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* From the Department of Internal Medicine (Drs. Patel, Bishay, George, and Saleh), Division of Pulmonary & Critical Care, New York Methodist Hospital, Brooklyn, NY; and St. John’s Clinic (Dr. Bakry), Springfield, MO.
Correspondence to: Neelam Patel, MD, New York Methodist Hospital, Internal Medicine/Division of Pulmonary & Critical Care, 506 Sixth St, Brooklyn, NY 11215; e-mail: neelampatel_md{at}yahoo.com
Abstract
We report a case of a 65-year-old male patient who presented with gradually worsening dyspnea over 2 years. History was significant for smoking and the absence of any hazardous occupational exposure. The clinical findings at presentation included absent breath sounds and stony dullness on the left side, with tracheal deviation contralaterally and clubbing. A chest roentgenogram showed a left-sided opacity occupying almost the entire left hemithorax. A subsequent CT scan of the chest revealed an intrathoracic, extrapulmonary lesion producing a mediastinal shift. Surgical resection of the mass was performed, and pathology, along with immunohistochemical studies positive for CD34 and negative for epithelial markers, confirmed the diagnosis of solitary fibrous tumor of the pleura (SFTP). SFTP is a rare neoplasm, and diagnosis is often difficult. Suspicion of SFTP should arise in the setting of a patient presenting with a paucity of symptoms (except in the case of an accompanying paraneoplastic syndrome), the absence of exposure to asbestos, and a large mass with sharp margins and encapsulation seen on a chest radiograph.
Key Words: CD34 • intrathoracic mass • pleural tumor • solitary fibrous tumor
A 65-year-old man presented with worsening dyspnea over 2 years. A thoracentesis had been performed about a year prior to presentation, and the patient revealed no further information about his history. A review of systems was unremarkable. He had quit smoking 25 years ago and had no hazardous occupational exposure. A physical examination revealed absent breath sounds and stony dullness on the left side, tracheal deviation to the right, and clubbing.
Laboratory test findings were within normal limits. A chest roentgenogram (Fig 1 ) at the time of presentation showed a large opacity occupying almost three quarters of the left hemithorax, with a tracheal shift to the right. No air bronchograms were seen. A subsequent CT scan (Fig 2 ) of the chest revealed a large, solid, pleural-based mass producing a significant shift of the mediastinum to the contralateral side. The mass was homogeneous with clear borders and demonstrated an acute angle with the abutting chest wall. There was no invasion of the ribs or lung parenchyma; no calcification or pleural effusion was visible.
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Diagnosis: solitary fibrous tumor of the pleura
A pleural tumor was suspected by radiologic evidence of an extrapulmonary mass, and the patient was sent for resection. A mass 23 x 22 x 9 cm in size was excised in two large fragments. On gross view, the tumor masses were seen to have lung tissue adhered to the outer surface as a result of compression. On the cut surface, areas of focal necrosis and hemorrhage were seen. Histopathology revealed a "whorled pattern" seen with hematoxylin-eosin (H-E) staining on low-power microscopy (Fig 3 ), and was reported to be of mesenchymal origin. Immunohistochemical reaction confirmed the diagnosis of solitary fibrous tumor of the pleura (SFTP) positive for CD34 and negative for cytokeratin. Microscopy on high-power field with H-E staining revealed mitotic figures (Fig 4 ) with a high rate of activity, cellular pleomorphism, and areas of necrosis and hemorrhage. These characteristics were strong indicators that this slow-growing tumor, which may have been benign initially, was now undergoing malignant transformation. The patient had a difficult recovery period requiring prolonged postoperative mechanical ventilation but had gradual reexpansion of the left lung with little residual scarring. His dyspnea was notably improved at a follow-up visit a few months later.
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SFTP, previously known as local, fibrous, or benign mesothelioma; subpleural, submesothelial, or pleural fibroma; and fibrosarcoma, is a rare neoplasm occurring in 2.8 cases per 100,000 persons, as recorded by the Mayo Clinic Registry. Although previously controversial, it is now believed to originate in the submesothelial connective tissue of the pleura. Two thirds of SFTPs arise from within the visceral pleura, with the remaining one third arising from the parietal, diaphragmatic, or mediastinal lining.1 It is usually diagnosed in the sixth to seventh decade of life with no gender preponderance. There is no link to smoking or environmental exposures, although occasional tumors have developed after radiation therapy to the chest wall.
About half of the patients are asymptomatic and receive diagnoses based on incidental radiographic findings. In cases of larger tumors resulting in compression of the surrounding structures, vague chest pain, dyspnea, or cough may be the main complaint. In a review of 350 cases, ipsilateral pleural effusion was observed in 17% of cases (more commonly found in malignant forms), hypertrophic osteoarthropathy was observed in 10% of cases, and hypoglycemia was observed in 5% of cases.1 These paraneoplastic syndromes will usually recede after resection.2 The association of osteoarthropathy is stronger with SFTP than with adenocarcinoma of the lung. In fact, a large thoracic mass with this paraneoplastic syndrome should raise suspicion of this diagnosis. Hypoglycemia is more common with right-sided tumors and is three times more common in women compared with men.3 Our patient did not have either osteoarthropathy or hypoglycemia.
Radiologically, the tumor often presents as a homogenous, well-encapsulated, or pedunculated mass. If pedunculated, changes in position of the tumor follow changes in respiration or body position. Otherwise, the mass should appear sharply delineated from the surrounding structures and show tapering margins. As the tumor enlarges into the pleural space, it compresses the surrounding structures. Tumors can grow to be of varying size, ranging in diameter from 1 to almost 40 cm.4 If the tumor size is small (usually < 4 cm), it will likely produce obtuse angles with the abutting wall, helping to distinguish it from an intrapulmonary thoracic mass. In tumors of larger proportion, an acute angle predominates, and this rule is of little assistance in establishing the origin of the tumor. Suspicion should be raised when this mass is seen in an extrapulmonary location with the typical radiographic features described above. On occasion, calcification or pleural effusion can be seen.
CT scanning is a reliable and cost-effective tool in the diagnosis of SFTP. Contrast enhancement on CT scans can be seen depending on the vascularity of the tumor. On the other hand, areas of low attenuation would correspond to areas of myxoid or cystic degeneration, and hemorrhage. The combination of these characteristics is typical and aids in establishing the diagnosis of SFTP.5 Since we did not have an image with contrast for our patient, we could not determine the extent of the vascularity of the tumor. With the areas of focal necrosis and hemorrhage seen on the gross cut section of the mass, we could speculate that these areas corresponded to areas of low attenuation on the CT scan. MRI can be a useful alternative, but its use is limited to establishing fibrous tissue characteristics.6 A benign characteristic can be predicted by low-intensity signals on T2-weighted imaging, in contrast to the high-intensity signals found in images of pulmonary carcinoma. At times, signal intensity may rise after the injection of IV gadolinium. MRI may also assist in evaluating the extent of growth and the possibility of invasive tumor types. Ultrasound and 18-fluorodeoxyglucose positron emission tomography are other alternate techniques used in the imaging of pleural disease, although they have not been shown to be superior to CT scanning.7
The differential diagnosis of SFTP includes all primary soft-tissue tumors arising from the mesenchymal layer and occupying the pleural space. These include lipoma, leiomyosarcoma, rhabdomyosarcoma, malignant fibrous histiocytoma, angiosarcoma, epithelioid hemangioendothelioma, and chondrosarcoma.8 Other tumors that can be included in the differential diagnosis are neurofibroma, intercostal nerve neurilemoma, peripheral lung cancers, and pleural metastasis. Since the radiologic features of these tumors are nonspecific, immunohistochemical confirmation is necessary. Another pleural tumor that must be distinguished from SFTP radiologically is malignant mesothelioma. In contrast, malignant mesothelioma usually presents with unremitting chest pain, is smaller in size, and tracks along the pleural space instead of projecting into the thorax. If prior asbestos exposure exists in these patients, pleural plaques can be seen (calcified and noncalcified) and, if present, are more likely to occur at the bases and in lower lung zones. The absence of pleural plaques does not exclude the diagnosis of mesothelioma, which still makes it difficult to differentiate it from other pleural tumors.
Grossly, the tumors are sharply defined, smooth, lobulated masses of homogeneous density. Due to compression of the surrounding structures, they may contain adherent lung parenchyma or soft tissue at the edges. This should not be mistaken for invasion. On cut sections, they show a lobulated or whorled appearance and must be differentiated from a leiomyoma. They can contain cystic cavities, calcification, hemorrhage, and necrosis. Histologically, most characteristic for this tumor is the "patternless pattern" in which spindle cells are haphazardly arranged. Occasionally, there is a storiform or pallisading pattern, and this must be differentiated from other soft-tissue tumors. The spindle cells are intermixed with varying amounts of collagen, focal myxoid changes, or hyalinization of fibrous tissue. Tissue sampling will confirm the diagnosis. In some cases, fine-needle aspiration biopsy, rather than cytology alone, can be sufficient.9 Occasionally, the diagnosis can be established only after resection. Confirmation should be gained through immunostaining that is positive for CD34; almost 80 to 100% will express this marker. The staining will also be negative for cytokeratin, S-100, and vimentin. In contrast, the sarcomatous form of diffuse malignant mesothelioma is positive for cytokeratin, and negative for CD34.10 Thus, immunostaining for CD34 is an essential step in differentiating SFTP from other mesothelial tumors arising in the pleura.
Malignancy should be suspected if hemorrhage, necrosis, and high mitotic rates (ie, 4 per 10 high-power fields) are present. The majority of these tumors are benign, with slow growth; one case was reported11 of a tumor being excised almost 20 years after its diagnosis. Rarely, tumors appearing benign at first may undergo malignant transformation. Malignant tumors are also found to have a higher association with pleural effusions, parietal pleural origin, and invasion of the chest wall. Metastasis may sometimes occur via the hematogenous route. Metastasis may be seen in the liver, CNS, spleen, peritoneum, adrenal gland, GI tract, and bone.6
Management of these tumors is accomplished by complete surgical resection, given its potential for malignancy; in one case series,1 malignancy was reported at a rate of 12%. After excision, recurrence can occasionally occur, although the rates are low in benign tumors. In a review of 223 cases of SFTP, a single excision cured 100% of patients with benign tumors, and 45% of patients with malignant tumors. The remaining patients with malignant tumors (55%) died due to tumor invasion or metastases.3 Perioperative mortality is reported to be very low. Techniques such as preoperative embolization of highly vascular SFTPs have been used to reduce intraoperative blood loss.12
In summary, SFTP is an uncommon tumor. The diagnosis of SFTP should be considered in the setting of a patient presenting with a paucity of symptoms (exceptions remain in the setting of a paraneoplastic syndrome or with tumors large enough to cause compression), the absence of exposure to asbestos, and the radiographic appearance of a mass with large size, sharply demarcated margins, and encapsulation on chest roentgenogram or CT scan. CT scanning is superior in establishing the diagnosis. Contrast CT scanning can be informative in recognizing additional characteristics such as vascularity, degeneration, and hemorrhage. MRI can determine the extent of growth and can be used in addition to CT scanning in determining resectability. Despite the clinical and radiographic characteristics that are typical of this diagnosis, tissue pathology with immunohistochemical confirmation of CD34 is necessary. Benign SFTPs can be cured by single excision, with low rates of local recurrence. Recurrence can occur even after several years; thus, it may be appropriate to follow up these patients periodically. Malignant SFTPs generally have a poor curative rate.
Footnotes
Abbreviations: H-E = hematoxylin-eosin; SFTP = solitary fibrous tumor of the pleura
The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Received for publication February 22, 2006. Accepted for publication July 27, 2006.
References
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