## Anatomical Distribution of Retinoblastoma **Key Point:** The equatorial region of the retina is the most common site of origin for retinoblastoma, accounting for approximately 50–60% of cases. ### Why the Equatorial Region? The equatorial zone (between the macula and the equator) contains the highest concentration of immature retinal cells (cone precursors and undifferentiated neural retina). This zone is a region of active proliferation during early childhood, making it the most susceptible site for malignant transformation of retinoblasts. ### Distribution Pattern | Site | Frequency | Characteristics | |------|-----------|------------------| | **Equatorial region** | 50–60% | Most common; high cell proliferation | | Peripheral retina | 20–30% | Near ora serrata; often larger at diagnosis | | Posterior pole/macula | 10–15% | Less common; may present late | | Optic disc | <5% | Rare; often advanced at presentation | **Clinical Pearl:** Equatorial tumors are often detected earlier because they are closer to the visual axis and more likely to cause media opacification (leukocoria) or affect the macula, prompting earlier parental concern. **High-Yield:** Remember that the equatorial region's high cell turnover and immature cell population make it the "hotspot" for retinoblastoma development. This is why screening and early detection in high-risk infants (family history, bilateral disease) focuses on careful fundoscopy of all retinal zones. [cite:Boyd & Melia, Retinoblastoma, Pediatric Ophthalmology textbooks]
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