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The Monocle Sign on 18 F-FDG PET Indicates Contralateral Peripheral Facial Nerve Palsy
Fatemeh Dana1, Alexander Maurer1, Urs J Muehlematter1
1From the Department of Nuclear Medicine, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
Clinical Nuclear Medicine
|April 23, 2024
Summary
The monocle sign, indicated by asymmetric FDG uptake in orbicularis oculi muscles, can identify peripheral facial nerve palsy. A SUV max ratio cutoff of 1.41 shows high specificity for detecting this condition.
Area of Science:
- Nuclear medicine
- Neurology
- Radiology
Background:
- Facial nerve palsy (FNP) diagnosis can be challenging.
- The "monocle sign" on FDG PET/CT may indicate FNP.
Purpose of the Study:
- To retrospectively analyze FDG PET/CT data in FNP patients.
- To evaluate the presence and significance of the monocle sign in FNP.
Main Methods:
- Retrospective analysis of 85 unilateral FNP patients (73 peripheral, 12 central) and 33 controls.
- Measured FDG uptake (SUV max, SUV mean, TGL) in orbicularis oculi muscles (OOMs).
- Compared OOM FDG uptake between patient groups and controls; determined optimal SUV max ratio cutoff using ROC analysis.
Main Results:
- The SUV max ratio of OOM was significantly higher in peripheral FNP vs. central FNP and controls (1.70 vs. 1.16 vs. 1.18, P < 0.001).
- An SUV max ratio cutoff of 1.41 demonstrated 94.4% specificity and 44.1% sensitivity for contralateral peripheral FNP.
- A cutoff of 1.91 achieved 100% specificity for peripheral FNP.
Conclusions:
- Asymmetric increased FDG uptake in OOM (monocle sign) indicates contralateral peripheral FNP.
- A nearly 2-fold higher SUV max ratio is a practically useful cutoff for diagnosing peripheral FNP.
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