Congenital diseases of the rectum and anus
CLASSIFICATION
Anorectal malformations (ARM) range from anal stenosis and anteriorly displaced anus to imperforate anus, rectal atresia and complex cloacal anomalies. They are described by the relation of the rectal pouch to the levator/puborectalis complex and by the presence/location of fistulas. Associated anomalies are common, particularly vertebral, anorectal, cardiac, tracheo-oesophageal, renal and limb abnormalities (VACTERL association).
EMBRYOLOGY AND PATHOPHYSIOLOGY
The cloaca is divided by the urorectal septum into anorectal and urogenital channels. Abnormal partitioning and development produce absent, ectopic or stenotic anal opening and abnormal communications. In boys, fistulas may open to the perineum, urethra or bladder neck; in girls, they may open to the vestibule or vagina, or form a cloaca. Obstruction prevents normal passage of meconium and may cause bowel distension, perforation and sepsis.
CLINICAL PRESENTATION AND INITIAL ASSESSMENT
At birth inspect the perineum for anal opening, position, stenosis, fistula, meconium staining and genital abnormalities. Failure to pass meconium, abdominal distension and bilious vomiting suggest obstruction. Meconium in urine indicates a urinary fistula; meconium at the vestibule suggests a vestibular fistula. Stabilise the newborn, assess hydration and sepsis, and avoid repeated traumatic probing.
INVESTIGATIONS
Evaluate associated anomalies with spinal/sacral radiographs or ultrasound, renal/pelvic ultrasound, echocardiography and examination for oesophageal atresia/tracheo-oesophageal fistula. Pelvic MRI helps define complex anatomy and sphincter/levator relationships. In selected cases, prone cross-table lateral radiograph after sufficient time allows distal pouch localisation. Distal colostogram is used in diverted patients to map fistula and rectal pouch before definitive repair.
MANAGEMENT
Management depends on anatomy and stability. A low perineal fistula may be treated with primary anoplasty or perineal repair. High/complex malformations often require diverting colostomy in the neonatal period followed by detailed imaging and posterior sagittal anorectoplasty (PSARP) or laparoscopic-assisted pull-through. Cloacal malformations require specialist reconstruction. Maintain urinary drainage where necessary, protect skin and provide parental support. Treat associated anomalies and plan long-term bowel management.
COMPLICATIONS AND PROGNOSIS
Long-term issues include constipation, faecal incontinence, soiling, urinary/sexual dysfunction, recurrent urinary infection, prolapse and psychosocial effects. Functional outcome depends on sacral development, sphincter muscles, spinal anomalies and exact malformation. Lifelong multidisciplinary follow-up may be needed.