Background: Brown tumors have rarely been described as involving the orbital bones. In this article we present the radiological and clinical properties, diagnosis and treatment of an orbital brown tumor case with primary HPT caused by parathyroid adenoma.
Case Report: A 38-year-old woman presented with left-sided facial pain and history of leg pain from 1.5 years before that time, with walking difficulties. In imaging, left maxillary erosion was found. She underwent an excisional biopsy and the mass was diagnosed histologically as eosinophilic granuloma. A few months later the patient had right-sided facial pain again and progressive visual loss. In images, fluid-fluid level was noted in the cystic component of the mass. Right side exophthalmus and downward deviation of the globe was seen. Magnetic resonance imaging showed a well-defined extra-conal complex mass, with hypointense on T-1 and hyperintense on T-2 weighted images with fluid-fluid levels. Postoperatively the patients vision improved dramatically. Excision of the parathyroid adenoma normalized her metabolic status.
Conclusions: Brown tumor is an extremely rare manifestation of primary HPT. Delay in diagnosis can result in unnecessary complications. The management is multi-disciplinary, and therapeutic options should target the underlying cause.

Keywords: orbital brown tumor, primary hyperparathyroidism, parathyroid adenoma