Iatrogenic Pudendal Nerve Injury from Lateral Internal Sphincterotomy
The patient's symptoms—decreased anal sensation, altered pressure perception, inner burning, and urinary sensory changes—are most consistent with iatrogenic pudendal nerve injury sustained during the lateral internal sphincterotomy, despite the surgeon's claim that "no cutting was done." 1, 2
Mechanism of Injury
The immediate onset of sensory changes following the fissure surgery, before the hemorrhoidectomy, clearly localizes the injury to the sphincterotomy procedure. The pudendal nerve provides sensory innervation to the anal canal, perineum, and external genitalia, and its terminal branches are vulnerable during lateral sphincterotomy, particularly when the dissection extends laterally or posteriorly beyond the intended plane between the internal and external sphincter 2, 3.
Key clinical features supporting nerve injury:
- Immediate sensory change post-fissurectomy/sphincterotomy (before hemorrhoidectomy) 2
- Preserved sphincter function on palpation (no stenosis, able to handle internal examination) but altered sensation 4, 2
- Burning dysesthesia consistent with neuropathic pain 5, 2
- Altered urinary sensation (pudendal nerve supplies sensory fibers to urethra) 2
- Ejaculatory difficulty at time of fissure injury (pudendal nerve involvement) 2
Why This Is Not Other Conditions
The absence of stenosis rules out cicatricial narrowing from excessive tissue removal 4, 2. The preserved sphincter tone on digital examination excludes significant sphincter disruption 6. The symptom onset before hemorrhoidectomy excludes that procedure as the primary cause 7, 2.
The surgeon's statement about "no cutting" is contradicted by the documented lateral sphincterotomy procedure. Even a "light" lateral sphincterotomy involves division of the internal sphincter muscle, and inadvertent injury to sensory nerve branches can occur with lateral dissection 1, 6, 3.
Diagnostic Workup Required
Immediate evaluation should include:
- Pudendal nerve terminal motor latency (PNTML) testing to document nerve injury, though this primarily assesses motor function 3
- Anorectal manometry to assess sphincter pressures and sensation thresholds 6, 3
- Neurological examination focusing on perineal sensation, anal wink reflex, and bulbocavernosus reflex 4, 3
Post-sphincterotomy patients typically show reduced resting anal pressure (from 138 mmHg pre-op to 110 mmHg at 12 months), but sensory deficits suggest nerve injury beyond intended muscle division 6.
Management Approach
Conservative management is the only option, as nerve injury is not surgically reversible:
- Neuropathic pain medications (gabapentin or pregabalin) for burning dysesthesia 5, 2
- Topical lidocaine for symptomatic relief of anal burning 1, 5
- Pelvic floor physical therapy to optimize remaining function 2
- Avoidance of further surgical intervention, which risks additional nerve damage 1, 2
The prognosis for sensory recovery is guarded. Pudendal nerve injuries may show partial improvement over 12-18 months, but complete recovery is uncommon when immediate sensory loss occurs 2, 3.
Critical Clinical Pitfall
The most important pitfall is attributing these symptoms to the hemorrhoidectomy when the timeline clearly implicates the earlier sphincterotomy. The hemorrhoidectomy complicated diagnosis but did not cause the primary sensory deficit 7, 2, 8. The patient correctly identified the fissure surgery as the inciting event, and this history must be respected 2.
Lateral internal sphincterotomy, while effective for chronic fissures (with healing rates of 90-95%), carries a 0-30% risk of minor incontinence and an underrecognized risk of sensory nerve injury when dissection extends beyond the intersphincteric plane 1, 2, 6, 3.