skin metastasis from a thyroid carcinoma is rarely a presenting feature of an underlying malignancy .
subcutaneous metastasis from differentiated thyroid carcinoma ( dtc ) is a rare manifestation of disseminated disease .
some of the authors believe that follicular carcinoma of the thyroid has a higher propensity to metastasize to the skin , followed by papillary carcinoma , then anaplastic carcinoma and finally medullary carcinoma .
others believe that papillary carcinoma is the most common thyroid carcinoma metastasizing to the skin .
all agree that the scalp is the most common site of thyroid carcinoma skin metastases .
there are no previous reports of positron emission tomography / computed tomography ( pet / ct ) in patients with loin metastasis from an unknown primary and identified as papillary cancer thyroid .
this was a case report of a 45-year - old male patient who presented with subcuataneous swelling in the left loin , which on biopsy showed metastatic papillary cancer .
pet / ct showed an intense uptake in the subcutaneous soft - tissue lesion in the left loin [ figure 1 ] .
a diagnosis of primary papillary carcinoma of thyroid with subcutaneous loin metastasis was made and he was advised total thyroidectomy and excision of metastasis
. whole body fluorodeoxyglucose - positron emission tomography/ computed tomography ( pet / ct ) maximum intensity projection image ( a ) axial ct ( b ) pet ( c ) fused pet / ct ( d ) showed a intense uptake in the subcutaneous soft tissue lesion in the left loin axial ct ( a ) pet ( b ) fused pet / ct ( c ) showed a intense uptake in the right lobe thyroid nodule
cutaneous metastasis from dtc is also a rare manifestation of thyroid cancer . a review on roughly 60 cases of dtc skin metastases , which have been documented in the literatures , stated that pc has a greater preponderance for skin metastases
dermal lesions typically present as slowly growing erythematous or purple plaques or nodules , usually on the scalp , face , or neck .
this may relate to local vascular factors essential for the highly complex nature of metastases .
pet / ct is very useful in identifying unknown primary cancer from the metastatic lesions .
there are reports of pet / ct in identifying occult papillary cancer in a thyroglossal cyst . however , 18 fluorine - fluorodeoxyglucose - pet / ct has a role in 131i - whole body scan negative patients with elevated thyroglobulin .
there are reports of pet / ct in identifying muscle and scalp metastasis from a papillary thyroid cancer .
this is the first case of identifying primary papillary cancer with subcutaneous metastasis in pet / ct . recognizing and understanding the clinical findings
 differentiated thyroid cancer frequently metastasizes but generally spreads to regional cervical lymph nodes and , in advanced cases , to the lungs and/or skeleton . 
 metastases to the skin / subcutaneous tissue are rare . 
 we report 45-year - old male patient presented with a loin swelling which on biopsy showed a papillary carcinoma and referred for fluorodeoxyglucose - positron emission tomography / computed tomography ( fdg pet / ct ) to find out the primary disease . 
 pet / ct showed abnormal fdg uptake within a loin metastasis and right lobe thyroid nodule . 
 fine - needle aspiration from nodule showed papillary carcinoma . 
 because thyroid cancer can rarely metastasize to the skin , attention should be given to that region during interpretation of the images . 
 he was advised total thyroidectomy and metastasis excision . 