Heather Alison Jacene MD, Presenter: Nothing to Disclose

Richard Leo Wahl MD, Abstract Co-Author: Nothing to Disclose

As more experience is gained regarding PET/CT, it is becoming evident that other processes, for example infection and inflammation, can also demonstrate significant FDG uptake. Physiologic patterns of FDG uptake in the neck and supraclavicular region have previously been described, including "USA-fat", which can be intense and focal. It is necessary, therefore, to continue to accurately define physiologic patterns of FDG uptake. The aim of this study is to describe increased FDG uptake in the scalene muscles.

Images from 410 consecutive referrals for FDG PET/CT imaging between May 2003 and July 2003 were retrospectively reviewed. Studies were evaluated for the presence or absence of FDG uptake in the neck which corresponded to the scalene muscles on the concurrent CT scan. Medical records were reviewed and data including age, sex, smoking history, and reason for referral were recorded and evaluated.

One hundred and fifty-seven of the 410 scans (38%) 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. The female-to-male ratio was higher in the group with scalene muscle uptake (1.61) versus the group without (1.12). The average age of patients with and without scalene muscle uptake was not significantly different (58 ± 13 y; range 15-84 y, versus 55 ± 17 y; range 6-88 y, respectively). In the group with scalene muscle uptake, the average age of the males was significantly higher than the females (61 ± 11 y versus 56 ± 14 y (p<0.01)). The 410 referrals included 25 patients under the age of 25, only five of whom had scalene muscle uptake. In the patients with FDG uptake in scalene muscles, 24% had the diagnosis of lung cancer. There was no significant difference in the frequency of smokers between the two groups.

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 as "USA-fat" or lymph node metastases.

R.L.W.: Richard L Wahl receives research support and honorarium from GE Medical Systems.

Jacene, H, Wahl, R, Scalene Muscle Uptake on PET/CT: A Normal Physiologic Variant.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4415067.html