Each pleural membrane is composed of five separate layers: the mesothelial layer; a thin submesothelial connective tissue layer; a superficial elastic tissue layer; a loose subpleural connective tissue layer, in which run lymphatics, nerves, arteries, and veins; and a fibroelastic layer that is adherent to the underlying structures (i.e., lung, mediastinum, diaphragm, chest wall)1 (Fig. 109-1).
Five layers of the pleural membrane: mesothelial layer, submesothelial connective tissue layer, superficial elastic tissue layer, loose subpleural connective tissue layer, and fibroelastic layer.
Benign tumors of the pleura constitute less than 5% of all pleural tumors. Metastatic cancers or diffuse malignant mesotheliomas are more common pleural tumors yet still very rare. They share common properties with benign pleural tumors in that they originate from or metastasize to mesothelial or submesothelial surfaces, they may recur after surgical removal, and there may be difficulty in establishing a diagnosis with small biopsy specimens.
The importance of distinguishing benign pleural tumors from the two other more common malignant tumors resides in the excellent survival potential they confer, the fact that some benign tumors can recur or metastasize, and the difficulty in establishing the diagnosis with small biopsy specimens because of the heterogeneous patterns of cellularity in these tumors.2
From a clinical perspective, primary pleural tumors span a pathologic spectrum from benign tumors to benign tumors with some malignant features to frankly malignant tumors. The most common pleural tumor (i.e., solitary fibrous tumor of the pleura) can occur in either a benign or a malignant form. Likewise, these tumors may recur in either a benign or a malignant form.2,3
Benign tumors of the pleura are recognized by a radiographic appearance of a thickened parietal layer with underlying lung compression (Figs. 109-2 and 109-3). Occasionally, they may present with the appearance of invasion of lung (particularly if they are based in the visceral pleura), as in the inverted fibroma form of solitary fibrous tumors. These pleural abnormalities are identified by a variable thickening of either the visceral or parietal pleura. They impose a diagnostic dilemma on the clinician owing to the multiple possible etiologies for pleural masses. Furthermore, fine-needle aspirates of these abnormalities are often unreliable for confirming the diagnosis of benign pleural tumor.4–7
Solitary fibrous tumor of the lung. Posteroanterior (A) and lateral (B) chest x-rays. (Courtesy of Dr. Daniel Cohen.)
CT scan of solitary fibrous tumor of the lung. Same patient as shown in Fig. 109-2. (Courtesy of Dr. Daniel Cohen.)