Retinal Dysplasia Mimicking Intraocular Tumor: MR Imaging Findings with Histopathologic Correlation

SUMMARY: We report a 6-month-old boy who presented with unilateral leukocoria, retinal detachment, and a retrolental mass in a microphthalmic eye based on retinal dysplasia with concurrent optic nerve aplasia. Dysplastic retinal tissue, a rare congenital defect, may create a clinical and radiologic picture of an intraocular mass closely resembling tumor tissue. MR imaging findings with histopathologic correlation are presented to facilitate discrimination of the more common causes of leukocoria.

A 6-month-old boy was admitted with a history of a smaller left eye since birth and leukocoria for 1 month. He was born to nonconsanguineous parents at 41 weeks' gestation. Ophthalmic examination revealed no abnormalities in the right eye. The left eye was microphthalmic, with a corneal diameter of 9 mm (right, 10 mm). A yellowish-white retrolental mass, projecting from the inferomedial quadrant into the vitreous, was present (Fig 1). The mass in combination with retinal detachment obscured clear visualization of optic nerve disc and macula. Prominent irregular feeder vessels and small focal hemorrhages covered the surface of the mass. Differential diagnosis based on these findings included ciliary body medulloepithelioma, anteriorly located retinoblastoma, and persistent hyperplastic primary vitreous (PHPV).
Ultrasonography showed a noncalcified mass with high reflectivity. MR imaging showed a mass arising from the nasal ciliary body region with high signal intensity (SI) on T1-weighted (T1WI) and low SI on T2-weighted (T2WI) images, combined with a normal-appearing vitreous and tent-shaped retinal detachment with subretinal exu-date (Fig 2). The anterior chamber and lens showed no abnormalities. The right orbit, optic nerve, and portions of the optic chiasm related to the nerve were normal. The optic nerve and sheath complex were not visible within the left orbit or anywhere along the usual course of the nerve (Fig 2). Total aplasia of the left optic nerve was not combined with other congenital central nervous system (CNS) abnormalities. The mass showed intense homogeneous enhancement. Ultrasonography and MR imaging findings were more consistent with medulloepithelioma or PHPV, and a retinoblastoma could be ruled out. Five weeks later, enucleation was required due to enlargement of the mass with an increase of intraocular pressure, shallowness of the anterior chamber, and progression toward a phthisis bulbi.
Histopathologic examination revealed a total absence of the optic nerve, scleral lamina cribrosa, and central retinal vessels. A vascularized mass was present anteriorly in the vitreous cavity on either side of the lens, adjacent to the ciliary body (Fig 3). The anterior eye segment showed no abnormalities. The mass consisted of an abnormal retinal differentiation, with disorganization, proliferation, and rosette formation in the photoreceptor cell layer. In the thin retina that was not incorporated in the mass, no ganglion cell layer was present. The posterior eye segment showed no persisting hyaloid artery nor a thin stalk connecting the posterior lens and the optic disc region, presumed to represent a remnant of the Cloquet canal. The pathologic diagnosis was retinal dysplasia with concurrent optic nerve aplasia.

Discussion
Retinal dysplasia is more of a descriptive term, rather than a delineation of a clinical condition and may be a component of a group of congenital disorders, such as Norrie disease, trisomy 13, or Walker-Warburg syndrome. Ocular findings in these disorders are mostly bilateral and accompanied by systemic and CNS abnormalities. Unilateral retinal dysplasia is usually not associated with a specific syndrome. Histopathologic examination demonstrates a reduction or complete absence of retinal ganglion cells, their nerve fibers, and retinal blood vessels, which can result in a congenital (usually tentshaped) retinal detachment, a retinal malformation combined with rosette formation and optic nerve aplasia.
Clinically, retinal dysplasia may present itself in a wide range of severity, from simple to massive folding of the retina, central stalks with retinal tissue extending from the optic disc to the back of the lens, and complete retinal detachment leading to highly disorganized microphthalmic eyes. 1 If the intraocular proliferation is large enough, it may produce leukocoria. Leukocoria and retinal detachment in children require prompt further investigation because retinoblastoma should be included in the differential diagnosis. Usually, the underlying disease causing leukocoria can be deducted by ophthalmoscopy alone or in combination with ultrasonography. When clinical diagnosis is uncertain, caused by an obscured view or an atypical-appearing tumor, MR imaging helps to characterize and differentiate between intraocular pathologies.
On MR imaging, a retinal detachment presents as a fine linear structure, which is limited anteriorly at the ora serrata and posteriorly at the optic disc. Compared with the vitreous, the SI of the detached retina is high on T1WI images, low on T2WI images, and might show some contrast enhancement. In our patient, retinal dysplasia showed the same SI characteristics as those of normal detached retinal tissue; however, the enhancement after gadolinium administration was much stronger. It is likely that enhancement of dysplastic retinal tissue varies with the quality and number of blood vessels. De- Axial T1WI (A) image shows a hyperintense mass in the anterior part of the vitreous (V), adjacent to the ciliary body (CB) on either side of the lens, combined with a tent-shaped retinal detachment with hyperintense subretinal fluid (SF). T2WI (B ) image shows retinal detachment as a hypointense fine linear structure (R) and clearly demarcates the dysplastic retinal tissue (D). After we applied the contrast material (C, contrast-enhanced fat-suppressed T1WI image), the latter shows enhancement (D), in contrast to the detached retina (R) and subretinal fluid. Coronal contrastenhanced fat-suppressed T1WI (D ) MR images reveal absence of the optic nerve (asterisk) in an otherwise normal orbit. sop indicates superior ophthalmic vein; oa, ophthalmic artery.