Anal Stenosis

   Definition

Anal stenosis is narrowing of the anal canal. Narrowing of the stool, passage of small stools, incomplete evacuation, painful defecation, and hematochezia Opens in new window (passage of red blood from the rectum) are symptoms of anal stenosis.

Anal stenosis can be congenital, but this is rare. Most commonly, anal stenosis is an acquired disorder associated with a variety of conditions. The most common cause of anal stenosis is prior hemorrhoidectomy.

Epidemiology

Anal stenosis results from any process that induces or causes scaring in the anoderm. Stenosis of the anal canal is defined by lack of the normal compliance of the anal canal lesions, or classified based on severity and symptoms, as mild, moderate, or severe.

Mild stenosis allows examination by index finger or medium Hill-Ferguson retractor, and with severe stenosis neither the little finger nor a small Hill-Ferguson retractor can be inserted without forceful dilatation. The most common position of stenosis lies in the lower anal canal.

Often there is little correlation of severity of stenosis and patient symptoms. Primarily patients complain of pain, constipation Opens in new window, bleeding Opens in new window, and incontinence.

Incontinence usually results from overflow diarrhea or failure of the anal os to close secondary to such severe fibrosis. Patients often resort to laxative abuse, enemas, or even digital disimpaction in order to maintain a normal lifestyle. Such practices may cause more injury and subsequent fibrosis. The majority of cases on anal stenosis are caused by trauma to the anal canal, with iatrogenic trauma being the most prevalent case.

Etiology

There is very little published data on the incidence and prevalence of anal stenosis in the literature. the vast majority of studies focus on the incidence following local anorectal procedures. Anal stenosis has been reported to be as high as 10% following radical amputative hemorrhoidectomy and other anorectal surgical procedures. Other causes include inflammatory diseases, neoplasia, ischemia, chronic diarrhea, functional disorders, and post-radiation.

Khubchandani classified anal stenosis based on etiology. Congenital stenotic lesions are the result of imperforate anus and anal atresia. Acquired stenosis may be primary, as is the case with iatrogenic trauma, or secondary, as in inflammatory bowel disease.

In the retrospective study by Milsom and Mazier, the most common cause of anal stenosis was posthemorrhoidectomy, representing 88% of 212 patients seen over 5 years at a colon and rectal surgery specialty clinic. The other most common etiologies are Bowen’s disease, fistulectomy, illeoanal anastomosis, and Paget’s disease. Classically, anal stenosis was linked to the complication of Whitehead hemorrhoidectomy, with the Whitehead deformity resulting in stenosis and ectropion of rectal mucosa. Most surgeons have abandoned the Whitehead hemorrhoidectomy. However, overaggressive excisional hemorrhoidectomy may result in a similar fate.

Management

1. Nonoperative

Minimal anal stenosis can often be managed with nonoperative conservative therapy. Initially, mild stenosis will respond to alterations in diet, the addition of bulking agents, and stool softeners. Primarily, dilatation should be the result of gentle passage of stool.

Patients can also be taught gentle digital dilatation or mechanical dilatation with reasonable results. Patients are taught to bear down and gently dilate the stenosis with bowel movements. A large proportion of patients, however, will find it difficult to comply with daily dilatation. If conservative measures fail, or patients find dilatation unacceptable, then often surgical intervention is required.

2. Surgical

Patients who have failed conservative management or are found to have moderate to severe stenosis often come to surgery for amelioration of symptoms. Multiple surgical techniques have been described in the literature to improve upon anal stenosis. For mild to moderate anal stenosis of the distal anal canal, simple sphincterotomy has been advocated with good functional results. Multiple sphincterotomies may also be used with favorable results, depending on the degree of stenosis.

Milsom and Mazier found that those who had multiple sphincterotomies had improved results compared to individuals with a single sphincterotomy for low moderate anal stenosis, and they advocated this approach. Prior to undertaking bilateral or multiple sphincterotomies, it is essential to ensure that a complete examination and history focusing on patients’ current continence status is determined to avoid unacceptable results with uncontrolled incontinence.

The results of bilateral or multiple sphincterotomies are poor in the setting of severe stenosis. The primary operative management of severe stenosis is based on bringing in healthy well-vacularized tissue from the anoderm into the anal canal to relieve stenosis. These procedures encompass island tissue transfer or advancement and rotational flaps.

3. Mucosal Advancement Flaps

Mucosal advancement anoplasty involves removal of the stenotic scar, sphincterotomy, and replacement of tissue with a rectal mucosal advancement. Careful placement of the distal aspect of the flap is required in order to prevent development of ectropion. Kubchandani reported his experience in 53 patients undergoing mucosal advancement flaps, with 82% of patients reporting a good outcome, and 11% reporting a fair improvement in symptoms.

Summary

Anal stenosis most often presents following local anorectal trauma that is primarily iatrogenic. The management depends on the location within the anal canal and the severity of the stricture. Minor stenosis may be managed with nonoperative therapies or sphincterotomy. More complex procedures including multiple sphincterotomies and anoplasties are required for more extensive structures. The choice of advancement flap primarily is based on the extent/proximity of the stenosis and the defect left following excision of scar tissue. The best long-term results appear to occur with uncomplicated advancement flaps.