Adult-Onset Xanthogranulomatous Inflammation Presenting as a Cervical Branchial-Cleft Cyst.

Xanthogranulomatous inflammation (XGI) is a rare benign histiocytic reaction in the head and neck. Adult-onset XGI within a branchial-cleft cyst (BCC) is exceptionally uncommon, with only two cases previously reported. We present the oldest documented patient and review the literature. A 71-year-old man presented with a painless 3-cm right lateral-neck mass. Ultrasound and MRI suggested a benign thin-walled cyst; fine-needle aspiration revealed foamy macrophages without atypia. Intraoperatively, dense fibrosis and firm adhesion to the carotid sheath raised concern for metastatic carcinoma. Frozen-section analysis demonstrated foamy histiocytes and Touton giant cells without epithelial atypia, confirming XGI. En-bloc excision was completed without radical neck dissection. Recovery was uneventful, and no recurrence was observed at 14 months. Only three adult BCC-XGI cases have been reported, including the present patient. All showed deceptively benign imaging, disproportionate intraoperative fibrosis, and reliance on frozen section to exclude malignancy. Chronic leakage or rupture of cyst contents - possibly potentiated by fine-needle aspiration - appears to trigger the xanthogranulomatous response. Surgeons should consider XGI when encountering fibrotic lateral cervical cysts in older adults. Prompt intraoperative frozen-section analysis enables conservative excision and prevents overtreatment.