Psammoma bodies in thyroid: are they always indicative of malignancy? A multi-institutional study

Traditionally, psammoma bodies (PB) have been considered as tale-tell evidence of papillary thyroid carcinoma (PTC) and are frequently encountered in classic and other subtypes of PTCs. However, the presence of PBs in the thyroid gland does not always indicate malignancy. The leading hypothesis on their origin suggests that PB are remnants of papillary structures that have undergone thrombosis, necrosis, and subsequent calcification. From January 2010 to May 2024, 26 patients with psammoma bodies associated with benign thyroid lesions, mainly thyroid follicular nodular disease (TFND), Hashimoto thyroiditis (HT), Graves' disease, and follicular adenomas, were found. The case cohort included 16 females and 10 males with a median age of 49.3 years. The series included 12 TFND, two HT, and 12 follicular adenomas (11 out of 12 were oncocytic adenomas). Twenty-four out of 26 underwent total thyroidectomy. In 24 out of 26 cases, the entire lobes and parenchyma were included and serial cuts at multiple levels were performed in cases with PB but without any evidence of malignancy. Even though the detection of PB is associated with a malignant thyroid lesion, especially PTC and its subtypes, our multi-institutional series showed that in a minority PB can be found in a variety of benign thyroid lesions. Evaluation of the entire thyroid parenchyma at multiple levels is mandatory to exclude sub-centimeter papillary thyroid carcinoma.