The Radiologic Evaluation of Imperforate Anus

In 1930 Wangensteen and Rice (9) introduced the still widely used technic of obtaining upside-down abdominal roentgenograms in newborn infants with “imperforate anus.” They made no measurement of any type, but merely employed the apparent distance between the rectal gas and anal dimple in planning surgical therapy. Subsequently, various measurements were devised including a distance of 1.5–2 cm between the rectal gas and anal marker; if this distance was exceeded, the perineal approach for correction was not used. Bony reference points were also considered (5), including the pubococcygeal line and ischial point (8); if the gas terminated above the pubococcygeal line, the perineal approach again was not advised.

All these methods obviously were aimed at guiding the surgeon by placing patients into two major groups: those amenable to repair by the perineal route (“low”anomalies) and those not approachable solely from the perineum (“high” anomalies) (4, 6, 8).

A basic assumption was implicit in all previous roentgen measurements: that the position of the rectal termination could be determined by these landmarks. In our experience the roentgen division of the anomalies has not been consistent or reliable. Indeed, the roentgen measurements have often been confusing and erroneous in assessing the length of the rectal pouch from the skin.

We will illustrate that such roentgen conclusions are largely derived from anatomic and physiologic mechanisms independent of the internal anatomy of the malformation. Our conclusions are based on knowledge of the clinical picture of this complex group of anomalies. The roentgen studies to be presented include both conventional radiologic and cinefluorographic examinations of the neonatal gas-filled rectum in patients with “imperforate anus.” In addition, radiopaque contrast material has been injected into the rectal pouch through the perineum with cinefluorographic studies of the ascent and descent of the rectum in response to changing physiologic states.

Basic Approach for Clinician and Radiologist

The radiologist, confronted with films of an infant with “imperforate anus” cannot give any meaningful interpretation without knowing the clinical picture. This includes the sex of the patient, the presence or absence of a visible perineal fistula, and the presence or absence of meconium either in the vagina or in the male infant's urine. Unfortunately, even today most radiologic requisitions on such patients merely say “imperforate anus.” Also, the films are obtained on a struggling crying infant hung by the heels with a penny placed, hopefully, on the anal dimple. Measurements are made of the distance from the rectal gas to the marker and a report submitted.