Anal membrane atresia (atresia of the anal membrane), also known as anal membranous atresia, is a congenital malformation where the anal membrane fails to rupture, completely separating the anus and rectum by a thin membrane, preventing defecation. In Chinese medicine, it is referred to as "anal skin wrapping."

bubble_chart Etiology

Anal membrane atresia is a common type of low malformation, caused by abnormal absorption of the anal membrane between the primitive anus and the distal rectum due to late-stage (third stage) embryonic developmental disorders. Sometimes it may be accompanied by a subcutaneous occult fistula running anteriorly to the anus. The development of the anal canal and rectum is generally normal, and it usually does not involve other malformations.

bubble_chart Clinical Manifestations

After birth, there is no passage of meconium, accompanied by restless crying, vomiting, abdominal distension, and fullness. A distinct depression is visible at the normal anal position, with the anal canal covered by a membranous septum. This septum is sometimes very thin, allowing the dark blue meconium retained in the anorectal canal to be seen through it. When the infant cries, the septum bulges outward noticeably, and a distinct impulse can be felt upon finger touch. Stimulation of the perianal area triggers contraction of the sphincter muscle.

bubble_chart Diagnosis

No meconium discharge, the anus is covered with a thin membrane. Puncture examination shows that the membrane thickness is mostly within 0.5cm. Digital examination reveals a significant impact sensation in the anal area when the child cries, and generally no inverted position radiography is required.

Due to the low position of the atresia, the surgical procedure is straightforward. Once diagnosed, an anal membrane incision or resection can be performed.

(1) Anal membrane incision: A longitudinal or cross-shaped incision is made at the depressed area of the perineal-anal region to open the anal membrane, creating a passage between the inside and outside of the anus. The anus is then dilated to accommodate the index finger. Postoperative anal dilation should begin early and continue until normal bowel movements are achieved. However, many believe that simply incising the anal membrane yields poor long-term results, often leading to stricture of the anus and requiring subsequent surgeries. As a result, this method is rarely used nowadays.

(2) Anal membrane resection: After incising the anal membrane and removing the meconium, the anal membrane is excised along the anal margin. The anal canal is dilated to allow the passage of the index finger, and the lower rectal mucosa is slightly freed. The rectal mucosa is then loosely sutured to the perianal skin. Anal dilation begins 10 days postoperatively, performed 2–3 times per week until no stenosis is observed and bowel movements are unobstructed.