Background: Most pleural neoplasms are metastatic in origin. Primary tumors of the pleura can be categorized as diffuse or localized. Diffuse malignant mesothelioma is more common, related to asbestos exposure, and associated with a poor prognosis. Localized mesothelioma is called localized fibrous tumor of the pleura (LFTP).

LFTP is a less common neoplasm of controversial histogenesis unrelated to asbestos exposure. LFTP exists in benign and malignant forms. Only rarely is the localized fibrous tumor invasive, causing local recurrence after resection; the ratio of benign to malignant tumors is 7:1. The diagnosis of LFTP is important because the tumor is potentially resectable for cure despite its typically large size.

Pathophysiology: The etiology of LFTP is unknown. No association exists with smoking or asbestos exposure. While some studies indicate that LFTP is mesothelial in origin, other reports suggest an origin from primitive submesothelial mesenchymal cells distinct from diffuse malignant mesothelioma. Histologically, the lesion is usually composed of spindle-shaped cells and variable fibrous stroma. Occasionally, oval or polygonal cell may be present. Areas of myxoid degeneration, hyalinization, necrosis, or hemorrhage can be present, especially with large masses.

The malignant variant of LFTP has high cellularity and nuclear pleomorphic mitotic activity. Hemorrhage and necrosis are more frequent in the malignant form. Grossly, LFTP is a firm, soft-tissue mass usually larger than 5 cm in diameter. The tumor arises anywhere in the chest along the pleura, more commonly from the visceral than from the parietal pleura. Lesions can arise from the interlobar fissures. The tumor is often attached by a short pedicle. In one study, approximately 50% of tumors were found to have pedicles, and 50% were broad based.

Intrapulmonary lesions are reported but are exceedingly rare. LFTP is solitary in the overwhelming majority of cases, and the presence of synchronous lesions is extremely rare.

Frequency:

• In the US: LFTP is a rare disease.

Mortality/Morbidity: Resectability has been shown to be the single most important determinant of the patient’s clinical outcome.

Race: No racial predilection has been described.

Sex: Males and females are affected in almost equal numbers.

Age: LFTP can affect all age groups, but it is seen most often in those in their sixth or seventh decades.

Clinical Details: Most patients are asymptomatic, and the lesion is discovered incidentally on chest radiographs (CXRs). When present, symptoms are usually related to the local mass effect of large lesions or to the associated paraneoplastic phenomena. Symptomatic patients may report dyspnea, cough, or vague chest or shoulder discomfort.

Paraneoplastic manifestations have been reported in LFTP, including hypertrophic pulmonary osteoarthropathy and hypoglycemia. Hypertrophic pulmonary osteoarthropathy was reported in 4-35% of patients in some series, and it was found to be associated with LFTP more frequently than with lung cancer. Hypoglycemia is less frequent; it is reported in 5% of patients and could be related to insulinlike growth factor type 2 [IGF-2].

The tumor may become large, occupying much of the hemithorax.

Preferred Examination: Usually, LFTP is incidentally discovered on CXRs. Both CT and MRI findings can suggest the diagnosis of LFTP. However, histopathologic examination is needed for a definitive diagnosis.

Limitations of Techniques: CXR findings are nonspecific, and sometimes, the lesion can be obscured by associated pleural effusion. CT scans and MRIs may show characteristic findings, which are suggestive of LFTP but are not always pathognomonic. The pleural origin of large lesions can be difficult to detect, especially on CXRs and even on CT scans and MRIs.

DIFFERENTIALS

Lung Cancer, Non-Small Cell
Mesothelioma, Malignant

Other Problems to be Considered:

Sarcoma
Elevated hemidiaphragm
Loculated pleural effusion
Pleural metastases

X-RAY

Findings: In most patients, the lesion is detected as an incidental finding on CXRs.

• The CXR appearance is a well-circumscribed, homogeneous, soft-tissue mass that is related closely to the pleura.

   

• The lesion arises anywhere along the pleura and can even be seen in the pulmonary fissures or along the mediastinal or diaphragm pleura.

   

• The margins with lung parenchyma are well defined in most patients.

   

• In 2% of patients, the lesion is somewhat ill defined, and in 2% of patients, the lesion is obscured completely by pleural effusion.

   

• The angle with the chest wall or mediastinum is either acute or obtuse. The obtuse angle is seen more often in small lesions, indicating the pleural origin of the lesion.

   

• Large tumors may present as opaque hemithorax.

   

• Pleural effusion was reported in 17% of patients, especially in patients with the malignant variant of LFTP.

Degree of Confidence: CXR findings are nonspecific; however, a change of the position of the lesion with respiration or gravity is particularly suggestive of a pedunculated LFTP.

False Positives/Negatives: The lesion may mimic a mass of parenchymal or mediastinal origin, and large lesions may simulate an elevated diaphragm.