Scalene muscle uptake: A potential pitfall in head and neck PET/CT

Purpose: To describe increased 2-deoxy-2-[¹⁸F] fluoro-D-glucose (FDG) uptake in the scalene muscles in a large population of patients referred for evaluation with FDG positron emission tomography/computed tomography (PET/CT) imaging. Methods: The study met criteria for institutional review board exemption. FDG PET/CT images from 410 patients (179 males; mean age 56.8 years, range 6-88) were retrospectively reviewed for the presence or absence of FDG uptake in the neck that corresponded to the scalene muscles on the concurrent CT scan. Medical records were reviewed and data including age, sex, smoking history, reason for referral, and history of obstructive airways disease, thoracotomy, and thoracic radiation were recorded and evaluated. Results: One hundred and forty-seven of the 410 scans (36%) demonstrated increased FDG uptake on PET that corresponded to the scalene muscles on the CT scan. The uptake was most often bilateral, symmetrical, and linear (n=117). Other patterns of scalene muscle uptake included unilateral and linear uptake (n=27) and unilateral and focal uptake (n=3). Scalene muscle uptake was more common in patients referred for evaluation of lung carcinomas compared to other types of tumors (52% vs. 32%, p=0.05). Conclusion: Linear FDG uptake in scalene muscles is a commonly seen pattern on PET/CT. This finding should be recognized as a distinct entity and not misinterpreted on transverse images as metastatic disease.