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

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 (SUV max , SUV mean , 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). SUV max ratios of OOM were compared. A receiver operating characteristic curve and Youden Index were used to determine the optimal cutoff SUV max ratio for the prevalence of contralateral peripheral FNP.

Results: The SUV max 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 SUV max 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 SUV max represents a practically useful cutoff.