Fineman_Retina (Color Atlas and Synopsis of Clinical Ophthal

254 6 Retinal and Choroidal Tumors

RETINOBLASTOMA R b is the most common primary intraocu- lar malignancy of children. Rb can occur either sporadically (as an isolated unilateral tumor in a family without prior disease) or secondary to a germline mutation (autosomal dominant familial disease often seen bilater ally in multiple family members). The tumor arises from cells in the developing retina of one or both eyes as a result of mutations in the RB1 tumor suppressor gene. Rb presents most often as a white intraocular retinal mass that has the potential to invade the underly ing choroid, sclera, and adjacent optic nerve. If there is considerable optic nerve invasion, direct intracranial extension is possible. Epidemiology and Etiology ● Rb occurs in approximately 1 in 15,000 live births. Most children are diagnosed at a mean of 18 months. ● Rb is rarely fatal in developed countries, but fatality may be seen in developing countries due to lack of timely intervention. ● No predilection for race or gender has been shown. ● Roughly two-thirds of the cases are unilat eral and one-third of the cases are bilateral. Unilateral cases are more likely to be diag nosed at an older age (mean of 24 months) and are most often nonfamilial (sporadic). Bilateral cases are diagnosed at a mean of 12 months, are usually familial, and are nearly always multifocal. ● Rb results from mutations or loss of both alleles of the RB1 gene, located on chromo some 13q14. The RB1 gene product appears to function as a regulator of cellular prolif eration through inhibitory effects on gene transcription at specific stages of the cell cycle. The timing of allelic inactivation deter mines whether the mutation is germinal (i.e., heritable by offspring of the affected child)

or somatic (nonheritable). In germinal cases, a mutant allele is present before fertilization, most commonly as a result of inheritance from either parent. In somatic cases, both alleles are present and active at fertilization, and spontaneous mutations in each allele arise subsequently. History ● A white pupillary reflex (leukocoria) and strabismus are the two most common find ings reported by parents. In fewer than 10% of cases is a family history known at the time of diagnosis. Important Clinical Signs ● Most patients present with leukocoria and strabismus. Small Rbs appear as flat or minimally elevated, translucent, white retinal lesions ( Fig. 6-2 ). With growth, the tumor appears more solid, elevated, and chalky white, with overlying dilated tortuous blood vessels. ● Three growth patterns have been described. Endophytic: The tumor grows from the retina inward to seed the vitreous cavity or anterior chamber ( Fig. 6-3 ). Exophytic: The tumor grows from the retina outward to occupy the subretinal space, often causing an exudative retinal detachment. Diffuse infiltrating: The least common form, this is characterized by a shallow spread of tumor along the entire retina and into the vitreous and anterior chamber. ● The other important findings are iris neovascularization, which occurs in nearly one-fifth of all cases, and “pseudohypopyon” (settling of tumor and inflammatory cells in the anterior chamber). Associated Clinical Signs ● Absence of cataract unless mass fills the posterior segment lens

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