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A 5 year old girl who failed her school vision screening
Digital Journal of Ophthalmology 2004
Volume 10, Number 5
February 19, 2004
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| Diagnosis and Discussion | Persistent fetal vasculature (PFV), also called persistent hyperplastic primary vitreous (PHPV), presents as a spectrum of anterior and posterior ocular anomalies associated with failed regression of the hyaloid arterial system during fetal development. Characteristic anterior segment findings in the disease are variable and can include microphthalmia, anterior remnants of the hyaloid arterial system and tunica vasculosa lentis, retrolental membranes, ectropion uveae, dragged ciliary processes, varying degrees of cataract, corneal opacification, and secondary angle closure glaucoma. Posterior segment findings include primary malformations of the optic disc, hyaloid arterial remnants, retinal dysplasia, macular hypoplasia, prepapillary cysts, retinal folds, retinal detachment, and congenital retinal nonattachment. (1,2) PFV is usually unilateral and non-genetic, although bilateral and familial cases have been reported, and it is occasionally associated with other ocular anomalies including Morning Glory Syndrome, Peters' anomaly, and ocular colobomata. Various forms of PFV are also known to be associated with clinical genetic syndromes, including Norrie's disease, trisomy-13, -15, -18, and Walker-Warburg syndrome, among others. (1)
Congenital vitreous cysts, although rare, are well-known ocular developmental anomalies, and several case series reviews have been published. (3,4) Vitreous cysts have been reported as free-floating masses or with anterior or posterior attachments. (5,6) Rare reports have described cysts in association with prepapillary hyaloid remnants. (7) We present an unusual case of a child with bilateral PFV associated with multiple bilateral congenital vitreous cysts.
Discussion
Congenital cysts of the vitreous are rare ocular developmental anomalies. Numerous isolated cases have been reported and occasional associations with other congenital ocular anomalies have been noted as described above. Vitreous cysts have been reported in cases of ocular inflammatory disease and following surgical trauma (8,9); however, the origin and embryology of congenital vitreous cysts remains controversial. Previous authors have speculated that vitreous cysts originate from various sites including the ciliary processes, the pars plana ciliaris, colobomata, Bergmeister's papilla, and cystic transformation of the hyaloid artery or its glial sheath. (2,7,10) Vitreous cysts have also been reported in association with juvenile retinoschisis (11) and retinitis pigmentosa. (12)
The embryological development of the vitreous is a 3-step process. The primary vitreous begins to develop at about 3 weeks of age and is complete by about 9 weeks. The hyaloid artery and its ramifications, the vasa hyaloidea propria and tunica vasculosa lentis, develop from mesodermally derived cells during formation of the primary vitreous. Following this, the inner retina begins liberating collagen, and Mueller cells and hyalocytes secrete the hyaluronic acid of the secondary vitreous. Formation of the secondary vitreous displaces the primary vitreous centrally, the condensed junction of which forms Cloquet's canal. The tertiary vitreous is secreted last and condenses to form the suspensory ligaments of the lens (zonules). Formation of the secondary vitreous is completed by the end of the first trimester, whereupon the vascular components of the hyaloid system begin a slow process of involution regulated in part by macrophage-mediated apoptosis. Recent studies of knockout mice have suggested possible roles for TGF-B2, TBDN-1, p53, and Arf in mediating vascular regression during vitreous development. (13,14)
Three vitreous cysts examined by light and/or electron microscopy have been reported in the literature. One developed following multiple retinal detachment surgeries and was found to contain gliotic retinal tissue, likely due to seeding of the vitreous with retinal tissue. (9) The origin of a congenital cyst was posited to be from the pigment epithelium of the pars plicata ciliaris in another patient. (10) A third report of a congenital vitreous cyst showed it to be composed of heavily pigmented cells connected by tight junctions and containing microvilli and melanosomes at various stages of maturity. Immunohistochemical analysis was positive for carbonic anhydrase. From these findings and location of the cyst in Cloquet's canal, the authors concluded that the cyst was a congenital choristoma of the primary hyaloidal system. (15)
These authors and others have recognized the association of congenital vitreous cysts with common embryologic remnants of hyaloid and vitreous development. (7,8,16) Cysts have been associated with anterior hyaloid remnants (Mittendorf dots) and posterior remnants (Bergmeister papillae), sometimes with connections between the structures. Our patient had different types of cysts in her eyes and at different locations. There was one large cyst in the right eye that appeared to be tethered to the hyaloid artery in the mid-vitreous. There were several smaller cysts in the left eye that appeared to be anchored at the level of the vitreous base. There were no attachments between the hyaloid artery and these structures in the left eye; however, small attachments to residual vessels of the vasa hyaloidea propria or posterior vessels of the TVL may have been present and not identified.
It has been previously proposed, and this case suggests, that vitreous cyst formation may result from events that lead to aberrant regression of the hyaloid vasculature during ocular embryogenesis and may reflect cystic transformation of the glial remnants of the hyaloid vasculature. (2,6-8,17) The mechanism of cyst formation in the anterior vitreous is thought to be due to similar cystic transformation of more anterior hyaloid vessels that ramify throughout the secondary vitreous. Myxomatous and osseous changes in the associated anterior fibrous tissue have also been reported. (2) This patient represents an unusual and extreme example of multiple congenital, bilateral vitreous cysts in association with PFV.
These studies supported in part by an unrestricted Departmental grant from Research to Prevent Blindness Inc., New York, NY, and The Plough Foundation, Memphis, TN. | |
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