Anal stenosis

Anal stenosis is a narrowing of the anal canal, typically caused by fibrous scar tissue. It develops in 6% of patients within a year following surgical hemorrhoidectomy. Other causes include inflammatory bowel disease (IBD), anal cancer, infections, radiation therapy, or trauma. Key clinical features include painful or difficult defecation, constipation, overflow diarrhea, and narrow stool caliber. Diagnosis is primarily based on history and physical examination, with biopsy or imaging reserved for suspected malignancy or IBD. Treatment ranges from symptom management with dietary changes and laxatives to anal dilation and surgical therapy such as sphincterotomy or anoplasty. In refractory cases, fecal diversion may be necessary. Prevention during anorectal surgery is crucial and relies on preserving viable anoderm tissue.

Anal canal narrowing due to either: ^[1]

• Fibrous scar tissue replacing the healthy anoderm
• Sphincter muscle spasm (functional anal stenosis)

Incidence: develops in 6% of patients within a year following surgical hemorrhoidectomy ^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Postoperative: following excisional hemorrhoidectomy
• IBD (e.g., Crohn disease)
• Anal cancer
• Infections (e.g., lymphogranuloma venereum)
• Iatrogenic: radiation therapy
• Other
  • Trauma
  • Severe sphincter muscle spasms (e.g., due to anal fissure)

• Painful or difficult defecation
• Constipation
• Diarrhea
• Narrow stools
• Examination findings
  • Visible anal canal narrowing
  • Inability to perform a digital rectal examination due to scar formation
  • If internal examination is possible: presence of fibrous scar tissue

Patients may also experience tenesmus, fecal incontinence, and/or hematochezia. ^[1]

Diagnosis of anal stenosis is typically made based on history and physical examination. Diagnostic studies are performed if cancer and/or IBD is suspected. ^[1]

• Biopsy (e.g., with anoscopy) ^[2]
• Imaging (e.g., MRI pelvis) ^[2]
• See also "Diagnostics of anal cancer" and "Diagnostics for Crohn disease."

Diagnostic studies are not needed for typical postoperative anal stenosis. ^[1]

Treatment is guided by the severity and location of the stenosis and involves the following: ^[1]

• Symptom management and supportive care
  • Dietary changes (e.g., fiber supplementation)
  • Laxatives (stool softening)
• Anal dilation
  • Initial dilation is performed under anesthesia.
  • Subsequent dilations are performed by the patient.
• Surgical therapy
  • Sphincterotomy: for scarring of the sphincter muscle
  • Anoplasty (advancement flap): for distal anal stenosis
  • Fecal diversion (e.g., colostomy): for refractory cases

Preserving viable anoderm tissue during anorectal surgery is key to reducing the risk of anal stenosis. ^[1]