Ten months after a low transphincteric (intersphincteric) fistulotomy, could the procedure have damaged or entrapped nerves that control bladder sensation or urethral sphincter tone long‑term?

Low Transphincteric Fistulotomy Does Not Transect Nerves Controlling Bladder or Urethral Sphincter Function

Low transphincteric fistulotomy does not cut or entrap nerves that control bladder sensation or urethral sphincter tone, because the pudendal nerve branches that innervate the urinary sphincter and bladder neck run well lateral and superior to the surgical field of a low anal fistula tract. 1

Anatomical Basis for Nerve Preservation

• The pudendal nerve divides into three terminal branches after exiting Alcock's canal: the inferior rectal nerve (supplying the external anal sphincter and perianal skin), the perineal nerve (supplying the perineum and anterior structures), and the dorsal nerve of the penis/clitoris (supplying genital sensation). 1

• Low transphincteric fistulotomy only divides the lower third of the external anal sphincter and the intersphincteric plane, leaving the pudendal nerve trunk and its urinary branches completely intact because these structures course laterally through the ischioanal fossa, several centimeters away from the anal canal. 2, 3

• Simple fistulotomy separates only superficial tissue planes and does not transect major pudendal nerve trunks; the procedure preserves both motor and sensory branches that innervate the sphincter complex. 1

Evidence from Fistulotomy Outcomes

• In a prospective cohort of 49 patients who underwent fistulotomy with 3D endoanal ultrasound documentation, a median of 41% of the external anal sphincter and 32% of the internal anal sphincter was divided, yet no patients reported urinary symptoms at 1-year follow-up, confirming that the procedure does not affect bladder or urethral function. 3

• A consecutive series of 22 patients treated with LIFT (ligation of intersphincteric fistula tract) for low transsphincteric fistulas showed no change in continence scores at 6 months, and no urinary complications were reported, supporting the anatomical separation between anal fistula surgery and urogenital innervation. 2

• In a series of 206 patients undergoing various fistula procedures, including 41 fistulotomies for low fistulas, healing rates were 100% with no reports of urinary dysfunction, indicating that the surgical field does not involve urogenital nerves. 4

Why Bladder and Urethral Symptoms Are Not Caused by Fistulotomy

• The inferior rectal nerve (the only pudendal branch near the anal canal) supplies only the external anal sphincter and perianal skin, not the bladder, urethral sphincter, or pelvic floor muscles involved in urinary control. 1

• Urinary sphincter innervation comes from the pelvic splanchnic nerves (S2-S4) and the pudendal nerve branches that course through the deep perineal pouch, anatomical planes that are never entered during low anal fistula surgery. 1

• Conservative management after fistulotomy yields success rates of 61-66% for anal symptoms, and the absence of urinary complications in these cohorts confirms that existing neuromuscular pathways to the bladder and urethra remain undisturbed. 1

Common Pitfalls to Avoid

• Do not confuse anal sphincter dysfunction (fecal incontinence) with urinary dysfunction; these are controlled by entirely separate nerve pathways, and low fistulotomy affects only the inferior rectal nerve branches to the anal sphincter. 1, 3

• Do not attribute urinary symptoms to fistulotomy if they appear months later; such symptoms are far more likely due to unrelated pelvic floor dysfunction, prostate issues (in men), or neurologic conditions affecting the sacral nerve roots. 1

• Avoid probing or extending the dissection beyond the fistula tract, as unnecessary lateral dissection into the ischioanal fossa could theoretically approach the pudendal nerve trunk, though this would represent a major surgical error far outside standard fistulotomy technique. 5

What Actually Causes Post-Fistulotomy Symptoms

• Transient fecal soiling was reported by 11.5% of patients with transsphincteric fistulas treated with setons, evolving into mild flatus incontinence in some cases, but no major fecal incontinence and no urinary symptoms were documented. 4

• Division of over two-thirds of the external anal sphincter was associated with the highest anal incontinence rates, but even in these cases, no bladder or urethral dysfunction occurred, confirming the anatomical separation. 3

• Pelvic floor muscle guarding and myofascial pain can develop after any anorectal surgery and may cause referred pelvic discomfort, but this does not represent nerve damage and responds to pelvic floor physical therapy. 1

Long-Term Nerve Integrity

• At 10 months post-fistulotomy, the surgical wound is fully healed and matured, and any nerve injury (if it had occurred) would have manifested within the first 3-6 months as acute neuropathic pain, not as delayed bladder symptoms. 6

• Pudendal nerve terminal motor latency testing can document baseline sphincter function and confirm that pudendal nerve conduction remains normal after fistulotomy, though this test is rarely indicated unless there is clinical suspicion of a separate neurologic process. 1