles are acute and small amounts of pleural fluid may be detected by blunting of these angles.

The fissures:

The left greater fissure is steeper than the right and terminates 5 cm behind the anterior cardiophrenic angle. Loculated interlobar effusions are well shown and displacement or thickening of the fissures should be noted.

The trachea:

This passes down in a slightly posterior direction to the T6/7 level of the spine. It is partly overlapped by the scapulae and axillary folds. Anterior to the carina lies the right pulmonary artery. The left pulmonary artery is posterior and superior, and the veins are inferior. The venous confluence creates a bulge on the posterior cardiac border.

The normal posterior tracheal wall is invariably visible and measures less than 5 mm. this measurement includes both tracheal and oesophageal walls plus the pleura. Widening may occur with disease of all these structures. A branch of the aorta seen end-on may appear as a nodule overlying the trachea and above the aortic arch. The right upper lobe bronchus is seen end-on as a circular structure overlying the lower trachea. Lying inferiorly is the left upper lobe bronchus seen end-on with its artery superiorly and vein inferiorly.

Opacity seen in the region of the anterior cardiophrenic angle is thought to be due to mediastinalcut and the interface between the two lungs.

The sternum:

This should be studied carefully in known cases of malignancy or when there is a history of trauma.

Technical Aspects of Chest Radiography

Technical aspects of Chest Radiography:

Centring: 

If the film is well centred, the medial end of the clavicles are equidistant from the vertebral spinous processes at the T4/5 level. Small degrees of rotation distort the mediastinal borders, and the lung nearest the film appears less translucent. Thoracic deformities, especially a scoliosis negate the value of conventional centering. The orientation of the aortic arch, gastric bubble and heart should be determined to confirm normal situs and that the side markers are correct.

Suggested scheme for viewing the PA film:

1.       Request form : Name, age, date, sex, clinical information

2.       Technical : Adequate inspiration, centring, patient position/rotation, side markers, exposure/adequate penetration, collimation

3.       Trachea : Position, outline

4.       Heart and mediastinum : Size, shape, displacement

5.       Diaphragms : Outline, shape, relative position

6.       Pleural spaces : Position of horizontal fissure, costophrenic and cardiophrenic angles

7.       Lungs : Local, generalized abnormality, comparison of the translucency and vascular markings of the lungs

8.       Hidden areas : Apices, posterior sulcus, mediastinum, hila, bones

9.       Hila : Density, position, shape

10.   Below diaphragms: Gas shadoes, calcification

11.   Soft tissues : Mastectomy, gas, densities, etc.

12.   Bones : Destructive lesions etc.

Penetration:

With a low KV film the vertebral bodies and disc spaces should be just visible down to the T8/9 level through the cardiac shadow. Underpenetration increases the likelihood of missing an abnormality overlain by another structure. Overpenetration results in loss of visibility of a low density lesions such as early consolidation, although a bright light may reveal the abnormality.

Degree of inspiration: On full inspiration, the anterior ends of the diaphragm although the degree of inspiration achieved varies with patient build. On expiration the heart shadows is larger and there is basal opacity due to crowding of the normal vascular markings. Pulmonary diseases such as fibrosing alveolitis are associated with reduced pulmonary compliance, which may result in reduced inflation with elevation of the diaphragms.

The trachea:

The trachea should be examined for narrowing, displacement and intraluminal lesions. It is midline in its upper one part, then deviates slightly to the right around the aortic knuckle. On expiration, deviation to the right becomes marked. In addition there is shorerring on expiration so that an endotracheal tube situated just above the carina on inspiration may occlude the main bronchus on expiration.

Its caliber should be even, with translucency of the tracheal air column decreasing caudally. Normal maximum coronal diameter is 25 mm for males and 21 mm for females. The right tracheal margin where the trachea is in contact with the lung, can be traced from the clavicles down to the right main bronchus. This border is the right paratracheal stripe and is seen in 60% of patients, normally measuring less than 5 mm. widening of the stripe occurs most commonly with mediastinal lymphadenopathy but also with tracheal malignancy, mediastinal tumours, mediastinitis and pleural effusions. A left paratracheal line is not visualized because the left border of the trachea lies adjacent to the great vessels and not the lung.

The azygos vein lies in the angle between the right main bronchus and trachea. On the erect film it should be less than 10 mm in diameter. Its size decreases with the Valsalva manoeuvre and on inspiration. Enlargement occurs in the supine position but also with enlarged subcarinal nodes, pregnancy, portal hypertension, IVC, and SVC obstruction, right heart failure and constrictive pericarditis.

Widening of the carina occurs on inspiration. The normal angle is 60-75⁰. Pathological causes of widening include an enlarged left atrium and enlarged carinal nodes.

The mediastinum and heart:

The central dense shadow seen on the PA chest film comprises the mediastinum, heart, spine and sternum. With good centering, two thirds of the cardiac shadow lies to the left midline and one-third to the right, although this is quite variable in normal subjects. The transverse cardiac diameter (normal for females less than 14.5 cm and for males less than 15.5 cm) and the cardiothoracic ratio are assessed. The normal cardiothoracic ratio is less than 50% on a PA film. Measurement in isolation is of less value than when previous figures are available. An increase in excess of 1.5 cm in the transverse diameter on comparable serial films is significant. However, the heart shadow is enlarged with a short FFD, on expiration, in the supine and AP projections and when the diaphragms are elevated. The normal AP value is less than 60%.

All borders of the heart and mediastinum are clearly defined except where the heart sits on the left hemidiaphragm. The right superior mediastinal shadow is formed by the SVC and innominate vessels, a dilated aorta may contribute to this border. On the left side the superior mediastinal border is less sharp. It is formed by the subclavian artery above the aortic knuckle.

Various junction lines may be visualized. These are formed by the pleura being outlined by the adjacent air-filled lung. The anterior junction line is formed by the lungs meeting anterior to the ascending aorta. It is only 1 mm thick and overlying the tracheal transluceny, runs downward from below the suprasternal notch, slightly curving from right to left. The posterior junction line, where the lungs meet posteriorly behind the oesophagus, is a straight or curved line convex to the left some 2 mm wide and extending from the lung apices to the aortic knuckle or below. The azygo-oesophageal interface is the shape of an inverted hockey stick and runs from the diaphragm on the left midline up and to the right extending to the tracheobronchial angle where the aygos vein drains into the IVC. The curved pleuro-oesophageal stripe, formed by the lung and right wall of the oesophagus, extends from the lung apex to the azygos but is only visualized if the oesophagus contains air. The left wall of the oesophagus is not normally seen.

In young women, the pulmonary trunk is frequently very prominent.

In babies and young children, the normal thymus is a triangular sail-shaped structure with well-defined borders projecting from one or both sides of the mediastinum. Both borders may be wavy in outline, the ‘wave sign of Mulvey’, as a consequence of indentation by the costal cartilages. The right border is straighter than the left, which may be rounded. Thymic size decreases on inspiration and in response to stress and illness. The thymus is absent in DiGeorge’s syndrome. Enlargement may occur following recovery from an illness. A large thymus is more commonly seen in boys.

Adjacent to the vertebral bodies run the paraspinal lines. On the left this is normally less than 10 mm wide; on the right less than 3 mm. The left paraspinal line is wider due to the descending thoracic aorta. Enlargement  occurs with osteophytes, a tortuous aorta, vertebral, and adjacent soft-tissue masses, a paravertebral haematoma, and a dilated azygous system.

A search should be made for abnormal densities, fluid levels, mediastinal emphysema and calcification. Spinal abnormalities may accompany mediastinal masses; for example, hemivertebrae are associated with neuroenteric cysts.

The diaphragm:

In most patients the right hemidiaphragm is higher than the left. This is due to the heart depressing the left side and not to the liver pushing up the right hemidiaphragm: in dextrocardia with normal abdominal situs the right hemidiaphragm is the lowest. The hemidiaphragms may lie at the same level, and in a small percentage of the population the left side is the higher: Felson (1973) reports an incidence of 3%. This is more likely to occur if the stomach or splenic flexure is distended with gas. A difference greater than 3 cm in height is considered significant.

On inspiration the domes of the diaphragms are at the level of the sixth rib anteriorly and at or below the tenth rib posteriorly. In the supine position, the diaphragm is higher. Both domes have gently curbes which steepen toward the posterior angles. The upper borders are clearly seen except on the left side where the heart is in contact with the diaphragm, and in the cardiophrenic angles when there are prominent fat pads. Otherwise loss of outline indicates that the adjacent tissue does not contain air, for example in consolidation or pleural disease.

Free intraperitoneal gas outlines the undersurface of the diaphragm and shows it to be normally 2-3 mm thick.

The fissures: 

The main fissures: 

These fissures separate the lobes of the lung but are usually incomplete allowing collateral air drift to occur between adjacent lobes. They are visualized when the x-ray beam is tangential. The horizontal fissure is seen, often incompletely on the PA film running from the hilum to the region of the sixth rib in the axillary line, and may be straight or have a slight downward curve. Occasionally it has a double appearance.

All fissures are clearly seen on the lateral film. The horizontal fissure runs anteriorly and often slightly downward. Both oblique fissures commence posteriorly at the level of T4 or T5, passing through the hilum. The left is steeper and finishes 5 cm behind the anterior costophrenic  angle, whereas the right ends just behind the angle.

Accessory fissures:

The azygos fissure is comma shaped with a triangular base peripherally and is nearly always right sided. It forms in the apex of the lung and consists of paired folds of parietal and visceral pleura plus the azygos vein which has failed to migrate normally. Enlargement occurs in the supine position. At postmortem the incidence is 1% but radiologically it is 0.4%.When left sided, the fissure contains an accessory hemi-azygos vein.

The superior accessory fissure separates the apical from the basal segments of the lower lobes. It is commoner on the right side and has an incidence of 5% at postmortem. On the PA film it resembles the horizontal fissure but on the lateral film it can be differentiated as it runs posteriorly from the hilum.

The inferior accessory fissure appears as an oblique line running cranially from the cardiophrenic angle toward the hilum and separating the medial basal from the other basal segments. It is commoner on the right side and has an incidence of 5-8% on the chest film.

The left sided horizontal fissure separates the lingual from the other upper lobe segments. This is rare but in one study was found in 8% of postmortem specimens.

The costophrenic angles:

The normal costophrenic  angles are acute and well-defined but become obliterated when the diaphragms are flat. Frequently the cardiophrenic angles contain low-density ill-defined opacity caused by fat pads.

The lungs:

By comparing the lungs, areas of abnormal translucency or uneven distribution of lung markings are more easily detected. The size of the upper and lower zone vessels is assessed.

An abnormal opacity should be closely studied to ensure that it is not a composite opacity formed by superimposed normal structures such as vessels, bones or costal cartilage. The extent and location of the opacity is determined and specific features such as calcification or cavitation noted. A general survey is made to look for further. A general survey is made to look for further lesions and displacement of the normal landmarks.

The hidden areas:

The apices:

On the PA film the apices arc partially obscured by ribs, costal cartilage, clavicles and soft tissues. Visualization is very limited on the lateral view.

Mediastinum and hila:

Central lesions may be obscured by these structures or appear as a superimposed density. The abnormality is usually detectable on the lateral film.

Diaphragms:

The posterior and lateral basal segments of the lower lobes and the posterior sulcus are partially obscured by the downward curve of the posterior diaphragm. Visualization is further diminished if the film is not taken on full inspiration.

Bones:

Costal cartilage or bone may obscure a lung lesion. In addition, determining whether a density is pulmonary or bony when overlying a rib may be difficult; AP, expiratory and oblique films may be helpful and preclude the need to proceed to CT.

The hila:

In 97% of subjects the left hilum is higher than the right and in 3% they are at the same level. The hila should be of equal density and similar size with clearly defined concave lateral borders where the superior pulmonary vein meets the basal pulmonary artery.  However, there is a wide range of normal appearances. Any opacity which is not obviously vascular must be regarded with a high index of suspicion and investigated further. Old films for comparison are helpful in this situation.

Of all the structures in the hilum only the pulmonary arteries and upper lobe veins contribute significantly to the hilar shadows on the plain radiograph. Normal lymph nodes are not seen. Air can be identified within the proximal bronchi but normal bronchial wall are only seen end on. The anterior segment bronchus of the upper lobe is seen as a ring adjacent to the upper hilum and is seen on the right side in 45% of cases and the left side in 50%. Normally, there is less than 5 mm of soft tissue lateral to this bronchus. Thickening of the soft tissues suggests the presence of abnormal malignancy such as malignancy.

The inferior pulmonary ligament:

This is a double layer of pleura extending caudally from the lower margin of the inferior pulmonary vein in the hilum as a sheet which may or may not be attached to the diaphragm and which attaches the lower lobe to the mediastinum. It is rarely identified on a simple radiograph but is frequently seen at CT.

The pulmonary vessels:

The left pulmonary artery lies above the left main bronchus before passing posteriorly, whereas on the right side the artery is anterior to the bronchus resulting in the right hilum being the lower. Hilar size is very variable. The maximum diameter of the descending branch of the pulmonary artery measured 1 cm medial and 1 cm lateral to the hilar point is 16 mm for males and 15 mm for females.

The upper lobe veins lies lateral to the arteries, which are separated from the mediastinum by approximately 1 cm of lung tissue. At the first intercostal space the normal vessels should not exceed 3 mm in diameter. The lower lobe vessles are larger than those of the upper lobes in the erect position, perfusion and aeration of the upper zones being reduced. In the supine position, the vessels equalize. In the right paracardiac region, the vessels are invariably prominent.

The peripheral lung markings are mainly vascular, veins and arteries having no distinguishing characteristics. There should be an even distribution throughout the lung fields.

Centrally the arteries and veins have different features. The arteries accompany the bronchi, lying posterosuperior, whereas veins do not follow the bronchi but drain via the interlobular septa eventually forming superior and basal veins which converge on the left atrium.

This confluence of veins may be seen as a rounded structure to the right of midline superimposed on the heart, sometimes, simulating an enlarged left atrium. It is visible in 5% of PA films according to Felson. Pulmonary veins have fewer branches than arteries and are straighter, larger and less well-defined.

The bronchial vessels:

These are normally not visualized on the plain chest film. They arise from the ventral surface of the descending aorta at the T5/6 level. Their anatomy is variable. Usually there are two branches on the left and one on the right which often shares a common origin with an intercostal artery. On entering the hila the bronchial arteries accompany the bronchi. The veins drain into the pulmonary veins and to a lesser extent the azygos system.

Enlarged bronchial arteries appear as multiple small nodules around the hilum and as short lines in the proximal lung fields. Enlargement may occur with cyanotic heart disease, and focal enlargement with a local pulmonary lesion. Occasionally enlarged arteries indent the oesophagus.

Causes of enlarged bronchial arteries:

a.       General-cyanotic congenital heart disease, e.g. pulmonary atresia, severe Fallot’s tetralogy

b.      Local bronchiectasis, bronchial carcinoma

Radiographic Anatomy of Shoulder Joint

Radiographic Anatomy of Shoulder Joint:

Fig: Shoulder AP and Axial views

Clavicle: The clavicle is a long bone having a shaft, and two ends. The shaft shows gentle S-shaped curve.

The lateral or acromial end of the clavicle bears a smooth facet which articulates with the acromion of the scapula to form the acromion-clavicular joint.

The medial or sternal end of the clavicle articulates with the manibrium sterni, and also with the first costal cartilage.

Conoid tubercle: This prominence lies near the acromial end of the clavicle.

Scapula: The greater part of the scapula consists of a flat triangular plate of bone called the body. The upper part of the body is broad, representing the base of the triangle. The inferior end is pointed and represents the apex. The body has anterior (or costal)) and posterior (or dorsal) surfaces.

Spine of Scapula: The upper part of the posterior surface gives off a large projection called the spine. The part of the posterior surface above the spine forms the supraspinous fossa, and the area below the spine forms the infraspinous fossa.

Humerus: It is a long bone. It has a cylindrical central part called the shaft, and enlarged upper and lower ends.

Humeral head: It is rounded and forms the shoulder joint along with the glenoid cavity of scapula.

Anatomic neck: The slightly constricted area directly below and lateral to the head is the anatomic neck which appears as a line of demarcation between the rounded head and the adjoining greater and lesser tubercles.

Lesser tubercle: It is the process or the prominence directly below the anatomic neck on the anterior surface.

Greater tubercle: The larger lateral process is the greater tubercle, to which the pectoralis major and supraspinatus muscles attach.

Intertubercular (bicipital) groove: It is the deep groove between these two tubercles (tuberosities).

Surgical neck: It is the tapered area below the head and tubercles, and distal to the surgical neck is the long body (shaft) of the humerus.

Deltoid tuberosity: It is the roughened raised triangular elevation along the anterolateral surface of the body (shaft) to which the deltoid muscle is attached.

Shoulder joint: This ball and socket joint is formed by the glenoid cavity of the scapula and the head of the humerus.

Glenoid cavity: It is a shallow, concave, oval fossa, directed anterolaterally and slightly superiorly- that is considerably smaller than the ball (head of the humerus) for which it serves as a socket.

Coracoid process: It is a beak-like process, superior to the glenoid cavity and projects anterolaterally.

 

 

Radiographic Anatomy of Elbow

Radiographic Anatomy of Elbow:

Elbow Joint: It is also a freely movable or diarthrodial synovial joint. It is generally considered a ginglymus (hinge) type of joint. In addition to the hinge joints between the humerus and ulna and the humerus and radius, the proximal radioulnar joint (trochoidal or pivot-joint) also is considered part of the elbow joint.

Radial head: The head of radius participates in two joints, the elbow and the superior radio-ulnar joint.

Lower end of humerus: It presents lateral epicondyle, capitulum, trochlea, and the medial epicondyle from lateral to medial side.

Fat pads: Three fat pads are present: in the radial fossa, in the coronoid fossa and in the olecranon fossa.

Upper end of ulna: It presents two processes: the olecranon and the coronoid processes. The olecranon and the coronoid processes having concavity presenting anteriorly. Articular surface of the coronoid process is like a seat of the chair while the articular surface of the olecranon is like the back rest of the chair.

Upper end of radius: It presents radial head having an articular facet on the top which articulates with the capitulum.

Capitulum: It articulates with the head of radius and the trochlea with the trochlear notch of the ulna. Above the capitulum, lies the radial fossa and the trochlear fossa is above the coronoid. The posterior aspect of the lower end of humerus presents the olecranon fossa. The head of radius presents a shallow articular depression for capitulum. The trochlear notch is formed by coronoid and olecranon processes.

Humerus: It is the long bone of the arm having the shaft, upper and the lower ends. It takes part in the formation of shoulder joint at the upper end and the elbow joint at the lower end.

Upper end of humerus: It consists of hemi-spherical head, covered with the articular cartilage, greater tubercle and the lesser tubercle. Head of humerus is directed backwards, upwards and medially. The head articulates with the glenoid cavity of the scapula and forms the shoulder joint. Area beyond the articular surface of the head is known as anatomical neck.

Lesser tubercle: It is situated in front of the upper end and forms the medial limit of the groove known as intertubercular groove or sulcus. This gives insertion to the subscapularis muscle.

Greater tubercle: It is the lateral prominence at the upper end. It forms the lateral boundary of the intertubercular groove. It presents three impression starting from the top to the back. They are for supraspinatus, infraspinatus and teres minor.

Surgical neck: It is at the upper end of the shaft of humerus below the anatomical neck.

Clavicle: It is a long bone placed horizontally in the body. It presents shaft, which is like letter “f”, two ends, acromial or lateral and sternal or medial. It articulates laterally with acromion to form acromio-clavicular joint and medially with manubrium sterni to form sternoclavicular joint.lz

Scapula: It is the flat triangular bone placed at the postero-lateral aspect of the chestwall. It has three borders, three processes, three angles and three fossae..

Infraglenoid tubercle: It is the rough triangular area situated below glenoid cavity.

Supraglenoid tubercle: It is above the glenoid cavity.

Glenoid cavity: It is a shallow, pear-shaped cavity at the lateral angle of the scapula, narrow above and broad below. It takes part in the formation of the shoulder joint with the head of humerus, which is larger in size of the glenoid cavity.

Coracoid process: It is a thick stout process above the supraglenoid tubercle like a bent thumb.

Neck of scapula: This is the part adjoining the glenoid cavity.

Supraspinatus fossa: It lies above the spine and infraspinatus fossa below. These two fossae communicate with each other through the spino-glenoid notch.

Acromion: It articulates with the lateral end of clavicle to form the acromioclavicular joint.

Fig: Lateral view of Elbow showing lines

Anterior humeral line: On a normal lateral radiograph, it is a line traced along the anterior cortex of the humerus will bisect the capitellum between its anterior and middle thirds. If less than one third of the capitellum lies anterior to the line then there may be a supracondylar fracture with posterior displacement of the distal fragment.

Radio-capitellar line: It is a line drawn along the center of the shaft of the proximal radius passing through the capitellum. If the line does not pass through the capitellum then either the radial head or the capitellum is displaced.

Mid-humeral line: It is a line coincident with the central axis of the humeral shaft, projects just posterior to the posterior margin of the capitulum.

Fig: Elbow AP and Lateral views

Radiographic Anatomy of Hand

RADIOGRAPHIC ANATOMY OF HAND:



Fig: Hand PA view

Phalanges: Each finger and thumb is called a digit and each digit consists of two or three separate small bones called phalanges. The phalanges are 14 in number; the thumb has 2 (proximal and distal) and 3 each for the remaining four fingers (proximal, middle and distal). Each phalanx consists of three parts: a distal rounded head, a bone (Shaft), and an expanded base, similar to that of the metacarpals.

Inter-phalangeal (IP) joint: Beginning distally with the phalanges, all IP joints are ginglymus or hinge-type joints with movements in two directions only- flexion and extension. This movement is in one plane only, around the transverse axis.

First metacarpal: It is placed laterally. It is the shortest and the strongest metacarpal. It has undergone medial rotation of 90⁰. Therefore, the plane of the four metacarpal bones is at right angle to the plane of first metacarpal bone. It articulates with trapezium to form an important joint known as the carpometacarpal joint.

Second metacarpal: It is the longest amongst the metacarpals. The base is expanded and has a groove which articulates with the trapezoid.

Third metacarpal: It has a styloid process which helps in its identification. Its base articulates with capitate.

Fourth metacarpal: It can be identified by means of a small oval facet on the medial side of the base. There are two separate oval facets on the base of its lateral surface. Proximally, it articulates with hamate by means of quadrilateral facet (quadrilateral base means fourth metacarpal bone).

Fifth metacarpal: It is relatively slender. It is identified by the fact that it has no articular facet on the medial side of its base, where a tubercle can be seen. Proximally, it articulates with hamate.

Sesamoid bone: They differ from normal bone in two respects; absence of periosteum and absence of Haversian canal. They develop in the tendon at the site of friction.

Scaphoid or Navicular: It resembles a boat. It is the largest in the proximal row and has the prominent scaphoid tubercle. Its location and articulation with the forearm make it important radiographically because it is the most frequently carpal bone.

Lunate or Semilunar: It is like a moon. It articulates with the triquetral, capitate, radius and the scaphoid. Medial surface of the lunate is quadrilateral in shape and articulates with the triquetral.

Triquetral: It is the medial most bone of the proximal row and articulats with lunate laterally. It is distinguished by its pyramidal shape and anterior articulation with small pisiform.

Pisiform: It is like a pea, and is the smallest of the carpal bones and is located anterior to the triquetrum. It is supposed to be a sesamoid bone which develops in the tendon of flexor carpi ulnaris muscle.

Trapezium or Greater Multangular: It is four sided bone and is the first bone of the distal row of the carpus. It articulates with trapezoid medially and scaphoid proximally. There is saddle-shaped facet for the base of first metacarpal bone distally.

Trapezoid or Lesser Multangular: It is like a boot (shoe). It articulates with second metacarpal bone, trapezium, capitate and scaphoid bones.

Capitate: It has head, hence named as capitate (caput means head) and the largest bone in the carpus. It articulates primarily with the third metacarpal distally and with the trapezoid, scaphoid, lunate and hamate.

Hamate: It is a wedge-shaped bone on the medial side of the hand; it articulates with the fourth and fifth metacarpal, capitate and triquetral bones; it has a distinctive hooked process, the hook of the hamate, that extends anteriorly.

Wrist Joint: It is a condyloid (ellipsoid) type of synovial joint, and is freely movable or diarthrodial of the synovial classification. Of the two bones of the forearm, only the radius articulates directly with two carpal bones, the scaphoid and lunate. This wrist joint is called the radio-carpal joint.

Radius: It is the long bone of the forearm situated on the lateral side. It is connected to the ulna at the upper, middle and lower sites. Head of radius articulates with the ulna and forms the superior radio-ulnar joint. Head of ulna articulates with the radius at the lower end and forms the inferior radio-ulnar joint. Middle articulation is formed by the inter-osseous membrane, connecting inter-osseous borders of radius and ulna.

Lower end of radius: It is broad and quadrilateral. The lower lateral part presents the styloid process (the sharp pointed bony projection). Tip of radial styloid is lower than the tip of ulnar styloid process. Distal surface of the lower end of the radius articulates with scaphoid and the lunate.

Ulna: It is the long bone of the forearm placed medially. It presents shaft, upper and the lower end. It articulates with the humerus and the radius above and the lower end of the radius below. Articulations with the radius, it forms superior radioulnar, middle radioulnar, and the inferior radioulnar joints.

Lower end of ulna: It presents the head and the styloid process.

MRI Scanning of Temporo-Mandibular Joint (TMJ)

The temporomandibular joint is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium (skull), and the lower jaw bone called the mandible. The unique feature of the TMJs is the articular disc. The disc is composed of fibrocartilagenous tissue (like the firm and flexible elastic cartilage of the ear) which is positioned between the two bones that form the joint. The disc divides each joint into two. The lower joint compartment formed by the mandible and the articular disc is involved in rotational movement - this is the initial movement of the jaw when the mouth opens.

Chest X-ray in Lung Consolidation

Consolidation:

Functionally the pulmonary airways can be divided into two groups. The proximal airways function purely as a conducting network: the airways distal to the terminal bronchioles are also conducting structures, but more importantly, are the site of gaseous exchange. These terminal airways are termed acini, an acinus comprising respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli arising from a terminal bronchiole. Consolidation implies replacement of air in one or more acini by fluid or solid material, but does not imply a particular pathology or aetiology. The smallest unit of consolidated lung is a single acinus, which casts a shadow approximately 7 mm in diameter. Communications between the terminal airways allow fluid to spread between adjacent acini, so that larger confluent areas of consolidation are generally visible and are frequently not confined to a single segment.

The commonest cause of consolidation is acute inflammatory exudate associated with pneumonia. Other causes include cardiogenic pulmonary edema, non-cardiogenic pulmonary edema, haemorrhage and aspiration. Neoplasms such as alveolar cell carcinoma and lymphoma can produce consolidation and alveolar proteinosis is a rare cause. In an individual patient, consolidation may be due to more than one basic aetiology. For example, a patient with major head trauma may be particularly susceptible to infection, aspiration and non-cardiogenic pulmonary edema.

When consolidation is associated with a patent conducting airway, an air bronchogram is often visible. This sign is produced by the radiographic contrast between the column of air in the airway and the surrounding opaque acini. If consolidation is secondary to bronchial obstruction, however, the air in the conducting airway is resorbed and replaced by fluid, and the affected area is of uniform density.

The volume of purely consolidated lung is similar to that of the normal lung since air is replaced by fluid or solid. However, collapse and consolidation are often associated with one another. When consolidation is due to fluid, its distribution is influenced by gravity, so that in acute pneumonitis, consolidation is often denser and more clearly demarcated inferiorly by a pleural surface, and is less dense and more indistinct superiorly.

Lobar consolidation:
Consolidation of a complete lobe produces a homogenous opacity possibly containing an air bronchogram, delineated by the chest wall, mediastinum or diaphragm and the appropriate interlobar fissure or fissures. Parts of the diaphragm and mediastinum adjacent to the non-aerated lung are obscured.

Right upper lobe consolidation:
This is confined by the horizontal fissure inferiorly and the upper half of the oblique fissure posteriorly and may obscure the right upper mediastinum.

Right middle lobe consolidation:
This is limited by the horizontal fissure above and the lower half of the oblique fissure posterioly, and may obscure the right heart border.

Lower lobe consolidation:
This is limited by the oblique fissure anteriorly and may obscure the diaphragm.

Left upper lobe and lingula consolidation:
These are limited by the oblique fissure posteriorly. Lingula consolidation may obscure the left heart border, and consolidation of the upper lobe may obscure the aortic knuckle.

Chest X-ray in Lung Collapse

Collapse:

Partial or complete loss of volume of a lung is referred to as collapse or atelectasis. This contrasts with consolidation in which a diminished volume of air in the lung is associated with normal lung volume.

Mechanisms of collapse:

1. Relaxation or passive collapse:

This is the mechanism whereby the lung tends to retract toward its hilum when air or increased fluid collects in the pleural space.

2. Cicatrisation collapse:

Normal lung expansion depends upon a balance between outward forces in the chest wall and opposite elastic forces in the lung. When the lung is abnormal stiff, this balance is disturbed, lung compliance is decreased and the volume of the affected lung is reduced. This occurs with pulmonary fibrosis.

3. Adhesive collapse:

The surface tension of the alveoli is decreased by surfactant. If this mechanism is disturbed as in the respiratory distress syndrome, collapse of alveoli occurs, although the central airways remain patent.

4. Resorption collapse:

In acute bronchial obstruction, the gases in the alveoli are steadily taken up by the blood in the pulmonary capillaries and are not replenished, causing alveolar collapse. The degree of collapse may be modified by collateral air drift if the obstruction is distal to the main bronchus, and also by infection and accumulation of secretions. If the obstruction becomes chronic, subsequent resorption of intra-alveolar secretions, and exudate may result in complete collapse. This is the ususal mechanism of collapse seen in carcinoma of the bronchus.

Radiological signs of collapse:

The radiographic appearance in pulmonary collapse depends upon the mechanism of collapse, the degree of collapse, the presence or absence of consolidation, and the pre-existing state of the pleura. Signs of collapse may be considered as direct or indirect. Indirect signs are the results of compensatory changes which occur in response to the volume loss.

Direct signs of  collapse:

1. Displacement of interlobar fissures:

This is the most reliable sign and the degree of displacement will depend on the extent of the collapse.

2. Loss of aeration:

Increased density of a collapsed area of lung may not become apparent until collapse is almost complete. However, if the collapsed lung is adjacent to the mediastinum or diaphragm, obscuration of the adjacent structures may indicate loss of aeration.

3. Vascular and bronchial signs:

If a lobe is partially collapsed, crowding of its vessels may be visible, if an air bronchogram is visible, the bronchi may be crowded.

Indirect signs of collapse:

1. Elevation of the hemidiaphragm:

This sign may be seen in lower lobe collapse, but is rare in collapse of the other lobes.

2. Mediastinal displacement:

In upper lobe collapse, the trachea is often displaced toward the affected side, and in lower lobe collapse, the heart may be displaced.

3. Hilar displacement:

The hilum may be elevated in upper lobe collapse and depressed in lower lobe collapse.

4. Compensatory hyperinflation:

The normal part of the lung may become hyperinflated, and it may appear hypertransradiant with its vessels more widely spaced than in the corresponding area of the contralateral lung. If there is considerable collapse of a lung, compensatory hyperinflation of the contralateral lung may occur, with herniation across the midline.

Patterns of collapse:

An air bronchogram is almost never seen in resorption collapse, but is usual in passive and adhesive collapse, and may be seen in cicatrisation collapse if fibrosis is particularly dense. Pre-existing lung disease such as fibrosis and pleural adhesions may alter the expected displacement of anatomic landmarks in lung collapse. There also tends to be a reciprocal relationship between the compensatory signs, e.g. in lower lobe collapse, if diaphramatic elevation is marked, hilar depression will be diminished.

Complete collapse of a lung:

Complete collapse of a lung in the absence of pneumothorax or large pleural effusion or extensive consolidation, causes opacification of the hemithorax, displacement of the mediastinum to the affected side and elevation of the diaphragm. compensatory hyperinflation of the contralateral lung occurs, often with herniation across the midline. Herniation most often occurs in the retrosternal space, anterior to the ascending aorta, but may occur posterior to the heart or under the aortic arch.

Lobar collapse:

a. Right upper lobe collapse:

The normal horizontal fissure is usually at the level of the right fourth rib anteriorly. As the right upper lobe collapses, the horizontal fissure pivots about the hilum, its lateral end moving upward and medially toward the superior mediastinum, and its anterior end moving upward toward the apex. The upper half of the oblique fissure moves anteriorly. The two fissures become concave superiorly. In severe collapse, the lobe may be flattened against the superior mediastinum, and may obscure the upper pole of the hilum. The hilum is elevated, and its lower pole may be prominent. Deviation of the trachea to the right is usual, and compensatory hyperinflation of the right middle and lower lobes may be apparent.

b. Right middle lobe collapse:

In right middle lobe collapse, the horizontal fissure and lower half of the oblique fissure move toward one another. This can best be seen in the lateral projection. The horizontal fissure tends to be more mobile, and therefore usually shows greater displacement. Signs of right middle lobe collapse are often subtle on the frontal projection since the horizontal fissure may not be visible, and increased opacity does not become apparent until collapse is almost complete. However, obscuration of the right heart border is often present, and may be the only clue in this projection. The lordotic AP projection brings the displaced fissure into the line of the X-ray beam, and may elegantly demonstrate right middle lobe collapse. Since the volume of this lobe is relatively small, indirect signs of volume loss are rarely present.

c. Lower lobe collapse:

The normal oblique fissures extend from the level of the fourth thoracic vertebra posteriorly to the diaphragm close to the sternum anteriorly. The position of these fissures on the lateral projection is the best index of lower lobe volumes. When a lower lobe collapses, its oblique fissure moves posteriorly but maintains its normal slope. In addition to posterior movement, the collapsing lower lobe causes medial displacement of the oblique fissure, which may then become visible in places on the frontal projection.

d. Right lower lobe collapse:

This causes depression and medial rotation of the hilum, elevation of the right hemidiaphragm and hyperinflation of the right upper lobe. A completely collapsed lower lobe may be so small that it flattens and merges with the mediastinum, producing a thin, wedge-shaped shadow. On the left, this shadow may be obscured by the heart and a penetrated view with a grid may be required for its visualization.

e. Lingula collpase:

The lingula is often involved in collapse of the left upper lobe, but it may collapse individually, when the radiological features are similar to right middle lobe collapse. However, the absence of a horizontal fissure on the left makes anterior displacement of the lower half of the oblique fissure and increased opacity anterior to it important signs. On the frontal projection the left heart border becomes obscured.

f. Left upper lobe collapse:

The pattern of upper lobe collapse is different in the two lungs. Left upper lobe collapse is apparent on the lateral  projection as anterior displacement of the entire oblique fissure, which becomes oriented almost parallel to the anterior chest wall. With increasing collapse the upper lobe retracts posteriorly and loses contact with the anterior chest wall. The space between the collapsed lobe and the sternum becomes occupied by either hyperinflated left lower lobe or herniated right upper lobe. With complete collapse, the left upper lobe may lose contact with the chest wall and diaphragm and retract medially against the mediastinum. On a lateral film, therefore, left upper lobe collapse appears as an elongated opacity extending front the apex and reaching, or almost reaching, the diaphragm: it is anterior to the hilum and is bounded by displaced oblique fissure posteriorly, and by hyperinflated lower lobe anteriorly.

A collapsed left upper lobe does not produce a sharp outline on the frontal view. An ill-defined hazy opacity is present in the upper, mid and sometimes lower zones, the opacity being densest near the hilum. Pulmonary vessels in the hyperinflated lower lobe are usually visible through the haze. The aortic knuckle is usually obscured, unless the upper lobe has collapsed anterior to it, allowing it to be outlined by lower lobe. If the lingula is involved, the left heart border is obscured. The hilum is often elevated, and the trachea is often deviated to the left.

Rounded atelectasis:

This is an unusual form of pulmonary collapse which may be misdiagnosed as a pulmonary mass. It appears as a homogeneous mass upto 5 cm in diameter, with ill-defined edges. It is always pleural based and associated with pleural thickening. Vascular shadows may be seen to radiate from part of the opacity, resembling a comet's tail. The appearance is caused by peripheral lung tissue folding in on itself. It is often related to asbestos exposure, but may occur secondary to any exudative pleural effusion.