A Large Solitary Fibrous Tumor of the Mediastinum

Discussion

Solitary fibrous tumors (SFTs) are rare mesenchymal spindle cell tumors, generally located in the pleura. They have been reported in various parts of the human body, including the peritoneum,^[1] mediastium,^[2] extremities,^[3] orbit,^[4] and parotid gland.^[5] SFT of the mediastinum has been rarely reported in the literature. The frequency of the mediastinal localization is the same in men as in women and the tumor generally develops between the 5th and 7th decade of life.^[6]

The patents may complain of cough, chest pain or dyspnea,^[7] but mostly are asymptomatic.^[6] It has been reported that some patients with SFT had severe hypoglycemia and high molecular weight serum IGF-II, which was found more in the tumor cystic fluid than in serum. Immunohisochemically, IGF-II was localized in the so-called Golgi area of the tumor cell. It was concluded that the tumor cells can secrete IGF-II. After surgical resection of the tumor, high molecular weight IGF-II was not detected in the serum and the hypoglycemia resolved.^{[8, 9]}

Radiological examination is important to diagnose SFT. The image of the tumor in the chest radiograph depends on its size and varies from a sharply delineated round or lobulated mass, with or without pleural effusion, to opacification of the complete hemothorax. CT scanning and MRI are important to evaluate the relationship of the tumor to neighboring structures and to evaluate the resectability of the tumor.^[10] However, CT-scanning and MR imaging are very useful but non-specific. SFTs can not be distinguished from other mediastinal tumors in radiological examinations.^[11]

Histologically, SFTs are characterized by fibroblastlike cells and connective tissue in varying proportions. The “patternless pattern” and the hemangiopericytoma-like pattern is the most common arrangement.^[12] Upon immunohistochemical analysis, most of the tumor cells are strongly positive for CD34, but negative for cytokeratin, S-100 protein, factorVIII-related antigen and smooth-muscle actin.^[13] CD34 immunoreactivity has been recognized to be an adjunct for the diagnosis of SFT. But in one study, CD34 immunoreactivity was found in other spindle cell neoplasms, such as neurofibromas, spindle cell lipomas and dermatofibrosarcomas, similar to SFT, but they were different in the immunoreactivity of the bcl-2 protein. Therefore this antigen can be used together with CD34 to distinguish solitarty fibrous tumor from other spindle cell neoplasms.^[14]

Needle aspiration biopsy for SFT produces inconclusive results because the tumor is composed of acellular and hypercellular portions and the method does not provide enough tissue for cytologic analysis. However, Apple et al.^[15] reported that with the help of CD34 immunoreactivity, accurate diagnosis was obtained in two cases of SFT by fine needle aspiration biopsy before surgery. In a study of a series of 5 patients with SFT of the pleura, 4 were diagnosed by thransthoracic cutting needle biopsy preoperation.^[16] By the same method, we also produced the correct diagnosis for our patient. Needle aspiration cytology combined with immunohistochemical analysis seems to be a safe and rapid method of providing a comfirmatory diagnosis, but it still needs future investigation on a large series of patients.

A SFT is usually a slow-growing tumor with favorable prognosis. Most extrapleural SFTs behave in a benign fashion even in a higher histologic grade group.^[17] Although SFT in the mediastinum shows more aggressive behavior than in the pleura,^[7] total resection of the tumor is also advisable for patients, which is the most important indicator for clinical outcome.^{[17, 18]}