Thyroid metastasis of a colonic adenocarcinoma.

In spite of being the organ of the body with the second greatest relative arterial perfusion (second only to the suprarenal glands), the thyroid is a rare location for metastases. In studies carried out in oncology patients, it is an incidental finding in 1.4%–3% of thyroidectomy surgical specimens and 1.9%–24.2% in necropsy studies. The prevalence, diagnosis and most appropriate management of thyroid metastases continue to be controversial. We present the case of a 70-year-old female patient with a history of adenocarcinoma of the sigmoid colon (stage pT3N1b) that had been treated with urgent sigmoidectomy due to perforation. During the extension CT study, the only finding of interest was a hypodense nodule measuring 17 mm in the left lobe of the thyroid. The patient initiated adjuvant chemotherapy in accordance with the XELOX regimen. After its completion, re-evaluation with PET-CT once again demonstrated the thyroid nodule with hypermetabolic characteristics (Fig. 1). Given the high suspicion for malignancy, ultrasoundguided fine needle aspiration was performed (Fig. 2), and the results were compatible with a poorly differentiated carcinoma that seemed to be secondary in origin. With this finding, and given the elevated suspicion for secondary thyroid metastasis, total thyroidectomy was performed along with cervical exploration and central lymphadenectomy. The pathology study of the piece reported thyroid nodular infiltration by an adenocarcinoma with a moderate degree of differentiation, compatible with an intestinal primary origin, and negative lymph nodes. Even though thyroid metastases may appear due to lymphatic as well as vascular dissemination, they are uncommon. There are 2 hypotheses for this phenomenon. One postulates that the rapid blood flow through the gland impedes the tumor cells to adhere, while the second argues that the high concentrations of oxygen and iodine in the gland would inhibit malignant cell growth. This seems to be confirmed by the higher frequency of this disease in previously pathologic thyroids, especially those affected by goiter or follicular adenomas. Club (Clear) cell renal carcinomas are the tumors that most frequently metastasize in the thyroid. These are followed by pulmonary, breast, melanoma, colorectal and sarcomas, although there have been isolated descriptions of several other types, such as: urothelial, bladder, testicular seminomas, endometrial, ovarian, carcinosarcoma, neuroendocrine tumors, meningioma, GIST, nasopharyngeal and pancreatic mucinous tumors. In the autopsy series, the most common tumor was pulmonary, followed by breast and melanoma. Mean age at presentation of thyroid metastases is 60, and there is a greater prevalence in women. The incidence is on the rise due to the wider use of imaging tests such as PET-CT and ultrasound. c i r e s p . 2 0 1 5 ; 9 3 ( 1 ) : 4 3 – 5 4