Correlation of histological findings with gadolinium enhanced MRI scans during healing of a PHEMA orbital implant in rabbits

Background/aims-To investigate a poly(2-hydroxyethyl methacrylate) (PBEMA) orbital implant with a spongy anterior hemisphere and a smooth gel posterio r hemisphere, by histology correlated with magnetic resonance images. Methods-Following enucleation, eight rabbits received PHEMA implants to whi ch the muscles were directly sutured, and underwent gadolinium enhanced mag netic resonance imaging (MRI) from 3 to 52 weeks. After the rabbits were ki lled, the implants were removed, cut in a plane corresponding to the scan, and processed for light and electron microscopy. Results-All eight rabbits retained their implant to the end of the study pe riod without complications. The scans demonstrated muscle attachment to the anterior half of the implant, and enhancement was seen on injection of gad olinium chelate. Histology confirmed muscle attachment, and cellular and va scular ingrowth. Over time, a transformation from reactive inflammatory to relatively non-vascular scar tissue was seen within the implant. Calcium de posits in one implant were detected by imaging and histology. Conclusion-The implants are readily visualised on MRI. Muscle attachment an d fibrovascular ingrowth irate the anterior hemisphere are seen, while enca psulation of the posterior hemisphere is minimal. Histological findings con firm the progress of the healing response, with initial inflammation and ma rked vascularisation, developing later into quiescent scar tissue predomina ntly of fibroblasts.