Imperforate anus

DR. CHIRANJIB MURMU, RESIDENT, RADIOLOGY

Anal atresia (or imperforate anus) refers to a spectrum of anorectal abnormalities ranging from a membranous separation to complete absence of the anus.

Anal Anatomy

Embryology of the imperforate anus

Between 4-6 weeks, the cloaca becomes the common depository for the developing urinary, genital and rectal systems.The cloaca is quite promptly divided into an anterior urogenital sinus and a posterior intestinal canal by the urorectal septum. Two lateral folds of cloacal tissue join the urorectal septum to complete the separation of the urinary and rectal tracts.

Imperforate anus Includes agenesis and atresia of the rectum and

anus Etiology: unknown Incidence: 1 in 4,500 to 5000 SEX: 60% male

ClassificationAnorectal malformations represent a wide spectrum of defects.

They are termed as “low,” “intermediate,” and “high” .

Newborn girl with imperforate anus. Newborn boy with imperforate anus.

ClassificationMales

1. Cutaneous (perineal fistula)

2. Rectourethral fistulaA. BulbarB. Prostatic

3. Recto–bladder neck fistula

4. Imperforate anus without fistula

5. Rectal atresia

Females1. Cutaneous (perineal fistula)2. Vestibular fistula3. Imperforate anus without

fistula4. Rectal atresia5. Cloaca

A. Short common channelB. Long common channel

6. Complex malformations

Radiographic featuresAbdominal radiographcan be variable depending on the site of atresia (e.g high or low) , level of impaction with meconium and physiological effects such as strainingmay show multiple dilated bowel loops with with absence of rectal gas.

Invertogram

A coin/metal piece is placed over the expected anus and the baby is turned upside down (for a minimum 3 minutes).

Distance of gas bubble in rectum from the metal piece is noted:>2 cm: denotes high type<2 cm: denotes low type

Cross-table lateral radiograph: -the patient in prone position

-If air in the rectum is located below the coccyx, and the patient is in good condition with no significant associated defects, one may consider performing a posterior sagittal operation with or without a protective colostomy-if the rectal gas does not extend beyond the coccyx, or the patient has meconium in the urine, an abnormal sacrum, or a flat bottom, a colostomy should be done.

Fluoroscopy: contrast studyto detect recto-urinary, recto-vaginal or rectoperineal fistulathe fistula is considered low (below levator ani plane) if it is below the pubooccygeal line (PCL) and considered high fistula if above the PCLUltrasound-the anus may be seen as an echogenic spot at the level of the perineum and in an atresia this echogenic spot may be absent -may show bowel dilatation

Complicationsmeconium peritonitis

ASSOCIATED DEFECTS

1. Sacrum and SpineSacral deformities appear to be the most frequently associated

defect.2. Genitourinary Defects

The frequency of associated genitourinary defects varies from 20% to 54%.

3. Anal atresia may occur as a part of the VACTERL group of anomalies

V Vertebral body segmentation defectA Anal atresiaC Cardiovascular (PDA, VSD)TE Tracheo esophagial fistulaR unilateral Renal agenesisL Limb anomaly (radial hypoplasia)

So, very careful examination of the baby must be made to exclude these anomalies STEP BY STEP.

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