Intracranial hemangiopericytomas: a wolf in sheep's clothing.

Hemangiopericytomas (HPCs) are extraordinarily rare tumors and comprise less than 1% of all intracranial neoplasms (3). HPCs resemble meningiomas, but they are derived from fibrohistiocytic precursor cells and exhibit molecular changes that are distinct from meningiomas. In their seminal work on meningiomas, Cushing and Eisenhardt (2) described an angioblastic meningioma with a predilection for aggressive behavior and local recurrence. Later, Stout and Murray (10) coined the term hemangiopericytoma to describe a malignant and vascular tumor of the soft tissues, and this tumor was noted to be comprised of capillary pericytes. Begg and Garret (1) subsequently published the first case of a primary intracranial HPC in 1954. HPCs often share radiographic features and clinical presentations of the much more commonly observed meningioma. A neurosurgeon will not quickly forget the experience of finding an HPC at the time of a tumor resection instead of the much more manageable World Health Organization grade I meningioma. The significant vascularity of HPCs and their frequent involvement with adjacent dural sinus and cranial osseous components can make surgical extirpation a harrowing experience. These tumors can thus be the neurosurgical metaphor of the Biblical wolf in sheep’s clothing. In the article by Melone et al. (5) in the March/April issue of WORLD NEUROSURGERY, they describe their extensive experience spanning 30 years with the management of 36 patients with HPC whowerefollowedforamediandurationof118months.Thestudy presentsadetailedanalysisofthesuccessesofcontemporaryHPC management and the challenges that remain. All patients were treated with initial surgical resection. The median overall survival (OS) was 84 months, and the actuarial survival rates at 5 and 10 yearswere 94%and72%,respectively.Preoperativeembolization was performed in 28% of tumors. Gross total resection (GTR) during theinitial treatment phase wasachieved in 70% of patients. Postoperative external beam radiotherapy (EBRT) was performed in 37% and 78% of patients who had GTR and subtotal resection (STR), respectively. Patients who underwent STR also received adjuvant treatment with gamma knife radiosurgery (50%) and proton beam therapy (50%). The overall and recurrence-free survival durations of the patients with GTR was significantly longer than those with STR (P ¼ 0.047 and P ¼ 0.0025, respectively). In a similar study of 63 patients with HPC treated at M.D. Anderson Cancer Center during a 30-year span, Ghia et al. (4) found GTR to be an independent predictor of improved local control (P ¼ 0.008) but not of OS. In a systematic review by the University of California San Francisco group, treatment outcomes for intracranial HPC, the rates of GTR alone, GTR and EBRT, STR alone, and STR and EBRT were 54%, 25%, 12%, and 9%, respectively (7). The OS of patients who underwent GTR was significantly longer than in those who had STR (P < 0.01). In addition, the OS of patients who underwent GTR alone was superior to those who underwent combined STR and EBRT (P < 0.0001). Postoperative EBRT for patients with GTR did not significantly improved OS. Although GTR cannot always be safely achieved in a portion of HPCs, attaining it appears to confer a reasonable survival benefit. Selection biases, differences in patient and tumor attributes, and variations in treatment algorithms could contribute to the differing findings regarding impact of GTR on OS. Nevertheless, surgical resection should intuitively proceed to the point of maximal safe reduction in tumor volume, yet preserving neurological function.