Neonatal anal and rectal anomalies

　　Anomalies of the neonatal anus and rectum are the result of obstacles in the normal embryonic development period. The earlier the developmental obstacle occurs, the higher the position of the anal and rectal anomaly. The causes of developmental disorders are not yet fully understood. Factors such as drugs, mechanical factors, and circulatory disorders can all lead to malformations. This disease is also related to genetic factors, with 1% of patients having a family history.

　　By the third weekend of embryonic development, the distal end of the hindgut swells and communicates with the anterior allantois, forming the cloaca. The distal end of the cloaca is sealed by a layer of epithelial cells of the ectoderm, known as the cloacal membrane, which separates it from the external environment. In the fourth week, the mesodermal folds between the cloaca and the hindgut form and grow caudally, at the same time, the sides of the cloaca are thickened inwardly, forming folds that grow into the lumen, these constitute the urachoroanal septum, dividing the cloaca into anterior and posterior parts. The former forms the urogenital system, and the latter develops into the rectum. The middle cavity gradually becomes smaller, known as the cloacal duct. By the end of the seventh week, the primitive perineum appears, causing the anterior part of the cloacal membrane to develop into the urogenital membrane, and the posterior part to develop into the anal membrane. At the primitive anus, the anal papillae rise on both sides and grow towards the abdominal direction, surrounding the distal end of the hindgut. A depression appears in the center of the nodules, which later evolves into the anus. The anal canal communicates with the hindgut by the eighth week of embryonic development. Anal and rectal anomalies are mostly formed during the seventh to eighth weeks of embryonic development due to abnormal or obstructed tail development. If the cloacal membrane and the primitive anus are not贯通, anal atresia may occur. Incomplete development of the cloaca and the primitive perineum can lead to fistulas between the urinary and reproductive systems and the rectum. Defects in tail development can also be accompanied by urethral stenosis, sacral and sacral nerve defects, etc., in addition to fistulas.

　　Neonatal anal and rectal anomalies can lead to low-positioned intestinal obstruction and electrolyte and water balance disorders, severely affecting the life of the child. This disease often involves the formation of fistulas. According to statistics, neonatal males, in addition to perineal fistulas, are more likely to have rectourethral fistulas, while females, in addition to perineal fistulas, are mainly affected by rectovaginal fistulas. The entire fistula wall is composed of thickened fibrous tissue, covered with a layer of granulation tissue, which is difficult to heal. The incidence rate is second only to hemorrhoids, and the incidence of anal atresia without fistula formation is only about 5% of all cases.

　　Anomalies of the neonatal anal and rectum vary in types, with different clinical manifestations and onset times. Most infants are without an anus, and careful examination of the perineum can reveal this, mainly presenting symptoms of low-positioned intestinal obstruction, such as abdominal pain, vomiting, abdominal distension, no defecation, and no anal gas. Most cases gradually develop symptoms after birth. Infants with anal-rectal atresia do not pass meconium after birth, and the abdomen gradually swells and vomits after eating, with vomit containing milk, bile, and fecal-like substances. Symptoms progressively worsen, leading to dehydration, electrolyte imbalance, and complications such as intestinal perforation, which can result in death within a week. Infants with anal-rectal stenosis and fistula may have significant differences in clinical manifestations due to the size and location of the fistula. Generally, boys with anal atresia and posterior urethral fistula associated with the rectum have thinner fistulas and more obvious intestinal obstruction symptoms, and may also present with symptoms such as meconium or gas in the urine, with a small amount of meconium on the urinary opening or diapers. There is no anal canal, and it can often be detected early and referred for treatment. If not treated promptly, it can lead to recurrent urethritis and anal-rectal stenosis. Girls with low rectovaginal fistula have thicker fistulas that can be used for defecation, and intestinal obstruction symptoms are usually not obvious, often appearing several months later when complementary foods are added and the stool becomes thick. Due to frequent poor defecation, feces can accumulate in the colon to form hard fecal stones or secondary megacolon, affecting growth and development, and can also cause vaginitis or ascending infection. Examination of the anus often shows flat and round buttocks, shallow anal grooves, no anal opening, or only a trace. In cases of low-positioned anomalies, digital examination can detect the distension of the rectal blind end.

　　The etiology of neonatal anal and rectal malformations has not been fully elucidated. Genetic counseling work should be done well, and various prenatal health care work should be done during pregnancy. Preventive measures should refer to birth defects, and prevention should be carried out from pre-pregnancy to prenatal. Pre-marital physical examination plays a positive role in preventing birth defects, and the size of the role depends on the items and content of the examination, mainly including serological tests (such as hepatitis B virus, syphilis spirochete, HIV), reproductive system examination (such as cervical inflammation screening), general physical examination (such as blood pressure, electrocardiogram), and inquiries about family medical history and personal medical history. Pregnant women should try to avoid harmful factors, including staying away from smoke, alcohol, drugs, radiation, pesticides, noise, volatile harmful gases, and toxic and harmful heavy metals. During the process of prenatal health care during pregnancy, systematic screening for birth defects should be carried out, including regular ultrasound examination, serological screening, and chromosome examination if necessary.

　　The diagnosis of congenital anal and rectal malformations is not difficult in clinical practice, but the key is how to correctly measure the height of the atresia, the relationship between the rectal blind end and the puborectalis muscle, and the presence or absence of urinary system fistula and skeletal malformation. The main examinations in clinical practice are as follows:

　　1. Urine examination:The presence of clear meconium or squamous epithelial cells detected by microscopic examination indicates rectourethral fistula and rectovesical fistula formation.

　　2. Blood count examination: White blood cells and neutrophils increase when there is infection. Hemoglobin concentration decreases and red blood cell count decreases when there is anemia.

　　3. Blood biochemical examination:There may be water and electrolyte imbalance, and blood sodium, potassium, chloride, calcium, magnesium, blood pH value, creatinine, and other tests should be performed.

　　4. X-ray inverted position film examination: X-ray examination is an indispensable diagnostic measure to understand the distance between the rectal end gas shadow and the perineal skin as a judgment of the position of the malformation.

　　5. Ultrasonic examination: Ultrasound can accurately measure the distance between the rectal blind end and the anal skin.

　　6. Fistulography: For those with fistula but difficult to diagnose, fistulography can be used, and iodine oil is used for lateral position photography.

　　7. Urethrovesical Angiography: It can be seen that the contrast agent fills the fistula or enters the rectum, which can confirm the diagnosis. This method is not easy to succeed in neonates, a positive result can confirm the diagnosis, and a negative result cannot exclude it.

　　8. X-ray Abdominal Flat Film Examination:: Finding gas or liquid level in the bladder at the same time on X-ray flat film is a simple and reliable method for diagnosing urinary system fistula, and other methods such as fistulography and urethrovesical造影术 are also often used for diagnosis.

　　9. X-ray Pelvic Anteroposterior View: About 45% of neonates with anal and rectal atresia have sacral developmental abnormalities, and this change is closely related to the future defecation function. Therefore, during radiography, anteroposterior pelvic films should be taken at the same time, and the proportion of sacral development can help pediatric surgeons judge the prognosis.

　　10. CT Scans and Magnetic Resonance Imaging: This is a non-invasive technique that has gradually begun to be used, and it can understand the position of the rectal blind pouch in anorectal atresia.

　　The diet of neonates with anal and rectal malformations should be light, with attention to hygiene and a reasonable diet. It is advisable to eat foods rich in trace elements and avoid eating fishy and spicy foods, greasy, spicy, and irritating foods.

　　Children with anal and rectal malformations generally have good conditions after birth, and the time of medical consultation is mostly within 5 days after birth. High-position anal and rectal atresia combined with fistula, which is usually small and cannot maintain normal defecation, should be treated with radical surgery as early as possible in the neonatal period. Low or intermediate position atresia, combined with fistula, is often large and can maintain normal defecation after birth, and surgery can be delayed until infancy. Congenital stricture can be expanded with a probe, and it needs to be continued for 1 year. If it is membranous atresia, the septum should be incised before expansion. The distance between the anal skin and the rectal blind end is within 2cm, and analoplasty is performed through the perineum after surgery. If the distance is more than 2cm, or there is a vesicorectal fistula, a temporary colostomy or a single perineal analoplasty can be performed first, and anal dilation is also required after surgery to prevent scar stricture. If the anus is normal and the rectum is atresia, laparotomy surgery is required.