| disease | Congenital Stricture of Anus |
| alias | Congenital Anorectal Stenosis |
Congenital stricture of the anus (congenital anorectal stenosis) is caused by abnormal embryonic development, resulting in an abnormally small anorectal diameter. It can occur in both males and females, manifesting as varying degrees of difficulty in defecation.
bubble_chart Pathological Changes
Congenital stricture of the anus can occur in various segments of the anus and rectum, broadly categorized into stricture of the anus, anal canal stenosis, anorectal junction stenosis, rectal stenosis, and anorectal stenosis. Apart from stricture of the anus being relatively common, the other types are extremely rare. Stricture of the anus is a low-level malformation, occurring in the late stage of embryonic development (third stage), where incomplete absorption of the anal membrane or excessive fusion of the genital folds partially covers the anus. The stenotic area is often found in the anal canal or anal opening, with a short, ring-like range, also referred to as anal membrane-like stenosis. Anal canal stenosis is also a low-level malformation, where the entire anal canal is narrow, presenting as a tubular stenotic segment. Anorectal junction stenosis is an intermediate-level malformation, where the anal canal and rectum develop normally, but there is a ring- or sickle-shaped band at the junction of the anal canal skin and rectal mucosa. Rectal stenosis is a high-level malformation, mostly occurring in the upper part of the rectal ampulla, presenting as ring-like or tubular. Anorectal stenosis often affects several centimeters from the anal opening to the lower rectum, presenting as tubular, with the stenotic rectum usually passing through the puborectalis muscle ring. The starting point is often located at the muscle ring, thus also mostly classified as a high-level malformation.
bubble_chart Clinical Manifestations
The manifestations vary depending on the degree of stenosis. Grade III stenosis presents with difficulty in defecation shortly after birth, characterized by straining and crying during bowel movements, and may develop signs of low intestinal obstruction within days to months. In Grade I stenosis, loose stools can be passed normally, but difficulty arises only with formed stools, resulting in thin, ribbon-like feces, frequent constipation, and even fecal impaction. Some patients may not seek medical attention until adulthood due to chronic difficulty in bowel movements. Long-term poor defecation can lead to gradual dilation of the proximal rectum and colon, causing secondary megacolon. Locally, the anus may appear narrow, sometimes reduced to a tiny opening that cannot even accommodate a catheter. In high or mid-level stenosis, the external appearance of the anus may seem normal, but during digital examination, the fifth finger cannot pass through the narrowed segment.
bubble_chart DiagnosisA history of difficult defecation combined with local examination can confirm the diagnosis. When it is difficult to determine the narrowed segment, a barium enema can be used to aid in diagnosis.
bubble_chart Treatment Measures
The appropriate treatment method should be selected based on the degree and type of stenosis. For grade I stenosis cases, repeated and prolonged anal dilation is employed, which can restore normal bowel function in most cases. For grade III stenosis cases, surgical treatment is necessary, and the timing of surgery should ideally be before obstruction occurs. Simple anal membrane-like stenosis can be treated with membrane resection; anal canal stenosis may be treated with longitudinal incision and transverse suturing or anal Y-V flap plasty to enlarge the anal canal diameter. Stenosis at the anorectal junction, which is ring-shaped, responds well to stenosis release surgery. Rectal stenosis and anorectal stenosis, due to their wider lesion range or higher location, often present difficulties when approached from the perineum. Forcibly performing stenosis release surgery may not achieve the desired outcome, and postoperative scar stenosis remains a possibility. Therefore, abdominoperineal anoplasty is preferred. Additionally, postoperative anal dilation is required for all surgical treatments, generally starting 2 weeks after surgery and continuing for 3 to 6 months until the anal canal can accommodate an index finger and bowel movements are smooth, preventing scar contracture and recurrent stenosis.
(1) Anal Dilation: Suitable for grade I stricture of anus and post-anoplasty cases. In the lateral or lithotomy position, a specialized metal probe (Hegar dilator) or a suitably sized pen with a rounded tip coated with lubricant is gently inserted into the rectum through the anus. Initially, this is performed once daily for 15–29 minutes each time for the first month. Based on improvement in bowel movement difficulty, the frequency is gradually reduced to every other day or twice weekly, typically lasting about 6 months. The dilator size is gradually increased until the stenotic segment can easily accommodate an index finger, ensuring smooth bowel movements without recurrence. Parents should be taught to perform the procedure themselves, with regular hospital follow-ups for consultation and medical guidance. Long-term adherence is crucial. If repeated dilation fails to maintain normal bowel movements, other surgical methods should be promptly considered.
(3) Longitudinal Incision and Transverse Suturing: A longitudinal incision is made on the posterior side of the anus, extending from the upper edge of the stenotic segment to 1 cm beyond the anal margin. The anal canal is dilated to allow passage of an index finger, and the surrounding subcutaneous tissue is mobilized. The rectal posterior wall mucosa and anal canal skin are then sutured transversely in an interrupted manner.
(4) Anal Y-V Flap Plasty: In the lithotomy position, an inverted Y-shaped incision is made on the posterior perianal area, centered at the anal margin. The intra-anal incision must extend beyond the stenotic segment, while the external incision is about 2 cm long with an angle of 90°–100°. After dilating the anal canal to accommodate an index finger, the external triangular flap is fully mobilized and advanced into the anal canal for suturing, resulting in an inverted V-shaped suture line.
(5) Stenosis Release Surgery: The stenotic ring at the anorectal junction is exposed through the anus. Typically, a longitudinal incision is made on the posterior side of the ring to divide the fibrous stenotic ring. The anal canal is dilated to allow passage of an index finger, and the rectal mucosa is slightly mobilized before suturing the upper and lower mucosa transversely. For severe stenosis, additional incisions may be made on both sides of the ring to facilitate release.
