Anal Sphincter Pressure Loss During Combined Lateral Sphincterotomy and Low Trans-Sphincteric Fistulotomy
Direct Answer to Pressure Loss
Lateral internal sphincterotomy alone reduces resting anal sphincter pressure by approximately 30–45% immediately post-procedure, dropping from baseline pressures of 85–140 mmHg to 32–86 mmHg, with partial recovery over 12 months to approximately 110 mmHg (still 20% below baseline). 1, 2, 3
Quantifying the Pressure Drop
In chronic anal fissure patients, preoperative mean resting pressure ranges from 85–140 mmHg (compared to 63–73 mmHg in healthy controls). 1, 2, 3
One week post-sphincterotomy, mean resting pressure drops to 50–86 mmHg, representing a 35–46% reduction. 1, 2, 3
One month post-procedure, pressure stabilizes around 32–86 mmHg depending on the extent of sphincter division. 4, 1, 2
At 12 months, partial sphincter recovery occurs with pressures rising to approximately 110 mmHg, but this remains 20% lower than preoperative baseline. 2
Adding Low Trans-Sphincteric Fistulotomy (<30%)
When combining lateral sphincterotomy with a low trans-sphincteric fistulotomy involving less than 30% of the external sphincter, the additional pressure loss is not well-quantified in the literature, but the combined procedure creates:
A segmental defect in the internal sphincter from the sphincterotomy. 3
An additional external sphincter disruption of up to 30% from the fistulotomy.
The cumulative effect likely produces a total resting pressure reduction of 40–55% from baseline, though this is extrapolated rather than directly measured.
The "Arousal-Related" vs. Continence-Related Loss
Understanding the Dual Impact
The majority of altered sensations and sexual dysfunction following lateral internal sphincterotomy are neuropathic and myofascial in origin, NOT due to mechanical sphincter failure or true incontinence. 5
Patients with sexual dysfunction after LIS typically have intact continence and preserved sphincter integrity. 5, 6
The problem stems from pelvic floor muscle tension and protective guarding patterns that developed during the painful fissure period and persist after surgery. 5, 6
Altered sensations during sexual activity are primarily neuropathic dysesthesia rather than structural sphincter damage. 5
Quantifying the Distinction
Incontinence rates after LIS alone: 1–10% experience minor permanent continence defects (typically flatus incontinence). 7
Sexual dysfunction/altered sensation rates: Not precisely quantified in guidelines, but recognized as a distinct entity from mechanical incontinence. 5
The pressure loss measured manometrically (30–45%) does not directly correlate with the subjective experience of altered sensation during sexual activity, which is predominantly neuropathic/myofascial rather than pressure-related. 5, 6
Clinical Implication
Of the 30–45% pressure loss from lateral sphincterotomy, the portion "perceived as unrelated to continence" (i.e., affecting sexual sensation/arousal) cannot be precisely quantified as a percentage of total pressure loss, because these are fundamentally different mechanisms:
Mechanical pressure loss → measured manometrically, correlates with continence function.
Neuropathic/myofascial dysfunction → causes altered sexual sensation, does NOT correlate with measured pressure loss. 5, 6
Management of Post-Procedure Altered Sensation
Treatment Algorithm for Sexual Dysfunction
Initiate specialized pelvic floor physical therapy 2–3 times weekly focusing on internal and external myofascial release, gradual desensitization exercises, and muscle coordination retraining. 5, 6
Apply topical lidocaine 5% ointment to affected areas for neuropathic pain control. 5, 6
Expected timeline: Dysesthesia and altered sensations typically improve significantly over 6–12 months with appropriate therapy. 6
Critical Pitfall
Never pursue additional surgical interventions for post-LIS sexual dysfunction, as this would likely worsen the neuropathic component rather than improve it. 5, 6
Alternative Approach to Avoid These Issues
Botulinum toxin injection represents a safer alternative to lateral internal sphincterotomy, achieving 75–95% cure rates with no risk of permanent incontinence or sexual dysfunction. 7, 5