- Email: [email protected]
How to read the chest X-ray — Part 1
How to Read the Chest X-ray -
Part 1
M. X. Pelling and R. Dick
Looking effectively at chest X-rays requires a knowledge of chest anatomy, pathology, and normal and abnormal appearances. With experience it is possible to scan a film and detect most abnormalities without consciously looking for them. This technique can be hazardous and a more systematic method is advised.
Looking at chest X-rays
pleura which become visible as fissures when parallel to the X-ray beam and identify the positions of the lobes. The oblique fissures separate the lower from the upper and middle lobes and extend forward and downward from about the 5th dorsal vertebra to just behind the anterior cardiophrenic angle. The horizontal fissure on the right separates the middle and upper lobes. This extends from the hilum to the 6th rib laterally usually within 10” of the horizontal. Further accessory fissures are occasionally seen. The azygos fissure is a double layer of parietal and visceral pleura pulled down by an aberrant azygos vein crossing rather than skirting lung to drain into the SVC. The vein can be seen in its lower end. It occurs in about 1% of the population. Occasionally a partial fissure can be seen on the left separating the lingular which mirrors the right horizontal fissure. A superior accessory fissure sometimes separates the apical segment of the lower lobe from the rest of the lobe. On a frontal film this can be mistaken for the horizontal fissure but on a lateral can be seen to extend backwards from the hilum. The anatomy of the hila is complicated. Normal bronchi and lymph nodes contribute little to the density at the hila which is mostly due to vascular structures. The course of the pulmonary arteries differs on each side. The left pulmonary artery is directed backwards over the left main bronchus and remains a posterolateral relation to the corresponding airway. The right main pulmonary artery crosses the mediastinum in front of the carina and divides to run anterolateral to the bronchi. The basal
First, practical points. Always use a viewing box and make sure the lighting conditions are adequate. Check the name, date, film markers and any other information the radiographer has noted and assess the film for technical quality. A poorly exposed film taken with the chest under-expanded, with the patient supine and rotated cannot be used to assess slight cardiac enlargement but might be adequate to check a central line. The sequence is personal but an effort should be made to look at every structure including soft tissues, breast shadows, bones and joints. Special attention must be paid to the pulmonary vasculature and overall tram-radiancy of both sides. The ‘review areas’ should be checked. These are regions of lung behind the cardiac shadow and diaphragms and at the apices. Although subtle, abnormalities can often be made out through these structures. Finally the indication for the examination should be considered and the film looked at with this in mind. Old films should be compared if available.
Normal anatomy The lungs are divided into lobes, two on the left and three on the right. Each lobe is enveloped in visceral
M. X. Pelling MB ChB MRCP FRCR, Senior Registrar in Radiology, R Dick MB BS MRACR FRCR, Consultant Radiologist, Department of Radiology, Royal Free Hospital, London NW3 2QG UK. Currenr Anaesrhesia 0
1994 Longman
and Crit;col Core (1994) 5, 102-108 Group Lfd
102
HOW TO READ THE CHEST X-RAY-PART
Fig. 1 -
1
103
Normal chest X-ray.
arteries on each side are the major branches and these can often be accurately measured (Fig. 1). The right is most easily defined and is measured before its segmental division. The normal adult range is 8-16 mm. The pulmonary veins course towards the left atrium which is below the main pulmonary artery. The orientation of the vessels is therefore distinct. In the mid zones the veins point inferomedially whereas the arteries are directed horizontally. In the lower zones the veins are directed obliquely forward and upwards beneath the divisions of the lower lobe arteries which are more vertically orientated. The hilar point on the left is normally OS1.5 cm higher than the right. This is defined as the point where the most lateral upper lobe vein crosses the basal artery and is at about the level of the 6th rib laterally. With upper lobe shrinkage the hilum will rise 2-3 cm. With loss of volume in the lower lobe this will be depressed by l-2 cm. The major bronchi differ on the two sides. The right main bronchus is shorter and steeper than the left. The right upper lobe bronchus arises closer to the carina than does the left and on a lateral film will appear higher than the left. The left upper lobe bronchus is often mistaken, on a lateral film, for the carina (which is not visible). The posterior wall of the right main and intermediate bronchi
are visible as a thin stripe as these are outlined by lung. On the left the pulmonary arteries lie between the bronchi and lung. Normal broncho-pulmonary and mediastinal lymph nodes are not visible. These are widely distributed throughout the mediastinum in sub-carinal, trachea-bronchial. para-tracheal. anterior and posterior mediastinal locations. On CT nodes less than 1 cm are considered benign, between l-2 cm possibly abnormal and over 2 cm certainly abnormal. The mediastinum is usually divided into superior, anterior, middle and posterior compartments. These do not follow anatomical divisions and are more for descriptive convenience. The transverse cardiac diameter is measured at the widest point. In adults, on a PA film, this should measure less than 16 cm or 50% of the widest thoracic diameter. Under the same conditions it should not vary by more than 1 cm and an increase of 1.5 cm or more is significant. Usually two-thirds of the cardiac shadow lies to the left of the mid-line, one-third to the right. The trachea is straight, lies centrally at the thoracic inlet and is slightly inclined to the right on the frontal view and posteriorly on the lateral view. Its posterior wall may be seen outlined by lung on the lateral. If
104
CURRENT ANAESTHESIA
AND CRITICAL
CARE
oesophagus is not interposed this posterior stripe should measure not more than 3 mm. Other lines or stripes are often seen on plain films. The right wall of the trachea forms the para-tracheal stripe which may also measure up to 3 mm. The lungs sometimes wrap around the mediastinum and touch anteriorly in front of the aortic arch or posteriorly above the arch. This may be seen as anterior or posterior junctional lines. The right wall of the oesophagus may be out-lined by lung on a frontal film. Posterior to the trachea this forms the pleuro-oesophageal stripe. Inferiorly, where the azygos vein runs adjacent to it, this forms the azygo-oesophageal line. Pleural reflections over the vertebral bodies form the paraspinal lines. The highest points of the diaphragms, on inspiration, normally lie between the 5th and 7th anterior rib interspace. The right is usually about 2 cm higher than the left although the left is higher in about 10% often due to physiological elevation from gas in stomach or colon. The cardiophrenic angles contain fat and appear a little indistinct. The costophrenic angles are usually well defined. The posterior costophrenic angle is significantly lower than the dome. The airways are not usually visible unless seen endon. The segmental bronchi divide in a tree-like fashion to terminate as respiratory bronchioles. These give rise to clumps of alveoli. One terminal bronchiole with its associated alveoli constitutes a functional unit, the acinus, which measures about 5 mm across. Three or four of these together make up a lobule which, at the periphery, are separated by septa. The septa are not normally visible but, if thickened in disease, give rise to septal or Kerley B lines.
Normal variants A number of normal variants may simulate disease. The first costo-chondral junction may hypertrophy and calcify and simulate an apical mass. A lordotic view can help differentiate the two. Other normal structures include skin folds which can mimic pneumothoraces, and hair braids which can mimic lung lesions. With a bright light these can usually be followed outside the lung. Nipple shadows tend to have a sharp lateral margin and ill-defined medial margin. A repeat film with markers, taken in expiration, can be obtained in doubtful cases. Pericardial fat pads are common, especially in fat people, and their relative lucency usually suggests their nature.
Radiological
signs of disease
The chest X-ray is as useful as it is because air in the lungs allows excellent contrast between it and adjacent soft tissues. A wide range of lung diseases produce a limited number of patterns and these consist mostly of various abnormal opacities. There are four main types of abnormal shadowing: consolidation; nodular shadows; linear shadows; and ring shadows. Collapse also causes ‘consolidation’ but there are other important features which will be covered at the end of this section.
Consolidation Any process which replaces air in the alveoli will increase the density of lung tissue and produce an opacity when compared to adjacent normal lung. This could be due to fluid, pus, blood or cells and the appearance would be similar. A list of causes is given in Table 1, The ‘silhouette sign’ is a term coined by Dr Benjamin Felson. It refers to the loss of a visible border when adjacent lung is consolidated and is valuable in localising pathology; for example middle lobe or lingular consolidation will obscure the heart border, whereas disease in either lower lobe will not. This general principle applies to any structure in the chest. This can be valuable when lung opacification is slight and is at times the only sign of an abnormality. Another useful sign is the air bronchogram. Normal bronchi and bronchioles are not visible unless seen end on. If the lung becomes consolidated and the bronchi remain air filled they will appear as lucent tubular structures. This is seen most commonly in pneumonia and pulmonary oedema. It can also be seen in collapsed lung unless the collapse is secondary to an obstructing lesion in which case the airways will be airless. Less common causes of an air bronchogram include lymphoma, alveolar cell carcinoma and sarcoid. It is sometimes a normal finding in children and on films taken in expiration. Areas of consolidation usually have ill defined margins except where limited by pleural surfaces, for example at fissures, where straight edges may be produced (Fig. 2). This occurs because of communications between alveoli, the pores of Kahn, which allow air and fluid drift. Fluid may spread from abnormal lung to adjacent normal lung giving an irregular margin to the consolidation. Segmental divisions are not respected. By the same process air drift may allow lung to remain aerated distal to a bronchial occlusion.
Table 1 -
Causes of air space shadowing
Transudates
Cardiogenic Pulmonary venous obstruction Nephrogenic Neurogenic Drug reactions Hypoalbuminaemia
Exudates
Infective pneumonia Eosinophilic pneumonia Collagen diseases Radiation pneumonitis Inhalation of noxious substances Alveolar proteinosis
Haemorrhage
Contusion/haematoma 2” to pulmonary embolus Blood aspiration Bleeding diathesis Anticoagulants Pulmonary haemosiderosis Goodpasture’s syndrome
Neoplasms
Alveolar cell carcinoma Lymphoma
Others
Sarcoid Alveolar microlithiasis
HOW TO READ THE CHEST
X-RAY--PART
I
105
Fig. 2 - Consolidation of right upper lobe with sharp border against horizontal fissure. Air bronchograms. More ill defined consolidation of middle lobe with loss of clear heart border Pulmonary TB.
Nod&r
shadowing
Nodules range in size from barely visible to 20 cm or more. They can be single or multiple, sharp or ill-defined, soft or dense, smooth or irregular in outline. Associated calcification is important and usually denotes a benign lesion although exceptions occur. Nodules can be distinguished from consolidation by their better definition although there is an overlap, especially with smaller lesions. Multiple nodules under 2 mm are often called miliary, from 220 mm nodules and over 20 mm masses. Solitary nodules under 5 mm are often missed (Table 2). Causes of multiple miliary shadowing and of multiple nodules are given in Table 2 Neoplasm
Infection
Causes of solitary nodules 0 0 0
Adenoma Hamatoma Carcinoma I a and 2’
0
Granuloma Abscear
l l
Vascular
Other
l
Fungus ball Hydatid cyst
a . 0
AV malformation Haematoma Pulmonary infarct
. . 0
Rheumatoid nodule Massive fibrosiS in coal miner Lipoid pneumonia Sequestration Lung cyst
l l
tables 3 and 4. On the whole granulomatous to be of uniform size whereas metastases (Figs 3 and 4).
nodules tend tend to vary
Linear shadowing
Linear opacities vary between a hair-line to a centimetre or more when they are usually called band shadows. There are some distinctive patterns. Septal lines are not usually visible on a normal film. The deep septa radiate from the hilum into the central portion of the lung. These measure up to 4 cm in length and do not reach the periphery. When thickened these form Kerley A lines. The Table 3 -Causes l l l l l
Table 4 l l l l l l l
of miliary shadowing
Tuberculosis Fungal disease Pneumoconiosis Sarcoidosis Metastatic malignancy
Causes of multiple nodules
Multiple metastases Rheumatoid nodules Wegener’s granuloma Sarcoid Abscesses Pulmonary infarcts AV malformations
106
CURRENT ANAESTHESIA
AND CRITICAL
CARE
Fig. 3 -64-year-old female. Widespread ill defined nodules of different sizes. Small right effusion. Right mastectomy. Breast carcinoma deposits.
Fig. 5 - 38-year-old male. Large left atrium (arrow) with perihilar shadowing, dilated upper lobe vessels and prominent Kerley B lines. Mitral stenosis.
Table 5 l l l l l
Causes of septal lines
Pulmonary oedema Lymphangitis carcinomatoia Pneumoconiosis Sarcoid Interstitial pneumonia
shadows are often seen at the bases, often in post-op or debilitated patients and represent areas of collapse. Vascular structures and fluid filled bronchi also cause band shadows. Branching is only seen in these two conditions and is helpful in limiting the differential. Bronchoceles sometimes look like gloved fingers; the bronchi radiating from the hilum. It implies an obstructing lesion at a segmental level with collateral air drift. Vascular causes include AV malformations and anomalous vessels such as seen in the scimitar syndrome. Ring shadows Fig. 4-Widespread well defined miliary nodules, all of the same size (3 mm). Miliary TB.
interlobular septa abut the pleural surface and are usually only about 1 cm in length. When thickened these form Kerley B lines (Fig. 5). They are most often basal. They are useful as they limit the differential diagnosis to just a few conditions (Table 5). They are most commonly seen in pulmonary oedema and, if transient, this diagnosis is almost certain. Parallel line shadows are due to bronchial wall thickening. Tramline shadows are thickened bronchi of normal diameter and are often seen in asthma and bronchitis. When wider than normal these are usually described as tubular shadows and indicate bronchiectasis. Band shadows are thicker than 5 mm. Horizontal band
Ring shadows are air-spaces surrounded by a wall usually 2 or 3 mm thick. If the wall is particularly thin these are usually referred to as cysts. Pneumatocoeles are cysts that develop following an infection, most often seen in children with Staph pneumonia. CT shows these to particular advantage (Table 6). Collapse This usually indicates bronchial obstruction (Table 7). When lung collapses there are two major effects. The lung may become more dense and there is loss of volume. With partial collapse the degree of opacification is variable as it depends on a balance between increasing density of lung tissue and reduced blood flow. However, as the lung continues to collapse the density invariably
HOW TO READ THE CHEST X-RAY-PART
Table 6 -
107
Causesof ring shadows 0
Congenital
l l
Infection
l
0 0 . l
Autoimmune
Airway limitation
0 0
Bronchogenic Metastases
l
Bullae Brochiectasis
l
0 Non-pulmonary
malformation
Pyogenic abscess Tuberculosis esp atypical Pneumocystis Fungi Septic infarct Hydatid (Ruptured) Rheumatoid nodule Wegener’s granuloma
0 Pneumatocoele
Bronchogenic cyst Cystic adenomatoid
0
l
Neoplastic
l l
Table 7 -
I
Infection especially Trauma
staphylococcus
Hiatus hernia Plombage
Causesof lobar or segmental collapse
Luminal obstruction
l l
. l
Mural obstruction
l l l l
Extrinsic lesion
l l l l
Endotracheal tube Foreign body Mucus plug Fungal plug Bronchial adenoma Bronchial carcinoma Inflammatory stricture (e.g. tuberculosis. sarcoid) Lymphadenopathy (e.g. middle lobe syndrome) Mediastinal malignancy AoFtic aneurysm
increases. Secondly as the lung shrinks the adjacent structures shift to take up space. This effect is most pronounced on the closest structures. The trachea, mediastinum, diaphragms. chest wall and adjacent lung may all
Fig. 6-Collapsed right upper lobe with mass in right hilum. Central bronchogenic carcinoma obstructing the upper lobe bronchus.
move to a variable degree. Mediastinal and diaphragmatic shift tend to occur first. Compensatory emphysema tends to take rather longer to develop. The appearance of lobar collapse is frequently characteristic and the site of the obstructing lesion can often be predicted. Sometimes the obstructing lesion can also be seen. This is the basis of the ‘S sign of Golden’ where the collapsed lung is seen draped round an obstructing mass giving an S shape, concave peripherally and convex centrally (Fig. 6). Collapsed lung is always connected to the hilum by its broncho-vascular pedicle. The appearance depends on
Fig. 7 - (a) 111defined opacity at right mid zone with loss of the right heart border. Middle lobe collapse. (b) Lateral film confirms this.
108
CURRENT ANAESTHESIA AND CRITICAL CARE
the lobe or lobes involved. In right upper lobe collapse the minor and major fissures come up towards each other as the upper lobe flattens against the upper mediastinum. The border of the WC is lost (silhouette sign) and the right paratracheal stripe is widened. The trachea will deviate to the right and the hilum be pulled up. The middle lobe collapses downwards. On a lateral film this will appear as a band density extending from the hilum towards the anterior costophrenic angle. Because on a frontal film this is oblique to the main beam it will only cause a subtle increase in density and may be inapparent (Fig. 7). The lobe is relatively small and the degree of mediastinal or diaphragmatic shift often minimal. The most reliable sign is loss of definition of the right heart border (silhouette sign again). A lordotic film with the main beam along the axis of the lobe will show a characteristic triangular opacity with its base adjacent to right heart border. Collapse of the larger volume lower lobes will cause significant shift of adjacent structures; usually mediastinal shift or elevation of a hemidiaphragm. The hilum will be pulled down and on the left may disappear behind the heart shadow. Both collapsed lower lobes have a similar triangular configuration with the apex at the hilum and
the base along the diaphragm. This is more obvious on the right but can be seen on the left on a well penetrated film. Expansion of the rest of the lung causes fanning of vessels. The right middle lobe and lingular are adjacent to the heart border so, as long as these remain aerated, the cardiac borders remain clear. The medial portion of the hemidiaphragm usually becomes invisible. On the lateral view the posterior diaphragm also disappears and the vertebrae, which normally appear progressively darker as one looks down the spine, appear lighter than those above. Left upper lobe collapse includes the lingular and therefore differs from right upper lobe collapse. The lobe collapses forwards pulling the lower lobe with it. On the frontal view there is a veil like increase in density which fades around the edges. The left mediastinal and cardiac borders are initially lost (silhouette sign) but the superior mediastinum often reappears as the overexpanded lower lobe comes to lie against it. The right upper lobe often prolapses across anteriorly giving a distinctive lucency across and to the left of the superior mediastinum. Collapse of the left upper lobe sparing the lingular or of the lingular in isolation resemble right upper and middle lobe collapse respectively.
Part 1
M. X. Pelling and R. Dick
Looking effectively at chest X-rays requires a knowledge of chest anatomy, pathology, and normal and abnormal appearances. With experience it is possible to scan a film and detect most abnormalities without consciously looking for them. This technique can be hazardous and a more systematic method is advised.
Looking at chest X-rays
pleura which become visible as fissures when parallel to the X-ray beam and identify the positions of the lobes. The oblique fissures separate the lower from the upper and middle lobes and extend forward and downward from about the 5th dorsal vertebra to just behind the anterior cardiophrenic angle. The horizontal fissure on the right separates the middle and upper lobes. This extends from the hilum to the 6th rib laterally usually within 10” of the horizontal. Further accessory fissures are occasionally seen. The azygos fissure is a double layer of parietal and visceral pleura pulled down by an aberrant azygos vein crossing rather than skirting lung to drain into the SVC. The vein can be seen in its lower end. It occurs in about 1% of the population. Occasionally a partial fissure can be seen on the left separating the lingular which mirrors the right horizontal fissure. A superior accessory fissure sometimes separates the apical segment of the lower lobe from the rest of the lobe. On a frontal film this can be mistaken for the horizontal fissure but on a lateral can be seen to extend backwards from the hilum. The anatomy of the hila is complicated. Normal bronchi and lymph nodes contribute little to the density at the hila which is mostly due to vascular structures. The course of the pulmonary arteries differs on each side. The left pulmonary artery is directed backwards over the left main bronchus and remains a posterolateral relation to the corresponding airway. The right main pulmonary artery crosses the mediastinum in front of the carina and divides to run anterolateral to the bronchi. The basal
First, practical points. Always use a viewing box and make sure the lighting conditions are adequate. Check the name, date, film markers and any other information the radiographer has noted and assess the film for technical quality. A poorly exposed film taken with the chest under-expanded, with the patient supine and rotated cannot be used to assess slight cardiac enlargement but might be adequate to check a central line. The sequence is personal but an effort should be made to look at every structure including soft tissues, breast shadows, bones and joints. Special attention must be paid to the pulmonary vasculature and overall tram-radiancy of both sides. The ‘review areas’ should be checked. These are regions of lung behind the cardiac shadow and diaphragms and at the apices. Although subtle, abnormalities can often be made out through these structures. Finally the indication for the examination should be considered and the film looked at with this in mind. Old films should be compared if available.
Normal anatomy The lungs are divided into lobes, two on the left and three on the right. Each lobe is enveloped in visceral
M. X. Pelling MB ChB MRCP FRCR, Senior Registrar in Radiology, R Dick MB BS MRACR FRCR, Consultant Radiologist, Department of Radiology, Royal Free Hospital, London NW3 2QG UK. Currenr Anaesrhesia 0
1994 Longman
and Crit;col Core (1994) 5, 102-108 Group Lfd
102
HOW TO READ THE CHEST X-RAY-PART
Fig. 1 -
1
103
Normal chest X-ray.
arteries on each side are the major branches and these can often be accurately measured (Fig. 1). The right is most easily defined and is measured before its segmental division. The normal adult range is 8-16 mm. The pulmonary veins course towards the left atrium which is below the main pulmonary artery. The orientation of the vessels is therefore distinct. In the mid zones the veins point inferomedially whereas the arteries are directed horizontally. In the lower zones the veins are directed obliquely forward and upwards beneath the divisions of the lower lobe arteries which are more vertically orientated. The hilar point on the left is normally OS1.5 cm higher than the right. This is defined as the point where the most lateral upper lobe vein crosses the basal artery and is at about the level of the 6th rib laterally. With upper lobe shrinkage the hilum will rise 2-3 cm. With loss of volume in the lower lobe this will be depressed by l-2 cm. The major bronchi differ on the two sides. The right main bronchus is shorter and steeper than the left. The right upper lobe bronchus arises closer to the carina than does the left and on a lateral film will appear higher than the left. The left upper lobe bronchus is often mistaken, on a lateral film, for the carina (which is not visible). The posterior wall of the right main and intermediate bronchi
are visible as a thin stripe as these are outlined by lung. On the left the pulmonary arteries lie between the bronchi and lung. Normal broncho-pulmonary and mediastinal lymph nodes are not visible. These are widely distributed throughout the mediastinum in sub-carinal, trachea-bronchial. para-tracheal. anterior and posterior mediastinal locations. On CT nodes less than 1 cm are considered benign, between l-2 cm possibly abnormal and over 2 cm certainly abnormal. The mediastinum is usually divided into superior, anterior, middle and posterior compartments. These do not follow anatomical divisions and are more for descriptive convenience. The transverse cardiac diameter is measured at the widest point. In adults, on a PA film, this should measure less than 16 cm or 50% of the widest thoracic diameter. Under the same conditions it should not vary by more than 1 cm and an increase of 1.5 cm or more is significant. Usually two-thirds of the cardiac shadow lies to the left of the mid-line, one-third to the right. The trachea is straight, lies centrally at the thoracic inlet and is slightly inclined to the right on the frontal view and posteriorly on the lateral view. Its posterior wall may be seen outlined by lung on the lateral. If
104
CURRENT ANAESTHESIA
AND CRITICAL
CARE
oesophagus is not interposed this posterior stripe should measure not more than 3 mm. Other lines or stripes are often seen on plain films. The right wall of the trachea forms the para-tracheal stripe which may also measure up to 3 mm. The lungs sometimes wrap around the mediastinum and touch anteriorly in front of the aortic arch or posteriorly above the arch. This may be seen as anterior or posterior junctional lines. The right wall of the oesophagus may be out-lined by lung on a frontal film. Posterior to the trachea this forms the pleuro-oesophageal stripe. Inferiorly, where the azygos vein runs adjacent to it, this forms the azygo-oesophageal line. Pleural reflections over the vertebral bodies form the paraspinal lines. The highest points of the diaphragms, on inspiration, normally lie between the 5th and 7th anterior rib interspace. The right is usually about 2 cm higher than the left although the left is higher in about 10% often due to physiological elevation from gas in stomach or colon. The cardiophrenic angles contain fat and appear a little indistinct. The costophrenic angles are usually well defined. The posterior costophrenic angle is significantly lower than the dome. The airways are not usually visible unless seen endon. The segmental bronchi divide in a tree-like fashion to terminate as respiratory bronchioles. These give rise to clumps of alveoli. One terminal bronchiole with its associated alveoli constitutes a functional unit, the acinus, which measures about 5 mm across. Three or four of these together make up a lobule which, at the periphery, are separated by septa. The septa are not normally visible but, if thickened in disease, give rise to septal or Kerley B lines.
Normal variants A number of normal variants may simulate disease. The first costo-chondral junction may hypertrophy and calcify and simulate an apical mass. A lordotic view can help differentiate the two. Other normal structures include skin folds which can mimic pneumothoraces, and hair braids which can mimic lung lesions. With a bright light these can usually be followed outside the lung. Nipple shadows tend to have a sharp lateral margin and ill-defined medial margin. A repeat film with markers, taken in expiration, can be obtained in doubtful cases. Pericardial fat pads are common, especially in fat people, and their relative lucency usually suggests their nature.
Radiological
signs of disease
The chest X-ray is as useful as it is because air in the lungs allows excellent contrast between it and adjacent soft tissues. A wide range of lung diseases produce a limited number of patterns and these consist mostly of various abnormal opacities. There are four main types of abnormal shadowing: consolidation; nodular shadows; linear shadows; and ring shadows. Collapse also causes ‘consolidation’ but there are other important features which will be covered at the end of this section.
Consolidation Any process which replaces air in the alveoli will increase the density of lung tissue and produce an opacity when compared to adjacent normal lung. This could be due to fluid, pus, blood or cells and the appearance would be similar. A list of causes is given in Table 1, The ‘silhouette sign’ is a term coined by Dr Benjamin Felson. It refers to the loss of a visible border when adjacent lung is consolidated and is valuable in localising pathology; for example middle lobe or lingular consolidation will obscure the heart border, whereas disease in either lower lobe will not. This general principle applies to any structure in the chest. This can be valuable when lung opacification is slight and is at times the only sign of an abnormality. Another useful sign is the air bronchogram. Normal bronchi and bronchioles are not visible unless seen end on. If the lung becomes consolidated and the bronchi remain air filled they will appear as lucent tubular structures. This is seen most commonly in pneumonia and pulmonary oedema. It can also be seen in collapsed lung unless the collapse is secondary to an obstructing lesion in which case the airways will be airless. Less common causes of an air bronchogram include lymphoma, alveolar cell carcinoma and sarcoid. It is sometimes a normal finding in children and on films taken in expiration. Areas of consolidation usually have ill defined margins except where limited by pleural surfaces, for example at fissures, where straight edges may be produced (Fig. 2). This occurs because of communications between alveoli, the pores of Kahn, which allow air and fluid drift. Fluid may spread from abnormal lung to adjacent normal lung giving an irregular margin to the consolidation. Segmental divisions are not respected. By the same process air drift may allow lung to remain aerated distal to a bronchial occlusion.
Table 1 -
Causes of air space shadowing
Transudates
Cardiogenic Pulmonary venous obstruction Nephrogenic Neurogenic Drug reactions Hypoalbuminaemia
Exudates
Infective pneumonia Eosinophilic pneumonia Collagen diseases Radiation pneumonitis Inhalation of noxious substances Alveolar proteinosis
Haemorrhage
Contusion/haematoma 2” to pulmonary embolus Blood aspiration Bleeding diathesis Anticoagulants Pulmonary haemosiderosis Goodpasture’s syndrome
Neoplasms
Alveolar cell carcinoma Lymphoma
Others
Sarcoid Alveolar microlithiasis
HOW TO READ THE CHEST
X-RAY--PART
I
105
Fig. 2 - Consolidation of right upper lobe with sharp border against horizontal fissure. Air bronchograms. More ill defined consolidation of middle lobe with loss of clear heart border Pulmonary TB.
Nod&r
shadowing
Nodules range in size from barely visible to 20 cm or more. They can be single or multiple, sharp or ill-defined, soft or dense, smooth or irregular in outline. Associated calcification is important and usually denotes a benign lesion although exceptions occur. Nodules can be distinguished from consolidation by their better definition although there is an overlap, especially with smaller lesions. Multiple nodules under 2 mm are often called miliary, from 220 mm nodules and over 20 mm masses. Solitary nodules under 5 mm are often missed (Table 2). Causes of multiple miliary shadowing and of multiple nodules are given in Table 2 Neoplasm
Infection
Causes of solitary nodules 0 0 0
Adenoma Hamatoma Carcinoma I a and 2’
0
Granuloma Abscear
l l
Vascular
Other
l
Fungus ball Hydatid cyst
a . 0
AV malformation Haematoma Pulmonary infarct
. . 0
Rheumatoid nodule Massive fibrosiS in coal miner Lipoid pneumonia Sequestration Lung cyst
l l
tables 3 and 4. On the whole granulomatous to be of uniform size whereas metastases (Figs 3 and 4).
nodules tend tend to vary
Linear shadowing
Linear opacities vary between a hair-line to a centimetre or more when they are usually called band shadows. There are some distinctive patterns. Septal lines are not usually visible on a normal film. The deep septa radiate from the hilum into the central portion of the lung. These measure up to 4 cm in length and do not reach the periphery. When thickened these form Kerley A lines. The Table 3 -Causes l l l l l
Table 4 l l l l l l l
of miliary shadowing
Tuberculosis Fungal disease Pneumoconiosis Sarcoidosis Metastatic malignancy
Causes of multiple nodules
Multiple metastases Rheumatoid nodules Wegener’s granuloma Sarcoid Abscesses Pulmonary infarcts AV malformations
106
CURRENT ANAESTHESIA
AND CRITICAL
CARE
Fig. 3 -64-year-old female. Widespread ill defined nodules of different sizes. Small right effusion. Right mastectomy. Breast carcinoma deposits.
Fig. 5 - 38-year-old male. Large left atrium (arrow) with perihilar shadowing, dilated upper lobe vessels and prominent Kerley B lines. Mitral stenosis.
Table 5 l l l l l
Causes of septal lines
Pulmonary oedema Lymphangitis carcinomatoia Pneumoconiosis Sarcoid Interstitial pneumonia
shadows are often seen at the bases, often in post-op or debilitated patients and represent areas of collapse. Vascular structures and fluid filled bronchi also cause band shadows. Branching is only seen in these two conditions and is helpful in limiting the differential. Bronchoceles sometimes look like gloved fingers; the bronchi radiating from the hilum. It implies an obstructing lesion at a segmental level with collateral air drift. Vascular causes include AV malformations and anomalous vessels such as seen in the scimitar syndrome. Ring shadows Fig. 4-Widespread well defined miliary nodules, all of the same size (3 mm). Miliary TB.
interlobular septa abut the pleural surface and are usually only about 1 cm in length. When thickened these form Kerley B lines (Fig. 5). They are most often basal. They are useful as they limit the differential diagnosis to just a few conditions (Table 5). They are most commonly seen in pulmonary oedema and, if transient, this diagnosis is almost certain. Parallel line shadows are due to bronchial wall thickening. Tramline shadows are thickened bronchi of normal diameter and are often seen in asthma and bronchitis. When wider than normal these are usually described as tubular shadows and indicate bronchiectasis. Band shadows are thicker than 5 mm. Horizontal band
Ring shadows are air-spaces surrounded by a wall usually 2 or 3 mm thick. If the wall is particularly thin these are usually referred to as cysts. Pneumatocoeles are cysts that develop following an infection, most often seen in children with Staph pneumonia. CT shows these to particular advantage (Table 6). Collapse This usually indicates bronchial obstruction (Table 7). When lung collapses there are two major effects. The lung may become more dense and there is loss of volume. With partial collapse the degree of opacification is variable as it depends on a balance between increasing density of lung tissue and reduced blood flow. However, as the lung continues to collapse the density invariably
HOW TO READ THE CHEST X-RAY-PART
Table 6 -
107
Causesof ring shadows 0
Congenital
l l
Infection
l
0 0 . l
Autoimmune
Airway limitation
0 0
Bronchogenic Metastases
l
Bullae Brochiectasis
l
0 Non-pulmonary
malformation
Pyogenic abscess Tuberculosis esp atypical Pneumocystis Fungi Septic infarct Hydatid (Ruptured) Rheumatoid nodule Wegener’s granuloma
0 Pneumatocoele
Bronchogenic cyst Cystic adenomatoid
0
l
Neoplastic
l l
Table 7 -
I
Infection especially Trauma
staphylococcus
Hiatus hernia Plombage
Causesof lobar or segmental collapse
Luminal obstruction
l l
. l
Mural obstruction
l l l l
Extrinsic lesion
l l l l
Endotracheal tube Foreign body Mucus plug Fungal plug Bronchial adenoma Bronchial carcinoma Inflammatory stricture (e.g. tuberculosis. sarcoid) Lymphadenopathy (e.g. middle lobe syndrome) Mediastinal malignancy AoFtic aneurysm
increases. Secondly as the lung shrinks the adjacent structures shift to take up space. This effect is most pronounced on the closest structures. The trachea, mediastinum, diaphragms. chest wall and adjacent lung may all
Fig. 6-Collapsed right upper lobe with mass in right hilum. Central bronchogenic carcinoma obstructing the upper lobe bronchus.
move to a variable degree. Mediastinal and diaphragmatic shift tend to occur first. Compensatory emphysema tends to take rather longer to develop. The appearance of lobar collapse is frequently characteristic and the site of the obstructing lesion can often be predicted. Sometimes the obstructing lesion can also be seen. This is the basis of the ‘S sign of Golden’ where the collapsed lung is seen draped round an obstructing mass giving an S shape, concave peripherally and convex centrally (Fig. 6). Collapsed lung is always connected to the hilum by its broncho-vascular pedicle. The appearance depends on
Fig. 7 - (a) 111defined opacity at right mid zone with loss of the right heart border. Middle lobe collapse. (b) Lateral film confirms this.
108
CURRENT ANAESTHESIA AND CRITICAL CARE
the lobe or lobes involved. In right upper lobe collapse the minor and major fissures come up towards each other as the upper lobe flattens against the upper mediastinum. The border of the WC is lost (silhouette sign) and the right paratracheal stripe is widened. The trachea will deviate to the right and the hilum be pulled up. The middle lobe collapses downwards. On a lateral film this will appear as a band density extending from the hilum towards the anterior costophrenic angle. Because on a frontal film this is oblique to the main beam it will only cause a subtle increase in density and may be inapparent (Fig. 7). The lobe is relatively small and the degree of mediastinal or diaphragmatic shift often minimal. The most reliable sign is loss of definition of the right heart border (silhouette sign again). A lordotic film with the main beam along the axis of the lobe will show a characteristic triangular opacity with its base adjacent to right heart border. Collapse of the larger volume lower lobes will cause significant shift of adjacent structures; usually mediastinal shift or elevation of a hemidiaphragm. The hilum will be pulled down and on the left may disappear behind the heart shadow. Both collapsed lower lobes have a similar triangular configuration with the apex at the hilum and
the base along the diaphragm. This is more obvious on the right but can be seen on the left on a well penetrated film. Expansion of the rest of the lung causes fanning of vessels. The right middle lobe and lingular are adjacent to the heart border so, as long as these remain aerated, the cardiac borders remain clear. The medial portion of the hemidiaphragm usually becomes invisible. On the lateral view the posterior diaphragm also disappears and the vertebrae, which normally appear progressively darker as one looks down the spine, appear lighter than those above. Left upper lobe collapse includes the lingular and therefore differs from right upper lobe collapse. The lobe collapses forwards pulling the lower lobe with it. On the frontal view there is a veil like increase in density which fades around the edges. The left mediastinal and cardiac borders are initially lost (silhouette sign) but the superior mediastinum often reappears as the overexpanded lower lobe comes to lie against it. The right upper lobe often prolapses across anteriorly giving a distinctive lucency across and to the left of the superior mediastinum. Collapse of the left upper lobe sparing the lingular or of the lingular in isolation resemble right upper and middle lobe collapse respectively.