BACKGROUNDMedullary thyroid carcinoma (MTC) is a rare malignant tumour and usually difficult to diagnose with ultrasound. The aim of the study is to summarize the sonographic features of MTC and evaluate their diagnostic values.

METHODSWe analyzed the sonographic features of 35 MTCs and 50 benign nodules with respect to nodular size, echogenecity, internal content, shape, height/width, border, peripheral halo, calcifications and colour flow pattern. The ratio of long to short axis, echogenecity, internal content and calcifications were also assessed in cervical lymph nodes. The differences in sonographic features between MTCs and benign nodules were analyzed with Chi square test. The diagnostic efficiency of each sonographic feature was determined.

RESULTSThe main sonographic features of MTC were hypoechogenicity (including marked hypoechogenicity) (n = 34, 97%), internal solid content (n = 29, 83%), taller than wide (n = 34, 97%), well defined border (n = 24, 69%), microcalcifications or macrocalcifications (n = 23, 66%). The echogenicity, internal content, shape, peripheral halo and calcifications were significantly different between these two groups, while the tall/wide, border, and perinodular and intranodular vascularisation were not significantly different. Among all the individual sonographic features, irregular shape had the highest diagnostic efficiency with a sensitivity of 51% and specificity of 92%. The combination of marked hypoechogenicity, microcalcifications, and irregular shape yielded a sensitivity of 77% and specificity of 86%.

CONCLUSIONSThe typical sonographic features of MTC are hypoechogenicity, predominantly solid, irregularly shaped with intranodular micro- or macro-calcifications. The combination of multiple sonographic features is helpful, but not definitive, for the diagnosis of MTC.