Congenital rectal and anal malformation

　　1. Causes of Disease

　　By the third weekend of embryogenesis, the distal end of the hindgut dilates and communicates with the anterior allantois, forming the cloaca. During the fourth week, the mesodermal ridges between the cloaca and the hindgut form and grow caudally, at the same time, mesenchymal cells proliferate on the inner side of the lateral walls of the cloaca, forming folds called lateral folds that grow into the lumen, constituting the uroroctal septum, dividing the cloaca into anterior and posterior parts. The former is the urinogenital sinus, and the latter is the rectum. The caudal end of the cloaca is sealed by a layer of ectodermal epithelial membrane, known as the cloacal membrane, which separates it from the external environment. The former is the urinogenital sinus membrane, and the latter is the anal membrane. At the 7th and 8th weeks, the two membranes rupture sequentially. After the anal membrane ruptures, the hindgut and the original anal canal are connected, forming a normal rectum and anal canal. If the hindgut or the original anal canal does not develop properly or is not fully connected, various types of anal atresia or stenosis may occur. If the urinogenital sinus and the hindgut are not fully separated, and the opening of the hindgut remains on the urinary tract organs, fistulas or rectovaginal fistulas, anal proctosis, and other malformations may occur. In summary, anal-rectal malformations are the result of disorders during the normal embryonic development period, and the causes are not yet clear. According to literature reports, less than 1% of anal-rectal malformations have a family history. Like other malformations, anal-rectal malformations may be related to the effects of viral infections, chemicals, environment, and nutritional factors during pregnancy, especially in the early stages of pregnancy (4-12 weeks). The earlier the developmental disorder occurs during embryogenesis, the higher and more complex the location of the malformation will be.

　　II. Pathogenesis

　　The international classification established in 1970 takes the relationship between the rectal terminal and the levator ani, especially the puborectalis muscle, as the standard, and divides anal and rectal malformations into three types: high, middle, and low. The rectal blind end terminating above the puborectalis muscle ring is a high-level malformation. The malformation located in the muscle and surrounded by it is a middle-level malformation. The malformation passing below the muscle is a low-level malformation. Each type is further divided into two groups: with fistula and without fistula. The incidence rate of fistula is about 50%, especially in girls. Girls have rectovaginal fistula, vestibular fistula, and perineal fistula, while boys have rectovesical fistula, urethral fistula, and perineal fistula.

　　1. Classification Method In 1984, Wingspread simplified the classification method, with specific classification:

　　2. Muscle changes In children with anal and rectal malformations, the levator ani muscle, including the puborectalis muscle, is well developed. Due to the different types of malformations, the position of the puborectalis muscle may change. In high-level malformations, this muscle is significantly upward and forwardly displaced and shortened, showing a closed lock-like shape, attached to the posterior side of the prostate, urethra, or vagina, and at a certain distance from the rectal blind end and the external sphincter. The external sphincter is underdeveloped in high-level malformations, with a disorderly direction of muscle fibers, or only a trace. In middle-level malformations, the external sphincter is normally developed, with muscle fibers arranged in an oblique direction, and the internal sphincter is absent in high-level malformations, poorly developed in middle-level malformations, and normally developed in low-level malformations.

　　3. Nerve changes Children with anal and rectal malformations often have sacral malformations. When the sacral vertebral bodies are absent, there may be changes in the sacral nerves. The more segments that are absent, the more obvious the changes in the sacral nerves, which can directly affect the treatment and prognosis of the disease. Anal and rectal malformations often occur with other congenital malformations, with an incidence rate of 30% to 40%. The most common are urogenital malformations and other malformations in other parts of the digestive tract. These multiple malformations increase the difficulty of treatment and can affect the prognosis.

　　1. Common complications

　　Children with low-position intestinal obstruction due to malformation often develop dehydration and acidosis, severe cases may develop shock and death; secondary colon巨, nutritional disorders; often associated with vulvitis and urinary tract infection.

　　2. Associated malformations

　　The incidence of associated malformations is 40% to 50%. The differentiation and development of the cloaca occur in the earliest stage of embryonic development. At the critical period of embryonic development, any non-specific factor can also affect the development of other organs simultaneously. Therefore, congenital anal-rectal malformations often occur with malformations of other organs. Generally, the incidence of high-position malformations is more than twice that of low-position malformations, and the malformations are severe. Due to the presence of associated malformations, the difficulty of treatment increases. Among the associated malformations, urinary system malformations are the most common, such as renal hypoplasia, unilateral or bilateral hydronephrosis, pyelonephrosis, etc. Other organ malformations include esophageal atresia with an incidence of up to 6% to 7%, congenital megacolon accounting for 2% to 3%. Skeletal malformations include hemivertebrae and vertebral fusion. Cardiovascular malformations such as ventricular septal defect and atrial septal defect account for about 7%. According to the statistics of the Toronto Children's Hospital, in the associated malformations of congenital anal-rectal malformation children, in addition to the most common urinary system malformations, 51% are skeletal malformations, heart, nervous system, and gastrointestinal malformations. Chinese scholars reported that the children with high and middle position congenital anal-rectal malformations have underdeveloped nerve endings in the puborectalis muscle and perianal tissues, with reduced density. There are a certain number of muscle spindles in the puborectalis muscle. In addition, the morphology of the sacrum and the number of motor neurons in the medial group of the anterior horn of the sacral nerve also have abnormal changes.

　　3. Postoperative complications: The common complications of this disease after surgery are as follows

　　1. Rectal mucosal inversion:It usually occurs within 3 months after surgery. With the softening of scars, the anal sphincter function in mild cases can be restored, but severe cases may require reoperation for excision.

　　2. Anal stenosis:To prevent stenosis, anal dilation should be maintained for 1 to 1.5 years after surgery. In severe cases of stenosis, a second operation should be considered.

　　3. Faecal incontinence:High position anal-rectal malformation after surgery is common and difficult to recover, so early postoperative defecation training should be performed.

　　4. Constipation:Early symptoms may be caused by pain from surgical trauma, while late symptoms are often due to anal stenosis or rectal retraction forming a tubular stenosis. A few children have associated aganglionosis of the rectum and sigmoid colon. In these cases, if conservative treatment such as dilatation of the anal canal and intestinal lavage is ineffective, different surgical treatments should be considered based on specific conditions.

　　1. Symptoms

　　1. Incomplete anal atresia with concurrent narrow fistula orifice: Complete anal atresia in boys with concurrent vesicoureteral fistula or urethral fistula, without meconium excretion within 24 hours after birth. If not discovered early, about 3/4 of the cases, including all cases of anal-rectal atresia without fistula and some cases with fistula but narrow orifice unable to excrete meconium or only able to excrete a small amount of meconium, only a small amount of meconium stain on the urinary meatus and diapers, presenting as low position intestinal obstruction. Vomiting occurs after feeding, with vomit containing milk and bile. Later, fecal-like matter may be vomited. The abdomen gradually swells, and the condition becomes increasingly severe. In the late stage, dehydration symptoms appear. Without diagnosis and treatment, more than 6 to 7 days may result in death.

　　2. Anal and rectal stenosis and fistula with larger fistula: In another group of cases, including anal and rectal stenosis and those with vaginal fistula, vestibular fistula, and perineal fistula with larger fistula, there is no intestinal obstruction symptoms for a period of time after birth, but排便困难, faecal strips become thin, chronic abdominal distension, abdominal pain, abdominal distension. Due to frequent incomplete defecation, feces accumulate in the colon and can form fecal stones. Sometimes, a large fecal mass can be felt in the lower abdomen, with secondary megacolon changes, affecting the growth and development of children.

　　Two, Anal

　　1. High or anal levator muscle malformation: accounting for about 40% of anal and rectal malformations, more common in boys than girls. Such children have a slightly concave skin at the normal anal position with deeper color, but no anal opening. When the child cries or strains, the concave area does not bulge outward, and there is no impact when touched with a finger. X-ray examination shows that the rectal end bubble is above the pubococcygeal line, and in both boys and girls, there is often a fistula present. However, due to the thin fistula, almost all have symptoms of intestinal obstruction. The rectal end position is high, above the levator muscle, and there is often a defect in the neural control of the pelvic muscles. They often have spinal and upper urinary tract malformations. Girls often have vaginal fistulas, which are more common at the fornix of the posterior vaginal wall. Such children have underdeveloped external genitalia,呈幼稚型, with urinary system fistulas almost all seen in boys, and rare in girls. The main symptoms of rectal urinary fistulas are exhaust from the external urethral orifice and meconium. Single meconium or mixed meconium in urine cannot distinguish between bladder fistula or urethral fistula. However, by carefully observing the child's urination, there may be a clear distinction. When there is a bladder fistula, meconium enters the bladder and mixes with urine, causing the child's urine to be green throughout the urination process, with the last part being darker. At the same time, gas accumulated in the bladder can be excreted. Due to the lack of sphincter control, feces often flow out from the fistula, easily causing genitourinary infections. If the bladder area is compressed, more meconium and gas are excreted. When not urinating, due to the control of the bladder sphincter, no gas is excreted. In rectal urethral fistulas, only a small amount of meconium is excreted at the beginning of urination, not mixed with urine, and the subsequent urine is transparent. Because there is no sphincter control, exhaust from the external urethral orifice is unrelated to the micturition action. The above symptoms are of great significance for the diagnosis of urinary system fistulas. However, due to the difference in the thickness of the fistula or often being blocked by thick meconium, the degree of manifestation is different, even completely absent. Therefore, it is very necessary to regularly check for meconium components in the child's urine. A negative urine test does not exclude the existence of urinary system fistulas, and multiple checks are required. Some cases can be diagnosed by X-ray films, urethro-vesical造影, showing gas or liquid level in the bladder. The contrast agent fills the fistula orifice or enters the rectum for confirmation.

　　2. Intermediate position anomalies: accounting for about 15%, this type of anomaly was previously classified as high by some and as low by others. In the absence of fistulas, the blind end of the rectum is at the edge of the bulbocavernosus muscle or near the lower end of the vagina, with the puborectalis muscle surrounding the distal end of the rectum. In the presence of fistulas, the fistula opening is at the bulb of the urethra, the lower segment of the vagina, or the vestibule. The appearance of the anal position is similar to that of high anomalies, and defecation can also occur through the urethra or vagina. The probe can pass through the fistula into the rectum, and the tip of the probe can be felt when touching the anal area. On X-ray films, the bubble shadow of the distal end of the rectum is located below the pubococcygeal line. Rectal vestibular fistulas in girls are more common than vaginal fistulas, with the fistula opening at the vaginal vestibular fossa, also known as the fossa navicularis fistula. The fistula is large enough to maintain normal defecation and normal development, with only incontinence during loose stools. If the fistula opening of the rectal vestibular fistula is very narrow, its clinical manifestations are similar to those of various low anomalies opening at the vulva. However, when a probe is inserted through the fistula, the probe runs toward the cranial side rather than the dorsal side. During infancy, due to frequent fecal discharge, poor care can lead to frequent stools in the vestibule of the vagina, which may cause vulvovaginitis or ascending infection. Anal-rectal stenosis is a rare anomaly, involving the anal and lower rectal segments, which may be confused with anal stenosis. Fistulography can determine the diagnosis.

　　3. Low or anal canal agenesis: accounting for about 40% of anal-rectal anomalies, caused by developmental arrest in the late embryonic stage. The rectum, anal canal, and sphincter develop normally, with the distal end of the rectum positioned lower, below the I line. This type of anomaly often accompanies fistulas but rarely other anomalies. Clinical manifestations include indentations at the normal anal position, the anal canal being completely occluded by a diaphragm, which is sometimes very thin and allows visibility of the meconium retained in the anal canal, appearing deep blue. During crying, the diaphragm protrudes outward prominently, and there is a significant shock sensation when touched with fingers, with a marked contraction in response to stimulation. Some anal membranes may be broken but not completely, with an aperture of only 2 to 3 mm, causing difficulty in defecation, thinning of the feces, and a squeezing-toothpaste-like sensation. Some have a normal anus but are positioned anteriorly, between the normal anal position and the root of the scrotum or posterior labial symphysis, known as perineal anterior anus. Generally, there are no clinical symptoms and no treatment is required. Many children with low anomalies have anal skin fistulas filled with meconium, appearing deep blue, with the fistula opening at the perineum or even further anterior to the scrotal suture or ventral side of the penis. In girls, the meconium is not easily visible, but if a probe is inserted into the fistula, it runs directly backward just under the skin. In girls, many low anomalies have an opening in the vulva near the posterior labial symphysis, some of which resemble a normal anus and are known as vestibular anus or vulvar anus. An anal-vulvar fistula is a variation of the anal diaphragm, where the anal vestibular fistula allows the intestinal tract to pass through the puborectalis muscle, with the anal canal ending through a small fistula to communicate with the vestibule. Clinically, the difference from a rectal vestibular fistula is that the probe inserted into the fistula opening goes slightly toward the dorsal side rather than the cranial side, and the probe tip can be easily felt when touching the normal anal orifice.

　　4. Rare malformations: In addition, there are some rare malformations, such as perineal cleft in girls, there is a moist and epithelial cleft between the anal and vaginal vestibule, and rectal vestibular fistula with normal anus, etc. There are also rare anorectal malformations in female infants, whose external genital development is幼稚型, the labia majora is small, and there is only one opening. Urine and feces are excreted from this opening.

　　1. It is believed to be related to early pregnancy viral infection, high fever, medication, radiation exposure, allergy, low immune response, and some genetic genes. Special attention should be paid to the health care and genetic counseling during pregnancy.

　　2. Pay enough attention to polyhydramnios and abnormal fetal movement at the end of pregnancy, make regular prenatal examinations, and prenatal ultrasound examination can usually suggest suspected lesions.

　　1. Peripheral blood:When there are symptoms of infection and systemic toxicity, peripheral blood leukocytes and neutrophils increase, and there may be manifestations such as a decrease in platelet count.

　　2. Blood biochemistry:When complications such as dehydration and acidosis occur, routine blood tests for sodium, potassium, chloride, calcium, blood pH value, blood urea nitrogen, creatinine, etc. are performed.

　　3. X-ray examination:Accurately measure the height of rectal atresia, whether there is a urinary system fistula, X-ray examination is indispensable. Some cases can be diagnosed by the presence of gas or liquid level in the bladder on X-ray films. Some people point out that calcified shadows in the intestinal cavity are also a basis for diagnosing rectal urinary fistula. Urethral bladderography, the contrast agent often can only fill the fistula part, appear diverticulum-like shadows, and the contrast agent entering the rectum is very little. When the fistula in the urethral membrane is thick, the metal catheter can be inserted through the urethra and enter the rectum along the posterior wall of the urethra. Fistula angiography can determine the diagnosis. The inverted lateral X-ray film is still used today. The method is to invert the child born within 24 hours, stick a small lead letter at the anal crypt, the distance from the lead letter to the pre-sacral inflated rectal blind end is the height of the atresia. Draw a straight line from the inferior margin of the pubic symphysis to the coccyx, the superior edge of the puborectalis muscle is called the pubococcygeal line. The gas shadow of the rectum's end on the X-ray film can be seen below the pubococcygeal line. The gas shadow higher than the pubococcygeal line is a high malformation, but the results of X-ray films sometimes have errors.

　　4. Computed Tomography (CT):It can show the development status and direction of the pelvic floor muscles, and can also be used as a reference for postoperative follow-up. In normal children, CT shows the puborectalis muscle as a soft tissue mass, fixed in front of the pubis, connected to the sides and posterior wall of the rectum, the external and internal anal sphincters form an oval mass, which is difficult to separate. Different types of anal and rectal malformation children have different CT manifestations, such as rectovaginal fistula, the puborectalis muscle surrounds the urethra and rectal blind end, and the anal sphincter is located just below the perineum.

　　5. B-ultrasound examination:This method is not time-limited, no special preparation is required before examination, it is safe and simple, the measured data is reliable, the error is smaller than X-ray, it can be repeated, and the pain of the child is small.

　　6. Magnetic Resonance Imaging (MRI):In the application of anal-rectal malformations, it can be observed the changes in the perianal muscle groups, and at the same time, it can judge the type of malformation and whether there is a malformation of the sacrum and coccyx. The changes in the perianal muscle groups can be observed from three aspects. To obtain clear images, sedatives can be administered before the examination, a marker can be placed in the anal crypt, and gas can be injected into the rectal blind end through the fistula if necessary to make the image clearer.

　　As far as possible, eat fresh vegetables, provide high-nutrition food, to supplement the body's consumption, eat more nutritious, easy to digest and absorb food, drink more water. Eat more foods rich in vitamin C or vitamin C tablets. Foods high in vitamin C include green leafy vegetables, tomatoes, cauliflower, green peppers, oranges, strawberries, kiwi, watermelons, grapes, etc. Try to avoid eating hard or fried foods, such as fish and meat products should be as boneless as possible, eat less spicy and刺激性 food, pay attention to food hygiene, avoid eating cold, leftover, or spoiled food.

　　1. Treatment:The treatment methods for congenital anal-rectal malformations vary according to their types and the height of the terminal. All cases without defecation dysfunction, such as those without anal stenosis in the perineal anterior anus, do not require treatment, except for surgery. Low-position anorectal atresia, stenosis, or rectovesical fistula all require perineal anal成形术. For middle-position anorectal atresia, such as rectourethral fistula, rectovaginal fistula, etc., sacral perineal anal成形术 can be performed. For high-position anorectal atresia, such as rectovesical fistula, high-position vaginal fistula, etc., abdominal sacral perineal anal成形术 is required. To prevent anal成形术后 scar stenosis, anal dilation should be performed one month after surgery, which may take about a year.

　　2. Prognosis:The prognosis of anal-rectal malformations depends on the type of malformation and whether there are associated malformations of other organs. Low-position anal atresia and fistula generally have good postoperative defecation control function, while the effect of high-position malformations is still not ideal. If the child defecates 1 to 3 times a day after surgery without soiled feces, it indicates a good effect. The defecation control ability will improve with age and continuous defecation training, but some residual problems of the reproductive and urinary systems still require long-term follow-up observation.