Thyroid nodule shape suggests malignancy

OBJECTIVE: To evaluate if a nodule with shape taller than wide (anteroposterior/transverse diameter ratio, A/T > or = 1) is a good predictor of malignancy independent of the size.

METHODS: We retrospectively examined the cytological and histological results of 7455 nodules (5198 patients) referred for ultrasound-guided-fine needle aspiration cytology (US-FNAC) in our hospital from January 1991 to September 2004.

RESULTS: A suitable FNAC was obtained from 6135 nodules (4495 patients); 34.6% were less than 1 cm in diameter (small nodules, SN). A diagnosis of carcinoma was histologically confirmed in 284/349 suspicious lesions after FNAC. The size of carcinoma nodules was not significantly associated with the occurrence of extracapsular growth (large nodules (LN): 10.5%, SN: 4.9%, NS) and lymph node metastasis (LN: 23.6%, SN: 25.0%, NS). Malignant lesions showed microcalcifications more frequently than benign nodules (72.2 vs 28.7%; P < 0.001; (odds ratio, OR(confidence intervals, CI) = 9.9(7.2-13.4)). Similarly, A/T > or = 1 (76 vs 40%; P < 0.001; OR(CI) = 8.6(5.5-13.1)), blurred margins (52.8 vs 18.8%; P < 0.001; OR(CI) = 7.7(5.6-10.2)), solid hypo-echoic appearance (80.6 vs 52.4%; P < 0.001; OR(CI) = 3.2(2.2-4.3)) and intranodular vascular pattern (type 2) (61.6 vs 49.7%; P < 0.001; OR(CI) = 1.7(1.3-2.3)) were significantly more frequent in malignant than in benign nodules.

CONCLUSIONS: Our data show that no single parameter, including nodule size, satisfactorily identifies a subset of patients to be electively investigated by FNAC. We concluded that A/T > or = 1 with at least two of US features (microcalcification, blurred margins, hypo-echoic pattern) is today the best compromise between missing cancers and cost-benefit.