Retinoblastoma is a rare, highly malignant tumor of the retina of young children. Retinoblastoma is the seventh most common pediatric malignancy in the United States. The worldwide incidence of retinoblastoma is relatively stable at 1 case per 18,000 to 30,000 live births. No significant difference in incidence exists between sexes or among races. The average age at presentation ranges between 13 and 18 months; more than 90% of the cases are diagnosed before age 5 years. Retinoblastoma is a relatively slow-growing tumor that usually remains confined to the eye for months or even years. With early diagnosis, the overall 5-year survival rate exceeds 90%.

Retinoblastoma occurs unilaterally in 70% to 75% of cases. In more than 70% of cases, the tumor originates from a single focus and, when clinically detected, involves more than one-half of the retina, with extension into the vitreous chamber. Multifocal involvement may be observed with unilateral retinoblastoma, but is more common with bilateral disease. Although multiple tumor foci usually present simultaneously, in as many as 25% of cases, new foci may develop within weeks to months after the original diagnosis. The potential for metachronous occurrence of retinoblastoma warrants careful follow-up examination, even of the previously unaffected retina. Bilateral disease is detected at an earlier age (median, 13 months) than unilateral disease (median, 24 months). The long-term outlook for bilateral disease is significantly worse than for unilateral disease because of an increased incidence of second, nonocular malignant tumors in bilaterally affected cases.

In the United States, most children with retinoblastoma are first identified by their parents. The most common presenting sign is a white pupillary reflex called leukokoria (Fig. 310.1 and Box 310.1). This abnormal reflex, present in 60% of patients, is the result of a centrally located tumor at the posterior pole. Replacement of the vitreous with tumor or retinal detachment also may be noted.

The second most common sign is strabismus, present in 20% of patients. In children younger than 4 years, strabismus is usually the result of esotropia. With retinoblastoma, both esotropia and exotropia may occur and usually indicate tumor involvement of the macular area. Other signs include a red, painful eye with glaucoma (7%), poor vision (5%), unilateral dilated pupil, heterochromia (different-colored irises), or nystagmus. Children with advanced stages of disease may present with signs of lethargy, anorexia, failure to thrive, neurologic defects, orbital mass, proptosis, or blindness.