Congenital orbital cysts of neural tissue in two dogs.

A 3-month-old English Cocker Spaniel and a 6-month-old miniature poodle presented with clinical signs related to an abnormal right eye since birth. In both dogs, the right globe could not be identified and was replaced by a fluctuant intraorbital mass covered by a vascularized mucous membrane. Ultrasonography demonstrated that both masses were cystic structures markedly larger in size than the normal contralateral globes. In both cases, surgical excision revealed a multilobular cyst filling the whole orbital cavity. Histopathologic examination and immunostaining for glial fibrillary acid protein and S100 protein supported a diagnosis of neural cysts associated with ocular dysplasia. The definitive diagnosis was congenital cystic eye and microphthalmos with cyst for the Cocker Spaniel and miniature poodle, respectively. Karyotype was normal in both dogs. Congenital cystic eye and microphthalmos with cyst result from defects in early embryonic life that arise following formation of the optic vesicle and prior to closure of the optic fissure. To the authors' knowledge neither has been reported in the canine species. They should be considered in the differential diagnosis of orbital cysts in dogs.