ByDr. Tarek Mansour

Plain radiography. Ultrasound. CT. MRI. PET/CT

The pleura consists of a visceral and parietal layer.

The visceral pleura covers the lungs and interlobar fissures, whereas the parietal pleura lines the ribs, diaphragm, and mediastinum.

A double fold of pleura extends from the hilum to the diaphragm to form the inferior pulmonary ligament..

There is no communication between the two pleural cavities. The pleural space is a potential space that contains 2 to 10 mL of pleural fluid in the normal individual.

The main manifestations of disease in the pleura include

Pleural effusion. Pleural thickening (which may or may not be

calcified). Pleural air (i.e., pneumothorax). Pleural neoplasms. Primary disease of the pleura is rare. Most pleural

abnormalities result from disease processes in other organs.

Physiologic Mechanisms in the development of Pleural Effusions

Increase in hydrostatic pressure in microvascular circulation (congestive heart failure)

Decrease in osmotic pressure in microvascular circulation (Hypoalbuminemia, Cirrhosis).

Decrease in pleural pressure (Atelectasis). Increase in permeability of microvascular

circulation (Inflammatory conditions, Neoplasms). Impaired lymphatic drainage (Tumor, Fibrosis). Transport of fluid from abdomen (Ascites).

Types of Effusions Transudates Exudates Empyema Hemothorax Chylothorax

1- Standard Radiography Free pleural effusion demonstrates a

meniscus sign, which is a concave, upward-sloping interface with the lung that causes sharp or indistinct blunting of the costophrenic angle.

Sub pulmonary effusion: On the frontal view, this produces a characteristic

appearance with elevation of the apparent ipsilateral hemidiaphragm, flattening of the medial aspect, and displacement of the peak of the apparent diaphragm laterally.

On the left side, this is easy to recognize because of separation of the stomach bubble from the apparent left hemidiaphragm.

Subpulmonic effusion. On the left, there is separation of the apparent hemidiaphragm from the stomach bubble. There is also minimal blunting of the lateral costophrenic angle. On the right, a large effusion extends to the major fissure, subtending a lucent area that represents the superior segment of the right lower lobe

A massive effusion produces a complete or nearly complete opacification of a hemithorax, with displacement of the mediastinum to the opposite side

Moderate to large amounts of pleural effusion may be missed on supine radiographs. These effusions layer posteriorly and produce a generalized increase in opacity of the hemithorax, through which the pulmonary vessels can be visualized

Fluid may occasionally accumulate within fissures, and these accumulations may produce the appearance of a mass or pseudotumor

Differentiation from a mass can be easily made because the fluid is free and shifts on decubitus views.

2- Ultrasound Pleural fluid collections may be anechoic or

echoic, and they may change shape during respiration. Most collections are anechoic and are delineated by an echogenic line of visceral pleura and lung. Anechoic effusions are usually transudates, whereas effusions that contain septations represent exudates in approximately 80% of cases

3- Computed Tomography Pleural fluid can be distinguished

from ascites by several CT features, including the displaced crus sign, the interface sign, the diaphragm sign, and the bare area sign.

Displaced crus sign. The pleural fluid lies inside the crus of the diaphragm (arrow) and displaces it away from the spine.

Interface sign. A hazy, indistinct interface is seen between the pleural effusion and liver laterally (arrows), and ascites can be seen anteriorly.

Diaphragm sign. Ascites (A) lies inside the diaphragm (arrows) and produces a sharp interface with the liver. The pleural effusion (E) is visualized outside the diaphragm.

4- Magnetic Resonance Imaging The role of MRI in the evaluation of the

pleura is somewhat limited. MRI does provide certain advantages because of its ability to image the thorax directly in the axial, sagittal, and coronal planes. MRI may be slightly superior to CT in the characterization of pleural fluid (high T2 & low T1).

Pneumothorax in an upright patient. The extremely thin visceral pleural line can be seen extending along the lateral aspect of the lung to the apex

Large bullae simulating pneumothorax. The left lung is lucent, devoid of vessels, and almost completely replaced by bullae. The bullae have concave margins

Large tension pneumothorax. The large pneumothorax on the right is associated with almost complete collapse of the right lung. The margins of the lobes can be seen. There is evidence of tension, with shift of the mediastinum to the left and depression of the right hemidiaphragm.

Hydropneumothorax. The erect frontal view shows an air-fluid level at the base of the left pleural space (black arrow). The pneumothorax can also be seen extending along the lateral chest wall and at the apex

The most common focal pleural abnormalities include

pleural plaques. Localized pleural tumors. And local extension of bronchogenic

carcinoma.

Progression of pleural plaques. A, Axial CT shows bilateral pleural plaques and calcification (arrows). B, Axial CT 5 years later shows progression of pleural plaques (arrows) and development of new plaques (open arrows).

Pleural plaques. Multiple, interrupted pleural plaques can be identified adjacent to the lateral chest wall (arrows). The apices and costophrenic angle are spared.

Localized Pleural Tumors Localized pleural tumors are

relatively uncommon. They usually are one of two types: fibrous tumors of the pleura or lipomas.

Liposarcomas are rare, but the pleura commonly may be invaded locally by adjacent bronchogenic carcinoma.

Fibrous tumor of the pleura. A, The precontrast CT scan shows a mass posteriorly of fairly uniform attenuation that makes an acute angle with the lateral chest wall. B, After the administration of contrast, focal areas of enhancement can be appreciated (arrow).

Fibrous tumor of the pleura. A, Spin-echo, T1-weighted MRI shows a mass posteriorly with signal intensity equal to that of muscle. B, On the T2-weighted image, most of the mass has low signal intensity with a slightly bright rim.

Lipoma. CT shows an intra pleural tumor of fatty composition (−90 HU).

Benign and malignant diseases may cause diffuse pleural abnormalities.

Causes include 1- Fibrothorax.2- Malignant tumors such as malignant

mesothelioma and metastatic carcinoma.

The radiographic definition of diffuse pleural thickening is somewhat arbitrary, and there is no general consensus on a definition.

However, it has been suggested that diffuse pleural thickening consists of a smooth, uninterrupted pleural opacity extending over at least one fourth of the chest wall, with or without obliteration of the costophrenic angles.

The CT definition that has been used in describing asbestos-related changes consists of thickening that extends more than 8 cm in the cranio-caudal direction and 5 cm laterally and a pleural thickness more than 3 mm.

Calcified fibrothorax in a patient with pneumothorax treated many years ago for tuberculosis. There is extensive calcification surrounding the entire lung. A, On the frontal view the calcification can be easily localized to the visceral pleura (arrow). B, On the lateral view, markedly thickened pleura can be seen anteriorly (arrows).

Asbestos-related pleural thickening. CT shows bilateral, diffuse thickening but no calcification.

Benign, diffuse pleural thickening caused by empyema.

CT shows smooth thickening without nodularity involving the lateral and posterior pleural surfaces but not the mediastinal pleural surfaces.

Malignant mesothelioma. A, The diffuse pleural thickening on the right is nodular and extends along the mediastinal pleural surface (arrow). The volume of the right hemithorax is slightly reduced. B, Coronal reformation image shows the extent of pleural disease to greater detail and shows intrafissural extension (arrow).

Malignant mesothelioma. A and B, There is diffuse, circumferential pleural thickening on the right, which is lobular. The tumor extends into the chest wall (arrows). Notice the pleural plaques on the left.

Malignant mesothelioma. A, Standard radiograph shows diffuse pleural thickening on the right and contracture of the right lung. B, CT shows involvement of the peritoneum and liver.

Malignant mesothelioma. MRI shows extensive left mesothelioma involving the pericardium (A) (arrows) and diaphragm (B) (arrow).

Metastatic disease to the right pleural space from renal cell carcinoma. Notice the nodular pleural thickening.

Invasive thymoma. A, Imaging shows a large, anterior mediastinal mass (arrows). B, Nodular pleural thickening is present along the left mediastinal pleural surfaces (arrows). Notice the left pleural effusion.

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