In a patient with an anal fissure, is the resting pressure of the internal anal sphincter required for the deep‑fullness sensation of pelvic sexual arousal, and will lowering that pressure with treatments (e.g., topical calcium‑channel blocker, nitroglycerin, botulinum toxin, or lateral internal sphincterotomy) affect sexual pleasure?

Lowering Internal Anal Sphincter Pressure Does Not Affect Sexual Arousal or Deep Pelvic Fullness Sensations

The internal anal sphincter (IAS) is anatomically and functionally isolated from deep pelvic arousal pathways, and reducing its resting tone—whether through topical calcium-channel blockers, nitroglycerin, botulinum toxin, or lateral internal sphincterotomy—will not diminish sexual pleasure or deep pelvic fullness sensations. 1

Anatomic Separation of the IAS from Deep Pelvic Structures

• The IAS is a superficial structure confined to the anal canal level, extending only approximately 1.2 cm cephalad from the proximal margin of the external anal sphincter. 1
• It is anatomically distinct from deep pelvic autonomic nerves and the neurovascular bundles that mediate sexual arousal and deep pelvic sensation. 1
• The IAS lies in close proximity to the anorectal mucosa and is thin and pale pink, making it a local sphincter mechanism rather than a deep pelvic structure. 1

Physiologic Role of the IAS: Continence, Not Sexual Function

• The IAS generates resting anal pressure (averaging ≈114 ± 17 cm H₂O in fissure patients versus ≈73 ± 27 cm H₂O in healthy individuals) to maintain passive fecal continence. 2
• IAS hypertonia in anal fissure patients creates a pain-spasm-ischemia cycle by reducing anodermal blood flow, which impairs fissure healing. 2
• No evidence exists linking IAS resting tone to sexual arousal receptors, deep pelvic fullness, or genital sensation pathways. 1

Evidence from IAS-Targeted Therapies

Topical Calcium-Channel Blockers (Nifedipine, Diltiazem)

• Compounded 0.3% nifedipine with 1.5% lidocaine achieves ≈95% fissure healing by blocking L-type calcium channels in IAS smooth muscle, lowering sphincter tone and improving perfusion. 2
• Healing rates of 65–95% are reported with topical diltiazem or nifedipine, with no documented sexual dysfunction or loss of pelvic sensation. 1

Botulinum Toxin Injection

• Botulinum toxin into the IAS demonstrates 75–95% cure rates with low morbidity. 2
• The only reported side effect is mild transient flatus incontinence (lasting ≈3 weeks), with no reports of altered sexual function or deep pelvic sensation. 3

Lateral Internal Sphincterotomy (LIS)

• LIS divides the IAS and achieves >95% healing with 1–3% recurrence. 2
• Wound-related complications occur in up to 3% of patients, and minor permanent continence defects (typically flatus incontinence) occur in 1–10%. 1
• No evidence links LIS to loss of sexual arousal or deep pelvic fullness; post-operative sensory changes are confined to the anal canal and perianal skin. 4

Post-Sphincterotomy Sensory Changes: Localized, Not Deep Pelvic

• Patients with altered sensations after LIS typically have intact continence and preserved sphincter integrity; the problem stems from pelvic floor muscle tension that developed during the painful fissure period and persists after surgery. 4
• Protective guarding patterns in the external anal sphincter and pelvic floor muscles (not the IAS) are responsible for ongoing symptoms. 4
• These sensory changes are treated with pelvic floor physical therapy (internal and external myofascial release, desensitization exercises, muscle coordination retraining) and topical lidocaine 5% for neuropathic pain control. 4
• Dysesthesia and altered sensations typically improve significantly over 6–12 months with appropriate therapy, confirming that the issue is superficial pelvic floor tension, not deep pelvic arousal pathways. 4

Critical Distinction: Superficial Anal Canal vs. Deep Pelvic Arousal

• The IAS is a local sphincter mechanism that controls passive fecal continence through resting tone. 1
• Deep pelvic fullness and sexual arousal sensations are mediated by autonomic nerves (hypogastric, pelvic splanchnic) and vascular engorgement of deep pelvic structures (prostate, vagina, rectovaginal septum, neurovascular bundles). 1
• Reducing IAS tone addresses anodermal ischemia and sphincter spasm in the anal canal, not deep pelvic neurovascular pathways. 2

Algorithmic Reassurance for Patients

1. Confirm the anatomic separation: The IAS is a superficial anal canal structure, not a deep pelvic organ. 1
2. Review the evidence: Thousands of patients treated with topical calcium-channel blockers, botulinum toxin, and LIS show no loss of sexual function or deep pelvic sensation. 2, 1, 4, 5, 3
3. Address post-treatment sensory changes: If altered sensations occur after LIS, they are due to pelvic floor muscle tension (treatable with physical therapy), not loss of deep pelvic arousal pathways. 4
4. Reassure regarding treatment safety: Lowering IAS tone will relieve fissure pain and spasm without affecting sexual pleasure or deep pelvic fullness. 2, 1

Common Pitfall to Avoid

• Do not conflate anal canal sensory changes with deep pelvic arousal pathways. Post-sphincterotomy dysesthesia is a localized, superficial phenomenon involving the anal canal and perianal skin, not deep pelvic structures. 4
• Do not pursue additional surgical interventions for post-LIS sensory changes, as this would worsen neuropathic symptoms rather than improve them. 4