Background: Retinoblastoma is the commonest intraocular pediatric neoplasm. With the recent scope of shifting to eye preserving therapies, preoperative MRI is becoming the primary noninvasive diagnostic method to confirm the diagnosis, assess the ocular coats and optic nerve, and detect extraocular tumor extension and intracranial primitive neuroectodermal tumor associated with retinoblastoma as funduscopy and ultrasound have limitations. Diffusion-weighted images (DWIs) detect abnormalities based on differences in tissue cellularity. Echoplanar-based (EP) DWI results in susceptibility artifacts and geometric distortions, which make DWI of the orbit a challenging technique. The purpose of our study is to evaluate preoperative magnetic resonance (MR) imaging diagnostic merits and indices in patients with retinoblastoma. Results: Fifty-eight eyes were prospectively reviewed in 30 girls and 27 boys (mean age at diagnosis was 23 months ± 18.9) with retinoblastoma by two radiologists on T1-weighted images, fat saturated T2-weighted images, DWIs, ADC, and postcontrast T1-weighted MR images with and without fat suppression. All patients included were primarily treated by surgical enucleation; one girl had bilateral enucleation. MRI shows accuracy, sensitivity, specificity, NPV, and PPV; 86.2%, 95.3%, 60%, 81.8%, and 87.2% respectively for choroidal invasion; 75.8%, 58.8%, 82.9%, 83%, and 58.8% in prelaminar optic nerve invasion; and 86.2%, 85.2%, 87%, 87%, and 85% in postlaminar optic nerve invasion (PLONI) respectively. For sclera and extrascleral tumor invasion, MRI show accuracy, sensitivity, specificity, NPV, and PPV of 93%, 55.6%, 100%, 92.5%, 100%, and 98.3%, 100%, 98%,100%, 80% respectively. On DWIs, the vital solid tumor shows hyperintense signal compared to the vitreous. The difference between the mean ADC value of the solid enhancing tumor (0.3[0.12-0.8] × 10 −3 s/mm 2) and nonenhancing necrotic parts (1.4[1.0-1.8] × 10 −3 s/mm 2) was statistically significant (p < 0.001). No correlation was found between the ADC values and high risk features for metastasis. Abnormal anterior chamber enhancement shows no statistically significant correlation with main MRI and histopathology findings. Maximum tumor diameter in mm show statistically significant correlation with postlaminar optic nerve invasion (ρ = .002) and choroidal invasion (ρ = .007). Sensitivity and specificity of different tumor size cutoff values are calculated using the ROC analysis. Conclusion: High-resolution ocular MR imaging can reliably detect postlaminar optic nerve invasion, choroid, and extrascleral invasion; meanwhile, it shows low sensitivity in prelaminar optic nerve, ciliary body, and sclera invasion. Significantly lower ADC values in viable tumor than necrotic parts are recorded.
