Ultrasonography features of medullary thyroid cancer as predictors of its biological behavior.

Background Although there are many well-known prognostic predictors of medullary thyroid carcinoma (MTC), the ultrasonography (US) findings of MTC have not been sufficiently validated in this regard. Purpose To investigate the US findings of MTC and their relationship with the biological behavior of MTC. Material and Methods The US findings and clinical and pathology records of 123 MTC nodules from 108 patients were retrospectively analyzed at two tertiary referral hospitals. MTCs were classified according to US findings, i.e. MTC with benign (B-MTC) and malignant US findings (M-MTC). We then compared the clinical and pathology findings between the two groups. Results Eighty-two M-MTCs (66.7%) and 41 B-MTCs (33.3%) were identified. M-MTCs showed a significantly higher prevalence of lateral lymph node metastases as well as extrathyroidal and extranodal extension (all P < 0.05). M-MTCs larger than 1 cm showed a significantly higher prevalence of multifocality, recurrence, extrathyroidal and extranodal extension than B-MTCs larger than 1 cm in the largest dimension (all P < 0.05). Tumors > 1 cm were more likely to be B-MTC and one-third of all MTCs had benign US features. The common findings of B-MTC included a solid, ovoid to round shape, with a smooth margin, hypoechogenicity, and without calcification. Conclusion The biological behavior of M-MTCs results in poorer outcomes than that of B-MTCs.