Acta Neurochir (Wien) (2006) 148: 1123–1125 DOI 10.1007/s00701-006-0879-1 Brief Report of Special Case Microphthalmia and colobomatous cyst of the orbit F. Doglietto 1 , L. Massimi 1 , A. Dickmann 2 , G. Tamburrini 1 , M. Caldarelli 1 , and C.Di Rocco 1 1 Institute of Pediatric Neurosurgery, Catholic University Medical School, Rome,Italy 2 Department of Ophthalmology, Catholic University Medical School, Rome, Italy Received February 25, 2005; accepted July 20, 2006; published online September 8, 2006 # Springer-Verlag 2006 Introduction Colobomatous cyst is a rare entity to be considered in the differential diagnosis of congenital orbital tumours [4, 6]. Ocular colobomata are congenital malformations caused by defective embryogenesis. Microphthalmia with cyst is a distinct phenotypic form of colobomatous malformation. We describe the case of a child who presented with con- genital exophthalmia due to a posterior colobomatous cyst. Case report This child, born at 38 weeks gestation, presented at birth with right exophthalmia. MRI showed a posterior orbital cystconnected to and displacing a microphthalmic eye, infero-medially (Fig. 1B).Ocular ex- amination documented microphtalmia and a right iris coloboma as- sociated with a corioretinal coloboma in the infero-nasal quadrant (Fig. 1A, F). Visual Evoked Potentials were not elicited on the colobo- matous eye. No other ocular, cerebral or systemic lesions were disclosed. When the child was 3 month old, an increase of the cyst with con- sequent orbital enlargement was evident at MRI (Fig. 1C, D) and caused further proptosis (Fig. 1F),eye extreme adduction and hypotropia. The child underwent a fronto-orbital craniotomy and excision of the cyst after ligature of the neck connecting it with the globe. The ocular globe was preserved. Histological examination documented neuroectodermal cells lining a fibro-muscular cystic wall.Post-operative course was characterised by resolution of exophthalmia (Fig. 1G).A CT scan re- corded the total excision of the cystic lesion (Fig. 1E). Notwithstanding the present orbitalenlargement, an orbitalimplantwill probably be needed in the future to ensure normal orbital growth. Discussion Colobomata generally result from a failure of the foe- tal or choroidal fissure to close during the 5th to 7th week of foetal life. This is the period between the in- vagination of the optic vesicle and the closure of the foetalfissure. Almostany ocular structure may be in- volved,including the cornea, iris, ciliary body, zonule (lens), choroid, retina, optic disc, and=or optic nerve [4]. Colobomata can occur as an isolated finding or in con- junction with other body malformations. The orbitvolume is usually reduced due to micro- phthalmia. Only rarely may the orbit enlarge when the coloboma is associated with an expansive cyst, as in our case. The mechanism of cyst formation is poorly under- stood,butsome authors have speculated that it results from prolapse of intra-ocular contents through a scleral defect. Another explanation is that microphthalmia with cyst represents ectasia of the colobomatous globe [4]. Three patterns of association of microphthalmia and intra-orbital cyst have been described: a relatively nor- maleye with a small cyst;an obvious cyst associated with a grossly deformed eye; a large cyst which pushes the globe backwards so that the latter is not visible on inspection. While the first condition might not require surgicaltreatment, if normalorbit enlargement can be expected and some vision is retained, surgery is usually the treatment of choice for the other two condi- tions,which are usually associated with clinical blind- ness [2]. Although a few cases of permanent collapse of the cystfollowing aspiration have been reported [5], the cysts tends to recur [1]. Consequenty total excision is reccomended [1, 3].