Assessment of Vascularization within Hydroxyapatite Ocular Implant by Bone Scintigraphy: Comparative Analysis of Planar and SPECT Imaging

Lim, Seok Tae; Sohn, Myung Hee; Park, Soon Ah

Abstract

PURPOSE: Complete fibrovascular ingrowth within the hydroxyapatite ocular implant is necessary for peg drilling which is performed to prevent infection and to provide motility to the ocular prosthesis. We compared planar bone scintigraphy and SPECT for the evaluation of the vascularization within hydroxyapatite ocular implants.
MATERIALS AND METHODS
Seventeen patients (M:F=12:5, mean age: 50.4+/-17.5 years) who had received a coralline hydroxyapatite ocular implant after enucleation surgery were enrolled. Patients underwent Tc-99m MDP planar bone and SPECT imaging by dual head gamma camera after their implant surgery (interval: 197+/-81 days). Uptake on planar and SPECT images was graded visually as less than (grade 1), equal to (grade 2), and greater than (grade 3) nasal bridge activity. Quantitative ratio of implanted to non-implanted intraorbital activity was also measured. Vascularization within hydroxyapatite implants was confirmed by slit lamp examination and ocular movement.
RESULTS
All but three patients were considered to be vascularized within hydroxyapatite implants. In visual analysis of planar image and SPECT, grade 1 was noted in 9/18 (50%) and 6/18 (33%), respectively. Grade 2 pattern was 7/18 (39%) and 4/18 (22%), and grade 3 pattern was 2/18 (11%) and 8/18 (44%) respectively. When grade 2 or 3 was considered to be positive for vascularization, the sensitivity of planar and SPECT imaging were 60% (9/15) and 80% (12/15), respectively. In 3 patients with incomplete vascularization, both planar and SPECT showed grade 1 uptake. The orbital activity ratios on planar imaging were not significantly different between complete and incomplete vascularization (1.96+/-0.87 vs 1.17+/-0.08, p>0.05), however, it was significantly higher on SPECT in patients with complete vascularization (8.44+/-5.45 vs 2.20+/-0.87, p<0.05).
CONCLUSION
In the assessment of fibrovascular ingrowth within ocular implants by Tc-99m MDP bone scintigraphy, SPECT image appears to be more effective than planar scintigraphy.