pleural disease

The Mediastinum and Heart: The mediastinum should be central and its silhouette, in general, sharp. Short segments in which the silhouette is ill defined are sometimes seen near the cardiophrenic angles, at the apices and near the right hilum. Other segments may be ill defined but should only be considered normal once local pathology has been excluded. The mediastinal margin should be inspected for any abnormality of shape; and the visible mediastinal lines and interfaces for their integrity, position and contour.
Hila: Hilar shadows are made up of pulmonary arteries and veins with 2 minor contributions from other components (airways, nodes). In general the hila are equally dense and approximately the same size. The detection of abnormalities in their size and contour requires considerable experience and familiarity with the normal anatomy.Such changes may be produced by an alteration in size (usually enlargement) of one or more of the normal components; by a re-orientation of normal components (e.g. secondary to lobar collapse); or by the development of abnormal tissue (e.g. bronchial carcinoma). A spurious hilar opacity may result from an overlapping lesion, particularly in the apical segment of the lower lobe. This should be suspected when hilar borders remain visible within the opacity (negative silhouette sign).
Fissures and Vessels: Apart from vessels, the only shadows visible in normal lungs are those due to fissures and end-on airways. Fissures should be checked for their position, configuration, and thickness. Normal fissures are of hairline thickness. The oblique fissures are usually only seen on lateral radiographs, they extend downwards and forwards from D4/5, reaching the diaphragm a few centimeters behind the sternum. The left fissure is the more vertical of the two and ends inferiorly just behind the right. The minor fissure is seen in both frontal and lateral views. In the frontal view it extends laterally to the chest wall from the margin of the basal pulmonary artery.

Abnormal Opacities: Opacities are also called shadows, densities, or infiltrates, though the last two terms are not recommended. Opacities must be described and analysed in detail, noting in particular their size, number, position (distribution), shape, contour, marginal clarity, and structure. Their structure may be homogeneous or non-homogeneous, and in the latter instance this is usually due to the presence of an air bronchogram, focal transradiancy, or calcification. If a series of radiographs has been taken, it is good practice to look at selected previous examinations in addition to the current and immediately preceding radiographs, because some changes are undetectable over the short term. The changes in opacity with time and therapy often provide valuable extra information that is useful in identifying its aetiology, e.g. in distinguishing between infective and oedematous consolidation.
a. Consolidation: Consolidation is caused by the replacement of air in distal airways and alveoli by fluid (transudate, exudate including eosinophilic exudate, blood) or, rarely, tissue.
(i) Ill-defined Margins: This results from piecemeal alveolar involvement at the edge of a consolidated area though once the process comes up against a pleural surface the margination becomes sharp.
(ii) Nonsegmental Distribution: In general consolidation does not respect segmental boundaries as these do not constitute a physical barrier to the spread of fluid.
(iii) Irregular Shape: Apart from the effect of gravity, alveolar fluid spreads in a rather arbitrary fashion, and regular shapes such as spheres are rarely produced. They can occasionally occur, however, particularly when the consolidation is caused by tissue rather than fluid. Conditions giving spherical lesions containing an air bronchogram include alveolar carcinoma, lymphoma, pneumonia (due to Strep. pneumoniae, or in children), and sarcoidosis.
(iv) Tendency for Coalescence
(v) No Volume Change: Usually there is a one-to-one replacement of air by fluid, and consolidation per se is an isovolumetric change. In some disorders, however, (e.g. infarction, pneumonia), additional volume loss is sometimes seen, and on other occasions the volume increases. Expansive consolidation is most commonly seen with pneumococcal and Klebsiella pneumonia, tuberculosis, abscess formation, and when the consolidation harbours a neoplasm.
(vi) Air Bronchogram: Normal intrapulmonary airways are invisible unless end-on to the X-ray beam. If they pass through a zone of increased radio-opacity secondary to the reduction or replacement of surrounding alveolar air, however, then the airways become visible as linear, branching transradiances. This radiographic appearance is called an air bronchogram. It is a reliable sign of an intrapulmonary lesion, since the airways have to be intimately surrounded by the opacifying process for it to be produced.
(vii) Vascular Changes: Blood vessels are normally seen because their soft tissue density is contrasted against air-containing lung. With consolidation they become obscured (silhouette sign) and this is a reliable sign of an intrapulmonary opacifying process.
(viii) Acinar Nodules: Ill-defined nodular shadows 5–10 mm in diameter are sometimes seen in consolidation, and represent consolidated acini contrasted against adjacent air-filled ones.
(ix) Ground-Glass Opacity: This is a finely granular, veil-like shadowing that is seen with both consolidation and interstitial processes. In clinical practice it is most commonly seen with diffuse pulmonary haemorrhage, extrinsic allergic alveolitis, Pneumocystis pneumonia, and fibrosing alveolitis.

b. Nodular Opacities:
Nodular opacities are essentially spherical. They may be single or multiple and range in size from massive (15 cm or more) to pinpoint (less than 1 mm — micronodules). Nodules more than 3 cm in diameter are called masses and multiple small nodules about 2 mm in diameter are called miliary nodules. An isolated nodule must be assessed for its position, size, shape, contour (smooth, umbilicated, lobulated) and marginal clarity (sharp, ill-defined, spiculated). Lack of homogeneity is usually due to either calcification or cavitation. When a nodule abuts a normal structure, the resultant silhouette sign often helps to localize the lesion. When nodules are multiple, several additional features must be evaluated, and these include their approximate number, distribution, size range, and density.
c. Ring Opacities: Ring shadows are annular opacities with a central transradiancy and a number are due to cavitation of pre-existing nodules, masses, or consolidations.
Neoplasms tend to have, at least in part, thick walls (16 mm or more) and irregular, nodular inner margins. Ring opacities with walls 4 mm or less in thickness are commonly benign.
Cysts appear as evenly thin-walled (1 mm) rings, 1 cm or more in diameter, which form a useful subset with a limited number of common causes(bulla, bleb, laceration, pneumatocele, bronchogenic cyst and bronchiectasis).

Pleural Effusion:
Less than 5 ml of fluid is normally present in the pleural space. Excess pleural fluid accumulates when inflow and outflow from the pleural space are mismatched. A number of different types of fluid may accumulate in the pleural space, the commonest being transudate(less than 3 g/dl of protein, often bilateral, the commonest cause is cardiac failure, others: hypoproteinemia, constrictive pericarditis….), exudate (more than 3g/dl, the commonest causes are bacterial pneumonia, pulmonary T.B., CA of lung….), blood and chyle. Occasionally effusions are highly specific, not falling into any of the above categories and containing, for example, bile, cerebrospinal fluid or iatrogenic fluids. A small amount of free fluid may be undetectable on an erect PA chest radiograph as it tends initially to collect under the lower lobes. Such small subpulmonic effusions can be demonstrated by ultrasound or CT. An alternative technique, the lateral decubitus chest radiograph, has largely been replaced by these newer modalities .As the amount of effusion increases, the posterior and then the lateral costophrenic angles become blunted, by which time a 100-200 ml effusion is present. Following this the classical signs develop. Homogeneous opacification of the lower chest with obliteration of the costophrenic angle and the hemidiaphragm. The upper margin of the opacity is concave to the lung and is higher laterally than medially. Above and medial to the meniscus there is a hazy increase in opacity owing to the presence of fluid behind and in front of the lungs. Massive effusions cause dense opacification of the hemithorax with contralateral mediastinal shift. Large effusions sometimes cause diaphragmatic inversion, particularly on the left where the diaphragm lacks the support of the liver.

Pneumothorax:
Air in the pleural space is a pneumothorax. When air and liquid are present the nomenclature depends on their relative volumes and the type of liquid. Small amounts of liquid are disregarded and the condition is still called a pneumothorax; otherwise the prefix hydro-, haemo-, pyo-, or chylo- is added, depending on the nature of the liquid. Spontaneous pneumothorax is the commonest cause(occurs in young men), other causes: chronic bronchitis and emphysema in older patients, rupture of subpleural T.B. focus or subpleural tension cysts in Ca bronchus, trauma….
Radiologically: those are seen on erect radiographs in which the pleural air rises to the lung apex. Under these conditions the visceral pleural line at the apex becomes separated from the chest wall by a transradiant zone devoid of vessels.
Open pneumothorax: if air can move freely in and out of pleural cavity during respiration.
Closed pneumothorax: if no movement of air occurs during respiration.
Tension Pneumothorax: This life-threatening complication is present when intrapleural pressure becomes positive relative to atmospheric pressure for a significant part of the respiratory cycle. Tension has an adverse effect on gas exchange and cardiovascular performance, causing a rapid deterioration in the patient s clinical condition. The diagnosis is usually made clinically and treatment instituted without a radiograph. Should a chest radiograph be taken, it will show contralateral mediastinal shift and ipsilateral diaphragm depression. Mild degrees of contralateral mediastinal shift are not unusual with a nontension pneumothorax because of the negative pressure in the normal pleural space. Moderate or gross mediastinal shift (mainly during inspiration noticed at fluoroscopy) should be taken as indicating tension, particularly if the ipsilateral hemidiaphragm is depressed. This latter sign is the more reliable and almost invariably present with significant tension. This is particularly true of the ventilated patient in whom mediastinal shift may be absent.

Pneumomediastinum:
Air may enter the mediastinum from a perforation of the pharynx, oesophagus or major airways. In many instances, however, a pneumomediastinum is the result of an air leak from a tear in a small intrapulmonary airway, the air dissecting through the lung via the hilum into the mediastinum. Asthma is the commonest precipitating cause. In other cases the leak is probably related to abrupt changes in intrathoracic pressure such as those associated with vomiting. Occasionally, air tracks into the mediastinum from retroperitoneal air collections.
On imaging examinations: the condition is recognized as streaky translucencies within the mediastinum that are usually most obvious adjacent to the left heart border, aortic knuckle, main pulmonary artery and adjacent left hilum .The air dissects through the perivascular areolar tissues and may track up into the neck, supraclavicular areas and axillae as well as down into the retroperitoneum.