A Case of the Monocle Sign in Facial Nerve Palsy Caused by External Auditory Canal Cancer on 18F-fluorodeoxyglucose-positron Emission Tomography/Computed Tomography

Abstract

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A 47-year-old woman with right external auditory canal cancer presented with an inability to close her left eyelid. Contrast-enhanced computed tomography (CT) identified a tumor extending from the right external auditory canal to the petrous bone, infiltrating the right facial nerve (Figure 1). ^18^F-fluorodeoxyglucose (^18^F-FDG)-positron emission tomography (PET)/CT revealed intense ^18^F-FDG uptake at the site. Notably, the left orbicularis oculi muscle (OOM) showed ^18^F-FDG uptake (maximum standardized uptake value: 3.08), whereas the right OOM showed no abnormal uptake (Figure 2).

Asymmetrical uptake by the OOM, referred to as the “monocle sign,” indicates contralateral peripheral facial nerve palsy (FNP) ^(1)^, which is believed to result from the overactivity of the nonparetic OOM. To the best of our knowledge, this is the first reported case of the monocle sign in a patient with external auditory canal cancer and FNP ^(1), (2)^.

Radiologists should recognize the monocle sign to prevent misdiagnosing unilateral ocular uptake under other conditions.

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Conflicts of Interest

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Acknowledgement

We used GPT-4o (https://chatgpt.com/) for Japanese-English translation and English proofreading. The authors read, revised, and proofread the generated text.

Author Contributions

Reiko Yagi wrote the first draft of the manuscript, and Tomoyuki Fujioka, Ken Yamagiwa, Junichi Tsuchiya, Tomoaki Asamori, and Takeshi Tsutsumi revised the manuscript. Tomoaki Asamori and Takeshi Tsutsumi contributed to patient care. Ukihide Tateishi supervised all the procedures.

Informed Consent

We have obtained informed consent for this case report.

Approval by Institutional Review Board (IRB)

Not applicable.