Unusual occurrence of orbital hemangiopericytoma in the zygomatic bone of an adolescent: a case report.

Background: Hemangiopericytoma and solitary fibrous tumor are considered related variants on the same spectrum and both may essentially be the same tumor. They are infrequently encountered in the orbital region while the zygomatic bone is an extremely rare location for these neoplasms to occur.

Case presentation: A 14-year-old boy presented with complaint of deformity of left infraorbital area and a firm, regular mass in the region. Orbital CT scan revealed a well-defined round isodense intraosseous lesion in the lowermost portion of the lateral orbital wall (zygomatic bone), expanding the bone and protruding anteriorly and medially. MRI showed the mass to be heterogenous and strongly enhancing with contrast medium. Inferior transconjunctival orbitotomy was performed and the mass was removed. The histopathologic examination and immunohistochemistry staining results (positive for CD34, CD31 and smooth muscle actin, but negative for CD99, S100, B-cell lymphoma 2 (bcl-2) and desmin) confirmed the diagnosis of hemangiopericytoma. The postoperative course was uneventful, with no evidence of recurrence after 5 years follow up.

Conclusions: This case represents the second hemangiopericytoma reported in the zygomatic bone. Although extremely rare, hemangiopericytoma/solitary fibrous tumor might be considered in the differential diagnosis of intraosseous lesions of the orbital and zygomatic region.