Computed tomography and magnetic resonance imaging of an unusual intraconal orbital osteoma

We report the case of a 64-year-old male patient with a 5 month history of proptosis, motility limitation and vision loss in OD. Visual acuity (VA) was 20/200 in OD and 20/20 in OS. CT showed a large, round, intraconal lesion, with bony density and no apparent connection to adjacent orbital walls. MRI showed a T1-weighted hypointense lesion surrounded by a contrast enhancing capsule. The orbital tumor was excised through a lateral orbitotomy revealing a nodular, round, osseous structure. Histological examination disclosed well-formed lamellar bone trabeculae, with no necrosis or mitosis figures. Immunohistochemical staining was negative for MDM2 and CDK4. After 3 years, there was no evidence of tumor recurrence and VA had improved to 20/30. Intraconal osteomas with no clear attachment to orbital walls are extremely rare. We are aware of a few reported cases in the lid, hand, thigh, tongue, pterygopalatine fossa and brain. To the authors' knowledge, this is the first report in English literature of an orbital intraconal osteoma without any visible relation to the orbital walls.