1. Embryology and etiology
2. Classification, especially Krickenbeck classification
3. Neonatal clinical assessment and associated anomalies
4. Diagnostic work-up and imaging
5. Initial stabilization and definitive surgery by subtype
6. Postoperative care, continence, and long-term follow-up

1. Embryology and etiology
2. Classification, especially Krickenbeck classification
3. Neonatal clinical assessment and associated anomalies
4. Diagnostic work-up and imaging
5. Initial stabilization and definitive surgery by subtype
6. Postoperative care, continence, and long-term follow-up

Anorectal malformation in a neonate

Definition and epidemiology

1. Embryology and etiology

Normal embryology

• During weeks 4-6 of gestation, the terminal hindgut and allantois empty into a common cavity, the cloaca.
• The urorectal septum descends caudally and divides the cloaca into:
  • Anterior urogenital sinus
  • Posterior anorectal canal
• The anal canal has dual origin:
  • Upper two-thirds: endoderm of hindgut
  • Lower one-third: ectoderm of proctodeum
• The cloacal membrane normally ruptures around week 7, establishing the anal opening.
• Proper development requires correct descent of rectum through the pelvic floor and appropriate relationship with the sphincter muscle complex.

Embryologic basis of ARM

• Failure of separation between urinary and gastrointestinal tracts in boys, causing rectourethral or rectovesical fistula.
• Failure of separation of genital, urinary, and intestinal tracts in girls, causing a persistent cloaca.
• Anterior displacement of the anal opening with a perineal fistula.
• Persistence of an anal membrane, anal stenosis, or a blind-ending rectal pouch.

Etiology

1. Genetic and developmental pathway abnormalities
   • Abnormalities in developmental signaling pathways, including SHH, WNT, FGF, BMP, and HOX-related pathways, have been implicated.
   • ARMs may occur in chromosomal and syndromic disorders.
2. Associated syndromes
   • VACTERL association
   • Townes-Brocks syndrome
   • Currarino syndrome
   • Pallister-Hall syndrome
   • Cat-eye syndrome
   • Trisomy 21, particularly with rectal atresia or stenosis
   • Caudal regression spectrum
3. Environmental and maternal factors
   • Evidence for specific teratogenic or maternal factors is inconsistent.
   • Maternal diabetes, obesity, some assisted reproductive techniques, and certain exposures have been reported as associations, not established direct causes.

2. Classification

A. Traditional Wingspread classification

B. Krickenbeck classification

Major clinical groups

Rare regional variants

• Pouch colon
• Rectal atresia or stenosis
• Rectovaginal fistula
• H-type anorectal fistula
• Other complex variants

C. Practical sex-based classification

Male

• Perineal fistula
• Rectobulbar urethral fistula
• Rectoprostatic urethral fistula
• Rectovesical or bladder-neck fistula
• Imperforate anus without fistula
• Rectal atresia/stenosis

Female

• Perineal fistula
• Rectovestibular fistula
• Imperforate anus without fistula
• Cloaca
• Rectal atresia/stenosis
• Rare rectovaginal or H-type fistula

3. Neonatal clinical assessment and associated anomalies

Clinical presentation

• Absent, misplaced, stenosed, or abnormal anal opening
• Failure to pass meconium per anus
• Progressive abdominal distension
• Bilious vomiting or feeding intolerance, if obstruction is significant
• Meconium from an abnormal site:
  • Perineal opening: perineal fistula
  • Vestibule in a girl: rectovestibular fistula
  • Urine in a boy: rectourethral or rectovesical fistula
• Meconium-stained urine, pneumaturia, or urinary tract infection can occur with urinary fistula.

Essential perineal examination

1. Presence and location of anal dimple.
2. Position of any fistulous opening.
3. Perineal body development.
4. Buttock development and gluteal cleft.
5. Sacral abnormalities, such as flat buttocks, sacral dimple, hemangioma, or asymmetric gluteal folds.
6. External genitalia.
7. Number of perineal openings in girls.

Clinical clues by type

Associated anomalies

• Genitourinary: hydronephrosis, reflux, neurogenic bladder, duplicated collecting system, urethral anomalies.
• Spinal/sacral: tethered cord, spinal lipoma, sacral agenesis, vertebral segmentation defects.
• Genital tract: hydrocolpos, uterine/vaginal anomalies, especially in cloaca.
• Gastrointestinal: esophageal atresia, duodenal atresia, Hirschsprung disease, pouch colon.
• Cardiac: congenital heart disease.
• Neurological: spinal cord abnormalities and syndromic neurodevelopmental issues.

4. Diagnostic work-up and imaging

Initial investigations in all neonates

1. Abdominal radiograph
   • Assesses intestinal obstruction, bowel dilatation, and associated vertebral/sacral anomalies.
   • Do not use it alone to decide the level of ARM.
2. Ultrasound abdomen and pelvis
   • Kidneys, ureters, bladder, hydronephrosis.
   • In girls, specifically look for hydrocolpos.
   • Assess bladder distension and pelvic fluid collection.
3. Echocardiography
   • Screen for congenital heart disease before major surgery.
4. Spinal ultrasound
   • Useful in neonates for occult spinal dysraphism and tethered cord.
   • MRI spine is indicated if ultrasound is abnormal, if there are sacral defects, neurological findings, or when clinically appropriate.
5. Sacral/spinal radiograph
   • Identifies sacral agenesis and vertebral anomalies.
   • Sacral ratio is useful in counseling about continence potential.
6. Renal function tests
   • Serum electrolytes, urea, creatinine.
   • Urinalysis and urine culture where urinary tract communication or infection is suspected.

Determining the level and fistula

Cross-table prone lateral radiograph

• Performed after approximately 18-24 hours of life, not immediately after birth.
• Baby is placed prone with pelvis elevated and a radiopaque marker at the expected anal site.
• It estimates the distance of the distal gas-filled rectal pouch from the perineum.
• It is more useful than the obsolete invertogram.

Distal colostogram

• Performed through the distal mucous fistula under pressure.
• Defines:
  • Distal rectal pouch
  • Presence and exact site of urinary fistula
  • Rectal relationship to bladder neck/urethra
  • Length of common channel or associated anatomy in selected cases
• It is essential for operative planning before definitive posterior sagittal anorectoplasty.

Additional studies

• Voiding cystourethrogram or cystoscopy for suspected urinary fistula/reflux.
• Genitogram, vaginoscopy, cystoscopy, and examination under anesthesia for cloaca.
• Pelvic MRI in complex cloaca or selected complex malformations to clarify pelvic anatomy and muscle complex.

5. Initial stabilization

At birth

1. Keep the infant nil per oral if there is obstruction, abdominal distension, or planned surgery.
2. Insert nasogastric tube for gastric decompression if vomiting or bowel obstruction is present.
3. Start intravenous fluids and correct hypoglycemia, electrolyte disturbance, and dehydration.
4. Give antibiotics if there is intestinal obstruction, sepsis concern, urinary contamination, or surgery.
5. Maintain warmth and monitor cardiorespiratory status.
6. Avoid blind probing, forceful dilatation, or attempted perineal incision.
7. Refer early to pediatric surgery and involve pediatric urology, neonatology, and pediatric anesthesia where required.

Urgent situations

• Intestinal obstruction and progressive distension
• Sepsis or perforation risk
• High ARM or no visible fistula
• Meconium in urine suggesting rectourinary fistula
• Cloaca
• Hydrocolpos with urinary obstruction/hydronephrosis
• Major associated anomalies requiring stabilization

6. Definitive treatment by subtype

Principles

• Place the rectum centrally within the sphincter muscle complex.
• Divide and close any fistula safely.
• Preserve urinary and genital structures.
• Avoid damage to pelvic nerves and muscles.
• Achieve continence potential while preventing constipation and megarectum.

A. Perineal fistula

• Primary perineal anoplasty or limited PSARP in the neonatal period, provided the baby is stable and anatomy is clear.
• A diverting colostomy is generally unnecessary in uncomplicated cases.
• In selected stable infants, repair may be delayed for several weeks or months with careful dilatation and bowel management.

B. Rectovestibular fistula in girls

• Primary PSARP/anorectoplasty in a stable infant in an experienced center.
• Alternatively, a divided sigmoid colostomy followed by delayed PSARP.
• If neonatal condition, local expertise, or anatomy is uncertain, staged repair is safer.

C. Rectourethral fistula in boys

1. Divided sigmoid colostomy in neonatal period.
2. Distal pressure colostogram after recovery to define fistula.
3. Definitive PSARP, usually at about 2-3 months of age, depending on infant condition and institutional practice.
4. Colostomy closure after healing, calibration, and satisfactory anorectal function.

D. Rectovesical or bladder-neck fistula

• Divided colostomy in the newborn period.
• Detailed distal colostogram, cystoscopy, and urologic assessment.
• Definitive repair by PSARP, laparoscopic-assisted pull-through, or combined approach in an experienced center.
• Careful separation of rectum from bladder neck is necessary to prevent urinary injury.

E. Cloaca

1. Divided colostomy.
2. Drain hydrocolpos if present. This may require catheterization of common channel, vaginostomy, or other drainage method.
3. Renal and bladder assessment, because hydrocolpos may compress urinary tract and cause hydronephrosis.
4. Detailed anatomical assessment with endoscopy, genitogram, cystoscopy, vaginoscopy, and selected MRI.

• Usually performed later in infancy by a multidisciplinary pediatric colorectal-urology-gynecology team.
• Procedure depends on common channel length and vaginal/urethral anatomy:
  • Total urogenital mobilization
  • Urogenital separation
  • PSARP with reconstruction of vagina and urinary tract as required

F. ARM without fistula

• If rectum is low and readily accessible, primary perineal repair may be possible.
• If high/uncertain, perform divided colostomy, then distal colostogram and delayed definitive repair.

G. Rectal atresia or stenosis

• Rectal atresia may be repaired by posterior sagittal approach, transanal pull-through, or other anatomy-specific procedure.
• Anal stenosis may respond to graded dilatation; severe stenosis requires anoplasty.
• Evaluate carefully for trisomy 21 and other associated anomalies where clinically indicated.

Colostomy principles

• Complete fecal diversion from distal bowel.
• Allows a high-pressure distal colostogram.
• Reduces fecal contamination of urinary fistula.
• Easier subsequent reconstruction than an ill-placed loop colostomy.

7. Postoperative care

Immediate postoperative care

• Analgesia and wound care.
• Monitor for sepsis, bleeding, wound dehiscence, and urinary complications.
• Maintain urinary catheter after repair of urinary fistula or complex reconstruction according to surgical plan.
• Resume feeds as tolerated.
• Monitor stoma output in staged repair.
• Treat constipation promptly to avoid megarectum and overflow soiling.

Anal dilatation

• Prevent anastomotic narrowing/anal stricture.
• Gradually achieve an age-appropriate anal caliber.
• Ensure painless passage of stools.

Colostomy closure

• Adequate healing of anorectoplasty
• Completion of dilatation or confirmation of adequate anal caliber
• No unresolved urinary or wound complication
• Infant is nutritionally stable

8. Continence, bowel function, and long-term follow-up

Determinants of continence

1. Type of malformation
   • Perineal and vestibular fistulae have better outcomes.
   • Rectovesical fistula and cloaca have poorer expected continence.
2. Sacral development
   • Normal sacrum predicts better continence.
   • Sacral agenesis/hypoplasia predicts poor continence.
3. Spinal cord integrity
   • Tethered cord, spinal dysraphism, and neurogenic bladder adversely affect bowel and urinary function.
4. Quality of pelvic muscle complex
   • Better developed muscles provide better potential for voluntary continence.
5. Quality of reconstruction and postoperative bowel management

Functional outcomes

• Constipation, often the most common problem
• Fecal soiling due to overflow from constipation
• True fecal incontinence
• Recurrent anal stenosis
• Rectal prolapse
• Neurogenic bladder
• Recurrent urinary tract infections
• Vesicoureteral reflux or renal impairment
• Sexual and reproductive concerns, particularly in females with cloaca
• Psychosocial distress, school difficulties, and reduced quality of life

Bowel management

• Dietary modification and adequate fluids
• Osmotic or stimulant laxatives for constipation
• Scheduled toileting
• Rectal enemas
• Transanal irrigation
• Antegrade continence enema through appendicostomy or cecostomy in selected children
• Avoiding constipation is essential, because a chronically dilated rectosigmoid can cause overflow pseudoincontinence.

Long-term multidisciplinary follow-up

• Pediatric colorectal surgeon
• Pediatric urologist
• Nephrologist if renal impairment exists
• Neurosurgeon for tethered cord/spinal abnormalities
• Gynecologist for cloaca and Müllerian anomalies
• Gastroenterologist/bowel management team
• Psychologist and continence nurse

• Growth and nutrition
• Stool frequency, constipation, soiling, continence
• Urinary continence and recurrent UTI
• Renal ultrasound and renal function
• Pubertal development and reproductive anatomy
• Psychosocial well-being and transition to adult services

MD Pediatrics exam summary

In a neonate with absent anus, first stabilize the infant and perform a careful perineal examination after sufficient time for fistulous meconium to appear. Look for meconium in urine, vestibule, or perineal skin; a single perineal opening in a girl indicates cloaca until proved otherwise. Screen for VACTERL and particularly renal, cardiac, spinal, sacral, and genital anomalies. Low perineal fistulae may undergo primary anoplasty. Rectourinary fistulae, high lesions, ARM without visible fistula, and cloaca usually require divided colostomy, detailed distal colostogram/anatomic evaluation, delayed PSARP or anatomy-specific reconstruction, and long-term bowel, urinary, sexual, and psychosocial follow-up.