What is a Patulous Anus?
A patulous anus is an abnormally open or gaping anal canal observed at rest, indicating loss of normal anal sphincter tone and co-aptation, typically associated with neurogenic dysfunction, severe sphincter injury, or denervation. 1
Clinical Definition and Significance
A patulous anus represents a physical examination finding where the anal verge demonstrates abnormal opening during simulated defecation or even at rest, rather than maintaining the normal closed configuration. This finding is specifically identified during digital rectal examination when the patient is positioned in the left lateral position with buttocks separated 1.
Key Clinical Associations
The presence of a patulous anus should raise immediate suspicion for:
- Neurogenic constipation with or without fecal incontinence - This is the primary association emphasized in clinical guidelines 1
- Severe anal sphincter injury involving multiple muscles (internal sphincter, external sphincter, or both) 2
- Anal denervation or damage to anal cushions beyond simple sphincter injury 2
Diagnostic Evaluation
Physical Examination Findings
During the rectal examination, observe for:
- Abnormal descent of the perineum during simulated evacuation
- Patulous opening of the anal verge during straining
- Reduced or absent resting sphincter tone on digital examination
- Evidence of fecal soiling on perianal skin 1
Quantitative Assessment
Research demonstrates that a patulous anal canal is typically defined as an anal diameter ≥35 mm 3. In healthy asymptomatic women, only 5% have a patulous anal canal, making this an abnormal finding when present 4.
Associated Manometric Findings
A patulous anal canal independently predicts:
- Reduced anal resting pressure (P < 0.001)
- Decreased anal squeeze pressure increment (P < 0.01)
- More severe overall anal sphincter dysfunction 2
Importantly, the patulous canal is associated with internal sphincter injury (P < 0.01) more strongly than external sphincter or puborectalis injury 2.
Clinical Implications
Impact on Continence
Patients with a patulous anus commonly present with:
- True fecal incontinence - inability to retain stool
- Severe soiling
- Loss of both passive and active continence mechanisms 5, 3
Prognostic Significance
The patulous anus serves as a marker of severe anorectal dysfunction that extends beyond simple sphincter injury. It indicates damage to multiple continence mechanisms including the anal cushions, sphincter complex, and potentially neural innervation 2. This finding suggests that standard laxative programs will fail, and specialized surgical intervention may be required 1.
Management Considerations
When Standard Therapy Fails
The presence of a patulous anus indicates that:
- Evacuatory disorders will not respond well to standard laxative programs
- Failure to recognize this component is a frequent reason for therapeutic failure 1
- Specialized surgical approaches may be necessary, including anal encirclement procedures or sphincter reconstruction 6, 3
Surgical Options
For patients with fecal incontinence and a patulous anus (diameter ≥35 mm), surgical options include:
- Anal canal plasty
- Anal encirclement with biological grafts or artificial ligaments
- Sphincter repair with augmentation 5, 6, 3
Common Pitfalls
Do not confuse a patulous anus with:
- Simple hemorrhoidal prolapse
- Rectal mucosal prolapse (though these may coexist) 1
Do not assume normal function if:
- The patient can squeeze during examination but has a patulous opening at rest
- Imaging shows only partial sphincter defects - the patulous canal indicates more extensive dysfunction 2
Critical point: A patulous anus in the context of constipation suggests neurogenic etiology rather than simple outlet obstruction, fundamentally changing the treatment approach 1.