Introduction
In 1973, the pyriform sinus fistula (PSF) was defined as a fistula that originated from the remnant of the 4th pharyngeal pouch.1 Then, in 1979, Takai et al. reported that recurrent acute suppurative thyroiditis was caused by PSF.2 Moreover, 3%–10% of congenital anomalies that originated from the pharyngeal pouch have been known as remnants from the 3rd and 4th pouch, which are considered as origins of PSF. It is different from brachial cyst, so called lateral cervical fistula. The inferior parathyroid glands and thymus that originated from the 3rd pouch moves caudally, whereas the superior parathyroid gland and C cells producing calcitonin that originated from the 4th pouch migrate caudally behind thyroid gland.3 These two tracts are considered as routes of PSF and sometimes presented as two simultaneous fistulas with two different origins as previously reported.4Most PSFs (93.5%) are located on the left side because the left side shows more complex vascular development and that the C cell precursor, ultimobranchial body, and part of the 4th pouch develop from the left side.5-7
The diagnosis of PSF is confirmed by fluoroscopy and/or computed tomography with enhancement by barium swallow with Valsalva technique.5 The decision of radical treatment of PSF depends on the frequency of recurrent acute onset and severity of acute phase with attentive consultation with patients and family members. In 1998, Jordan et al. proposed endoscopic cauterization of PSF8 although this palliative treatment frequently causes recurrences (25%) as reported in 15 previous studies.9 In contrast, 18 cases of surgically complete fistulectomy in India presented no recurrence.10
There were case reports on severe acute suppurative thyroiditis and deep neck abscess caused by PSF, but no report has mentioned about the routes and origins of PSF. We analyzed 19 cases of completely resected PSF and found two different pathways of fistulas at surgery. In this study, we distinguished two origins of PSF and compared their routes, histology, and clinical manifestations to understand the pathology and improve treatment of PSF.