The Monocle Sign on 18F-FDG PET Indicates Contralateral Peripheral Facial Nerve Palsy

Abstract

Background The aim of our study was to retrospectively analyze FDG PET/CT data in patients with facial nerve palsy (FNP) for the presence of the monocle sign. Patients and Methods A total of 85 patients with unilateral FNP were included into our study, thereof 73 with peripheral FNP and 12 with central FNP. FDG uptake (SUVmax, SUVmean, total lesion glycolysis) was measured in both orbicularis oculi muscles (OOMs). FDG uptake of paretic and nonparetic muscles was compared in patients with FNP (Wilcoxon test and Mann-Whitney U test) and was also compared with FDG uptake in 33 patients without FNP (Mann-Whitney U test). SUVmax ratios of OOM were compared. A receiver operating characteristic curve and Youden Index were used to determine the optimal cutoff SUVmax ratio for the prevalence of contralateral peripheral FNP. Results The SUVmax ratio of OOM was significantly higher in patients with peripheral FNP compared with patients with central FNP and those without FNP (1.70 ± 0.94 vs 1.16 ± 0.09 vs 1.18 ± 0.21, respectively; P < 0.001). The SUVmax ratio of OOM yielded an area under the curve (AUC) of 0.719 (95% confidence interval, 0.630–0.809), with an optimal cutoff of 1.41, yielding a specificity of 94.4% and a sensitivity of 44.1% for identifying contralateral peripheral FNP. One hundred percent specificity is achieved using a cutoff of 1.91 (sensitivity, 29.4%). Conclusions Asymmetrically increased FDG uptake of the OOM (the “monocle sign”) indicates contralateral peripheral FNP. A nearly 2-fold higher SUVmax represents a practically useful cutoff.