Skeletal muscle metastases as the initial manifestation of an unknown primary lung cancer detected on F-18 fluorodeoxyglucose positron emission tomography/computed tomography
A 65-year-old male presented with pain and swelling of the right forearm. Fine needle aspiration cytology of the swelling showed metastatic squamous cell carcinoma. The patient underwent a whole body F-18 FDG PET/CT to identify the site of the primary malignancy. Increased FDG avidity (standardized uptake value [SUVmax] 9.0) was detected in an irregular heterogeneously enhancing soft-tissue mass in the right paravertebral region in the upper lobe of the right lung with a focus of calcification within the mass [Figure and , white arrow]. Abnormal FDG uptake was also noted in a presacral mass [Figure and ], the bulky left adrenal gland, several dorsal vertebrae and multiple lesions in the trapezius [Figure and , red arrow], right brachioradialis [], deltoid, and right external oblique muscles [], suggestive of metastatic involvement. A diagnosis of primary squamous cell carcinoma of the lung was pathologically confirmed. The patient was treated with 4 cycles of chemotherapy, after which significant decrease in FDG uptake (SUVmax = 5.1) was seen in the primary as well as the right brachioradialis muscle lesion (not shown here).