Retinoblastoma: High-Yield Board Review
Master retinoblastoma presentation, RB1 genetics, imaging clues and leukocoria differentials for NBEO and OKAP exam preparation.
Retinoblastoma is the most common primary intraocular malignancy of which group?
Retinoblastoma in 30 Seconds
Retinoblastoma is the most common primary intraocular malignancy of childhood and the most common ocular cancer in children. It arises from immature retinal cells and can threaten life through extraocular spread. Early recognition of leukocoria or strabismus prompts urgent evaluation, improves survival and may preserve the globe.
Presentation and Signs
- Leukocoria: white pupillary reflex and the most common presenting sign. Exam relevance: treat leukocoria as retinoblastoma until proven otherwise.
- Strabismus: the second most common presenting sign. Exam relevance: new strabismus in a young child requires a dilated fundus examination.
- Age: diagnosis usually occurs before age 5. Exam relevance: infancy and early childhood strongly support the diagnosis.
- Laterality: unilateral disease is usually sporadic. Bilateral or multifocal disease strongly suggests a germline RB1 mutation. Exam relevance: bilateral tumors imply heritable disease.
- Advanced signs: red painful eye, glaucoma or orbital extension. Exam relevance: these findings suggest advanced disease and a poor visual prognosis.
Genetics
- RB1 is a tumor suppressor gene on chromosome 13q14 that regulates the G1 to S cell-cycle checkpoint. Exam relevance: identify RB1 and its function when asked about retinoblastoma genetics.
- Knudson two-hit hypothesis: both RB1 alleles must be inactivated. Exam relevance: germline disease needs one additional somatic hit.
- Heritable disease involves a germline mutation and is often bilateral, multifocal and earlier in onset. Exam relevance: bilateral disease is the classic heritable pattern.
- Sporadic disease usually presents unilaterally and later. Exam relevance: unilateral disease does not exclude heritable retinoblastoma.
- Heritable patients have increased lifetime risk of second primary malignancies, especially osteosarcoma, and radiotherapy further raises this risk. Exam relevance: remember osteosarcoma and the radiation link for NBEO and OKAP.
- Histopathology classically shows Flexner-Wintersteiner rosettes, indicating retinal differentiation. Exam relevance: this rosette is a favorite board detail.
4 Facts Exams Always Ask
- Leukocoria is the most common presenting sign of retinoblastoma.
- RB1 on chromosome 13q14 is a tumor suppressor that follows the two-hit hypothesis.
- Bilateral or multifocal disease strongly suggests a heritable germline RB1 mutation.
- Heritable cases carry increased risk of second primary malignancies, especially osteosarcoma, and of trilateral retinoblastoma with a pineal or suprasellar tumor.
The Classic Trap
The major board trap is leukocoria. Retinoblastoma must be distinguished from Coats disease, persistent fetal vasculature, toxocariasis and retinopathy of prematurity. Calcification on B-scan strongly supports retinoblastoma. Any child with leukocoria needs urgent evaluation to exclude this life-threatening tumor.
Clinical Pearl
Calcification is the key imaging feature. B-scan ultrasound shows a calcified intraocular mass with high reflectivity and acoustic shadowing, helping distinguish retinoblastoma from other causes of leukocoria. MRI is preferred for evaluating optic nerve or intracranial extension, while CT is generally avoided because of ionizing radiation in children with germline RB1 mutations. Management has shifted toward globe-sparing intra-arterial and intravitreal chemotherapy, with enucleation reserved for advanced disease.
Checkpoint 1
What is the most common presenting sign of retinoblastoma?
Checkpoint 2
Which imaging finding strongly supports the diagnosis of retinoblastoma?
A 2-year-old child is brought in after parents notice a white pupillary reflex in flash photographs. The child has no pain but recently developed a new inward eye turn. Fundus examination identifies an intraocular mass. What diagnosis must be urgently excluded before considering other causes of leukocoria?
The most common presenting sign of retinoblastoma is:
Sources & Reviewer Info
References
- American Academy of Ophthalmology. BCSC Section 4: Ophthalmic Pathology and Intraocular Tumors.
- American Academy of Ophthalmology. BCSC Section 6: Pediatric Ophthalmology and Strabismus.
- Shields CL, Shields JA. Clinical Ocular Oncology.
- American Academy of Ophthalmology. EyeWiki: Retinoblastoma.
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