The value of CT annular calcification in identifying benign and malignant thyroid nodules

Objective: To evaluate the value of annular calcification in CT in the diagnosis and differential diagnosis for benign and malignant thyroid nodules. Methods: CT findings of 67 nodules in 67 patients pathologically diagnosed with annular calcifications were retrospectively analyzed to identify 49 benign nodules and 18 malignant nodules. The interior or boundaries of annular calcification before and after contrast-enhancement were compared, and the degree of enhancements of both interior annular calcification and thyroid tissues were observed. After contrast-enhancement, the numbers of lesions showing clearer boundaries and higher degree of enhancement were summarized. Statistic analysis was conducted by using X test. Results Among 67 nodules with annular calcifications, clearer boundaries after contrast-enhancement were observed in 61.2% (30/49) benign nodules and 16.7% (3/18) malignant nodules, showing significant statistical difference (χ² = 10.457, P <0.05). The sensitivity and specificity of clearer edge after contrast-enhancement for benign nodules were 61.2% (30/49) and 83.3% (15/18) respectively. Higher degree of enhancement were observed in 16.3% (8/49) in benign nodules and 0(0/18) malignant nodules, showing no significant statistical difference (χ² = 3.337, P > 0.05). The sensitivity and specificity of higher degree of enhancement for benign nodules were 16.3% (8/49) and 100.0% (18/18) respectively. The combination of clearer boundaries and higher degree of enhancement after contrast-enhancement was observed in 11.6% (38/49) benign nodules and 16.7% (3/18) malignant nodules, showing significant statistical difference (χ² = 20.549 , P < 0.05). Meanwhile, the sensitivity and specificity of such combination for benign nodules were 77.6% (38/49) and 83.3% (15/18) respectively. Conclusions: CT is important in the diagnosis of thyroid nodules with annular calcification. Clearer boundary after contrast-enhancement and its combination with higher degree of enhancement are helpful for the diagnosis of benign nodules. Boundaries that similar to or more obscure than that of plain scan indicate malignant nodules. (authors)