Diagnosis of follicular neoplasm in thyroid nodules by fine needle aspiration cytology: does the result, benign vs. suspicious for a malignant process, in these nodules make a difference?

Objective: To address the likelihood of thyroid malignancy for each cytologic interpretation, highly cellular and benign vs. follicular carcinoma, with particular attention to the indeterminate cytologic result, follicular neoplasm.
Study Design: We retrospectively reviewed thyroid nodule cytologic and histologic interpretations from 1994 to 2002 in a tertiary medical center setting. Patients were referred for evaluation of thyroid nodules found incidentally or on physical examination.
Results: A total of 886 thyroid nodules were aspirated in 802 patients (500 benign, 195 indeterminate, 129 inadequate, 62 malignant). Of 195 indeterminate lesions, 180 were classified as follicular neoplasm or "cannot rule out/possible" follicular neoplasm, with 144 of these ultimately removed and with malignant histologic findings in 28. Any mention of follicular neoplasm in the cytology report conferred a 19.4% risk of malignancy in patients who went on to surgery (including an unexpected 18.2% rate of malignancy in the subcategory in which a possible follicular neoplasm was a secondary listing in an otherwise-benign cytologic differential diagnosis).
Conclusion: There was no difference in the likelihood of histologic malignancy between the cytologic subcategories of "definite "follicular neoplasm and "cannot rule out/possible" follicular neoplasm. We recommend that cytologic reports on fine needle aspiration of thyroid nodules with a diagnosis of follicular neoplasm reflect this fact.