Objective To describe the diagnostic validity of a gadolinium-enhanced routine brain MRI scan with 5 mm section thickness for the detection of optic nerve involvement in patients with retinoblastoma.

Methods Medical records of primarily enucleated retinoblastoma patients who underwent routine preoperative brain MRI scan with section thickness of 5 mm were retrospectively reviewed. Preoperative magnetic resonance images were independently reviewed in a masked fashion by two radiologists and compared with histological findings.

Results 41 eyes of 41 patients were included and the mean age at enucleation was 23.1 months. Among 41 eyes, 14 eyes were diagnosed to have post-laminar optic nerve invasion on histopathology. The accuracy, sensitivity and specificity of MRI for the diagnosis of post-laminar invasion were 73.2%, 35.7% and 92.6%, respectively, by the first radiologist and 78.0%, 42.9% and 96.3%, respectively, by the second radiologist. Moderate agreement was found between two radiologists (κ =0.48, p<0.01).

Conclusions Compared with the results of previous studies using orbital MRI with less than 3 mm section thickness, routine brain MRI with section thickness of 5 mm showed comparable specificity but inferior sensitivity in detecting optic nerve involvement of retinoblastoma.