Subacute granulomatous thyroiditis: histopathological spectrum, perineural inflammation, and coexisting lesions

Subacute granulomatous thyroiditis is a self-limited inflammatory disorder and the most common cause of painful thyroid disease. Surgically treated cases offer a unique opportunity to explore its histopathological spectrum and co-occurring thyroid pathologies.

We retrospectively analyzed 44 thyroidectomy specimens diagnosed with subacute granulomatous thyroiditis between 2009 and 2019, evaluating clinical data and detailed histopathological features including inflammation extent and associated thyroid lesions.

The cohort comprised 36 females and 8 males (mean age 48.1±8.9 years). Preoperative fine-needle aspiration cytology was performed in 68.2% but correctly suggested subacute granulomatous thyroiditis in only one case. Surgery was most indicated for multinodular goiter (63.6%). All cases exhibited confluent folliculocentric granulomas; additional findings included fibrosis (90.9%), neutrophilic infiltration (63.6%), follicular atrophy (63.6%), and perineural inflammation (63.6%). Coexisting follicular nodular disease was present in 88.6% and chronic lymphocytic thyroiditis in 15.9%. Concomitant malignancy was identified in 13 cases (29.5%), predominantly subcentimeter papillary thyroid carcinomas, with no significant clinicopathological associations (p>0.05).

Subacute granulomatous thyroiditis demonstrates broader pathological significance than traditionally recognized. Perineural inflammation may contribute to pain generation, and the elevated malignancy rate most likely reflects incidental detection due to extensive sampling. These findings highlight diagnostic pitfalls and underscore the importance of careful pathological assessment.