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Figure 9c.  Asymmetric or isolated FDG uptake in skeletal muscle. (a) Coronal FDG PET image of a patient who used his left arm before FDG injection reveals FDG uptake in only a small portion of the left trapezius muscle (arrow). (b) Axial FDG PET image of the same patient shows FDG uptake (arrowhead) with an appearance suggestive of a large metastatic or primary neoplasm of the chest wall. (c) Axial FDG PET image shows FDG uptake in the left pterygoid muscle (arrow) in a patient who underwent contralateral neck surgery. Although the patient did not speak during the FDG uptake phase, muscle imbalance due to loss of the contralateral musculature resulted in the FDG uptake, which could be misinterpreted as a neoplasm of the skull base. c = normal cerebellar tracer uptake.