Relevance of CT and MRI in retinoblastoma for the diagnosis of postlaminar invasion with normal-size optic nerve: a retrospective study of 150 patients with histological comparison

Background Detection of optic nerve invasion is mandatory in children primarily enucleated for retinoblastoma to ensure a free resection margin. Objective To assess the accuracy of CT and MRI for the detection of postlaminar invasion in normal-size nerves. Materials and methods A total of 150 patients enucleated for retinoblastoma were included. Imaging data (119 CT and 46 MRI) were retrospectively reviewed and compared with histological findings. Abnormal contrast enhancement of the optic nerve was used as diagnostic criterion for invasion. The associations between postlaminar invasion and several indirect signs were also assessed. Statistical analysis was performed with the Kruskal-Wallis and Fisher exact tests. Results Postlaminar invasion on histology was observed in 8% (12/150). The sensitivity, specificity, accuracy and negative and positive predictive values were 60%, 95%, 91%, 95% and 60% for MRI, and 0%, 100%, 94% and 94% (PPV not assessable) for CT, respectively. Tumour diameter was the only indirect radiological sign significantly associated with postlaminar optic nerve invasion (P=0.002). Conclusion Our results suggest that MRI is more relevant than CT for preoperative detection of optic nerve invasion in patients with retinoblastoma. Tumour diameter is the only indirect sign significantly associated with postlaminar invasion.