Tumor protrusion with intensive blood signals on ultrasonography is a strongly suggestive finding of follicular thyroid carcinoma

Aim: It is difficult to differentiate follicular carcinomas (FC) from follicular adenomas (FA) because ultrasonography and cytology provide very similar findings. FC is histopathologically diagnosed to have capsular and/or vascular invasion. In a few patients, tumor protrusions are observed by preoperative ultrasonography as large forms of capsular invasion of follicular carcinomas. The aim of the study was to clarify the predictive value of tumor protrusions on preoperative ultrasonography for follicular carcinomas. Material and methods: A total of 531 patients (FC: 184 patients, FA: 347 patients) undergoing thyroid surgery were included in this study. A tumor protrusion on ultrasonography was defined as follows: 1) a solid tumor extending beyond a marginal line of capsular zone of the main tumor on B-mode ultrasonography; 2) intensive blood signals observed within the protrusion area on Doppler ultrasonography. The large form of capsular invasion was defined if the protrusion lesion was histopathologically diagnosed to be a capsular invasion of follicular carcinoma. Results: The sensitivity of tumor protrusion was 0.071, specificity 0.994, positive predictive value 0.867, and negative predictive value 0.669 for FC diagnosis. For the large form of capsular invasion in FC the sensitivity of tumor protrusion was 0.813, specificity 0.982, positive predictive value 0.684, and negative predictive value 0.982. Conclusions: A tumor protrusion with intensive blood signals extending from the main tumor on ultrasonography strongly suggests a large form of capsular invasion of follicular carcinoma.