Case Report: Use of Reinforced Buccal Mucosa Graft over Gracilis Muscle Flap in Management of Post High Intensity Focused Ultrasound (hifu) Rectourethral Fistula [version 2; Referees: 2 Approved] Report Report Report Case Report: Use of Reinforced Buccal Mucosa Graft over Gracilis Muscle Flap in Man

High intensity focused ultrasound (HIFU) has come forward as alternative treatment for carcinoma of the prostate. Though minimally invasive,HIFUhas potential side effects. Urethrorectal fistula is one such rare side effect. Management of these fistulas has been described by Vanni et al. This case report describes points of technique that will help successful management of resilient rectourethral fistula. Urinary and faecal diversion in the form of suprapubic catheter and colostomy is vital. Adequate time between stoma formation, fistula closure and then finally stoma closure is needed. Lithotomy position and perineal approach gives best exposure to the fistula. The rectum should be dissected 2cm above the fistula; this aids in tension free closure of the rectal defect. Similarly buccal mucosal graft was used on the urethra to achieve tension free closure. A good vascular pedicle gracilis muscle flap is used to interpose between the two repairs. This not only provides a physical barrier but also provides a vascular bed for BMG uptake. Perfect haemostasis is essential, as any collection may become a site of infection thus compromising results. We strongly recommend rectourethral fistula be directly repaired with gracilis muscle flap with reinforced buccal mucosa graft without attempting any less invasive repairs because the " first chance is the best chance ". Copyright: et al Creative Commons Attribution Licence permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Data associated with the article are available under the terms of the (CC0 1.0 Public domain dedication). Creative Commons Zero "No rights reserved" data waiver The author(s) declared that no grants were involved in supporting this work.

Urethrorectal fistula is a serious complication of HIFU. Literature reports a rate of urethrorectal fistula following HIFU 2 of approximately 0.7%. This case report describes management of recurrent urethrorectal fistula after HIFU with buccal mucosa graft (BMG) over a bed of gracilis flap.

Case report
A 52-year-old man was evaluated for lower urinary tract symptoms (LUTS) and found to have raised PSA levels of 18.70 ng/ml. Transrectal ultrasound (TRUS) guided biopsy showed adenocarcinoma of the prostate with a Gleason's score of 3+4 with evidence of extracapsular spread on the left side. Bone scan showed osteoblastic activity at the distal end of the right femur. Ultrasound (USG) showed 30 g prostate. He underwent an initial TURP to debulk the gland. Following the intervention in the same sitting he underwent HIFU. Histopathology showed 50% of the cores were positive for adenocarcinoma with a Gleason's score of 4+4. The Foley catheter (PUC) was removed on the 5 th post-operative day (POD). On the 15 th POD, the patient had urine leak via the rectum. Diagnostic cystoscopy showed a single fistulous opening above the level of the external sphincter. As conservative management failed in form of suprapubic catheter (SPC), he underwent robotic assisted laparoscopic excision of the fistula. The bladder and rectum were closed separately with interposition of an a cellular matrix sheet in between.
On the 6 th POD following robotic repair, the patient developed fecaluria which was managed with loop sigmoid colostomy and SPC. Repeat cystoscopy after 3 months showed persistent fistula ( Figure 1). He was planned for repeat surgery via perineal approach in view of his previous failed abdominal surgery and faecal contamination of abdomen.
The patient was placed in lithotomy position with the perineum nearly horizontal. An inverted smiling incision was made in the perineum above the anus ( Figure 2). Dissection showed dense adhesions between the rectum and surrounding tissue. Digital rectal examination done intraoperatively ensured rectal wall integrity. The fistula was at the 1 o' clock position between the prostatic urethra and rectum ( Figure 3). All scar tissue and fistula was excised to create healthy margins. The rectal defect was repaired in transverse fashion in a single layer with monocryl       2-0 sutures (Figure 4). BMG was harvested and positioned to bridge the urethral defect; it was anchored with interrupted 3-0 monofilament sutures ( Figure 5). A separate incision was made on the left thigh from the adductor tubercle to 2cm above the medial condyle. The gracilis muscle flap was harvested, rotated towards the perineum ( Figure 6) and interposed between the rectal and urethal repair (Figure 7). Prior to closure of wound, adequate haemostasis was ensured.
On the 14 th POD the PUC was removed and SPC blocked. The patient was voiding well with a satisfactory uroflow without any leak of urine from the rectum. Colostomy closure was done after 3 months. On follow-up visits at 3 and 6 months, the patient was asymptomatic. In a series of 35 patients by Ulrich et al 5 , 4 patients had fistula post radical prostatectomy and all were treated successfully with a mean follow up time of 28 months. The patients included those with iatrogenic rectal injury during retropubic prostatectomy. Our case represents an injury due to high intensity focal ultrasound given for prostate cancer.
In a series of 11 cases by Zmora et al 6 , 9 patients healed without complication and 2 others required further surgical management. Thus a success rate of 81% was achieved. This series included two patients with post radical prostatectomy fistula in two instances. The authors advocated this approach in failed previous repairs as in our case.
The technique of harvesting BMG was first described by Allen F. Morey et al 7 in 1996. Andrich DE 8 reported better results for dorsal as opposed to ventral onlay due to more vascular and better bed of corporal bodies for graft uptake. Further it was found that strictures in sittings of ischemia are better repaired with flaps due to poor surrounding blood supply. In our case the urethral defect was 2.5cm and in the prostatic urethra with local ischemia, thus a BMG without the grascilis muscle flap bed would result in a poorer outcome.
More recently Vanni et al 9 published case series of 74 patients with rectourethral fistula which included 2 patients with post-HIFU rectourethral fistula. There patients under went fistula repair with interposition muscle flaps with or without BMG with overall success rate of 84%. This article confirms the feasibility of combined BMG and gracilis muscle flap repair and thus provides a proof of concept for our case report.

Conclusion
Rectourethral fistula secondary to HIFU should be categorised as acomplicated fistula owing to the hostile environment caused by the local heat generated by primary treatment. This report suggests rectourethral fistula post HIFU should be repaired with gracilis muscle flap with reinforced buccal mucosa graft as the "first chance in the best chance" in such situations.
Key messages from our case report 1. Good exposure and adequate dissection is vital; this was achieved by the perineal approach.
2. Tension free repair of the rectum was achieved by dissection of rectum 2 cm cranial to the fistula and on the urethral side; buccal mucosa graft was used for tension free repair.
3. As both rectum and urethra are high pressure zones, there is a high probability of failure if both the repairs are not separated by live tissue 10 . Ideal tissue for this interposition is a tissue with its own blood supply, in this case a pedicle gracilis muscle flap. The advantage of this flap was it acts as a physical barrier as well as a vascular bed for BMG.
4. Adequate haemostasis and good closure is equally important, as any collection is likely to get infected leading to recurrent fistula. Closure over suction drain helps in reducing the chances of collection, and also to keep buccal mucosal graft adherent to surrounding vascular tissue, thus helping in graft uptake.

Consent
Written informed consent for publication of the patient's clinical details and clinical images was obtained from the patient.
Author contributions AG,SJ,AS and MV wrote, revised the manuscript. SJ,AG, AS,MV, VB,RS, and MD are responsible for the concept and content.

Competing interests
No competing interests were disclosed.

Grant information
The author(s) declared that no grants were involved in supporting this work.
"Zinman described 68 patients with rectourethral fistula who underwent gracilis muscle flap repair out of which 27 were performed in combination with BMG".
This reference is antiquated and we have published 2 more extensive papers on the topic more recently that should be cited instead of the one used by the authors. Vanni is a better reference for this et al sentence and the one I previously mentioned above. In this paper, 74 patients had RUF repair with a gracilis muscle flap. 39 of these patients had a RUF from an ablative source (radiation and 2 HIFU). Of these 39 patients, 34 had a buccal mucosa graft (including the 2 HIFU cases) used to close the urethral defect. 37 of these patients had at least 1 gracilis muscle flap, while the other 2 patients had an inferior gluteus maximus flap and a Singapore fasciocutaneous flap.
I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
No competing interests were disclosed.