Colobomatous ocular cyst presenting as an orbital tumor

Colobomatous orbital cyst is a rare malformation consisting of a cavity lined by neuroectodermic tissue and communicating with the vitreous cavity. It may be associated with microphthalmos and is caused by the impaired closure of the embryonic fissure. The authors report a case observed in a four-month-old male child who had been referred for a suspected orbital angioma. In the left inferior orbit, a round, elastic, bluish mass was seen. LE appeared slightly microphthalmic. RE fundus was characterized by a posterior coloboma. MRI showed a large round mass occupying the whole inferior left orbit; no communication with the vitreous cavity was evident, nor had the mass a cystic appearance. On T1, T2 and proton-weighted images the signal intensity of the mass was slightly superior to that of the vitreous. CT-scan and B-scan ultrasonography showed in LE a large elliptic coloboma communicating with a normally structured eyeball; on CT the cyst and the eyeball had isodense contents. The possibly different fluid contents of eyeball and colobomatous cyst make, in such cases, MRI an unreliable imaging technique compared with ultrasonography and, especially CT scan. CT is able to better demonstrate the eyeball and the cyst walls, as well as the communication between them. © 1992 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.