Pearls and pitfalls of thyroid nodule sonography and fine-needle aspiration.

PURPOSE: To review the ultrasound appearances of thyroid nodules with an emphasis on morphological features and to illustrate pearls and pitfalls related to ultrasound interpretation and fine-needle aspiration.

METHODS: The ultrasound features of 156 consecutive thyroid nodules with available cytological diagnoses were retrospectively reviewed. The presence of "honeycomb" morphology, aspect ratio, taller-than-wide shape, presence of colloid, consistency, echogenicity, presence of halo, margin definition, multiplicity of the nodules, largest nodule dimension, and lesion vascularity were compared between benign and malignant nodules.

RESULTS: Sonographic features that are significantly more common among malignant lesions include the presence of microcalcifications, coarse internal calcifications, markedly hypoechoic components, mostly solid-to-solid contents, infiltrative or microlobulated margins, taller-than-wide shape, and a high aspect ratio (0.85 vs 0.71). Characteristics that are statistically significantly associated with benignity include peripheral calcification and purely cystic composition. The honeycomb morphology was 100% specific for nodular hyperplasia. Benign and malignant follicular and Hürthle cell neoplasms can have identical sonographic and cytological features. Colloid on both ultrasound and cytology may be found in malignant lesions, whereas microcalcifications can sometimes be found in benign lesions. Cystic components in malignant nodules are not uncommon and should not be dismissed as benign on this basis alone. Fine-needle aspiration may alter the appearance of thyroid nodules.

CONCLUSIONS: Certain morphological sonographic features are helpful for differentiating between benign and malignant thyroid nodules and guided subsequent management. However, thyroid nodule ultrasound and fine-needle aspiration must be interpreted with awareness of potential pitfalls.