Intraosseous schwannoma of the frontal bone.

Schwannomas or neurilemomas are relatively frequent benign tumors; however, intraosseous schwannomas are rare. The most common site for intraosseous schwannoma is the mandible. Other sites include the vertebra, ulna, humerus, femur, tibia, patella, scapula, rib, and small bones of the hands. The skull vault is a rare site for intraosseous schwannoma, and only 4 cases have been reported previously in the literature. This article presents a case of intraosseous schwannoma in the frontal bone in an 11-year-old boy. Radiologically, intraosseous schwannomas are lytic, sharply demarcated defects that often expand the involved bone. Perilesional sclerosis may surround the area of central lucency. Histologic features of intraosseous schwannomas are similar to that observed for soft-tissue schwannomas including Antoni type A areas (compactly arranged spindle-shaped cells with palisading or Verocay bodies) and Antoni type B areas (widely separated cells with loose intervening collagenous matrix). In our patient, typical radiologic and histologic findings including immunohistochemistry and electron microscopy results led to a diagnosis of intraosseous schwannoma.