Postcontrast magnetic resonance imaging assessment of porous polyethylene orbital implant (Medpor)

Objective: To evaluate the fibrovascular ingrowth progression within the po rous polyethylene orbital implant (Medpor) with serial magnetic resonance i maging (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 enha ncement was calculated by use of manual planimetric contouring unenhanced a reas at the equator of each sphere on axial and coronal planes. Results: All the implants showed enhancing areas as early as 1.5 months aft er enucleation, In 8 of the 10 patients, the areas of enhancement at the eq uator of the implant consistently showed similar centripetal progression pr imarily during the first 6 months after enucleation, The presence of fibrov ascular tissue at the equator was associated in all cases with enhancing zo nes at the anterior portion of the implant. None of the implants showed dif fuse complete enhancement after 12 months. Two patients failed to demonstra te further enhancement progression 1.5 months after implantation. No histop athologic study to equate with the MRI findings was performed in this serie s. Conclusions: Postcontrast magnetic resonance studies seem to be the best-su ited imaging modality for assessing the fibrovascular tissue progression in to porous polyethylene spheres after enucleation and for identifying patien ts 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 co existing arterial hypertension may slow the progression of fibrovascular in growth. Ophthalmology 2000;107:1656-1660 (C) 2000 by the American Academy o f Ophthalmology.