Value of F-18 FDG PET/CT in staging of orbital and ocular adnexal mucosa-associated lymphoid tissue (MALT)-type lymphomas

Objectives Despite the widespread use of F-18 fluorodeoxyglucose positron emission tomography (FDG PET) in the diagnosis and follow-up of patients with lymphoma, few studies have assessed its value in ocular adnexal lymphomas, especially those subtypes with lower avidity. The purpose of this study was to evaluate the role of FDG PET/CT in staging of low-grade orbital and ocular adnexal lymphomas, and to compare its diagnostic accuracy to magnetic resonance (MR) imaging.

Methods Patients with biopsy-confirmed ocular adnexal MALT-type lymphomas who underwent pretreatment FDG PET/CT scans were retrospectively identified. Maximum standardized uptake value (SUVmax) and peak standardized uptake value (SUVpeak) were measured for all lesions. These metabolic parameters were also measured for the contralateral side. Findings were compared to MR imaging. Further analysis was done by ophthalmologic site, namely nonconjunctival or conjunctiva.

Results Of the 57 patients included in this study, 19 (33.3%) showed positive FDG uptake with mean SUVmax 4.4 and SUVpeak 3.7, while the detection rate for MR imaging was 18/57 (31.6%), and not statistically different. There were 9 discordant cases, and 39 cases were false negative for both modalities. Sensitivity was significantly higher in nonconjunctival sites, with 14/17 (82.4%) positive FDG uptake compared to 5/40 (12.5%) in the conjunctiva (p<0.001). Mean SUVmax and SUVpeak were 6.5 and 5.5 for nonconjunctival sites, both higher than in the conjunctiva, 2.3 and 2.0, respectively (p=0.039 and p=0.035).

Conclusions In this retrospective study, FDG PET proved comparable to MR imaging in the evaluation of even low-grade orbital and ocular adnexal lymphomas. Both SUVmax and SUVpeak were informative parameters, and the value of FDG PET was especially highlighted in nonconjunctival sites.