Follicular variant of papillary carcinoma: The diagnostic limitations of preoperative fine-needle aspiration and intraoperative frozen section evaluation

Objective: Fine-needle aspiration (FNA) and frozen section (FS) have been widely reported in the literature as having high sensitivity in the diagnosis of papillary carcinoma. With the increased recognition of the follicular variant of papillary thyroid carcinoma (FVPTC), several reports have pointed out the difficulty in diagnosing this variant of papillary carcinoma owing to its overlapping cytomorphological features with benign and malignant follicular lesions. We undertook this study to determine the sensitivity of FNA and FS in the diagnosis of FVPTC. Methods: Retrospective review of patients who underwent thyroidectomy from June 1994 to June 1999. Of the 63 patients found with a final pathological diagnosis of papillary thyroid carcinoma, only 47 had an adequate FNA and FS and were included in the study. These patients were divided into two groups, the usual type (n = 23) and the follicular variant (n = 24) of papillary carcinoma. Sensitivities of FNA and FS for these two groups of papillary carcinoma were then determined. Results: The sensitivity of the FNA was 25% and of the FS was 29% for the follicular variant of papillary thyroid carcinoma. This is in contrast to the sensitivity of FNA and FS for the usual papillary carcinoma, which were 74% and 87%, respectively. Conclusion: FNA and FS have low sensitivity in the diagnosis of the FVPTC. High degree of suspicion may increase the accuracy in the diagnosis of this variant of papillary carcinoma before or during surgery. However, the thyroid surgeon needs to realize that, like follicular carcinoma, FVPTC is often diagnosed only on final pathological examination.