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Hot nodules are rarely found to be carcinomas. We report a case of a nonmetastatic follicular carcinoma that presented as a hot nodule that was causing hyperthyroidism. A base substitution (ATC for TTC) was found in codon 486 of the TSH receptor gene and this resulted in the substitution of an isoleucine for a phenylalanine in the first extracellular loop of the receptor. This was absent in the deoxyribonucleic acid from the surrounding normal thyroid tissue indicating its somatic origin. This mutation, which was previously reported to activate both cyclic adenosine monophosphate and the inositol phosphate-diacylglycerol cascades, may have been responsible for the constitutive activation of the thyrotropin receptor and resulting hyperfunction of this follicular carcinoma.

Ultrasound-guided fine needle aspiration (USG-FNA) is a safe, effective, and dependable test used to assess thyroid nodules. However, the size of the lesion can adversely affect the outcome of the procedure. The aim of this study was to assess specimen adequacy and diagnostic specificity in USG-FNA of thyroid nodules measuring < or = 1.5 cm. A total of 219 thyroid FNAs were performed in a one year; 26 were obtained by pathologists, 139 by clinicians, and 54 by radiologists under ultrasound guidance. Of the 54 ultrasound-guided aspirates, 19 cases (35%) were performed on nodules < or = 1.5 cm (range 0.8-1.5 cm, mean 1.3 cm). Cytologic material from these 19 cases was reviewed along with corresponding available follow-up surgical material. Standard criteria for specimen adequacy and established morphologic criteria for diagnostic specificity were assessed in each case. All 19 cases met criteria for specimen adequacy, and in 17 cases (89%) specific cytologic diagnoses were made (cellular/adenomatous nodule--2 cases, colloid nodule--10 cases, Hashimoto's thyroiditis--4 cases, and papillary cystic carcinoma--1 case). The diagnoses were confirmed by surgical follow-up in six cases including the case of papillary carcinoma. One case diagnosed as suspicious for a papillary carcinoma subsequently was found to be a follicular adenoma by histology. In one case, a diagnosis of lymphocytic thyroiditis versus intrathyroidal lymphoid tissue was made (See Table I). In majority of cases of USG-FNA of nonpalpable thyroid nodules, adequate material may be obtained for a specific cytopathologic diagnosis.

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