Focal Muscle Uptake

Unless accompanied by an identifiable CT abnormality, nearly all FDG uptake in muscles is presumed physiologic – usually due to exercise, muscle strain or poor patient preparation prior to the exam.

Diffuse Skeletal Muscle Uptake:

Diffuse skeletal muscle uptake is a result of either poor patient preparation or strenuous exercise within the 24-hour prior to imaging (discussed in detail, here).

Focal Skeletal Muscle Uptake:

Focal skeletal uptake (in the absence of an associated CT abnormality) is typically the result of “muscle activation or strain”.

• Head & Neck: Most commonly affects the muscles of mastication (gum chewers and teeth grinders), longus colli muscles, extraocular muscles, paraspinal muscles and the sternocleidomastoid muscles.
• Chest: Most commonly affects the pectoralis muscles, shoulder musculature, the crura of the diaphragm and the muscles of respiration (occasionally seen in patients with respiratory difficulties).
• Abdomen & Pelvis: Most commonly affects the abdominal wall musculature, the psoas muscles, the iliacus muscles and the gluteal musculature.
• Extremities:   Very commonly, significant muscle uptake will be seen within the extremities, usually the result of nervous movements by the patient while waiting for the scan (e.g. hand clenching, bouncing of legs, etc.).  Although almost always physiologic, careful attention to the co-registered CT images is required to exclude the rare case of malignancy.