Extrusion of porous polyethylene orbital implant in recurrent retinoblastoma.

High-density porous polyethylene allografts are used as orbital implants in reconstruction of anophthalmic sockets. The use of this material for integrated buried implants is rather new, and studies on removed implants from humans are limited. We studied the case of a 6-year-old boy with an extruded porous polyethylene implant due to orbital recurrence of retinoblastoma. The clinical and morphological features are reported. Histopathology revealed fibrovascular downgrowth in the outer two thirds of the sphere. Scanning electron microscopy, however, documented further downgrowth of fibrous tissue into the central core. Transmission electron microscopy depicted a spectrum of collagen fiber orientations to polyethylene material, ranging from perpendicular to concentric. Immunohistochemistry studies were inconclusive.