Gadolinium-enhanced Magnetic Resonance Imaging Assessment of Hydroxyapatite Orbital Implants

Abstract

Successful prosthesis attachment depends on complete vascularization of porous coralline hydroxyapatite when it is used as an orbital implant. We retrospectively assessed the utility of gadolinium-enhanced magnetic resonance imaging to evaluate and characterize the temporal progression of this fibrovascular process, which has been histologically documented elsewhere. Serial T1-weighted gadolinium-enhanced orbital magnetic resonance examinations were performed in five patients receiving hydroxyapatite orbital implants. Retrospective evaluation of the enhancement patterns was performed. Magnetic resonance imaging enhancement patterns guided timing of final drilling for prosthesis fixation. Serial gadolinium-enhanced T1-weighted sequences consistently demonstrated centrally advancing, peripheral enhancement centered on the drilled access channels. Progression over time varied, with the following two patterns demonstrated: (1) rapid peripheral enhancement, which led to diffuse enhancement (three patients); and (2) enhancement limited to the periphery, which failed to advance centrally. The temporal enhancement seen on magnetic resonance imaging is identical to the histologically proven fibrovascular ingrowth pattern and most likely reflects this process. Magnetic resonance imaging can identify progression of fibrovascular ingrowth into the hydroxyapatite orbital implants and guide surgical planning. It may also identify implants that fail to vascularize, thereby preventing the morbidity encountered by drilling into an avascular hydroxyapatite implant.