skeletal muscle metastasis as the initial presentation of an unknown primary lung cancer is unusual .
f-18 fluorodeoxyglucose ( fdg ) positron emission tomography / computed tomography ( pet / ct ) imaging is useful in the identification of primary in carcinoma of unknown origin .
we describe a patient showing fdg - avid metastases to the skeletal muscles along with a previously unknown primary tumor in the right lung , in a patient presenting with initial muscular symptoms without any pulmonary manifestations .
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 1b and d , white arrow ] .
abnormal fdg uptake was also noted in a presacral mass [ figure 1c and e ] , the bulky left adrenal gland , several dorsal vertebrae and multiple lesions in the trapezius [ figure 1b and d , red arrow ] , right brachioradialis [ figure 2 ] , deltoid , and right external oblique muscles [ figure 3 ] , suggestive of metastatic involvement . a diagnosis of primary squamous cell carcinoma of the lung was pathologically
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 ) .
fluorodeoxyglucose ( fdg ) positron emission tomography / computed tomography ( pet / ct ) maximum intensity projection ( mip ) image ( a ) showing multiple foci of abnormal tracer uptake .
transaxial thoracic ct ( b ) and fused pet / ct image ( d ) show increased fdg uptake in an irregular , heterogeneously enhancing soft - tissue mass ( white arrow ) in the paravertebral region in the upper lobe of the right lung with calcification within the mass .
increased fdg uptake is also seen in a peripherally enhancing ring like lesion in the trapezius ( red arrow ) .
axial ct ( c ) and fused pet / ct ( e ) images at the level of the rectum show increased fdg uptake in a heterogeneously enhancing pre - sacral soft - tissue deposit coronal and transaxial computed tomography ( ct ) ( a and c ) and fused positron emission tomography / ct ( b and d ) images of the right hand showing increased fluorodeoxyglucose uptake in the right brachioradialis muscle with no increase in attenuation ( probably because the images were acquired after completion of the whole body pet scan ) axial computed tomography ( a ) and fused positron emission tomography / computed tomography ( b ) images showing increased tracer uptake in a ring - like hyperenhancing lesion in the right external oblique muscle suggestive of muscle metastasis
found that only 4 patients ( 0.16% ) among 2,557 patients with lung cancer developed metastasis to the skeletal muscle .
whole - body fdg pet / ct imaging is useful in detection of muscle metastases in lung cancer patients .
multiple muscle metastases from lung cancer are rare , and fdg pet / ct imaging is useful in the identification of unsuspected metastatic sites
. primary presentation of a skeletal muscle metastasis , such as in our case , remains an unusual occurrence .
the present case , where the initial presentation was of metastatic muscular involvement , highlights the role of fdg pet / ct in tracing the location of primary lung malignancy and unsuspected sites of multiple muscle metastases in a patient with muscle metastases of unknown primary .
 skeletal muscle metastasis as the initial presentation of the unknown primary lung cancer is unusual . a 65-year - old male patient presented with pain and swelling of the right forearm . 
 fine needle aspiration of the swelling revealed metastatic squamous cell carcinoma . 
 the patient underwent whole body f-18 fluorodeoxyglucose ( fdg ) positron emission tomography / computed tomography ( pet / ct ) to identify the site of the primary malignancy . 
 the authors present pet / ct images showing fdg - avid metastases to the skeletal muscles along with a previously unknown primary tumor in the right lung , in a patient presenting with initial muscular symptoms without any pulmonary manifestations . 