Congenital anomalous rectal malformation

Last updated date: 16-Jun-2023

Originally Written in English

Congenital Anomalous Rectal Malformation

Rectal malformations (RM), with an estimated prevalence ranging between 1 in 2000 and 1 in 5000 live births, are among the more frequent congenital defects encountered in pediatric surgery. Rare is the antenatal diagnosis of an isolated RM. The majority of instances are discovered in the early neonatal stage. There is a wide range of presentations, from modest anomalies with simple therapy of a perineal fistula to severe anomalies with complex management. The diagnosis and initial care of RM cases have been improved thanks to improvements in imaging techniques and an increased understanding of the embryology, anatomy, and physiology of RM patients. Over the past century, the patient survival rate has seen a noticeable improvement. From traditional treatments to PSARP and minimally invasive techniques, RM management has advanced. However, even with a great anatomic repair, fecal and urine incontinence might still happen, mostly because of related issues. There has been a paradigm shift in how these individuals are treated; now, the syndrome of anorectal anomalies is approached comprehensively with the long-term goal of achieving complete fecal and urine continence with high quality of life.

 

Anorectal Malformation

Anorectal Malformation

Imperforate anus is a term that refers to several diagnoses collectively known as anorectal malformations. Instead of having a normal anal opening, patients with this diagnosis have a fistulous tract that opens onto the perineum anterior to the anal muscle complex or onto nearby anatomical structures. The fistulous tract can join the feminine gynecological structures and the male urine system in a male. The severity of the deformity is typically determined by how far the fistulous tract opens from the appropriate site of the anal orifice. There will be more likely to be additional complications, such as underdeveloped musculature and anal muscle complex, the farther the fistulous tract extends from the typical anatomic site. To accurately assess the patient's prognosis and determine their long-term potential for bowel control, the anorectal malformation must be properly classified.

 

Anorectal Malformation Pathophysiology

Anorectal Malformation Pathophysiology

The pathophysiology and development of anorectal malformations are covered by several theories. One theory claims that the digestive tract, reproductive tract, and urine tract initially form a single channel known as the cloaca, which is followed by their separation and the migration of the anorectal septum around the seventh week of pregnancy. According to this theory, anorectal deformities are formed as a result of improper anorectal septum development. The septum's formation and whether it contributes to the development of anorectal abnormalities are still up for debate. According to a second theory, anorectal malformations occur when the rectum abnormally migrates toward the perineum during development. Both of these hypotheses lack support from embryologic models, and further research is required to better understand anorectal abnormalities and their causes.

 

Anorectal Malformation Causes

Anorectal Malformation Causes

Although the exact etiology of anorectal malformations is unknown, genetic factors are most likely a part of how they develop. A second child born with an anorectal malformation happens about one percent of the time. Numerous genetic syndromes are known to be associated with an increased prevalence of anorectal malformations, including the Currarino triad, which has autosomal dominant inheritance, and people with trisomy 21. Comparatively, only 5% of patients with anorectal malformations have trisomy 21, while around 95% of those patients have anorectal malformations without fistula. Additionally, some evidence suggests that environmental exposures such as in vitro fertilization, thalidomide exposure, and diabetes mellitus may be related to the emergence of anorectal malformations. Additionally, trans-retinoic acid exposure and the anorectal abnormalities caused by ethylene thiourea have been correlated in animal models.

 

Anorectal Malformation Symptoms

Anorectal Malformation Symptoms

Most patients with anorectal malformations are diagnosed while they are quite young. In these patients, a complete neonatal physical examination is essential, as is a thorough workup because about 60% of patients will have an accompanying abnormality.

A full physical newborn evaluation of a patient with an anorectal malformation includes listening to cardiac sounds to see if a murmur can be auscultated, inspecting the limbs for any anatomic deformity, and performing a thorough genitourinary exam, in addition to the perineal/anal exam, which is required.

Anus needs to be in the appropriate location and the appropriate size for their age to be considered normal. A full-term infant's anus should measure between 10 and 12 Hegar dilator in size, while a 12-month-anus old's size should be around 15 Hegar dilator. The anal opening's position in the complex of anal muscles serves as the basis for the correct positioning. To accurately determine the location of the anal opening to the muscle complex in the clinic, anesthesia is frequently needed.

It is important to perform a comprehensive inspection of the perineum, paying close attention to details like the growth of the buttocks, the presence of a gluteal fold, and the look for any openings or orifices. A comprehensive vaginal exam should also be performed on female patients who have an anorectal abnormality, paying attention to the number of openings on the perineum. These physical examination features can provide information about the type of anorectal malformation.

 

Anorectal Malformation Diagnosis

Anorectal Malformation Diagnosis

For patients who have an anorectal malformation, numerous diagnostic tests are required. There is a correlation between anorectal malformations and the VACTERL defects (vertebral, anorectal, cardiac, tracheoesophageal fistula/esophageal atresia, renal, and limb), even though anorectal malformations can occur as an isolated finding. Additionally, 60% of patients have an associated anomaly.

The following radiographic examinations are required for every newborn who is physically diagnosed with an anorectal malformation due to the documented link between VACTERL and anorectal malformations. To rule out the occurrence of esophageal atresia with or without a tracheoesophageal fistula, plain abdominal and chest films should be taken after the installation of a nasogastric or orogastric tube. It is also advisable to get a spine radiograph to rule out any vertebral anomalies. A lateral prone film, also known as an invertogram, should be taken in male patients if meconium on the perineum does not appear within 24 hours of birth even if there is no evident perineal fistula. The patient should be lying on their back with their buttocks raised for at least 15 minutes before getting an invertogram so that air in the digestive system has time to move to the most distal rectum. This will help assess the most distal level of the bowel and help determine whether a colostomy is necessary. An abdominal ultrasound should be performed on female patients with a single perineal orifice and cloaca diagnosis to assess for hydrocolpos and hydronephrosis. All patients with anorectal malformations should also get echocardiography to rule out any congenital cardiac problems, and a spinal ultrasound to check for a tethered spinal cord. Anteroposterior and lateral films should also be used to calculate the sacral ratio as this aids in providing families with prognostic information about the child's bowel control as they develop and grow.

 

Differential Diagnosis

Few patients with anorectal malformations may experience a delayed diagnosis, even though practically all patients without a perineal opening are identified at the newborn stage. Most frequently, these kids have anal stenosis or perineal fistulas that may go unnoticed throughout the neonatal stage. A pediatric surgeon should examine the anus under anesthesia if there is any doubt about the occurrence of an anorectal malformation to determine whether the opening is the right size and in the right anatomical location (centered within the muscle complex). A normal variant occurs when a patient occasionally presents with an anal opening that seems to be more anterior than is typical for most patients and is located in the middle of the muscle complex.

 

Anorectal Malformation Treatment

Anorectal Malformation Treatment

Perianal and Rectovestibular Fistulas

If the surgeon is confident doing the treatment and there are no further anomalies, such as a cardiac defect, that would prevent anesthesia from being administered, a repair of perineal fistulas can be done in the newborn period for individuals who have them. If the fistulous tract is large enough to be dilated with a Hegar dilator and stool evacuation is possible, the doctor may choose to postpone the repair. The same dilation technique is effective for female patients with rectovestibular fistulas since the anatomy might be complex in the neonatal stage, and dilation can help the infant grow and make surgery easier.

Making sure the child doesn't become distended and the stool decompresses properly with dilation management is essential for any patient population. At around three months of age, if treated with dilations, surgical repair should take place. By doing this, the flaw can be fixed before switching to solid meals, lowering the risk of constipation forming and causing rectal dilation, which would affect function. The abdominal entry is not required for surgical treatment of these anomalies, which often take place through a posterior sagittal incision.

 

Cloaca and Rectourethral Fistula

Any male patient with a urinary fistula should have a diverting descending sigmoid colostomy with a separated mucus fistula during the neonatal period. This approach enables the infant to grow without the need for surgery while also removing stool from the distal limb of the intestine that connects to the urinary system. Additionally, the mucus fistula makes it possible to perform a distal colostogram before surgery to identify the specific type of rectourethral fistula, aiding in preoperative planning and the surgical approach for repair.

Patients diagnosed with cloaca should additionally have a diverting ostomy and a mucous fistula performed in the newborn period if they have a single perineal opening. These patients should be given strong consideration for referral to a specialized facility because they also need much more complex preoperative and surgical management, as well as lifelong care.

The actual nature of the malformation and other concomitant anomalies, particularly cardiac problems, can affect when the definitive correction of high malformations is performed. Surgery to repair a lesion typically takes place around or after 3 months of age. If the rectum and the fistula are visible on the distal colostogram below the level of the coccyx, surgical treatment can still be done with a posterior sagittal incision. For severe anomalies such as recto-bladder neck fistula, laparoscopy can be an essential surgical technique.

 

Anorectal Malformation Prognosis

Prognosis

The long-term possibility for bowel control, or the capacity to be continent, is related to the prognosis for people with an anorectal abnormality. The type of anorectal malformation, the sacral ratio, and the spinal cord integrity are the three variables that can assist predict continence. The child's chances of maintaining continence as they get older decrease the more away the fistula is from its normal anatomical placement. Decreased continence may also be indicated by a low sacral ratio. If present, spinal conditions like a tethered cord also correlate poorly with continence. With the right bowel management program and specialized care, a child with these prognostic factors can nevertheless be clean and sociable despite the presence of these predictors.

 

Anorectal Malformation Complications

Anorectal Malformation Complications

Intraoperative complications can happen if caution is not taken to remain in the proper tissue plane, which can also result in the anus being misplaced or placed outside the center of the anal muscle complex. Injuries to the urinary structures, such as the urethra, seminal vesicles, and vas deferens, can also occur during surgery in males. The vagina in females can become injured.

Deep and superficial wound infections, anastomosis dehiscence, anoplasty prolapse, and anoplasty stricture are a few examples of post-operative problems. Recurrent fistulas between the female gynecological system or the male urinary system can also happen. These typically happen if the surgical repair is under too much tension or the rectum doesn't receive enough blood flow. Recurrent fistulas can also develop when the anterior structures, like the urethra or vagina, receive intraoperative injuries. Care should be taken in this situation to protect the healthy rectal wall rather than the repaired structure, and a fat pad should also be positioned to support the repair.

 

Conclusion

A complex range of congenital defects affecting the distal anus and rectum is known as anorectal malformations (ARMs). They occur from the urorectal septum's aberrant fetal development. The Crackenback Conference in 2005 created a new classification of ARMs based on the level of the rectal pouch as well as the presence or absence of fistulas and their description, factors that are useful in identifying the best surgical approach. An important aspect of ARM evaluation is imaging. Early classification of ARMs and the option to perform an urgent colostomy is made possible in the first few days of life thanks to clinical and imaging findings. Preoperative pelvic MR imaging after the neonatal period allows precise estimation of the morphology and grade of development of the sphincteric muscle complex in infants with moderate and high types of ARMs. The medical and surgical teams can better understand the chances of continence following surgery with the use of this data.