Clinical value of IMP-SPECT in diagnosis of ocular melanoma: Comparison with MRI and FDG-PET

Objectives Malignant melanoma (MM) is the most common primary ocular malignant tumor. Despite various diagnostic modalities, it is still difficult to differentiate MM from non-MM lesions. The purpose of this study was to address the clinical value of N-isopropyl-p-[I-123]-iodoamphetamine SPECT (IMP-SPECT) in diagnosis of ocular MM in comparison with MRI and FDG-PET.

Methods Forty-one patients (24 females, 17 males) with clinically suspected ocular MM were examined in this study. All patients underwent both IMP-SPECT and MRI before any treatment. Nine of 41 patients (seven were diagnosed as MM) also underwent FDG-PET around the same time. Patients’ age ranged from 8 to 85 years (mean±SD, 56.5±17.6 years). Sixteen patients (39.0%) were histopathologically diagnosed as ocular MM. Orbital SPECT images were taken 15 minutes, 4 hours, 24 hours and 48 hours after intravenous injection of 111-222 MBq IMP. IMP uptake in the orbital tumor was visually evaluated. For MRI study, the lesion whose signal intensity was higher in T1-weighted image and lower in T2-weighted image than that of vitreous body was diagnosed as MM lesion. When FDG accumulation in the lesion was higher than surrounding tissue was defined as positive for FDG-PET. The diagnostic ability of IMP-SPECT was compared with that of MRI and FDG-PET.

Results For visual evaluation, the highest accuracy was 85.4 %, which was obtained at 48 hours after IMP administration. High sensitivity (93.8 %) and specificity (80.0 %) were also obtained at this time point. For MRI examination, the sensitivity, specificity, and accuracy were calculated as 60.0%, 75.0%, and 67.7%, respectively. Only 3 out of 7 (42.9%) MM patients who underwent PET study demonstrated high FDG uptake in the ocular tumors.

Conclusions This study shows that IMP-SPECT is more useful tool for the diagnosis of ocular MM than MRI and FDG-PET