Postcontrast Magnetic Resonance Imaging Assessment of Porous Polyethylene Orbital Implant (Medpor)

Objective: To evaluate the fibrovascular ingrowth progression within the porous polyethylene orbital implant (Medpor) with serial magnetic resonance imaging (MRI).

Design: Prospective, nonrandomized, comparative (self-controlled) trial.

Participants: Ten patients who underwent enucleation and implantation of a 20-mm porous polyethylene implant wrapped with heterologous sclera.

Methods: Serial precontrast and postcontrast T1-weighted MRI were obtained at 1.5, 3, 6, and 12 months after implantation. The percentage area of enhancement was calculated by use of manual planimetric contouring unenhanced areas at the equator of each sphere on axial and coronal planes.

Results: All the implants showed enhancing areas as early as 1.5 months after enucleation. In 8 of the 10 patients, the areas of enhancement at the equator of the implant consistently showed similar centripetal progression primarily during the first 6 months after enucleation. The presence of fibrovascular tissue at the equator was associated in all cases with enhancing zones at the anterior portion of the implant. None of the implants showed diffuse complete enhancement after 12 months. Two patients failed to demonstrate further enhancement progression 1.5 months after implantation. No histopathologic study to equate with the MRI findings was performed in this series.

Conclusions: Postcontrast magnetic resonance studies seem to be the best-suited imaging modality for assessing the fibrovascular tissue progression into porous polyethylene spheres after enucleation and for identifying patients in whom failure of vascularization occurs. Incomplete vascularization at the equator of the porous polyethylene sphere does not prove an absence of fibrovascular ingrowth in the anterior region. Prior ocular surgery and coexisting arterial hypertension may slow the progression of fibrovascular ingrowth.