Is the urorectal septum (urorectal septum) involved in the formation of a perineal fistula in cases of low Anorectal Malformations (ARM)?

Role of the Urorectal Septum in Perineal Fistula in Low Anorectal Malformations

The urorectal septum is directly involved in the formation of perineal fistulas in low anorectal malformations (ARMs), as these malformations result from abnormal development of the urorectal septum during early embryogenesis. 1

Embryological Basis of Perineal Fistulas in Low ARMs

• Anorectal malformations develop due to abnormal formation during early embryogenesis involving the caudal spinal cord, anorectal, and urogenital systems due to their intimate temporospatial relationships 2
• The urorectal septum malformation sequence consists of absent perineal and anal openings in association with ambiguous genitalia and urogenital, colonic, and lumbosacral anomalies 1
• Defects in mesodermal proliferation early in embryogenesis result in this condition, with the partial sequence characterized by a single perineal opening draining a common cloaca 1
• Low ARMs specifically represent the milder end of the spectrum of urorectal septal malformations 3

Anatomical Considerations in Low ARMs with Perineal Fistulas

• In low ARMs with perineal fistulas, the distal rectum and anal canal development are abnormal, with the fistula representing the abnormal termination of the enteric component 4
• The classification of ARMs is based on the position of the rectal pouch relative to the puborectal sling, the presence or absence of fistulas, and the types and locations of the fistulas 4
• Perineal fistulas in low ARMs are characterized by an abnormal muscle coat in 100% of cases, showing disorganization of the circular and longitudinal layers 5
• The connective tissue is irregular and abnormally represented in 100% of cases of perineal fistulas 5

Clinical Implications of Urorectal Septum Involvement

• Low-type ARMs with perineal fistulas have an 11% association with sacral anomalies, compared to 43% in complex malformations 2
• Patients with perineal fistulas may present with an inadequate or shortened perineal body, which can impact fecal continence and sexual function 6
• Constipation is a frequent complaint in the long-term follow-up of patients with "low" ARMs, reported in 42%-70% of cases 5
• Enteric nervous system (ENS) anomalies are present in 71.8% of perineal fistulas, which may contribute to functional bowel issues 5

Surgical Management Considerations

• Low malformations with perineal fistulas typically require perineoplasty in the neonatal period 2
• Resection of a significant portion (approximately 3 cm) of the distal fistula during repair appears to permit better functional results 5
• In patients with anorectal abscess and an obvious fistula, fistulotomy should only be performed at the time of abscess drainage in cases of low fistula not involving sphincter muscle 7
• Multidisciplinary evaluation to assess and identify abnormalities is crucial to ensure optimal patient outcomes 6

Common Pitfalls and Caveats

• Not recognizing associated anomalies: Between 10% and 52% of children with anorectal malformations have associated dysraphic spinal malformations 2
• Inadequate surgical approach: Failure to resect the abnormal distal portion of the fistula may lead to poorer functional outcomes 5
• Post-surgical complications: Patients may develop gynecologic concerns after previous posterior sagittal anorectoplasty (PSARP) for repair of an ARM, including inadequate perineal body, introital stenosis, retained vaginal septum, and remnant rectovestibular fistula 6
• Failure to recognize the embryological basis: Understanding that the urorectal septum malformation is the underlying cause helps guide appropriate management 1, 3