MRI Features for Identifying MYCN-amplified RB1 Wild-type Retinoblastoma

Background: MYCN-amplified RB1 wild-type (MYCN^ARB1^+/+) retinoblastoma is a rare but clinically important subtype of retinoblastoma due to its aggressive character and relative resistance to typical therapeutic approaches. Because biopsy is not indicated in retinoblastoma, specific MRI features might be valuable to identify children with this genetic subtype. Purpose: To define the MRI phenotype of MYCN^ARB1^+/+ retinoblastoma and evaluate the ability of qualitative MRI features to help identify this specific genetic subtype. Materials and Methods: In this retrospective, multicenter, case-control study, MRI scans in children with MYCN^ARB1^+/+ retinoblastoma and age-matched children with RB1^−/− subtype retinoblastoma were included (case-control ratio, 1:4; scans acquired from June 2001 to February 2021; scans collected from May 2018 to October 2021). Patients with histopathologically confirmed unilateral retinoblastoma, genetic testing (RB1/MYCN status), and MRI scans were included. Associations between radiologist-scored imaging features and diagnosis were assessed with the Fisher exact test or Fisher-Freeman-Halton test, and Bonferroni-corrected P values were calculated. Results: A total of 110 patients from 10 retinoblastoma referral centers were included: 22 children with MYCN^ARB1^+/+ retinoblastoma and 88 control children with RB1^−/− retinoblastoma. Children in the MYCN^ARB1^+/+ group had a median age of 7.0 months (IQR, 5.0–9.0 months) (13 boys), while children in the RB1^−/− group had a median age of 9.0 months (IQR, 4.6–13.4 months) (46 boys). MYCN^ARB1^+/+ retinoblastomas were typically peripherally located (in 10 of 17 children; specificity, 97%; P < .001) and exhibited plaque or pleomorphic shape (in 20 of 22 children; specificity, 51%; P = .011) with irregular margins (in 16 of 22 children; specificity, 70%; P = .008) and extensive retina folding with vitreous enclosure (specificity, 94%; P < .001). MYCN^ARB1^+/+ retinoblastomas showed peritumoral hemorrhage (in 17 of 21 children; specificity, 88%; P < .001), subretinal hemorrhage with a fluid-fluid level (in eight of 22 children; specificity, 95%; P = .005), and strong anterior chamber enhancement (in 13 of 21 children; specificity, 80%; P = .008). Conclusion: MYCN^ARB1^+/+ retinoblastomas show distinct MRI features that could enable early identification of these tumors. This may improve patient selection for tailored treatment in the future.