The subjects were 83 patients with PSF who underwent treatment for fistula elimination between January 2007 and December 2018 at Kuma Hospital, which is a tertiary thyroid treatment hospital. Data were collected from the medical records. Imaging techniques used for diagnosis included ultrasonography, computed tomography (CT) scans with or without contrast enhancement, and barium swallow studies. Ultrasonography and CT imaging were used to evaluate the site and extent of the inflammation. CT was performed under a trumpet maneuver with the intention of using the air as a contrast agent to reveal the fistula [12]. Except for one patient, diagnoses were confirmed using barium swallow studies. The remaining patient presented with clinical features typical for PSF, but the results of the barium swallow study were inconclusive. The patient underwent suspension laryngoscopy for ECC, and the fistula was confirmed via endoscopy.
Of the 83 patients, 74 patients underwent endoscopic cauterization (ECC, 60 patients; ELC, 14 patients), whereas the remaining nine patients underwent open fistulectomy with or without partial hemithyroidectomy.
Treatment protocol and follow-up
For the endoscopic procedures, the patient’s neck was flexed, and the head was placed in a suspended position under general anesthesia. Then, the suspension laryngoscope (Karl Storz GmbH & Co. KG, Germany) was inserted to access the pharynx. As the orifice of the PSF was usually located at the most caudal part of the pyriform recess, which was typically not fully open, we opened the recess with a silicon tube attached to the laryngoscope to obtain a clear view of the orifice. Then, the orifice of the PSF was identified with a rigid endoscope.
Endoscopic chemo-cauterization
The ECC procedure is described in detail in our previous report [6]. Briefly, under the rigid endoscope, a small cotton ball soaked in 30% trichloroacetic acid was placed into the orifice for one minute, and the procedure was repeated 3–6 times until the cauterized membrane turned white. The membrane was then left to heal secondarily.
Endoscopic laser-cauterization
ELC was performed using a Diode Laser System ADL-20 (Asuka Medical Inc., Kyoto, Japan) that generates 810-nm wavelength diode laser [11]. The diode laser is guided through a glass fiber. A metal cap attached to the top of the glass fiber is selectively heated with the laser during the active mode (Fig. 1). We thought that this system would be appropriate to cauterize the mucosa of the fistula selectively. The device has been approved by the Ministry of Health, Labor and Welfare and is covered by the healthcare insurance system in Japan to use for cutting, coagulating, and establishing hemostasis during surgical, otolaryngological [11], and bronchoscopic treatments. Prior to clinical use, we conducted a pre-clinical experiment using a raw chicken esophagus to test the amount of heat needed to cauterize the mucosal layer selectively, with minimal heat denaturing of the muscle layer (Fig. 1). We found that the optimal total dose was 360 J delivered intermittently at 20 s for 0.01 s at 6 J/s, repeated six times (unpublished data).
After identification of the orifice of the PSF with a rigid endoscope (Fig. 2a), the operator replaced the endoscope to a flexible one. A metal-capped glass fiber was inserted through an instrument channel of the flexible endoscope into the PSF and was heated on active mode for 10 s (Fig. 2b). The procedure was repeated three times to coagulate for about 0.5 cm until the cauterized membrane turned white (Fig. 2c). The membrane was then left to heal secondarily. For precision, the operating mode was set to an intermittent pulse mode, alternately turning on and off every 0.01 s. The total energy delivery ranged from 60 to 300 J. Initially, air was sent to the metal cap through a channel within the glass fiber to avoid overheating during the procedure. However, this step was eliminated after we encountered a complication of subcutaneous emphysema in a patient as we describe below and considering that the use lasted for only 10 s.
All patients or their parents were informed that these endoscopic procedures were novel trials. They were also given the option of conversion to open fistulectomy when the endoscopic procedures were not possible. ECC and ELC for PSF treatments were approved by the institutional Ethical Committee at Kuma Hospital (20060713-1 and 20150709-2). All patients or their parents provided informed consent to undergo their preferred procedure.
Open fistulectomy
Open fistulectomy was performed through a collar skin incision under general anesthesia using the pharyngeal approach technique reported by Nonomura et al. [13] in the four difficult cases.
Postoperative course and follow-up
After the endoscopic procedures were carried out, patients received antibiotic treatment via intravenous infusion for five days to prevent local infection. The patients were provided with liquid diets one day after the procedures and solid diets four days after the procedures.
For open fistulectomy, patients received antibiotic treatment via intravenous infusion only during the operation. The patients were provided with solid diet one day after surgery.
The length of hospital stays for patients who underwent endoscopic procedures ranged from seven to eight days, which was the same as for patients who underwent open fistulectomy.
Posttreatment follow-up involved barium swallow studies and CT imaging under a trumpet maneuver to evaluate obliteration of the fistula at three months and one year after treatment. The patients were followed up for a median of 12 months (range, 1–144 months).
Statistical analysis
The Mann–Whitney U test was used to compare variables. A Fisher’s exact test was used on 2 × 2 contingency tables. All statistical analyses were performed using StatFlex 6.0 software (Artech Co., Osaka, Japan). A p value < 0.05 was considered significant.