Anorectal Malformations
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Direct answer
Anorectal malformations are congenital anomalies in which the rectal pouch ends either above or below the levator ani muscle, classed as high or low lesions. The level is confirmed by an invertogram and by the physical examination, and associated urinary, spinal and sacral anomalies are common. High lesions are usually managed with a colostomy first and a staged posterior sagittal anorectoplasty, while low lesions may be repaired in one stage.
What you must remember
- High lesion: the rectal pouch lies above the levator ani, often with a fistula to the urinary tract in males or to the vagina in females; a vestibular fistula is usually low or intermediate.
- Low lesion: the rectum ends below the levator ani, often with a perineal or anocutaneous fistula, and generally has a better outcome.
- Invertogram: a lateral X-ray with the baby inverted, in which a distance of more than 1 cm between the rectal air and the skin marker indicates a high lesion.
- Physical signs: an absent or displaced anal opening, with a perineal fistula visible in many low lesions.
- Associated anomalies: VACTERL features, tethered cord, sacral anomalies and urinary tract defects, which change management.
- Diverting colostomy: created first in high lesions to divert faeces before definitive repair.
- Staged repair: posterior sagittal anorectoplasty as the definitive pull-through, followed by colostomy closure.
A staged approach to repair
Management follows the level of the lesion and the associated anomalies, and a diverting colostomy is used in many cases. The steps below set out the usual sequence in paediatric surgery, though the exact choices depend on the lesion and the baby's condition.
- Classify the lesion: examine the perineum for a fistula and confirm the level with an invertogram or lateral X-ray.
- Screen for associated anomalies: check for VACTERL features, the spine and sacrum, the urinary tract and the heart before surgery.
- Choose the route: low lesions with a perineal fistula may be repaired in a single stage, while high lesions need a diverting colostomy first.
- Create a colostomy: divert faeces in high lesions so that the bowel and the pelvic floor can recover before definitive surgery.
- Perform the definitive repair: posterior sagittal anorectoplasty is the usual pull-through for high and many intermediate lesions.
- Close the colostomy and follow up: the stoma is closed after the repair heals, and bowel function and continence are assessed over the following years.
Where the exam tries to catch you
Anorectal malformation questions test the level of the lesion, the invertogram and the staging of surgery.
- Trap: performing a primary pull-through in every high lesion. Correct: high lesions are usually diverted first and the pull-through is staged, which is safer for the baby.
- Trap: deciding the level from the perineal appearance alone. Correct: a flat perineum or a visible fistula does not confirm the level, so the invertogram or lateral X-ray is needed.
- Trap: ignoring the spine in anorectal malformations. Correct: sacral and tethered cord anomalies are common and must be screened, because they change both management and prognosis.
Frequently asked questions
What is an invertogram in anorectal malformations?
An invertogram in anorectal malformations is a lateral X-ray taken with the baby inverted, so that air rises to the distal rectal pouch. The distance between the air column and a skin marker is measured. A distance greater than 1 cm indicates a high lesion, which guides the surgical approach.
How do high and low anorectal malformations differ?
High anorectal malformations have a rectal pouch that lies above the levator ani muscle, while low lesions lie below it. High lesions usually need a colostomy and staged repair, whereas low lesions often have a perineal fistula and may be repaired in one stage. The level is confirmed by the invertogram and the physical examination.
Why is a colostomy created first in high anorectal malformations?
A colostomy is created first in high anorectal malformations to divert faeces from the distal bowel and allow the baby to grow before the definitive repair. Staging reduces the risk of complications during the pull-through. The colostomy is closed once the repair has healed.
Which associated anomalies are screened for in anorectal malformations?
Babies with anorectal malformations are screened for VACTERL features, sacral and spinal anomalies including tethered cord, urinary tract anomalies and cardiac defects. These associations change the surgical planning and the prognosis. Screening is therefore completed before definitive surgery.