Exophthalmos from aneurysmal bone cyst of the orbital roof.

An aneurysmal bone cyst of the orbital roof, causing a monolateral exophthalmos in a 15-month-old child with no previous history of head injury, was operated upon and histologically misdiagnosed as a giant cell tumor. Radiation treatment in a dosage (3,740 rad) appropriate for the latter diagnosis apparently caused a massive calcification of the residual mass with persisting exophthalmos. At a second operation the lesion was removed completely and a radical change in the histopathological features was found. 12 years after surgery, there is no evidence of residuals upon roentgenographic and CT scan examinations and the exophthalmos has practically disappeared, while there is a normal visual function in the affected eye. Some points of histopathological and gross pathological differential diagnosis between aneurysmal bone cysts and giant cell ("myeloplaxis") tumors are discussed.