Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography imaging of an isolated subcutaneous loin metastasis from primary papillary carcinoma of the thyroid.

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.

INTRODUCTION

Skin metastasis from a thyroid carcinoma is rarely a presenting feature of an underlying malignancy.[1] 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.[2] Others believe that papillary carcinoma is the most common thyroid carcinoma metastasizing to the skin.[3] All agree that the scalp is the most common site of thyroid carcinoma skin metastases. Loin metastasis is rare. 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.

CASE REPORT

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. He was referred for whole body PET/CT for detection of primary site. PET/CT showed an intense uptake in the subcutaneous soft-tissue lesion in the left loin [Figure 1]. Also uptake noted in right lobe thyroid nodule [Figure 2]. Patient underwent fine needle aspiration of the thyroid nodule which confirmed papillary carcinoma. A diagnosis of primary papillary carcinoma of thyroid with subcutaneous loin metastasis was made and he was advised total thyroidectomy and excision of metastasis.

Figure 1

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

Figure 2

Axial CT (a) PET (b) fused PET/CT (c) showed a intense uptake in the right lobe thyroid nodule

DISCUSSION

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.[2] They can be the initial manifestation of an occult thyroid cancer.[34] Dermal lesions typically present as slowly growing erythematous or purple plaques or nodules, usually on the scalp, face, or neck. Clinically, scalp is the most common site for cutaneous metastases. This may relate to local vascular factors essential for the highly complex nature of metastases.[5] Subcutaneous metastases in the loin are extremely rare. 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.[6] However, 18 fluorine-fluorodeoxyglucose-PET/CT has a role in 131I-whole body Scan negative patients with elevated thyroglobulin. Reports related to thyroid cancer rare metastases are limited.[7] There are reports of PET/CT in identifying muscle and scalp metastasis from a papillary thyroid cancer.[89] This is the first case of identifying primary papillary cancer with subcutaneous metastasis in PET/CT. Recognizing and understanding the clinical findings may determine the overall management of the patients.