Cystic Thyroid Nodules

Abstract

• A retrospective study of 221 surgically resected thyroid nodules disclosed that 71(32%) were cystic and 150(68%) were solid lesions. Ultrasonography correctly characterized cystic nodules in all but one case. Comparing cystic and solid nodules, there were no differences in patient demographics (mean ages, 47.7±1.8 SEM vs 45.9±1.2 years; sex, 78% females both groups), the proportion that were solitary (39% vs 40%), or the nodule size (49% vs 47% ≥2 cm in diameter). Of cystic thyroid lesions, 4% were simple cysts, 82% were degenerating benign adenomas or colloid nodules, and 14% were malignant compared with 23% of solid lesions that were malignant. Most cystic lesions (81%) contained bloody fluid. One benign true cyst was filled with thick brown fluid, while clear yellow fluid was repeatedly aspirated from one malignant cystic nodule. Malignant fineneedle aspiration cytology was the best predictor of cancer (100%). Much less predictable were signs of local compression or invasion (43%), a history of head or neck irradiation (33%), cyst recurrence after aspiration (29%), or an increase in the cystic nodule's size (7%). Indeterminate cytology identified malignancy with about half the frequency in cystic lesions as compared with solid nodules (13% vs 27%). The only false-negative fine-needle aspiration cytology occurred in a cystic lesion. In patients with cystic papillary cancers, needle aspirates contained insufficient material for diagnosis in 20% that occurred in no patient with solid papillary carcinoma. The sensitivities and specificities of fine-needle aspiration cytology for solid nodules were 100% and 55%, and for cystic nodules were 88% and 52%. Thus, cystic lesions are as likely as solid thyroid lesions to harbor a maligancy that cannot be predicted from the cyst's clinical characteristics or the patient's demographic data. Although fine-needle biopsy is the best predictor of malignancy in either cystic or solid thyroid lesions, it is slightly less reliable when a thyroid lesion is fluid filled rather than solid. We believe that most cysts not abolished by aspiration should be surgically excised. (Arch Intern Med. 1990;150:1422-1427)