Diseases of the Pleura, Diaphragm, and Chest Wall

9 Diseases of the Pleura, Diaphragm, and Chest Wall

A pleural effusion is a pathologic fluid collection within the pleural cavity. Normally 10–15 mL of fluid is present and this serves as a lubricant between the parietal and visceral pleural layers. Pleural effusions may reach volumes of up to a few liters and these large effusions result in compression of the underlying lung, contralateral displacement of the mediastinum, and depression of the hemidiaphragm.

Goals of Diagnostic Imaging

Detection of the effusion and differentiation from other pathological pleural processes such as tumor and fibrous thickening. The mobility of the fluid with postural change and its computed tomography (CT) attenuation value may help in differentiation.

Detection of underlying pulmonary, cardiac, and abdominal pathology including pneumonia, bronchial carcinoma, pulmonary embolism, left ventricular failure, and hepatic cirrhosis (Tables 9.1 and 9.2).

Further evaluation of a pleural effusion may require thoracentesis with biochemical, cytologic, and bacteriologic analysis of aspirates.

Table 9.1 Etiology of pleural effusions in the U.S. (from R. W. Light: Pleural Diseases, 1983)

Heart failure	500 000
Bacterial pneumonia	300 000
Malignant tumors	200 000
• Lung	60 000
• Breast	50 000
• Lymphoma	40 000
• Miscellaneous	50 000
Thromboembolism	150 000
Viral pneumonia	100 000
Hepatic cirrhosis with ascites	50 000
Gastrointestinal disease (e. g., pancreatitis)	25 000
Collagen diseases	6 000
Tuberculosis	2 600
Asbestosis	2 000
Mesothelioma	450

Table 9.2 Causes of pleural effusion

Vascular
O	Pulmonary infarction
M	Heart failure
O	Constrictive pericarditis
Inflammatory
O	Tuberculosis
M	Parapneumonic effusion (viral, mycoplasma, bacterial, fungal)
O	Collagen diseases (SLE, rheumatoid arthritis)
O	Postinfarction Dressler“s syndrome
O	Whipple disease
O	Mediterranean fever
O	Recurrent familial polyserositis
Neoplastic
M	Bronchial carcinoma
O	Lymphoma
O	Metastatic pleural adenocarcinoma
O	Mesothelioma
Iatrogenic
O	Intrapleural infusion (e. g., due to faulty catheter placement)
M	Postthoracotomy
M	Radiotherapy
Traumatic
O	Hemothorax
O	Esophageal rupture
O	Chylothorax
Mediastinal
M	Superior vena caval obstruction
M	Aortic rupture
O	Esophageal fistula (e. g., carcinoma)
O	Thoracic duct fistula (filariasis, carcinoma)
M	Ruptured dermoid cyst
Subphrenic Abdominal
O	Pancreatitis
O	Subphrenic abscess
O	Cirrhosis with ascites
O	Meigs’ syndrome (ascites associated with ovarian tumor)
Miscellaneous
O	Asbestosis
O	Nephrotic syndrome
O	Myxedema
O	Uremia
O	Spontaneous pleural hemorrhage due to coagulopathy
O	Congenital lymphedema (Milroy)

M = diseases in which the chest radiograph generally shows other changes besides pleural effusion. O = diseases in which pleural effusion may be the only radiographic finding (from Light).

Pathology

Pleural effusions may be classified according to their composition:

Pleural transudate: Clear fluid with a specific gravity of less than 1.016 and a protein content of less than 3 g/dL The Pandy test is negative. Left ventricular failure is the most common cause of a transudate. Ascites in hepatic cirrhosis, nephrotic syndrome, and myxedema may also cause transudative effusions.

Pleural exudate: An opaque fluid with a protein content of more than 3 g/dL, a specific gravity of greater than 1.016, and a positive Pandy test. The microscopic identification of cellular elements such as granulocytes, lymphocytes, erythrocytes, and malignant cells narrows the differential diagnosis. Parapneumonic effusions are most common and are usually secondary to pulmonary infections. Tuberculous exudate is distinguished by its high lymphocyte content. Malignant pleural effusions are also exudates although malignant cells may not always be detected on cytologic evaluation.

Empyema: This suppurative intrapleural exudate is usually either parapneumonic or postpneumonic. Less commonly it may result from transdiaphragmatic extension of a liver abscess.

Hemothorax: Bleeding into the pleural space may be secondary to trauma, aortic rupture, or pleural malignancy. Occasionally, it is seen in thromboembolic disease when complicated by pulmonary infarction.

Chylothorax: A turbid, milky fluid containing microscopic chylomicrons is an uncommon cause of a pleural effusion. It may be seen in neoplastic and traumatic fistulae of the thoracic duct (Table 9.3) and is also associated characteristically with pulmonary lymphangiomatosis (LAM).
Bilious and cerebrospinal fluid (CSF) pleural effusions: Both are extremely rare. Bilious effusions are seen posthepatic and after diaphragmatic lacerations. A traumatic fistula to the spinal subarachnoid space allows CSF to enter the pleural space.

Clinical Features

Effusions are frequently asymptomatic but may cause pleuritic chest pain and splinting of the hemidiaphragm with decreased respiratory excursion. Large effusions may result in dyspnea. On auscultation, breathing sounds are diminished.

Table 9.3 Causes of chylothorax (modified from Reeder and Felson 2003)

Traumatic

Tumor invasion (bronchial carcinoma, mesothelioma, Hodgkin“s disease, etc.)

Filariasis

Left subclavian vein thrombosis

Lymphangioma, lymphangiomatosis, lymphangioleiomyomatosis

Iatrogenic (postthoracic surgery)

Idiopathic

Fig. 9.1 Pleural effusion on PA chest radiograph. The effusion surrounds the entire lung base but it is visible as a meniscus only when it is tangential to the x-ray beam (from Greene, McLoud, and Stark 1977).

Radiologic Findings

Chest Radiograph

The shape of the effusion results from:

The adhesive and cohesive forces between the pleura and the effusion.
Elastic recoil which decreases lung volume while preserving its shape and proportions and especially.
Gravity, which accounts for the dependent distribution of the effusion.

Pleural fluid is mobile and therefore its distribution is position-dependent. This accounts for its varying radiographic appearances (Figs. 9.1–9.3).

Upright position:

The lateral chest radiograph shows homogeneous opacification of the posterior costophrenic angle with a superiorly concave meniscus. At least 100 mL of fluid is present before an effusion becomes visible. Smaller effusions collect between the diaphragm and the undersurface of the lung and may only be seen on decubitus views. For clinical purposes, a significant effusion is excluded if both posterior costophrenic angles are clear.
The posteroanterior (PA) chest radiograph shows obliteration of the costophrenic and cardiophrenic angles if the effusion is greater than approximately 175 mL The meniscus is concave toward the lung and becomes thinner superiorly. Opacification of the mediastinal pleural space is lower and less marked because of fusion of the pleural layers at the pulmonary ligament.

Fig. 9.2 Limits of detectability of pleural effusion (from Moskowitz 1973).

Fig. 9.3a-d Chylothorax. Fluid layering dependently in the lateral decubitus view appears as a crescent-shaped opacity entering the minor fissure (b). On the supine view, the fluid causes general haziness of the hemithorax (d). The etiology of the chylothorax was a Milroy-Trenaunay malformation of the lymphatic vessels.

Fig. 9.4a-c Variants of pleural effusion.

Supine position:

Effusions are only visible on supine radiographs when they exceed 500 mL

Manifestations include:

The diaphragmatic contour is obscured
Opacification of the lateral costophrenic angles
Generalized “haziness” of the hemithorax
Apical caps may indicate pooling of fluid in the upper zones

In contrast to pneumonia or atelectasis, the pulmonary vessels are well defined with small to moderate effusions and there is no evidence of an air bronchogram.

Lateral decubitus position:

Fluid collects between the lateral chest wall and the lung, producing a band of opacification which may enter the minor fissure.

Postmortem studies have shown that as little as 5 mL of fluid may be detected on the lateral decubitus view (Moskowitz et al. 1973). If the depth of the effusion (“band” thickness) is less than 1 cm, then the effusion is small.

Atypical forms of pleural effusion (Figs. 9.4, 9.5):

Loculated effusion: Adhesions between the visceral and parietal pleura result in development of loculated collections along the inner aspect of the chest wall. En face, they may appear as ill-defined round opacities but tangentially they produce a semicircular opacity whose margins form an obtuse angle with the chest wall. This helps to distinguish them from peripheral pulmonary tumors, which usually form an acute angle with the chest wall.
Interlobar effusion (Figs. 9.6, 9.7): This may develop in the minor or major fissures. Chest radiographs show a biconvex, spherical, or elliptical homogeneous opacity. An effusion in the right minor fissure should be distinguished from right middle lobe atelectasis. The following features help in differentiation:
- – The effusion is biconvex while lobar atelectasis is flat or concave.
- – Only atelectasis obliterates the right cardiac border and
- – Atelectasis obscures the interlobar fissure but an effusion preserves the contour of the fissure as a linear structure in its peripheral portion.
Conventional tomography allows more accurate differentiation based on the homogeneity of the effusion versus the heterogeneity of atelectatic lung. However, today CT is usually performed when there is diagnostic difficulty.
Posteromedial loculated effusion: The fluid column is higher and wider toward the mediastinum. This results from volume loss in the lower lobe and thus lower lobe atelectasis is included in the differential diagnosis.
Subpulmonic effusion. Occasionally up to a liter of fluid may accumulate between the diaphragm and lung without spill into the costophrenic sulcus. Reasons for this phenomenon are not fully understood. Radiographs show elevation of the lung-soft tissue interface or apparent elevation of the hemidiaphragm. The “dome” has a relatively lateral peak and then shows a steep lateral downslope. When the subpulmonic effusion is left-sided, the distance between the inferior surface of the left lung and the gastric bubble measures more than 2 cm. The lateral decubitus view will show fluid layering along the dependent chest wall.
Inversion of the diaphragm: Large effusions may cause inversion of the hemidiaphragm. Radiographs show inferomedial displacement of gastric and colonic gas. During inspiration, the diaphragm contracts and this reduces the volume of the hemithorax. This leads to significant dyspnea and paradoxical diaphragmatic motion.

Fig. 9.5a-c Malignant pleural effusion in breast carcinoma (a). Hydropneumothorax developed following thoracentesis (b). CT shows visceral pleural thickening and fluid extending into the major fissure (c).

Fig. 9.6 Interlobar effusions.

Fig. 9.7a,b Fissural effusion appears as a round opacity in the minor fissure in a patient with congestive heart failure. Radiograph post treatment shows minimal residual fissural thickening.