From Cytology to Frozen Section: Diagnostic Challenges in Riedel’s Thyroiditis—A Case Report and Brief Literature Review

Background: Riedel’s thyroiditis is a rare fibrosing thyroid disorder that remains one of the most difficult to diagnose, often being initially interpreted as malignant due to its clinical, radiological, and histopathological similarities with anaplastic carcinoma or other infiltrative thyroid diseases. Preoperative investigations, including fine-needle aspiration cytology (FNAC), may be misleading and contribute to an erroneous diagnosis of cancer. Methods: We report the case of a 44-year-old woman presenting with a rapidly enlarging, hard goiter associated with compressive symptoms and cytological findings suspicious for papillary thyroid carcinoma (Bethesda V). Based on these findings and the multidisciplinary team’s assessment, surgical intervention was undertaken. Intraoperatively, the thyroid gland was densely fibrotic and adherent to adjacent structures, prompting frozen-section analysis that revealed a benign fibroinflammatory process consistent with Riedel’s thyroiditis. This intraoperative finding guided the surgical team toward a near-total thyroidectomy, preventing unnecessary radical excision. Results: The paraffin-embedded section confirmed the diagnosis. Postoperative recovery was favorable, with complete resolution of compressive symptoms. Conclusions: This case highlights the persistent diagnostic challenges of Riedel’s thyroiditis and illustrates how intraoperative frozen-section examination can contribute to differentiating it from malignancy when preoperative findings remain inconclusive. A multidisciplinary approach and surgical expertise are essential in tailoring the extent of resection, preventing complications, and achieving both diagnostic confirmation and symptom relief.