Role of computed tomography in the preoperative diagnosis of giant benign solitary fibrous tumor pleura

Sir, We read with interest the article entitled “Giant solitary fibrous tumor: Clinical dilemma and diagnosis” published in the April-June issue of Lung India.[1] Solitary fibrous tumor pleura (SFTP) is a localized, well-circumscribed, mesenchymal tumor of uncertain cell origin. Though the majority of these tumors are benign, about 22-36% can be malignant.[2,3] The majority of benign SFTPs are cured with local resection. Even patient with massive benign lesions may do well with re-expansion of the compressed lung after surgery. The average size of benign and malignant SFTP is 13.2 cm and 14.4 cm, respectively.[3] Sixty-two percent of SFTPs are >10 cm.[2] Sometimes SFTP grow to a diameter of 30-40 cm. Numerous reports described “giant” benign SFTP but the precise size has not been established in the definition of “giant” lesions. We believed that benign SFTPs may be defined “giant” when the lesions have a diameter >15 cm and benignancy criteria have been established with accuracy. The mitotic-figure-per-10-high-power fields (HPFs) index was determined by counting two to five sets of 10 consecutive HPFs (×400) in most cellular tumors and then proceeding randomly. Benign SFTPs may fill the hemithorax, compress the adjacent lung and produce symptoms, but they are slow growing and do not invade adjacent tissues. We recently observed a 61-year-old female who was referred to our hospital with cough and dyspnea. Computed tomography (CT) showed a large mass, with well-defined borders, occupying the left hemithorax with partial saving apex of ipsilateral lung displacing the mediastinum to the right. A thoracotomy with complete surgical resection of the tumor was performed. Histologically the tumor showed a “patternless” architecture characterized by the coexistence of hypo- and hypercellular areas separated by fibrous stroma having “hemangiopericytoma-like” branching blood vessels. The lesion appeared as a sharply circumscribed mass pushing, but not invading, the borders with the adjacent lung parenchyma. Mitotic figures were <4 per 10 HPFs, necrosis and hemorrhage was not evident, and pleomorphic, hyperchromatic, or anaplastic nuclei were absent. The diagnosis of “benign SFTP” was performed. The neoplastic spindle cells were immunopositive for CD34 and vimentin, and immunonegative for cytokeratins, smooth muscle actin, desmin, muscle-specific actin, S-100 protein, CD31, and factor VIII. This staining pattern assists in differentiating SFTPs from other spindle cell neoplasms of the pleura including diffuse malignant mesothelioma. SFTP was probably first mentioned by Wagner in 1870, but pathologic description did not appear until 1931 (Klemperer and Rabin).[4] The first large collected review series of SFTPs describing the clinicopathologic features appeared subsequently in 1981, reported by Briselli et al.[5] (368 cases), in 1989 by England et al.[2] (223 cases), and in 2003 by Rosado-de-Christenson[3] (82 cases). The usual initial diagnostic test for SFTP is a chest radiograph, which is not specific but serves to document the presence of a mass in the chest. The chest CT scan is the key examination, which more clearly shows the size and location of tumor and aids in surgical planning. The CT morphologic features of 78 localized fibrous tumors of the pleura (61 benign and 17 malignant) have been examined by Rosado-de-Christenson et al.[3] These authors concluded that small tumors without gloss necrosis, hemorrhage, or cystic change may exhibit homogeneous alteration on unenhanced and less frequently on contrast-enhanced chest CT scans. The majority of SFTPs exhibit heterogeneous attenuation on CT scans characterized as intraregional geographic, focal or linear areas of low attenuation that often correlate with hemorrhage, necrosis, or cystic changes. Calcifications may occur in one-fourth of cases. Atelectasis of the adjacent lung and mass effect on the mediastinum are common associated findings. Briselli et al.'s study[5] examined 360 cases of SFTPs taken from the literature and reported eight new cases. These authors examined clinical findings, gross, light and electron microscopic findings of the tumors but the radiological features were not reported. In England et al.'s study[2] a CT scan was been performed only in two cases. Cardillo et al.[6] examined 55 cases of SFTPs but distinction between benign and malignant lesions was not been made. The radiological findings of giant benign SFTPs have been reported with accuracy only in single cases or small series [Table 1].[1,5,7–16] In the large collected review series the radiology of large SFTPs has been reported in the “Results” section of the paper. But specific radiological characteristics of >15 cm SFTPs have been described with accuracy only in few cases. In conclusion CT scan is the diagnostic preoperative procedure of choice for benign SFTP. CT scan may establish the complete excision of the lesion and the presence of a distinct peduncle. Fine needle-aspiration biopsy is not a reliable diagnostic tool.[17] Symptomatic presentation and the impression of a nonpleural tumor by CT have been reported to be related to a malignant pathologic diagnosis.[18]