Pudendal Nerve Risk in Perianal Fistula Surgery
The pudendal nerve is not at significant risk during standard perianal fistula surgery when proper surgical technique is employed, as the nerve trunk lies well outside the operative field of typical fistula procedures. 1
Anatomical Safety of Standard Fistula Surgery
The pudendal nerve is anatomically protected during routine fistula operations because:
Simple fistulotomy does not transect major pudendal nerve trunks; the procedure only separates superficial tissue planes, preserving both motor and sensory branches of the pudendal nerve that innervate the sphincter complex. 1
Direct electrophysiological evidence confirms safety: A prospective study measuring pudendal nerve terminal motor latency (PNTML) before and after fistula surgery in 33 patients found no difference in nerve conduction postoperatively (ΔPNTML = 0.03±0.40 ms on diseased side, 0.06±0.42 ms on healthy side, p=0.84), demonstrating that nervous conduction of the pudendal nerves is not altered by either the infectious process or the surgical procedure. 2
Critical Technical Consideration to Avoid Nerve Injury
The only scenario where pudendal nerve injury becomes a real risk is when surgeons extend dissection laterally beyond the fistula tract into the ischioanal fossa. 1
Extending dissection laterally into the ischioanal fossa during low transphincteric fistulotomy can approach the pudendal nerve trunk; therefore, surgeons should limit probing and tissue division strictly to the fistula tract to prevent inadvertent pudendal nerve injury. 1
This is particularly relevant during complex procedures or when aggressive probing is performed during examination under anesthesia. 3
Procedure-Specific Risk Profile
Low-Risk Procedures (Standard Fistulotomy, LIFT)
LIFT procedure works by ligating the fistula tract at the intersphincteric level, which is anatomically distant from the pudendal nerve trunk and its major branches. 4
The intersphincteric groove dissection used in LIFT remains medial to any pudendal nerve structures. 5
Higher-Risk Procedures (Proctectomy)
Main risks of proctectomy include damage to the pelvic nerves, presacral abscesses, and delayed perineal wound healing—this is the only perianal surgery where pudendal and other pelvic nerve injury is a recognized major complication. 5
During proctectomy for inflammatory bowel disease, the intersphincteric groove may not be identifiable due to scarring in up to 78% of patients with perianal Crohn's disease, limiting the ability to perform an intersphincteric dissection and increasing the risk of nerve injury. 5
Leaving as little rectum as possible (dividing the middle rectum within the pelvis) is not recommended because such an approach will impose difficulties at subsequent proctectomy, with a probable increase in the risk of pelvic nerve injury. 5
Clinical Algorithm for Nerve Protection
Preoperative Assessment
- Identify fistula anatomy with MRI to plan the most direct surgical approach. 5
- Confirm absence of extensive lateral extension that would require ischioanal fossa dissection. 1
Intraoperative Technique
- Confine all dissection strictly to the fistula tract itself—do not extend laterally into the ischioanal fossa. 1
- Avoid aggressive probing that could create false passages toward lateral structures. 3
- For LIFT procedures, stay within the intersphincteric plane without lateral deviation. 4
Postoperative Monitoring
- Pudendal nerve injury would manifest as perineal numbness, erectile dysfunction, or urinary symptoms—these are exceedingly rare after standard fistula surgery. 6, 7
Common Pitfalls to Avoid
Do not confuse sphincter injury with pudendal nerve injury: Incontinence after fistula surgery is almost always due to direct sphincter muscle division, not nerve damage. 2
Avoid unnecessary lateral dissection: The temptation to "explore" or "ensure complete drainage" by extending dissection laterally is the only way to put the pudendal nerve at risk during routine fistula surgery. 1
Recognize that proctectomy is a completely different operation: The nerve risks associated with proctectomy for severe perianal disease should not be conflated with the negligible nerve risks of standard fistula procedures. 5