Pyriform sinus fistula (PSF) is a rare congenital branchial anomaly that commonly found in children. It can result in recurrent cervical infection or acute suppurative thyroiditis (AST). Confirming the fistula tract is the key point for the diagnosis of PSF. Ultrasound plays an important role in the diagnosis of PSF and its complications. We examine a case of AST secondary to PSF by ultrasonography, and successfully demonstrate its fistula through local injection of ultrasound contrast agent into the thyroid abscess cavity. This is the first report that confirms a fistula tract through local injection of ultrasound contrast agent, and it can serve as an accurate modality for the fistula detection of PSF.