Correlation of histological findings with gadolinium enhanced MRI scans during healing of a PHEMA orbital implant in rabbits.
OBJECTIVE
To investigate a poly(2-hydroxyethyl methacrylate) (PHEMA) orbital implant with a spongy anterior hemisphere and a smooth gel posterior hemisphere, by histology correlated with magnetic resonance images.


METHODS
Following enucleation, eight rabbits received PHEMA implants to which the muscles were directly sutured, and underwent gadolinium enhanced magnetic resonance imaging (MRI) from 3 to 52 weeks. After the rabbits were killed, 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 period without complications. The scans demonstrated muscle attachment to the anterior half of the implant, and enhancement was seen on injection of gadolinium chelate. Histology confirmed muscle attachment, and cellular and vascular ingrowth. Over time, a transformation from reactive inflammatory to relatively non-vascular scar tissue was seen within the implant. Calcium deposits in one implant were detected by imaging and histology.


CONCLUSIONS
The implants are readily visualised on MRI. Muscle attachment and fibrovascular ingrowth into the anterior hemisphere are seen, while encapsulation of the posterior hemisphere is minimal. Histological findings confirm the progress of the healing response, with initial inflammation and marked vascularisation, developing later into quiescent scar tissue predominantly of fibroblasts.
Hicks
C R
CR
Lions Eye Institute and Centre for Ophthalmology and Visual Science, University of Western Australia, Australia.
Morris
I T
IT
Vijayasekaran
S
S
Fallon
M J
MJ
McAllister
J
J
Clayton
A B
AB
Chirila
T V
TV
Crawford
G J
GJ
Constable
I J
IJ
D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage; D019786:Gadolinium DTPA / Q000008:administration & dosage; D008279:Magnetic Resonance Imaging / Q000379:methods; D020273:Orbital Implants; D011102:Polyhydroxyethyl Methacrylate / Q000627:therapeutic use*; D011817:Rabbits; D014945:Wound Healing / Q000502:physiology*
D003287:Contrast Media; D011102:Polyhydroxyethyl Methacrylate; C064925:gadodiamide; D019786:Gadolinium DTPA