A 2-year-old girl is brought to the paediatric clinic with a history of recurrent upper respiratory tract infections and mild hearing loss. On examination, there is a small opening in the anterior border of the sternocleidomastoid muscle at the junction of the upper and middle thirds of the neck. A small amount of mucoid discharge is noted. Imaging confirms a tract extending upward toward the tonsillar fossa. What is the most appropriate next step in management?