Asymptomatic intrathyroidal pyriform sinus fistula mimicking thyroid cancer

RATIONALE: There have been many reports of non-thyroidal lesions which can be mistaken for thyroidal lesions on ultrasound (US) examination. However, it is not known that pyriform sinus fistula (PSF) can manifest as an incidental thyroid nodule and cause serious complication on fine-needle aspiration (FNA). PATIENT CONCERNS: We present a 34-year-old man with PSF incidentally detected on US. US examination showed hypoechoic nodule with several bright echogenic spots at the uppermost part of left thyroid gland. With the suspicion of thyroid cancer, although there would have been some morphologic changes between the 2 US examinations, FNA was performed. DIAGNOSES: Cytologic specimen revealed some clusters of ciliated columnar cells mixed with inflammatory and lymphoid cells. On computed tomography (CT) before FNA, there were tiny air bubbles within the thyroid nodule. Laryngoscopy revealed fistula originating from the pyriform sinus. INTERVENTIONS: After FNA, he had to undergo tracheostomy and removal of abscess due to infectious complication. OUTCOMES: The deep neck abscesses and infections were controlled after the treatment. At 1 year after FNA, successful chemocauterization with 40% trichloracetic acid solution was performed for PSF found on laryngoscopy. LESSONS: PSF can manifest as an incidental thyroid nodule mimicking thyroid cancer. Special care should be taken when FNA is planned for the nodule with air foci and morphologic changeability at the uppermost part of left thyroid gland.