Definition, Epidemiology and Pattern of Growth
Hemangiopericytoma is a mesenchymal tumor originating from Zimmermann's pericytes (i.e. extravas-cular cells surrounding small vessels) (Zimmerman 1923; Serrano et al. 2002). Hemangiopericytoma, first described in 1942 (Stout and Murray 1942), accounts for only 1% of all vascular neoplasms and for 3-5% of sarcomas (Batsakis 1979). The most frequently involved sites are the lower limbs and trunk (Enzinger and Smith 1976). The rate of head and neck involvement ranges between 15% and 25%, with sinonasal tract localization present in 5% of patients (Batsakis 1979); ethmoid, nasal cavity, and sphenoid are the preferential sites of origin (Serrano et al. 2002).
Over 120 cases of sinonasal hemangiopericytomas have been reported in the English literature, with age at presentation ranging between 4 and 80 years (mean 55) (Catalano et al. 1996). An exceptional case of congenital hemangiopericytoma had also been described (Gotte et al. 1999). No gender predominance is reported (Herve et al. 1999).
Etiology of such a neoplasm remains unknown, even though trauma, steroid therapy and altered hormone secretions are considered predisposing factors
(Reiner et al. 1990; Castelnuovo et al. 2003). Some authors (Catalano et al. 1996), in fact, have hypothesized that previous facial traumas, found in two out of seven patients with sinonasal hemangiopericy-toma, could have led to an abnormal capillary and pericyte proliferation.
Hemangiopericytoma usually does not display a particularly aggressive pattern of growth, producing obstructive symptoms at presentation, even though tendency to bone erosion, with consequent intracra-nial and/or intraorbital extension, has been observed (Hekkenberg et al. 1997).
Hemangiopericytoma of the sinonasal tract are characterized by a less aggressive biologic behavior, if compared to those affecting other sites, such as the pelvis (Catalano et al. 1996).
In fact, malignant transformation with regional or distant spreading are rarely observed. The reason is not clear, even though some speculations have been put forward. According to some authors (Catalano et al. 1996), paranasal sinus hemangiopericytomas may be discovered before than in other sites (i.e. pelvis), due to an earlier clinic presentation.
Differential diagnosis includes benign and malignant lesions, such as lobular capillary heman-gioma, leiomyoma, hemangiomas, solitary fibrous tumor, synovial sarcoma, mesenchymal chondro-sarcoma and other soft tissue tumors, olfactory neuroblastoma, Ewing's sarcoma, non-Hodgkin lymphomas.
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