Preoperative diagnosis of the follicular variant of papillary carcinoma of the thyroid: discrepancy between image and cytologic diagnoses.

Preoperative diagnosis of the follicular variant of thyroid papillary carcinoma has not been examined sufficiently. The preoperative diagnosis of six patients with the follicular variant was investigated retrospectively as compared with 46 cases of the common type of papillary carcinoma (papillary structure dominant type), four of follicular carcinoma, 27 of follicular adenoma, and 42 of adenomatous goiter. Cervical soft radiography of the disease exhibited calcification in three of six cases (50%), all of which showed coarse calcification not accompanied by minute type. 201Tl scintigraphy of the disease revealed that four of six cases (66.7%) showed abnormal accumulation in the delayed phase. Four cases had favorable washout and one (16.7%) unfavorable washout. On ultrasonography, one of six cases (16.7%) was diagnosed as papillary carcinoma, four as follicular adenoma, and one as adenomatous goiter. In fine-needle aspiration cytology, two of five cases were diagnosed as papillary carcinoma of class V, two as papillary carcinoma of class IV, and one as follicular tumor suspected of class IIIa. On the other hand, true positive diagnostic rates of the histological types of tumors other than follicular carcinoma by ultrasonography or fine-needle aspiration cytology were approximately 80% and relatively satisfactory. Fine-needle aspiration cytology was the most useful method of diagnosing the follicular variant of papillary carcinoma. It seems necessary to consider the possibility of the follicular variant in diagnosis when papillary carcinoma is suspected from fine-needle aspiration cytology by preoperative diagnosis, while imaging suggests follicular tumor.