# Anorectal Malformations > NEET-PG Surgery notes on anorectal malformations: high and low lesions, fistula types, invertogram, PSARP repair and VACTERL association. - Canonical URL: https://prepelephant.com/topics/neet-pg/surgery/anorectal-malformations - Exam / course: NEET-PG · Subject: Surgery - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Anorectal Malformations", PrepElephant, https://prepelephant.com/topics/neet-pg/surgery/anorectal-malformations ## Direct answer Anorectal malformations are congenital failures of the terminal bowel to reach the perineum, opening instead through a fistula to the urinary tract in males or the genital tract and perineum in females. Classification turns on the levator complex and pubococcygeal line: high lesions (rectoprostatic fistula in males, cloaca in females) need colostomy followed by pull-through, while low lesions (rectoperineal fistula) can often be repaired by anoplasty. The first 24 hours decide the route — inspection for meconium at the perineum, in the urine or from the vestibule, with a prone cross-table lateral film at 24 hours localising gas relative to the pubococcygeal line. Definitive repair is the posterior sagittal anorectoplasty, and every baby is screened for associated VACTERL defects. ## What you must remember - **Classification logic:** high (supralevator) lesions communicate with the bladder neck or prostatic urethra in males, or cloaca in females; intermediate lesions open at the bulbar urethra or low vagina; low lesions open on the perineum — the modern Krinkenbeck classification names the fistula itself. - **Male fistulas:** rectoprostatic urethral (high), rectobulbar urethral (intermediate), rectoperineal (low), rarely rectovesical. - **Female fistulas:** rectovestibular fistula is the commonest female malformation, with rectoperineal (low), rectovaginal, and cloaca — a single common channel for urethra and vagina — as the high end. - **Bedside clues:** a flat perineum with no anal dimple and no midline raphe pigmentation suggests a high lesion; meconium in the urine or ballooning of the perineum confirms a urinary fistula; the female perineum is inspected for three versus two orifices. - **Imaging:** prone cross-table lateral shoot-through radiograph (the invertogram) at 24 hours — rectal gas above the pubococcygeal line means high, below it low; perineal ultrasound and MRI refine, and echo and renal ultrasound screen for associated defects. - **Management pathway:** low lesions — primary anoplasty or limited PSARP in the newborn; high and intermediate lesions — divided sigmoid colostomy in the first 48 hours, PSARP at around 3-6 months, colostomy closure after healing. - **Cloaca specifics:** length of the common channel (over about 3 cm) predicts the need for laparotomy or laparoscopy and urological reconstruction; tethered cord and uterine anomalies coexist. ## Sorting high from low in the first 48 hours Examine the baby warm and undisturbed under a light. In a male, look for an anal dimple that puckers on perineal stimulation — its presence with a visible meconium-stained track means a low lesion suitable for primary repair. A flat, featureless perineum with meconium tinting the urine (dipstick or the "oil-drop" sign in the diaper) declares a rectourethral fistula: diverting colostomy first. When the perineum is ambiguous, wait the full 24 hours of life, then obtain the prone cross-table lateral film with the baby head-down and the hips flexed: the column of rectal gas is measured against the pubococcygeal line and the ischial line — above the PC line is high, between PC and ischial intermediate, below low. In females, count the orifices: three separate openings with meconium from the vestibule means a rectovestibular fistula (these can often be repaired primarily in expert hands); one common opening means cloaca, and the channel length determines whether reconstruction is perineal or abdominal. In parallel, echo-cardiography, renal ultrasound and a vertebral survey complete the VACTERL screen before any anaesthetic. ## Exam favourites from this topic Meconium per urethram equals rectourethral fistula; a single perineal orifice in a female equals cloaca until defined; a "flat bottom" without an anal dimple equals a high lesion. The invertogram is examined as technique as much as reading — 24 hours of life, prone, head down, hips flexed, cross-table beam — because a film taken too early underestimates the gas level. The colostomy question tests judgement: a divided (not loop) sigmoid colostomy with separated stomas keeps urine and faeces apart and prevents prolapse of the distal limb through a communal opening. PSARP, credited to Pena, maps the sphincter complex by electrical stimulation and delivers the bowel within it through a midline incision onto the closed fistula. Long-term, constipation dominates low lesions and soiling high ones, and the bowel management programme, not repeat surgery, is what tames both. ## Frequently asked questions ### How is a high anorectal malformation distinguished from a low one? By perineal inspection for the anal dimple and meconium location, and by the prone cross-table lateral radiograph at 24 hours — rectal gas above the pubococcygeal line indicates a high lesion. ### What is the initial management of a high anorectal malformation? A diverting divided sigmoid colostomy in the first days of life, followed by posterior sagittal anorectoplasty at around three to six months of age. ### What does meconium in the urine signify? A rectourethral fistula — a high malformation in a male, requiring colostomy and later pull-through. ### Which is the commonest anorectal malformation in females? Rectovestibular fistula, in which the bowel opens just inside the vestibule behind the vagina. ### What is the VACTERL association? The non-random clustering of vertebral, anorectal, cardiac, tracheo-oesophageal, renal and limb anomalies — mandating systematic screening in every affected newborn.