RESUMO
Retinoblastoma is the prototypic genetic tumor. Caused by mutations in the RB1 gene, retinoblastomas are heritable in 40% of the cases and, in such cases, tumors are bilateral in 80%, unilateral in 15%, and trilateral in 5% of the cases. Trilateral retinoblastoma is a term that describes bilateral retinoblastomas plus a midline suprasellar or pineal neuroectodermal tumor. Patients with a germline RB1 mutation have 45% chance of having an offspring with retinoblastoma. Prenatal diagnosis is important because the doubling time is fast, ranging from 7 to 15 days. Thus, late diagnosis during infancy is associated with larger tumors and increased risk of death, need for globe enucleation and vision loss. We report a case of bilateral retinoblastomas diagnosed by targeted high-resolution ultrasonography of the orbits at 32 weeks of gestation in a patient at risk. This report demonstrates the feasibility of accurately detecting even tiny retinoblastomas by ultrasound with current technology. We also review prenatally published cases to date and comment on the technical strengths and limitations of ultrasound and fetal MRI for prenatal diagnosis of retinoblastomas.