Type V Congenital Pouch Colon: An Extremely Rare Variant of Anorectal Malformations.

Type V is the rarest form of congenital pouch colon with only four cases reported till date. We report this anomaly in a 6-month-old boy. He was managed successfully with excision of distal pouch and coloplasty of proximal pouch along with abdominoperineal posterior sagittal anorectoplasty. We recommend preservation of proximal pouch in such cases.

Introduction

Congenital pouch colon (CPC) is a rare regional variant of Anorectal malformation comprising 2%–9% of cases.[1] The most commonly accepted Narasimharao's classification divides this entity into four subtypes based on the length of normal colon proximal to the colonic pouch.[2] Recently, Saxena and Mathur classified CPC-based on the anatomic morphology of the pouch, adding a Type V variant, i.e., a double pouch colon with a short normal colonic segment interposition between the two pouches.[3] Only four cases of this clinical entity have been reported till date.[3456] We describe a similar case of Type V CPC and recommend preservation of proximal pouch for a tabularizing coloplasty in such cases.

Case Report

A 6-month-old boy was transferred to our hospital as a case of CPC with a window colostomy in situ done at another hospital on day two of life. He was the first child born from a nonconsanguineous marriage by spontaneous vaginal delivery at full term. Plain X-ray abdomen done after birth showed feature of CPC. Renal ultrasonography and echocardiography detected no other abnormality. The window colostomy was fashioned in the left lower abdomen. The patient was explored for the definitive abdominoperineal procedure. At exploration, a Type V CPC was found [Figure 1a]. The ileum was opening directly into a hugely distended dumbbell shaped pouch with normal looking intervening colon of six centimeters. The stoma was fashioned in the distal pouch [Figure 1b]. The distal pouch was opening into the bladder neck through a wide fistula. There was no appendix. The distal pouch was excised as it was hugely dilated and the tubularizing coloplasty done using the proximal pouch was of acceptable length [Figure 1c and d]. This tube was pulled through the abdominoperineal route and was placed within the muscle complex which was fairly well developed. The repair was protected by a diverting proximal ileostomy that was closed after 8 weeks. To begin with the child had problems of stool frequency and perineal excoriations for about 6 months. Gradually, his condition improved and now at the age of 21 months, he has a stool frequency of three to four times a day. The stool consistency has also improved with decreased excoriations.

Figure 1

(a) Intraoperative photograph showing a double pouch colon with interposed normal colon, (b) Window colostomy site and urinary fistula site, (c and d) tubularization of proximal colon

Discussion

First reported by Chadha et al. and classified separately by Saxena and Mathur, only four cases of Type V CPC have been described till date.[3456] The anomaly consists of two colonic pouches with an intervening normal colon. The proximal pouch is akin to a segmental dilatation of colon (SDC), while the distal pouch is a CPC. In all the reported cases, the ileum opens into the proximal pouch, with the interposing normal colonic segment length varying from 2 to 7 cm.[3456] In all, but one case report, there was an absence of appendix.[4] The exact embryological cause for this defect is not known but has been attributed to vascular insult to the inferior mesenteric artery and ileocecal branch of the superior mesenteric artery with a normal middle colic branch of a superior mesenteric artery supplying the normal interposing segment.[3] As per the vascular hypothesis of Earlam, the fate of the developing bowel depends on the severity and duration of the vascular insult.[7] Atresia (with or without a band), stenosis are the result of a severe prolonged injury whereas mild injuries result in an aganglionic bowel. However, one is not able to explain the simultaneous occurrence of SDC and CPC with an intervening normal segment on the basis of vascular theory alone. A defective organogenesis rather than a vascular insult may be responsible for this anomaly.

In two cases, the distal pouch was excised due to massive dilatation and in one case due to gangrenous changes presumably secondary to dilatation.[568] In our case also, the distal pouch was massively dilated. Preservation of proximal pouch along with the interposing normal colon, a subsequent tapering coloplasty, and an abdominoperineal pull through with an ileostomy cover was done in two cases, whereas both the pouches were excised by one author.[458] This may depend on which school of thought one belongs to as far as management of pouch in CPC is concerned. We excised the distal pouch since it was hugely dilated and an appropriate length (including the normal interposing colon) was available after the tapering coloplasty of proximal pouch. It seems prudent that in cases of Type V pouch colon, the proximal pouch should always be preserved since there is always some length of interposing normal colon distal to this pouch. The proximal pouch, which is an SDC, has been reported to return to a normal caliber following ostomy of the normal interposing colon.[6] Moreover, segmental dilatation of near total colon has been managed by tubularizing coloplasty and postoperative barium enema done at 6 months showed normal caliber colon. In addition, there was no constipation at 1-year follow-up.[9] In these cases, one should start tabularizing the proximal pouch first. If the total length obtained by the coloplasty of the proximal pouch plus the intervening normal colon is sufficient for pull through, the distal pouch can be excised. Otherwise, the surgeon can use the distal pouch to gain length if he believes in pouch preservation.

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Conflicts of interest

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