Excision of a Giant Bilobed Second Branchial Cleft Cyst: A Case Report.

Second branchial cleft cysts (BCCs) are congenital cystic anomalies of the lateral neck that rarely attain giant proportions exceeding 10 cm. When they do, their size and proximity to critical neurovascular structures present distinctive diagnostic and surgical challenges. We present the case of a 24-year-old woman with a one-year history of a painless, enlarging left neck mass. Imaging revealed a large, bilobed cystic lesion deep to the sternocleidomastoid muscle extending from the skull base to the subclavicular region. Fine-needle aspiration cytology excluded malignancy, and the cyst recurred after ultrasound-guided aspiration. The patient underwent complete surgical excision with preservation of the spinal accessory nerve and all adjacent neurovascular structures. The postoperative course was uncomplicated, and pathology confirmed the diagnosis. This case illustrates that second BCCs can attain extraordinary dimensions and exhibit complex morphology while remaining benign. A multimodal preoperative workup is essential to exclude malignancy and guide surgical planning. Controlled intraoperative decompression can facilitate safer dissection in unusually large lesions. Complete surgical excision remains the definitive treatment and is critical for preventing recurrence and complications.