Paediatric Imaging

Coloboma

fissure or gap in the eyeball that may involve the eyelid, iris, retina, lens or optic nerve. Colobomas are usually congenital but may be acquired. There is an equal sex predilection. Associated conditions include Aicardis syndrome, Warburg syndrome and the CHARGE syndrome (Colobomatous microphthalmos, Heart defects, choanal Atresia, Retarded growth, Genital anomalies, Ear anomalies) association.

Colobomas result from incomplete closure of the primitive optic fissure. A defect in the anterior aspect of the embryonic fissure causes a cleft in the iris pigment epithelium, which results in an iris coloboma. When the sensory components of the retina fail to converge with the retinal pigment layer a retinochoroidal coloboma is formed. The optic nerve head is commonly involved. Colobomas can be unilateral but are more commonly bilateral although often asymmetric in size. Colobomas may be isolated or associated with other ocular abnormalities, including microphthalmos, optic nerve sheath cyst, tilted disc syndrome (Fuchs coloboma) and congenital optic pit. Intracranial abnormalities such as a basal encephalocele or dysgenesis of the corpus callosum may be found in association in addition to cardiac anomalies.

Colobomas involving the eyelid and iris are readily apparent on clinical examination. Ultrasound, CT and MRI reveal more posterior colobomas as cystic outpouchings arising from the periphery of the globe (Fig.1). The lesions are in continuity with the vitreous humour and are enclosed by a deformed and enhancing sclera. The globe is commonly reduced in size. Retro-ocular cysts (colobomatous cysts) may also be present.

KMc/MH

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Fig.1

Axial CT examination showing bilateral colobomata manifested as low attenuation outpouchings from the posterior aspect of each eye globe in the reigon of the optic nerves. (Image courtesy of Dr. W.K. 'Kling' Chong).
Coloboma, Fig.1