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1965, Brit. J. RadioL, 38, 444-448

Radiological assessment of imperforate anusBy D. A. R. Robertson, M.B., Ch.B., D.M.R.D.,* Eric Samuel M.D., F.R.C.S., F.R.C.P.E., F.F.R., andW. Macleod, M.B., F.R.C.P.E., F.F.R.(R.C.S.L)Radiodiagnostic Departments, Royal Infirmary and Royal Hospital for Sick Children, Edinburgh{Received August, 1964)Impe rforate anus occurs with a frequency of approxi-mately 1 in 5,000 births. T he results of surgical treat-ment in these cases have been variable and this haslargely depended on the type of lesion present. Forthis reason, th e use of radiology in differentiatingbetween a high rectal atresia and a true imperforateanus is more than an academic exercise.The purpose of this study was to carry out anindependent radiological assessment of the level ofthe lesion by a retrospective analysis of the radio-graphs. This was then compared with the findingsat operation. Eighteen cases of imperforate anusadmitted to the Royal Hospital for Sick Childrenwere reviewed. As the results of operation are sodependent upon the type of ano-rectal abnor-mality present, it was felt that this review mightoffer to the paediatric surgeon a more definite indi-cation of the level of the lesion, and hence a betterguide to the choice of surgical approach.

Lesions were classified according to their relationto the pelvic floor"high" lesions above the esti-mated level of the pelvic floor, "low" lesions belowthe floor. The low lesions are treated by a perinealapproach, whilst the high lesions are considered tobe treated better by an abdomino-perineal approach.The abdominal approach is advisable in high lesions,as many are complicated by fistula formation, forwhich extensive rectal mobilisation is necessary. Italso avoids an extensive dissection of the pelvic floorfrom below, with consequent possible damage.

Various classifications of rectal and anal mal-formation have been suggested, but that of Ladd andGross (1934) has received widest recognition. Theydescribed four types as follows:Ty pe I Incomp lete rupture of anal mem brane orstenosis at 3 point 1-4 cm above the anus.Typ e II Imperforate anus. Obstruction due to apersistent membrane.Type III Imperforate anus, but with a rectal pouchseparated from the anal membrane Therectal pouch ended blindly in or above thepelvis.Ty pe IV Anus and pouch normal. Th e rectal pouchended blindly. There was either mem-

branous obstruction or separation of thesetwo pouches.Browne (1955), however, classified imperforateanus into high and low types, i.e. those with rectalagenesis and those without, but with a malformed ormisplaced anus. The essential difference is that inthe high type of deformity with rectal agenesis thebowel ends above the levator ani (the pelvic floor),whereas in the low type it passes through thismuscle, which exercises sphincteric control throughthe pubo-rectalis.Th e level of the pelvic floor may be estimated frombony landmarks and thus the classification of highand low types of anomaly can be based on thismeasurement. Scott and Swenson (1959) stated thatthe pubo-coccygeal line indicates the position of thepelvic floor; lesions ending above this line wereclassified as high and those below as low lesions.Th e line was defined as runn ing from the lower border

Laddand Grossl5cmK i e s e w e t t e r2-0 cm

Stephens

\ Scott andSwenson

Present address: Kingston General Hospital, Surrey.F I G . 1.

Line drawing of pubo-coccygeal line.444

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of the pubis to the sacro-coccygeal junction (Fig. 1.)Stephens (1953), on the other hand, located thepubo-coccygeal line from the upper border of thepubis to the sacro-coccygeal junction. He consideredthis is the common level at which the rectal lumenis narrowed or obliterated at its junction with theupper cloacal canal, due to failure of subdivision ofrectum from cloaca. This line is the approximateanatomical level of the verumontanum, peritonealpouch, the external os of the cervix and Houston'sthird valve of the rectum.Ladd and Gross (1934) stated that lesions 1-5 cmor more from the anal dimple should be consideredhigh lesions and that an abdomino-perineal ap-proach should be used in their surgical treatment.Kiesewetter and Turner (1963) accepted 2 cm as themeasurement from the anal dimple that corre-sponded to the level of the pelvic floor.Since the pubo-coccygeal line of Scott andSwenson (1959) gives the position of the pelvic floorand corresponds to the classification of Browne(1955), this line has been taken as the division bet-ween high and low lesions in the present study.

RadiographyThe basis of the radiological examination, em-ploying the Wangensteen-Rice principle (1930), isa lateral radiograph of the pelvis with the infant in-verted. The level of air in the distal pouch of bowelin relation to the pubo-coccygeal line can thus bedetermined. Air on or above the line indicates a high

lesion and below the line a low lesion (Figs. 2, 3,4 and 5).A metallic marker is placed at the anal dimple andthe distance from marker to distal pouch of bowel ismeasured.Certain criteria should be followed when takingthe films. The centring point is the upper aspect ofthe greater trochanter w ith the inverted infant in thetrue lateral position. Some authors recommend anA.F.D. distance of as much as 6 ft. to minimisemagnification. Films taken before 8-12 hours areunlikely to show gas at the true level of the distalpouch and serial films at three-hour intervals havebeen advocated until no further distal movement ofgas is noted (Figs. 6 and 7). Accurate placement ofthe marker at the anal pit is important.An antero-posterior film of the pelvis is of valueto demonstrate the degree of distension of proximalbowel and possible associated sacral bone anomalies.

MethodThe films were examined before the surgicalapproach used in each case was known and thefollowing observations made:(i) Th e relation of gas to the pubo-coccyge al line ofScott and Swenson (1959);(ii) the distance of gas from the anal marker;(iii) the presence of gas in the genito-urinary tract;(iv) associated congenital abnormalities.The results were recorded as follows: Firstly,using the pubo-coccygeal line as the sole indication

F I G . 2. F I G . 3.FIG. 2. High lesion.

FIG. 3. High lesion. Gas at S3 level.FIG. 4. High lesion. Gas at pubo-coccygeal line. Sacral anomaly.445

F I G . 4.

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FIG. 5. Low lesion.FIG. 6. Low lesion. Incomplete descent of gas.FIG. 7. After three hours gas outlines true level of lesion.FIG. 8. Apparent low lesion. High surgical approach. Fistula present.of the level of the lesion. Secondly, an assessmentof our own using the pubo-coccygeal line in con-junction with the distance of gas from the analmarker and the presence of gas in the genito-urinary tract. On these three premises it was thoughtthat a perineal or abdomino-perineal surgicalapproach could be suggested. Our suggested surgi-

cal approach was then compared with that actuallyused. The anatomical findings at operation or post-mortem were also recorded.ResultsFrom 18 cases reviewed, five were excluded fromthe final correlation for lack of precise information.

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FIG. 9. Gas in bladder. Low surgical approach. ? Fistula pres ent.FIG. 10. Antero-posterior view of gas in bladder.

FIG. 11. Cloaca formation. Gas in uterus and Fallopian tubes.FIG. 12. Antero-posterior view of cloaca.

FIG. 13. High lesion. Gas in bladder. Wide fistula to posterior urethra.FIG. 14. Sacral anomaly. Rectal atresia and fistula.

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Of the remaining 13 cases, seven were high lesionsan d six were low lesions.Using the pubo-coccygeal line as the sole indi-cation, the level was correct in nine and incorrect infour cases. Using our assessment with the additionalfactors taken into account, the level was correct inten instances of the 13 considered.The cases in which radiological errors arose ascompared with the surgical findings were reviewed.The first case indicated a low lesion radiologically,but an abdomino-perineal approach was used (Fig.8). The rectum was brought through levator ani andby dissection a small recto-prostatic urethral fistulafound.The second case showed gas on the pubo-coccygeal line and at a distance of 2-2 cm from theanal marker. A high lesion was diagnosed. A lowrecto-perineal fistula, evident at clinical examina-tion, was present and a perineal approach made.Th e third case indicated a high lesion and gas waspresent in the bladder, though not appreciated at thetime of examination of the films (Figs. 9 and 10). Ananal skin flap was remov ed u sing a low approac h. Anabdomino-perineal approach should have beenundertaken since the high level of bowel and thepresence of gas in the bladder pointed to a highlesion with fistula formation.Gas was present in the genito-urinary tract infive cases, though a total of eight fistulae weredemonstrated. In one case, gas was present in thebladder with a recto-urethral fistula, whilst in twoother such fistulae, no gas could be demonstrated.In one child there was a persistent cloaca withgrossly distended bilobed uterus and Fallopiantubes (Figs. 11 and 12). The gas shadows in cloacaand Fallopian tubes are characteristic.Anomalies such as oesophageal atresia, congenitalpyloric stenosis, hyaline membrane disease andrenal disease were present in nine of the 18 cases.They were occasionally the governing factor in thetype of operation performed, e.g. warranting only agastrostomy or colostomy.

DISCUSSIONWhilst the relation of the distal pouch to the pubo-coccygeal line indicates correctly the type of lesionin the majority of cases, it is not infallible. In onechild in this series, gas below this line was asso-ciated with a high lesion with a recto-urethralfistula.Conversely, gas above the line does not exclude alow lesion. The reasons for this may be:(i) insufficient time to allow gas to reach the distalpouch;(ii) a meconium plug in the distal pouch;

(iii) internal rectal sphincters not relaxed at thetime of X-ray examinations,(iv) difficulty in defining bony end points, especiallywhen there are sacral anomalies;(v) distortion due to radiological magnification.Other authors (Winslow, Litt and Altman, 1961)have found that similar errors in interpretationcould arise from these factors. Gas in the genito-urinary tract is a valuable sign as it indicates a fistulawith a high lesion and an abdomino-perineal opera-tive approach would be indicated (Fig. 9). Occas-ionally difficulty may be experienced in determiningwhether gas lies in bowel or bladder. The posteriorborder of the rectum lies in relation to the anterioraspect of the sacrum, whilst the bladder lies anter-iorly, behind and above the pubic bones (Fig. 13).The use of the Ladd and Gross (1934) method of

measurement from anal marker to bowel gave afallacious indication of the level of the lesion in twoof 13 cases. In these, high lesions were indicated, asthe gas shadows were over 2 cm from the anal marker,when low lesions were in fact present. The samepoints hold as above when gas fails to outline thedistal pouch of bowel.The presence of sacral anomalies is of importanceas severe sacral agenesis deprives the bladder andlower rectum of its full sensory supply and is asso-ciated with a poorly developed pelvic floor (Fig. 14).CONCLUSION

It is felt that a relatively firm indication of thelevel of an ano-rectal anomaly can be given in themajority of cases, bearing in mind the possiblecauses of error and the precautions which can betaken to minimise these errors. The presence of gasin the genito-urinary tract is a valuable adjunct inthe diagnosis of internal fistulae and in placing thedefect at its proper level.ACKNOWLEDGMENTSWe acknowledge gratefully the generosity of the Sur-geons-in-charge at the Royal Hospital for Sick Children,Edinburgh, for allowing us to refer to and extract informa-tion from the operative notes of the cases reviewed. Weshould like to acknowledge also the assistance of the radio-graphers at the above hospital and Miss H. Garvie and MissP. Hoban for their assistance with the manuscript.

REFERENCESBROWNE, D., 1955, Arch. D is. Child., 30, 42.KIESEWETTER, W. B ., and TURNER, C. R., 1963, Ann. Surg.,158, 498.LADD, W. E., and GROSS, R. E., 1934, Amer. J. Surg., 23,167.SCOTT, J. E. S., and SWENSON, O., 1959, Ann. Surg., 150,477.STEPHENS, F. D., 1953, Aust. N. Z.J. Surg., 22, 161.WANGENSTEEN, O. H., and RICE, C. O., 1930, Ann. Surg.,92 , 77.WINSLOW, O., LITT, R., and ALTMAN, D., 1961, Amer. J.Roentgenol., 85 , 719.448