Contrast-enhanced magnetic resonance imaging of fibrovascular tissue ingrowth within synthetic hydroxyapatite orbital implants in children

Purpose. To assess the usefulness of magnetic resonance imaging (MRI) in assessing fibrovascularization progression into synthetic hydroxyapatite (HA) implants inserted in anophthalmic sockets of children submitted to enucleation. Methods. We studied 23 HA orbital implants in 23 children who underwent enucleation for retinoblastoma. Each patient was examined by MRI within to 9 to 69 weeks after implant insertion (mean 34 weeks, median 30 weeks). No patient had received chemotherapy or radiotherapy at MRI examination. From each T1-weighted, fat-suppressed enhanced axial examination, the image depicting the center of the implant was identified. Enhancement was evaluated using a 5-point scale. Additionally, possible associated orbital and intracranial pathologies and implant migration or extrusion were evaluated. Results. All patients showed areas of enhancement of the implant consistent with the presence of fibrovascular ingrowth. There was no grade 1 enhancement in our series. Grade 2 was observed in 1 patient (4.34%), grade 3 in 7 patients (30.43%), grade 4 in 11 patients (47.82%), and grade 5 in 4 patients (17.39%). During follow-up there were no cases of clinically evident orbital infection, implant migration, or implant extrusion. No second tumor, optic nerve invasion, orbital extension, tumor relapse, or leptomeningeal brain seeding were noted. Conclusions. In this series, enhanced MRI showed satisfactory fibrovascular ingrowth of orbital implants since the 13th week after HA spheres insertion, with a trend towards progressive enhancement during the following weeks. The data also confirm the advice to wait at least 5-6 months after enucleation to perform drilling and peg placement.