Case Report of Five Cases with Mummified Thyroid Nodule: Shrinkage Probably be Considered a Benign Feature to Differentiate Mummified Thyroid Nodules from Papillary Thyroid Carcinoma

Abstract Mummified thyroid nodules are benign lesions that decrease in size over time but may resemble papillary thyroid carcinoma on imaging examination. We reviewed five representative cases and evaluated both clinical imaging findings and changes in the American College of Radiology Thyroid Imaging Reporting and Data System (ACR-TIRADS) classification. Based on initial examination, all thyroid nodules were likely benign. However, all nodules shrank over time, achieving TR5 according to ACR-TIRADS, resulting in a diagnosis of malignancy. Cytological examinations were performed on all nodules during their clinical course, with results of class II or I, and no findings suggestive of malignancy. Benign thyroid nodules are unlikely to shrink during malignant transformation. Therefore, if previous imaging findings confirm a significant reduction in nodule size, a more cautious approach should be taken, potentially avoiding fine-needle aspiration cytology. This approach may not only reduce excessive cytological examinations and unnecessary follow-up but also contribute to improved diagnostic performance.