Incidence of Minor Fecal Soiling After Fistulotomy
Minor fecal soiling occurs in approximately 10-40% of patients after fistulotomy, representing the most common functional complication of this procedure. 1, 2
Reported Rates from High-Quality Studies
The incidence varies based on how soiling is defined and measured:
- Soiling specifically: 4-13% of patients report postdefecation soiling as an isolated symptom 1, 3
- Any minor incontinence symptoms (including soiling, flatus incontinence, or mucus leakage): 20-40% of patients 1, 2
- Transient soiling: 11.5% of patients experience temporary soiling for 4-6 months that either resolves or evolves into milder flatus incontinence 4
Breakdown by Symptom Type
When examining specific functional disturbances after fistulotomy for intersphincteric fistulas, one prospective study of 148 patients found 1:
- Soiling alone: 4% (6 patients)
- Flatus incontinence: 18% (27 patients)
- Liquid stool incontinence: 3% (4 patients)
- Overall incontinence rate: 20.3% (30 patients)
Critical Context: Soiling vs. Major Incontinence
It is essential to distinguish minor soiling from major fecal incontinence—the latter is rare after fistulotomy. 5, 3 The soiling typically consists of:
- Inadvertent passage of flatus
- Mucus leakage
- Postdefecation soiling (small amounts of stool on underwear)
Major incontinence to solid stool is uncommon and should not be expected as a routine outcome 5.
Risk Factors for Higher Soiling Rates
Certain patient characteristics increase the likelihood of postoperative soiling 1, 3:
- Low preoperative voluntary contraction pressure on manometry (independent predictor) 1
- Multiple previous drainage surgeries (independent predictor) 1
- Complex or recurrent fistulas (3-6 times higher risk) 3
- Previous seton drainage (5-fold increased risk) 3
- Presence of secondary tracts (8-fold increased risk) 3
Comparison: Low vs. High Fistulas
The rate of minor sphincter disturbance is similar whether treating low or high fistulas with fistulotomy (approximately one-quarter to one-third of patients experience mild leakage of flatus and mucus). 5 This challenges the assumption that high fistulas automatically have worse functional outcomes when treated with lay-open technique.
Clinical Implications for Patient Counseling
When counseling patients preoperatively, you should explain 3, 2:
- Expect a 10-20% baseline risk of some degree of continence disturbance, primarily minor soiling 6, 1
- Most soiling is mild and consists of postdefecation staining or mucus leakage 5, 2
- Transient symptoms may improve over 4-6 months 4
- Despite these symptoms, overall patient satisfaction remains high (mean 9.3/10) 3
- The trade-off is near 100% healing rates for simple fistulas 6, 5
Common Pitfall to Avoid
Do not minimize the 40% soiling rate when it includes all minor symptoms (flatus, mucus, and stool). 2 While this sounds alarming, most patients consider these symptoms acceptable given the high cure rate and absence of major incontinence. However, patients whose quality of life depends on perfect continence (such as those engaging in receptive anal intercourse) may find even minor soiling functionally devastating. 7