Two cases of piriform sinus fistula: Ultrasonographic characteristics and strategic points

Piriform sinus fistula （PSF） is an anomaly of embryologic development of the branchial apparatus and sometimes causes acute suppurative thyroiditis. Two cases of piriform sinus fistula recorded in the Fukushima Thyroid Ultrasound Examination （FTUE） are presented. The patients in cases 1 and 2 were a 14-year-old girl and a 15-year-old girl, respectively. Thyroiditis was observed with right PSF before the FTUE in case 1, while thyroiditis and left PSF were observed after the FTUE in case 2. Both cases underwent complete removal of the sinus tract and showed a favorable course. In the ultrasound examination of FTUE, a hypoechoic tubular lesion that emerged from the posterolateral aspect of the thyroid cartilage and across the thyroid gland and other characteristics that were difficult to distinguish from malignancy were identified in each case. Generally, ultrasound findings of PSF with thyroiditis include some doubtful characteristics of malignancy. Although other inspections are warranted for diagnosis, a hypoechoic tubular lesion that emerges from the thyroid cartilage and across the thyroid gland should be suspected as a characteristic of PSF.