What are the developmental anomalies of the hindgut, their typical newborn presentation, diagnostic work‑up, and definitive surgical management?

Developmental Anomalies of the Hindgut

Overview

Hindgut developmental anomalies primarily include Hirschsprung disease, anorectal malformations (ARM), and intestinal malrotation/atresia affecting the distal colon, with newborns typically presenting with delayed meconium passage beyond 24-48 hours, abdominal distension, and bilious vomiting requiring immediate surgical consultation. 1

Major Hindgut Anomalies

Hirschsprung Disease

Clinical Presentation:

• Delayed passage of first meconium beyond 24-48 hours of life 1
• Progressive abdominal distension 1
• Bilious vomiting 1
• Functional distal bowel obstruction from aganglionosis of the distal gut 2
• Most commonly involves the rectosigmoid region (short segment disease) 3

Diagnostic Work-up:

• Plain abdominal radiographs as initial imaging to evaluate bowel obstruction patterns 1, 4
• Contrast enema demonstrating transition zone between dilated proximal bowel and narrowed distal aganglionic segment (80% sensitivity, 20% false-negative rate) 5, 1
• Rectal suction biopsy for definitive diagnosis showing absence of ganglion cells 5, 1
• The American College of Radiology emphasizes that contrast enema is a screening tool only, not definitive for excluding Hirschsprung disease 1

Immediate Management:

• NPO status with nasogastric tube decompression 1
• Intravenous fluid resuscitation to correct dehydration and electrolyte abnormalities 1
• Immediate pediatric surgical consultation 1
• Screen for associated syndromes including congenital central hypoventilation syndrome (CCHS) in confirmed cases 1

Definitive Surgical Management:

• Pull-through surgery for short segment disease 3
• Posterior anorectal myotomy for selected ultrashort segment candidates 3

Anorectal Malformations (ARM)

Clinical Presentation:

• Mechanical bowel obstruction from anatomical anomalies 2
• Spectrum ranging from anal stenosis to complete anorectal agenesis 5
• May present with visible perineal abnormalities or absent anal opening 5
• Between 10-52% have associated spinal dysraphic malformations 5

Associated Findings:

• Currarino Triad (rare): anorectal malformation + sacral bony defect (scimitar sacrum) + presacral mass (teratoma or meningocele) 5
• Higher association with complex ARM (43%) versus simple ARM (11%) 5
• Frequently associated with urologic manifestations and spinal cord tethering 5
• May occur with VACTERL association 5

Diagnostic Work-up:

• Plain abdominal radiographs showing distal obstruction pattern 5
• Contrast enema to delineate anatomy 5
• Spinal imaging (MRI or ultrasound) mandatory to evaluate for associated dysraphism, especially with cutaneous markers (sacral dimples above gluteal cleft, hair tufts, vascular lesions, skin tags) 5
• Renal ultrasonography for associated genitourinary anomalies 5
• Sacral radiographs to assess for sacral agenesis 5

Definitive Surgical Management:

• Surgical correction tailored to specific anatomic defect 2
• Avoid using distal rectal pouch and fistula parts in reconstruction if dysganglionosis present 6
• Long-term follow-up essential for managing fecal incontinence 2

Colonic Atresia

Clinical Presentation:

• Multiple distended bowel loops with absent or decreased distal gas on radiographs 5, 4
• Bilious vomiting within first 2 days of life 5
• Less common than ileal atresia 5

Diagnostic Work-up:

• Plain abdominal radiographs showing distal obstruction 5, 4
• Contrast enema is the diagnostic procedure of choice, demonstrating microcolon from lack of contents moving through bowel 5, 4
• Ultrasound has no relevant supporting literature for distal obstruction evaluation 5, 4

Definitive Surgical Management:

• Surgical resection of atretic segment with primary anastomosis 5
• Multiple atresias occur in approximately 15% of cases, identifiable at initial surgical exploration 5

Intestinal Malrotation (Hindgut Involvement)

Clinical Presentation:

• Bilious vomiting within first 2 days of life 5
• May have normal bowel gas pattern with incomplete obstruction 5
• Can present with cecal malposition affecting hindgut 5

Diagnostic Work-up:

• Upper GI series is the reference standard showing abnormal duodenojejunal junction position (96% sensitivity, 3% false-negative, 10-15% false-positive) 5, 7
• Contrast enema less direct with 20% false-negative rate and 15% false-positive rate from high mobile cecum 5
• Ultrasound showing abnormal SMV/SMA relationship has limited data as primary modality 5

Definitive Surgical Management:

• Urgent Ladd procedure if midgut volvulus present 5
• Division of Ladd bands and appendectomy 5

Critical Pitfalls to Avoid

• Never delay surgical consultation in any neonate with bilious vomiting—assume malrotation with volvulus until proven otherwise 5, 1
• Do not rely solely on contrast enema to exclude Hirschsprung disease; rectal biopsy is definitive 1
• Always evaluate for spinal dysraphism in ARM patients, particularly with cutaneous markers above the gluteal cleft 5
• Recognize that 3% of ARM patients have true Hirschsprung disease association, not just dysganglionosis 6
• Maternal gestational diabetes is a risk factor for sacral agenesis and associated ARM 5
• In ARM with confirmed aganglionosis beyond the rectal pouch, additional surgical intervention beyond ARM repair is required 6

Associated Syndromes Requiring Screening

• 22q11.2 deletion syndrome: Hirschsprung disease and imperforate anus are recognized associations 5
• Down syndrome: Higher association with both Hirschsprung disease and ARM 6
• VACTERL association: Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal, Limb anomalies 5