GADOLINIUM-ENHANCED MAGNETIC-RESONANCE-IMAGING ASSESSMENT OF HYDROXYAPATITE ORBITAL IMPLANTS

PURPOSE: Successful prosthesis attachment depends on complete vascular ization of porous coral-line hydroxyapatite when it is used as an orbi tal implant. We retrospectively assessed the utility of gadolinium-enh anced magnetic resonance imaging to evaluate and characterize the temp oral progression of this fibrovascular process, which has been histolo gically documented elsewhere. METHODS: Serial T-1-weighted gadolinium enhanced orbital magnetic resonance examinations were performed in fiv e patients receiving hydroxyapatite orbital implants. Retrospective ev aluation of the enhancement patterns was per formed. Magnetic resonanc e imaging enhance ment patterns guided timing of final drilling for pr osthesis fixation. RESULTS: Serial gadolinium enhanced T-1-weighted se quences consistently demonstrated centrally advancing, peripheral enha ncement cen tered on the drilled access channels. Progression over tim e varied, with the following two patterns demonstrated: (1) rapid peri pheral enhancement, which led to diffuse enhancement (three patients); and (2) enhancement limited to the periphery, which failed to advance centrally. CONCLUSIONS: The temporal enhancement seen on magnetic res onance imaging is identical to the histologically proven fibrovascular ingrowth pattern and most likely reflects this process. Magnetic reso nance imaging can identify progression of fibrovascular ingrowth into the hydroxyapatite orbital implants and guide surgical planning. It ma y also identify implants that fail to vascularize, thereby preventing the morbidity encountered by drilling into an avascular hydroxyapatite implant.