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extraskeletal osteosarcoma ( esos ) is a rare aggressive tumor , which commonly presents with disseminated metastases .
lungs and bones are common sites of metastatic involvement in osteosarcoma at initial presentation as well as after completion of treatment . computed tomography ( ct ) scan of the chest and bone scan are routinely used to detect lung and bone metastases in osteogenic sarcomas . with the advent of f - fluoro - deoxyglucose ( f - fdg )
positron emission tomography / computed tomography ( pet / ct ) imaging , unusual and often rare sites of metastatic spread have been uncovered in several malignancies . in this report , we describe an extremely rare combination of unusual metastatic sites from esos on fdg pet / ct .
a 32-year - old female patient presented to our institution with a bulky left supraclavicular mass .
the swelling was noticed 3 months back and had rapidly grown in size over the past month , with no accompanying pain . on examination ,
a hard , non - tender , mobile mass was felt in the left supraclavicular fossa , separate from the adjacent bones , in a relaxed posture , which became taut on shrugging or moving left shoulder .
a biopsy specimen from the mass , on histopathological examination revealed osteoid deposition by tumor cells , with osteoclastic giant cells and pleomorphic malignant cells within the osteoid , suggestive of osteosarcoma [ figure 1 ] .
thus , correlation of clinical , imaging and histopathological findings confirmed the diagnosis of esos .
patient was then referred for a whole body f - fdg pet / ct study for pre - treatment staging .
maximum intensity projection ( mip ) images [ figure 2a ] revealed a large focus of tracer concentration in left supraclavicular region [ figure 2a arrow ] , with multiple foci of uptake in the right hemithorax , region of the right kidney , left pelvis , mid thorax and abdomen [ figure 2a all arrowheads ] .
fused axial pet / ct images showed tracer uptake in a bulky soft - tissue mass arising from the left trapezius muscle , [ figure 2b arrow ] , which was the site of primary malignancy .
there was no involvement of left scapula noted on the ct component of the study , confirmed on coronal oblique ct [ figure 2c arrow ] and pet / ct [ figure 2d arrow ] images .
furthermore seen was intense fdg uptake in the right lung mass , left iliac bone marrow [ figure 3b arrow ] , d12 vertebra [ figure 3c arrow ] , within a soft - tissue deposit in the left internal oblique muscle [ figure 3d arrow ] , in right renal cortex [ figure 3e arrow ] and in medial end of left clavicle .
also noted was tracer uptake in the brain , which correlated to a soft - tissue lesion in right paraventricular region , with specks of calcification within , seen on axial fused pet / ct [ figure 3a arrow ] .
thus , in addition to the common sites of metastases in the lungs and bones , fdg pet / ct detected metastatic deposits at unusual sites such as brain , renal parenchyma , marrow and skeletal muscle .
photomicrograph of pathology section showing osteoclastic giant cells and pleomorphic malignant cells amidst osteoid ( h and e ,  200 ) ( a ) maximum intensity projection image showing tracer uptake in left supraclavicular region ( 2a - arrow ) , in the region of mid thorax , mid abdomen , right lung , right kidney , left pelvis ( all arrow heads ) ( b ) axial fused pet / ct images show fdg avid mass arising from left trapezius muscle ( arrow ) ( c ) oblique coronal ct and fused pet / ct ( d ) images show origin of the mass from left trapezius , with no involvement of left scapula axial fused pet / ct images show fdg avid metastatic lesions in brain ( a  arrow ) , left iliac marrow ( b  arrow ) , d12 vertebral body ( c  arrow ) , left internal oblique muscle ( d  arrow ) and right renal cortex ( e  arrow )
esos is a rare tumor , accounting for 1% of all soft - tissue sarcomas and 4% of osteogenic osteosarcomas . though it is histologically similar to osteogenic osteosarcoma , it is demographically , clinically and therapeutically different from it .
it most commonly presents as a rapidly growing soft - tissue mass , either with or without pain ; with lower extremity being the most common site and thigh accounting for 48% of the lesions , followed by upper extremity ( 8 - 23% ) , retroperitoneum ( 8 - 17% ) and trunk ( 10 - 11% ) .
lung is the most common site of metastases ( 80 - 88% ) , similar to osteogenic osteosarcoma ; other metastatic sites being soft - tissue , bone ( 8 - 19% ) , liver ( 8 - 17% ) , peritoneum and adrenal glands ( < 5% ) . since esos is generally a high grade spindle cell malignancy , the primary tumor as well as metastatic sites demonstrate fdg avidity .
fusion with ct helps to characterize the lesions , which show the presence of mineralized material within the soft - tissue and also provides an anatomical dimension to the fdg uptake . the existing literature on fdg pet / ct in esos confirms the fact that these tumors are fdg avid
, however all these reports demonstrate a single metastatic site , unlike multiple and rare sites demonstrated in our report .
metastases to the brain are extremely rare , with only a single case detected on histopathology , after surgical resection was performed in 21 patients with intraparenchymal brain metastases from sarcoma .
though bone involvement is commonly seen , discrete marrow metastases have not been reported yet .
thus , a whole body metabolic imaging modality like fdg pet / ct is the investigation of choice in such high grade rare malignancies , which are aggressive at presentation .
it is very well - known that the management of metastatic disease is not altered based on the number of sites of distant metastases .
fdg pet / ct detects rare metastatic sites , which are not only an interesting finding , but also a valuable addition to the existing literature on metastatic sites of esos .
such documentation is of value , for a rare subgroup of patients who can present with metastases , from an unknown primary site , wherein , esos can emerge as one of the likely primary .
extraskeletal osteosarcoma ( esos ) is a rare malignancy , which commonly presents with metastatic disease . like their osteogenic counterparts , these tumors commonly metastasize to lungs and bones . 
 we report the fluoro - deoxyglucose positron emission tomography findings in a case of esos presenting with a combination of rare metastatic sites such as brain , kidney and the bone marrow .