Infected third branchial cleft cyst: retropharyngeal extension to the superior mediastinum.

The presentation of an infected branchial cleft cyst extending into the retropharyngeal space is extremely rare. However, differentiation of this lesion from a simple retropharyngeal abscess is important for surgical planning. The authors describe a 44-year-old woman in whom an infected third branchial cleft cyst was initially misdiagnosed as an abscess and drained surgically. Repeat surgery was necessary when the patient's symptoms recurred several weeks later.