Asymmetric Tongue Muscle Uptake of F-18 FDG

The Monocle Sign in FDG-PET: A Sign of Contralateral Facial Nerve Palsy

We report three cases of unilateral F-FDG uptake in the orbicularis oculi muscle in subjects with contralateral peripheral facial nerve palsy. We argue that this asymmetric uptake pattern in fact reflects lack of metabolism on the side affected by facial nerve palsy, owing to denervation. Since the unilateral periorbital uptake resembles a monocle, we chose to call this finding the monocle sign. The monocle sign should not be confused with inflammation or tumor, but should prompt a neurological assessment for facial nerve palsy and a potential underlying disease.

Changes in the distributions of fluorine-18-labelled fluoro-2-deoxy-d-glucose accumulation into tongue-related muscles after dissection in patients with tongue cancer

OBJECTIVES

To elucidate the changes in the distributions of fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸F-FDG) accumulation in the tongue muscles of patients following four kinds of surgical operations for tongue cancers.

METHODS

The changes in the distributions of ¹⁸F-FDG accumulations in the tongue muscles on positron emission tomography (PET)-CT, in association with imaging findings on CT and MRI, were retrospectively analyzed before and after four kinds of surgical operations for 50 patients with tongue cancers.

RESULTS

¹⁸F-FDG-PET-positive areas appeared at the back of the intrinsic muscles of the tongue after invasive surgery for tongue cancers despite the absence of abnormal findings on CT and MRI. A correlation between the standardized uptake value maximum of ¹⁸F-FDG in the intrinsic muscles and the degree of invasiveness of the surgical procedures for tongue cancers (r = 0.539, p < 0.01) was found.

CONCLUSIONS

It is important to pay attention to the changes in ¹⁸F-FDG distributions in the intrinsic muscles of the tongue before and after invasive surgery despite the absence of abnormal findings on CT and MRI when evaluating the tongue on ¹⁸F-FDG-PET.

Hypoglossal nerve paralysis results in hypermetabolic activity on positron emission tomography/computed tomography in the contralateral tongue

False-positive results on combined positron emission tomography/computed tomography can complicate detection and surveillance of head and neck cancers. We present a rare case of false-positive contralateral [18F]-2-fluoro-2-deoxy-D-glucose tongue uptake after hypoglossal nerve paralysis caused by squamous cell carcinoma originating from the base of the tongue.

Physiology and pathophysiology of incidental findings detected on FDG-PET scintigraphy

A routine feature of positron emission tomography/computed tomography (PET/CT) imaging is whole-body acquisition that results in many unexpected findings identified outside of the primary region of abnormality. Furthermore, (18)F-fluorodeoxyglucose (FDG) is a marker of glycolysis and does not specifically accumulate in malignancy. Understanding the physiology and pathophysiology of normal FDG distribution and common incidental findings is therefore essential to the physician interpreting whole-body FDG-PET/CT studies. Whereas many incidental findings are benign and of limited clinical significance, others represent uncommon manifestations of the primary malignancy, second malignancies, or various clinically significant pathologic processes. Patients with a single malignancy are at greater risk of developing synchronous or metachronous second malignancies, possibly related to exposure to shared carcinogenic agents or presence of prooncogenic mutations. The decision of how to pursue an intervention on the basis of an incidental finding is generally left to clinical judgment.

PET/CT-MR Imaging in Head and Neck Cancer Including Pitfalls and Physiologic Variations

This article emphasizes the strengths and potential pitfalls of functional and anatomic imaging in patients who have head and neck cancer with an emphasis on the treated neck, including patients who have undergone surgery and/or radiation therapy. Anatomic and molecular imaging together allow optimal evaluation and interpretation of a patient who has cancer. Effective assessment of patients who have head and neck cancer can be achieved through a careful review of pertinent anatomy, with awareness of the physiologic variations (especially those in the treated head and neck) seen in PET imaging, and analysis of both the PET and cross-sectional images.

False-positive positron emission tomography appearance with 18F-fluorodeoxyglucose after definitive radiotherapy for cancer of the mobile tongue

(18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) is an effective tool for evaluating the results of radiotherapy. However, some false-positive appearances caused by physiological or pathological accumulation are reported. We report on three patients who showed a high accumulation of FDG in the lingual muscles but had no recurrent tumour after definitive radiotherapy for the mobile tongue. All patients had squamous cell carcinoma of the tongue and received interstitial radiotherapy with small sources. High uptake was seen in the lingual muscles without recurrence or inflammation, based on physical and MR examinations. This false-positive appearance is thought to relate to ill-balanced high activity of the lingual muscles after definitive radiotherapy.