Cystic Thyroid Nodules: Diagnostic and Therapeutic Dilemmas

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Abstract
Cystic thyroid nodules are common, comprising as many as 40% of thyroid nodules encountered by the endocrinologist. Their differential diagnosis is relatively broad and includes lesions that may not fit a stereotypical presentation, such as intrathyroidal thyroglossal duct cysts, branchial cleft cysts that are close to the midline, and cystic lesions that are malignant. Benign cystic thyroid nodules not infrequently present with symptoms and signs that mimic an aggressive thyroid cancer, including pressure symptoms and rapid growth; however, a cystic papillary thyroid carcinoma may provide few clues of its malignant nature, including a soft consistency to palpation and little or no apparent growth over the course of several years. The physical and biochemical features of the aspirated fluid of a nodule provide little diagnostic information; both benign and malignant lesions may yield grossly bloody aspirates or translucent yellow fluid. Cystic thyroid nodules not only have a higher than usual likelihood of yielding cytology specimens that are inadequate for diagnosis but also have higher than usual rates of false-negative cytology specimens. However, using a careful clinical assessment, ultrasonography, Doppler studies and ultrasound-guided fine-needle aspiration biopsy, the malignant or benign nature of most cystic thyroid nodules can be identified. This article reviews the differential diagnosis, diagnostic approach, and treatment of cystic nodules.