Adrenal metastasis from differentiated thyroid carcinoma documented on post-therapy131I scan: A case based discussion

Adrenal metastasis is an unusual site of disease involvement in the natural course of differentiated thyroid carcinoma (DTC). This paper discusses the clinical and imaging features of DTC with adrenal metastasis. An unusual case of unilateral solitary asymptomatic adrenal metastasis in the setting of DTC is described in this report with the imaging features including (131)I scintigraphy and Fluorodeoxyglucose- Positron emission tomography/computed tomography. The adrenal metastasis was associated with other sites of metastatic disease involvement and was unidentified on initial pre-treatment evaluation studies. All such suspicious lesions should be further evaluated with clinicoradiological correlation by other imaging modalities. A post-radioiodine therapy scan revealed radioiodine uptake in the thyroid bed, sternum and a focus of intense radioiodine concentration in the left suprarenal region. Spot oblique images and single photon emission computed tomography of the upper abdomen was undertaken to ascertain the position and better characterization of the lesion. A subsequent whole body PET-CT (non-contrast) was done which revealed a well defined 6.5 cm × 5.0 cm left adrenal lesion with a SUVmax (standardized uptake value-maximum) of 9.5 in addition to a fluorodeoxyglucose avid osteolytic sternal lesion. The serum thyroglobulin level was significantly raised (more than 250 ng/mL) with thyroid stimulating hormone being 4.9 μΙU/mL (even following an adequate period of levothyroxine withdrawal), indicating the functioning nature of the metastases. In addition to demonstrating an atypical site of metastatic disease in DTC patients, this case emphasizes the importance of carefully interpreting and correlating a post radio-iodine therapy scan, particularly those with focal abdominal radio-iodine uptake which could aid in detecting metastatic lesions that are not characterized or identified on initial evaluation. The other important feature that can be deciphered from this report is that an adrenal metastasis could be unilateral and solitary, unlike that of renal metastases which are almost always bilateral and multiple at presentation, although both are usually asymptomatic.