The emerging echogenic tract sign of pyriform sinus fistula: an early indicator in the recovery stage of acute suppurative thyroiditis.

AST is commonly associated with pyriform sinus-thyroid fistula in children. Radiologic findings of AST are documented in a few reports. We report a new sign we term the "emerging echogenic tract sign," which reflects a patent air-containing pyriform sinus-thyroid fistula on follow-up US. Recognition of this sign is an important finding suggesting an associated pyriform sinus-thyroid fistula in a patient with AST and also suggesting the adequate timing of barium esophagography to confirm the fistula.