[Clinical case of the month. Left recurrent neck abscess revealing a fourth branchial cleft fistula].

The fourth branchial cleft fistula, which can be the origin of a recurrent left neck abscess, is a rare congenital malformation. Its diagnosis can be difficult. A ten-year-old girl presented with a left painful swelling of the neck. At ultrasonography and tomodensitometry, the diagnosis of thyroglossal cyst was suspected. Antibiotics were prescribed before surgical resection. The intervention was successful and the peroperative macroscopic aspect of the lesion suggested a dermoid cyst. Four months later, the same symptoms reappeared with fever. An intravenous antibiotic therapy was started while a magnetic resonance imaging demonstrated a possible aero-digestive tract fistula. Two days later, the patient developed an aero-cutaneous fistula. Oral antibiotics were started. Five months later, the girl came back for a second recurrence. A few days after her admission, she developed again an aero-cutaneous fistula. The diagnosis of surinfected fourth cleft fistula was made. An antibiotic therapy was started until the second intervention. After discussion about embryology, we describe the physiopathology, the differential diagnosis and the management of a fourth branchial cleft fistula causing recurrent left neck abscess.