Spontaneous Involution of a Thyroid Nodule: When Nodules Can't Be Trusted.

A thyroid nodule (TN) is an abnormal growth within the thyroid gland, with a large prevalence in adults. They can be classified as benign or malignant based on their characteristics. Most nodules are non-palpable and require ultrasound and histopathological analysis for identification. This study reports a rare case of TN involution despite initially exhibiting malignant ultrasound characteristics. The patient presented with a cystic TN of 27.43 x 13.31 x 35.84 mm, initially classified as Thyroid Imaging Reporting and Data System (TIRADS)-2 and Bethesda II, which later transformed into a solid mass classified as TIRADS-5 and Bethesda I. Over time, the nodule demonstrated an 88% reduction in size to 5.93 x 6.34 x 10.17 mm, while maintaining a TIRADS-5 classification. Surveillance remains the primary management approach, with a follow-up scheduled for 2025. No lymphadenopathy was detected. The observed regression supports evidence that fine needle aspiration biopsy of cystic thyroid nodules may induce necrotic and fibrotic changes, potentially due to post-procedural hemorrhage leading to hematoma formation, tissue compression, and eventual involution. The primary focus of this case review is to contribute to the relatively limited research on TN involution and to briefly discuss the underlying mechanisms.