Solitary fibrous tumor of the central nervous system: a clinicopathologic study of 24 cases
OBJECTIVES Hemangiopericytomas (HPCs) are rare neoplasms with relatively high rates of recurrence and extracranial metastasis. Though the differential diagnoses from angiomatous meningiomas and from solitary fibrous tumors (SFTs) are both important, the latter diagnosis is somewhat more important in light of the benign prognosis of SFTs and the difficulties in distinguishing SFTs from HPCs. Newly developed immunohistochemical methods reveal differences in the specific immunohistochemical features of HPCs and SFTs. To elucidate whether SFTs have been misdiagnosed as HPCs in the past, our group used recent immunohistochemical methods to re-evaluate tissues that had been originally diagnosed as HPCs. We also compared the clinical features of these cases. PATIENTS AND METHODS Thirteen sequential cases of HPC diagnosed in Kanazawa University Hospital and Kumamoto University Hospital between 1970 and 2006 were retrospectively analyzed by immunohistochemical staining for CD34, Bcl-2, epithelial membrane antigen (EMA), vimentin, and S100 protein, and by measurement of the MIB-1 labeling index (LI). The cases were then re-evaluated and newly diagnosed based on the results of the immunohistochemical stainings. The clinical course of each case was also evaluated. RESULTS Four of the 13 cases were newly diagnosed as SFTs and eight were reconfirmed as HPCs, based on the immunohistochemical studies for CD34, Bcl-2, and reticulin staining. One case was newly diagnosed as meningioma on the basis of a strong EMA positivity. The MIB-1 LI was less than 1% in 12 of the cases. In two cases, one case of HPC and the other of meningioma, the MIB-1 LI was relatively high, 8% and 4% respectively. All eight of the HPCs recurred, and 5 of the HPC patients died of the disease. Only one case of the SFTs recurred. CONCLUSION Our study suggests that a relatively high percentage of the tumors diagnosed as HPCs in the past may have in fact been intracranial SFTs. Immunohistochemical examinations of CD34, Bcl-2, and reticulin stains are keys for the differential diagnosis. Given that SFTs have a considerably better prognosis than HPCs, it is important to carry out meticulous immunohistochemical examinations for the primary diagnosis.