26 yo F presenting with severe sore throat.
1. Multiloculated, irregular fluid collection with foci of gas compatible with abscess. Lesion is centered on the superior left lobe of the thyroid and extends into the retropharyngeal space in the expected location of the upper esophagus. Additionally, there is a likely fistula between a portion of the fluid collection and the left piriform sinus (series 6, images 177-181). Overall these findings are most compatible with a congenital 4th branchial cleft cyst that has now has developed an abscess.
(Infected fourth branchial cleft cyst with piriform sinus fistula)