Urinary Retention Discomfort Following Lateral Internal Sphincterotomy and Trans-Sphincteric Fistulotomy
The discomfort from urinary retention after these anorectal procedures originates from pelvic floor muscle spasm and disrupted coordination between the bladder detrusor muscle and the external urethral sphincter, a phenomenon known as pelvic floor dyssynergia. 1
Primary Mechanism: Pelvic Floor Muscle Dysfunction
The pelvic floor muscles—particularly the levator ani and external urethral sphincter—share neural pathways and reflexive connections with the anal sphincter complex. When surgical trauma occurs to the anal sphincter during sphincterotomy and fistulotomy, it triggers protective spasm in the entire pelvic floor musculature. 1, 2
Reflex arc disruption: The sacral nerve roots (S2-S4) innervate both the anal sphincter complex and the external urethral sphincter through interconnected reflex pathways. Surgical manipulation of the anal sphincter creates aberrant reflex activity that causes involuntary contraction of the urethral sphincter during attempted voiding. 2, 3
Guarding reflex activation: Pelvic floor trauma activates the "guarding reflex," where somatic afferent signals from the surgical site trigger sustained contraction of the external urethral sphincter, preventing normal bladder emptying even when the detrusor muscle contracts. 4, 2
Secondary Mechanism: Bladder Outlet Obstruction
The spastic pelvic floor creates functional bladder outlet obstruction, forcing patients to generate abnormally high detrusor pressures to overcome the resistance. 5, 6
Elevated voiding pressures: Patients must use abdominal straining (Valsalva maneuver) to generate sufficient pressure to overcome the spastic external sphincter, which is the source of the discomfort and sensation of incomplete emptying. 5
Detrusor-sphincter dyssynergia: The bladder muscle contracts while the urethral sphincter simultaneously contracts rather than relaxing, creating a functional obstruction that causes bladder distension, suprapubic pressure, and pain. 3
Pain Localization and Character
The discomfort manifests in three distinct patterns:
Suprapubic distension pain: Bladder overdistension from incomplete emptying causes stretching of bladder wall mechanoreceptors, producing deep pelvic pressure and aching. 5, 7
Urethral burning/pressure: Forced voiding against a spastic sphincter creates urethral mucosal irritation and pressure sensation in the perineum. 1
Referred pelvic floor pain: Sustained levator ani spasm produces diffuse pelvic floor discomfort that patients often cannot precisely localize but describe as "heaviness" or "pressure" in the pelvis. 1
Critical Diagnostic Pitfall to Avoid
Never assume urinary retention after anorectal surgery is simply due to pain medication or postoperative immobility—measure post-void residual immediately. 5, 6 A PVR >250-300 mL confirms significant retention requiring intervention, not just reassurance. 5
Why This Occurs Specifically After Anorectal Surgery
The anatomic proximity and shared neural control of the anal and urethral sphincters makes this complication predictable:
Sacral nerve cross-talk: The pudendal nerve branches supply both sphincter complexes, so surgical trauma to anal structures creates reflex dysfunction in urethral structures through shared sacral segments. 2, 3
Pelvic floor unity: The levator ani muscle forms a continuous sheet supporting both the rectum and bladder neck, so disruption at one site affects the entire muscular complex. 1
Expected Timeline and Resolution
Most cases resolve spontaneously as surgical inflammation subsides and normal reflex coordination returns within 24-72 hours. 8 However, prolonged catheterization beyond 24 hours increases infection risk without improving outcomes. 8
- Early catheter removal preferred: Remove urinary catheters within 24 hours even with epidural analgesia, as retention rates are acceptably low (8-9%) and can be managed with single intermittent catheterization if needed. 8