Pinkard and associates⁵⁰ described the occurrence of a benign pleural-based tumor in three young adults. The pleural lesions were identified on standard chest radiography and did not reveal any calcification. Computed tomography (CT), however, revealed calcification within the masses; Erasmus and colleagues¹⁶ published the significant radiographic and CT features in these three patients. On resection, the masses were found to be unencapsulated and were seen to arise from either the parietal or visceral pleural surface. In two of the patients, the lesions were solitary, whereas multiple lesions were seen in the other. Histologically, the tumors were composed of hyalinized collagenous fibrotic tissue interspersed with lymphoplasmacytic infiltrates and calcification; many of these had psammomatous features. Heinaut and coworkers³⁰ also recorded a patient with multiple pleural calcifying fibrous tumors. An additional case was reported by Ammar and associates.² These authors noted that the spindle cells in the tumor were positive for cytokeratin, vimentin, and S-100 protein. No evidence of malignancy existed in these tumors. Surgical resection appears to be curative.

The adenomatoid tumors are small nodular pleural lesions found incidentally at the time of a thoracotomy or on examination of a resected lung specimen. They have been found in the visceral pleura as well as in a pulmonary ligament. These lesions, according to Kaplan and coworkers,³⁴ are made up of epithelial cells with mesothelial differentiation of areas of vacuoles and tubular spaces present in a fibrous stroma. The epithelial nature is confirmed by the cells’ positivity for the presence of keratin on immunohistologic tissue staining. These rare tumors are benign, and their only importance is to differentiate them from pleural metastatic disease in patients with malignancy.

Sclerosing hemangioma is almost always a benign epithelial tumor primarily found in the lungs, and approximately 200 cases have been recorded. In the report of 100 cases by Devouassoux-Shisheboran and associates,¹⁴ four sclerosing hemangiomas were identified as arising in the pleura. The details concerning the cellular origin, pathology, clinical features, and treatment are presented in Chapter 124. The treatment of the pleural-based tumors is surgical resection, and the prognosis should be excellent.

Battifora⁵ reported one case and Gaertner and associates²² reported five cases of biphasic tumors that were interpreted as synovial sarcomas arising from the pleura. These tumors resembled the synovial (biphasic) tumors of the mediastinum reported by Witkin and colleagues⁶¹ (see Chapter 199). In 2002, Colwell and coworkers reported two monophasic and one biphasic synovial sarcomas arising from the pleura.¹⁰ In the monophasic type, the tumor was composed of plump, spindle-shaped cells arranged in short fascicles. In the biphasic tumor, glandular epithelium was interspersed with the aforementioned spindle-shaped cells.
Immunohistochemical studies were positive for pankeratin and epithelial membrane antigen in all these tumors and all were negative for S-100 protein. Translocation t(x:18) was positive in one case. These tumors occur in young adults and are generally rapidly fatal. Although the use of a multimodality approach of surgery and chemotherapy may prolong survival, multiple recurrences are seen. Many chemotherapeutic agents have been used, but the best regimen has yet to be determined. Henderson and associates³¹ stress that it is necessary to separate this tumor from a primary malignant mesothelioma so that the most appropriate therapy may be used in the management of either tumor type.

Hemangiopericytomas are rare tumors arising from the pericytes that encase the basement membrane of the capillaries and small vessels. The tumor was first recorded by Stout and Murray.⁵⁵ These tumors occur very infrequently in the chest and only a few have occurred in the pleura. Cheng and associates⁸ reported a massive hemothorax that was stated to have arisen from a hemangiopericytoma of the pleura. Subsequently, Takahama and colleagues⁵⁶ reported a large pedunculated hemangiopericytoma arising from the visceral pleura of the right lower lobe that was removed by video-assisted thoracic surgery.

These tumors are thought to be of low-grade malignancy. The diagnosis is confirmed by its histologic appearance and its immunohistologic features: positive for vimentin but negative for CD 34, epithelial membrane antigen, keratin, and s-100. Treatment is complete surgical resection.

Dail¹² and Battifora⁶ reported the occurrence of an epithelioid hemangioendothelioma involving the pleura. Lin and associates³⁹ reported seven similar cases. These tumors markedly resemble malignant mesotheliomas but can be differentiated by labeling the tumor with antibodies to von Willebrand’s factor (factor VIII) and to other monoclonal antibodies of epithelioid vascular endothelial-derived cells (CD34, UEA-I, QBEND10, and CD31). Furthermore, these tumors are negative to or have low reactivity to low-molecular-weight cytokeratin. The clinical outlook of these patients is grave; the tumor responds poorly to treatment, and early death is the result of disseminated disease.

A few cases of angiosarcoma of the pleura have been recorded. McCaughey and colleagues⁴¹ reported one case, and Hammar²⁷ noted the observation of one case. Although this tumor, when it occurs in the pleura, may resemble a diffuse malignant mesothelioma, its true nature may be suggested by the presence of vascular-appearing spaces by light microscopy. The presence of Weibel-Palade bodies and the tumor’s positive reaction to vimentin and factor VIII–related antigen, plus its negative reaction to cytokeratin antigens, establishes its vascular origin. The clinical course of the patient is poor.

Moran and colleagues⁴⁴ have described five cases of primary smooth muscle tumors of the pleura. These tumors are extremely rare and should be distinguished from other spindle-cell neoplasms. They test positive for muscle markers, such as smooth muscle actin and desmin, by immunohistochemistry. It should be noted that Gibbs²³ is not convinced that these tumors represent a true entity.

This rare tumor is associated with pleural thickening and hemorrhagic effusion and is readily confused with a malignant mesothelioma. The tumor is made up of large endothelial cells, and the histologic features range from those of an epithelioid hemangioendothelioma to a frank epithelioid angiosarcoma. Immunohistochemical studies by Falconieri and associates¹⁹ revealed the tumor cells to be strongly positive for vimentin and to show weak focal positivity for keratin. Also, at least two or more of the common endothelial markers (CD31, CD34, factor VIII–related antigen, and Ulex europaeus agglutinin-I) are present. The tumor is very aggressive in its malignant behavior; patients usually succumb within a few months of diagnosis.

Liposarcomas of the pleura are exceedingly rare. Only a small number of cases, 15 according to Peng and associates,⁴⁹ of primary pleural liposarcomas have been reported. Wong and associates,⁶² in their report of a single case, also reviewed eight other cases reported in the literature at that time. Histologically, three were myxoid liposarcomas, one was a well-differentiated liposarcoma, and four liposarcomas were not subtyped. Patients were symptomatic only when the tumors reached a large size. The most common symptom was dyspnea. Iqbal and colleagues³² reported a lymphocyte-rich pleural liposarcoma mimicking a right-sided pericardial cyst. This subtype of liposarcoma was initially described by Argani and coworkers in 1997³; none originated in the pleura. The relationship between this subtype of liposarcoma and the well-differentiated inflammatory liposarcoma described by Krauss and associates³⁷ is undetermined.