13 Rectal Duplication and Anal Canal Duplication Devendra K. Gupta and Shilpa Sharma

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13.1 Rectal Duplication

13.1.1 Introduction

Alimentary tract duplications are rare congenital malformations. They can occur at any level of the gastro- intestinal tract, although the majority is found in the ileum. Rectal duplications form only 5% of alimentary tract duplications, with less than 100 cases reported in the English literature up to the present date.

The first case of rectal duplication was described in 1885 [1]. Since then, a confusing and varied termi- nology has been used to represent rectal duplication, including enterocystoma of the rectum, enterogenous cyst of the rectum, tail gut cyst, precoccygeal cyst, rectal cyst, and cystic hamartoma [2]. The majority of rectal duplications are located in the retrorectal space as a cystic mass, which is both diagnostically and therapeutically challenging to the surgeon because of their rarity and polymorphic anatomic-clinical presentation. In a national survey from various teaching centers in India, only anecdotal case reports on rectal

Contents

13.1 Rectal Duplication . . . 231 13.1.1 Introduction . . . 231 13.1.2 Pathology . . . 231 13.1.3 Embryogenesis . . . 231 13.1.4 Classification . . . 232 13.1.5 Clinical Features . . . 232 13.1.6 Differential Diagnosis . . . 233 13.1.7 Investigations . . . 233 13.1.8 Treatment . . . 233 13.1.9 Summary . . . 234

13.2 Anal Canal Duplication . . . 234 13.2.1 Introduction . . . 234

13.2.2 Clinical Presentation . . . 234 13.2.3 Investigations . . . 235 13.2.4 Treatment . . . 235

13.2.5 Management of Associated Anomalies . . . 236 References . . . 237

duplication cyst were obtained. The authors have had personal experience of only four cases of rectal duplications, all of which presented in unique ways.

13.1.2 Pathology

The definition of rectal duplication relies on histologi- cal appearance and includes three essential criteria for alimentary tract duplications as defined by Ladd and Gross: (1) continuity or contiguity with the rectum, (2) the presence of smooth muscle tissue in two layers, and (3) a mucosal lining normally present in the gut of that region or even distantly in the alimentary tract [3]. Rarely, a cyst containing ectopic gastric mucosa or pancreatic tissue may be observed [4,5]. Lymphan- giomas and mesenteric cysts are not included in the definition because the wall of these lesions does not contain a muscular layer or intestinal mucosa.

13.1.3 Embryogenesis

Many hypotheses have been put forward to explain how alimentary duplications develop. Two of these are the Veeneklass theory and the Lewis–Thyng theory. The Veeneklass theory seems to be accepted by most authors for isolated duplications with no spinal involvement. According to Veeneklass, duplications result from a disorder during separation of the notochord due to defective adherence of the endoderm to the notochord [6]. Migration of cells during embryonic development and metaplasia of undifferentiated cells (totipotent cells) of the embryonic gut could explain the presence of heterotopic mucosa.

The Lewis–Thyng theory proposes that the embryogenesis of rectal duplication is attributed to

“pinching off” of diverticula present in the 20- to 30- mm (8- to 9-week) embryo [7]. This is in contrast to the process “caudal twinning” (caudal twinning theory), which occurs at the 10-mm embryonic stage and is associated with complicated hindgut twinning anomalies. By this mechanism it is possible that the

13 Rectal Duplication and Anal Canal Duplication

Devendra K. Gupta and Shilpa Sharma

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Devendra K. Gupta and Shilpa Sharma

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urothelial elements noted in these lesions are derived from cloacal tissues.

13.1.4 Classification

Rectal duplications can be anterior or more commonly posterior and these can be further classified as type I (cystic) and type II (tubular; Fig. 13.1). Type I is the most common anomaly reported. Based on their embryogenesis, rectal duplications are expected to appear posterior to the rectum. Anterior rectal duplications are very rare, with only few cases reported [4, 8–10]. Type II can be further divided into blind ending (A), communicating with the rectum (B), associated with a fistulous communication in the perineum (C), and multiple cysts(D). Type IIC should be differentiated from double ani, in which the anal sphincter is well formed and looks clinically like an additional anal opening rather than a fistulous tract. Most of the rectal duplications are thus cystic and in 90% of cases do not communicate with the rectum [11].

Fig. 13.1 Cystic and various types of tubular (A–D) rectal du- plication cysts

13.1.5 Clinical Features

Although a female:male ratio of 2–3:1 is reported in the literature [5], all the four cases in the author’s series were males. The presentation of a rectal duplication depends on the following factors: (1) the size and therefore the mass effect of the duplication, (2) the presence of a fistula, (3) infection in the duplication, (4) the presence of ectopic gastric mucosa with ulceration, and (5) malignant degeneration.

Rectal duplications are rarely symptomatic during the immediate neonatal period unless presenting as a rectal mass bulging outside the anal canal or a mucosal-lined fistulous tract opening in the midline posteriorly or, rarely, anteriorly [11–14]. Since the cyst expands slowly and is located in the retrorectal area, compression of the rectum and lower urinary tract may result. The lack of suspicion due to its rarity explains the diagnostic difficulties. The cystic rectal

duplication can be palpated on rectal examination as a smooth, firm mass that bulges into the rectal lumen from the sacral hollow.

As the duplication cyst slowly fills with the fluid, it enlarges causing local symptoms such as tenderness, low back pain, suprapubic pain, intestinal obstruction, dysuria, dystocia, or sciatic pain. Drainage of mucus or pus from the anus or from a perianal fistula is a frequent presenting sign. Fistulae are reported to occur in approximately 20% of cystic rectal duplications and involve the perianal skin posterior to the anus or the distal canal in the midline [15]. The fistula rate of 45% in one series was based on both clinical and pathological examination, suggesting that not all communications are clinically evident [5]. A characteristic finding is a cone-shaped dimple in the midline just posterior or anterior to the anal verge. It may rarely present as a perforated ulcer [16]. No case with communication to the urinary tract has been reported, although some patients presented with urinary tract symptoms due to compression by a large duplication. Many of these patients who were misdi- agnosed initially underwent drainage of an apparent perirectal abscess or marsupialization of a fistula-in- ano only to suffer multiple recurrences.

Patients may present with a nonspecific picture of gastroenteritis in a setting of failure to thrive and a past history of recurrent urinary tract infections. Ma- lignant degeneration in rectal duplications has also been reported in the adult age group; usually adenocarcinoma, rarely carcinoid [17,18].

The authors’ experience with the management of four rectal duplication cysts is as follows:

Case 1. A 9-month-old-male child was found to have three duplication cysts in the midline posterior to the rectum, during a posterior sagittal anorectoplasty (PSARP) procedure. The cysts were very small (0.5–1.0 cm), tubular, looked like segments of intestine, and were attached loosely to each other lon- gitudinally; however, they were not adherent to the rectum. The cysts were easily excised and the diagnosis established histopathology. Rectal duplication was not suspected preoperatively and it was only a chance finding during the surgery.

Case 2. A newborn male child presented with a defect in the perineum around the anus anteriorly. A tongue of the anal mucosa extended from the anal verge high up for about 3 cm. There was mucus discharge and the baby was incontinent. On examination, there was an incomplete tubular structure about 3 cm long situated in the midline just anterior to the anal verge. It was lined by mucosa that communi- cated freely with the rectum and the anal canal. The

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cyst was excised from the perineum and the defect repaired. The anal sphincter was reconstructed and the postoperative result was good, with development of full continence.

Case 3. A 6-month-old male baby presented with constipation and a cystic mass bulging from the anal verge. A computed tomography (CT) scan confirmed the presence of a fluid-filled mass located posterior to the rectum. It extended up for 5 cm from the anal verge. Needle aspiration of the cyst revealed fluid mixed with mucus. The cyst was located posteriorly but extended laterally more on the left side. The cyst and the rectum shared a common muscular wall that could be separated carefully. It was excised via a posterior sagittal route. The rectal wall was repaired and the postoperative result was excellent.

Case 4. A 12-year-old boy presented with perineal hypospadias and ARM. A fistulous opening was present in the perineum between the neoanus and the hy- pospadiac meatus. A fistulogram delineated a 4-cm- long tract anterior to the rectum ending in a blind tubular structure. An anorectoplasty was done and the hypospadias was repaired, separating the urethra from the fistulous tract and the anus, under cover of a colostomy. Excision of the rectal duplication cyst has been deferred for fear of injury to the posterior urethra and the possible risk of fecal incontinence re- sulting from the surgical intervention. The patient is under regular follow-up with the complaint of only an occasional mild discharge from the fistula.

Case 5. An 18-month-old male baby presented with acute urinary retention and constipation from the previous 6 months. On examination, the bladder was palpable. Per rectal examination revealed a retrorectal cystic mass. CT scan confirmed the findings of a retrorectal cystic mass (Fig. 13.2). Surgery via a posterior sagittal route revealed a common wall between the cyst and the rectum. The cyst could be separated carefully from the common muscular wall and was excised completely. The rectal wall was repaired. A covering colostomy was performed, which was closed after 2 months. A histopathological examination established the diagnosis.

13.1.6 Differential Diagnosis

The diagnosis of rectal duplications should be distin- guished from other lesions occurring in the retrorectal space including dermoid cysts, cystic endopelvic sacrococcygeal teratoma, hydrocolpos, hydrometro- colpos, hydrosalpinx, cystic neuroblastoma, or men- ingeal herniation (pre-sacral meningocele), sarcoma,

hamartomas, anal gland cysts, and retrorectal cysts lined with squamous epithelium.

13.1.7 Investigations

Modalities that allow diagnosis include abdominal x-ray, ultrasonography, CT, and magnetic resonance imaging (MRI). Cystography together with rectogra- phy may be helpful for visualizing a large, retrorectal mass leading to pelvic compression of the rectum and bladder. MRI is the most accurate preoperative inves- tigation for defining the localization, volume, and anatomic relationships of the duplicated rectal segment, with its multiplanar capabilities clearly ruling out a uterine source of pathology. Absence of involvement of the sacral vertebrae (erosion, spina bifida, scimitar sacrum) and fat component would rule out anterior meningocele, lipomeningocele, and teratomas. Cor- domas usually present at around puberty.

13.1.8 Treatment

Once diagnosed, the treatment of rectal duplication cysts is surgical. Total removal of the lesion is the rule so as to avoid peptic, septic, and carcinogenic complications. Rarely, only the mucosal lining need be extirpated if the duplication cyst and the normal rectum share a common muscularis layer. The surgical procedure should not be more radical than necessary to eliminate the patient’s complaints and prevent further recurrence [19]. While resecting a rectal duplication, care should be observed as the lesions may

Fig. 13.2 Computed tomography scan showing a fluid-filled retrorectal cyst suggestive of rectal duplication (photograph and case 5 details, courtesy of Dr. Shivkumar, Trivandrum, In- dia)

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be multilocular or have diverticula extending laterally or cephalad. Complete excision of at least all of the lining mucosa should be performed. Infected duplications may require initial drainage followed by a staged resection.

There are several surgical approaches, the decision being based primarily on the location of the duplication. A posterior sagittal approach is now the preferred approach for most of these since it allows good access for complete surgical removal. Large cysts may require a combined approach (abdominal with posterior sagittal or perineal approach). An abdominal approach is preferred for the high, anteriorly located and long tubular duplication cysts.

1. Marsupialization is only indicated in cases with infection, to allow resolution of the sepsis before complete resection of the duplication can be performed.

2. For transanal excision, the anus is dilated and re- tracted causing the lesion to bulge forward, an incision of the rectal mucosa with subsequent strip- ping of the mucosal lining of the duplication cyst may then be accomplished by keeping the dissec- tion in the submucosal plane.

3. For the transcoccygeal or Kraske approach, a transverse incision is made posterior to the anus (similar to the Kraske approach to low rectal tu- mors). It may be necessary to remove the coccyx.

Cyst excision using a transcoccygeal route was common prior to the development of the PSARP approach; it is not popular these days.

4. The posterior sagittal approach with or without an additional abdominal/perineal approach is now the preferred approach. It provides better access and is similar to Peña’s approach for ARM. This approach is also useful for other types of retrorectal masses.

The rectum may be dissected from the muscles and lifted off or bisected to reach the lesion. This approach can be combined with an abdominal approach to remove long and large cysts that are not attainable by the posterior sagittal route. The additional abdominal and/or perineal approach is required in cases where the lesion is large, if it is in association with genitourinary malformations and ARM, and if there is extension of the cyst into the abdomen, especially in anterior duplication cysts [20].

13.1.9 Summary

Rectal duplications are rare anomalies that present in a variable fashion. A suspicion of such an anom-

aly helps in investigative planning. A cyst of variable shape and often distended with mucus, lying in the presacral space, forms the diagnosis. These need to be differentiated from other types of anorectal pathology. A single-stage excision of the cyst, usually by the transanal, perineal, or posterior sagittal route is curative in most cases. However, associated ARM and severe hypospadias with perineal duplication cysts, may require complex surgical procedures (involving repair of hypospadias, anorectum, and excision of the cyst) under a covering colostomy to achieve a suc- cessful repair.

13.2 Anal Canal Duplication

13.2.1 Introduction

Anal canal duplication can be an isolated anorectal pathology or a part of caudal twinning syndrome that is characterized by the presence of twinning of the hindgut derivatives, giving rise to doubling of its derivatives, namely the colon, rectum, bladder, urethra, genital organs, and kidney. It usually occurs in association with colonic duplication. Cases of isolated colonic duplication without involving the anal canal have been excluded in this chapter.

13.2.2 Clinical Presentation

After an extensive review of the previously reported cases, three anatomical patterns of anal canal duplications have been seen (Fig. 13.3 A–C).

1. Two separate perineal openings externally giving rise to double perineal ani, occurring in association with colonic duplication.

2. Colonic duplication with one normal and one imperforate anus terminating with or without a fistula to the genitourinary tract.

3. Colonic duplication with both imperforate ani terminating with or without a fistula to the genitourinary tract.

Fig. 13.3 Types of duplication of the anal canal

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Double perineal ani is extremely rare and only a few cases with true double anal openings in the perineum have been reported in the world literature.

There could even be a triplication of the colon, with or without any normal opening in the perineum. In case of double ani, these may lie on either side of the midline with the external corresponding genitalia, or may be located along the anteroposterior axis in the midline. One of them is, however, better developed than the other. The sites of the ani were initially reported to be seen more commonly on either side of the midline [21]. However, recent reports have found the openings to be anteroposterior in location [22]. The two ani may be separated only by a thin septum or may lie wide apart from each other for about 1.5 cm [21].

Each anal canal passes through the sphincter complex separately. Each is lined by normal anal canal lining epithelium (Fig. 13.4).

Double ani in association with colonic duplications are usually tubular. Of the 32 cases reported in the literature up till 1988, only two cases had communications at the lower end, starting from the rectum to the anal verge. The remaining cases all had proxi- mal communications in the region of colon, cecum, or even in the ileum [21].

Over 90% of cases are females, with the female:

male ratio being 9:1 [21,22]. The anomaly is apparent in the newborn; however, its detection may be delayed if the additional colon is ending blindly in

the perineum without external evidence. The age range in this group is from 1 to 24 months. Even the patients with perineal communications remain as- ymptomatic but may present with mucus discharge, infection, diarrhea, ulceration, and bleeding due to the presence of gastric heterotopy. Malignancy is rare but has been reported in adults. Both the ani function simultaneously and with normal continence as they pass through the puborectalis and levator ani muscle separately. However, the amount of fecal matter com- ing in each is variable.

13.2.3 Investigations

Investigations such as fistulogram, contrast enema, micturating cystourethrography (MCU), renogram, ultrasonography, and MRI, are performed to gain in- formation about the location and communication of the double ani with the genitourinary and intestinal tracts. It may sometimes be difficult to differentiate this anomaly from fistula-in-ano, which mimics this condition closely. The fistula-in-ano is also uncom- mon in the pediatric age group and, if present, would not open in the midline, unlike the double ani. Also, a solid mass would persist even after drainage, a characteristic that is not seen with a fistula.

Diagnosis of double ani is made histologically, showing a smooth muscle wall with gastrointesti- nal epithelial lining and the presence of anal glands.

Contrast studies performed through each anal orifice and the urogenital orifices show complete duplication of the rectum and colon as far as the ascending colon. Two separate bladders, vaginas and uteri may be seen.

13.2.4 Treatment

Treatment for patients with double ani remains con- troversial and involves many considerations. In the present scenario, the decision would be in favor of surgery to provide the patient with as near a normal state of external genitalia and continence as possible, excising the unwanted component of the duplicated colon. In the past it was felt that if the second anus was not embarrassing to the patient it could be left untouched [21]. Also, if there is no neurogenic bladder or bowel problem (as with associated spina bifida), a good continence and a normal function can be expected through both the ani and the urethrae.

The levator and sphincter muscles, being mesodermal structures, are not related to hindgut development,

Fig. 13.4 Double ani. The normal-located anus and the ectopi- cally placed anus; both have independent anal sphincters (photograph courtesy of Professor Tahmina Banu, Bangladesh)

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and are thus single structures (except if the spine and sacrum are also duplicated).

The main reason for the excision of the extra anus is cosmetic and prevention of malignancy in the re- dundant rectal pouch in cases in whom the colon needs to be excised due to obstructive symptoms in the duplicated colon. Alternatively, the mucosa of the rectal stump may be evaginated to achieve its non- function.

The thin septum between the ani can be resected, or the distal continuity with the colon can be excised and made into a single channel if obstructive symptoms arise, using a combined abdominal and PSARP approach.

The colonic duplications that are associated with duplication of the genitalia are usually not fused and have a separate blood supply, so that resection of one colon from the other is usually possible [23]. Genital reconstruction is also performed only for cosmetic reasons. In females, construction of a single vulva provides a desirable external appearance in which the two urethrae and two vaginae open unimpeded [21].

Simultaneous continent streams prove no disadvan- tage if covered with a single vulva. Urethral removal or closure may only be required if its presence interferes with vulval reconstruction. Vaginal duplication does not interfere with menstruation, coitus, or parturition, unless there is stenosis. Fertility has been reported in patients with double ani and double vaginae.

Most cases reported in the earlier literature had a very high mortality that was mostly due to severe associated anomalies and because of obstruction to one or both of the coli. However, with modern amenities available, the patient should have as near a normal perineum as possible, passing stool and urine at will through single orifices.

In cases of colonic duplication with one normal anus and one imperforate anus, the imperforate anus may or may not terminate as a fistulous communication into the genital, urinary tract, rectum, or perineum. The appearance of the external genitalia is highly variable in this group. Most cases have nondu- plicated external genitalia.

These patients present early because of complications of intestinal obstruction and sepsis. None reach adult age without surgery. If left untreated, the patients die of intestinal obstruction [21]. From the data available in the literature, patients in this group with one normal anus and one imperforate anus without a fistula had the worst outcome.

It has been observed that when the external genitalia are single, the double colons tend to be intimately fused, so that colonic resection of both coli together

is necessary [23]. Treatment consists of anastomosis of the two coli together so that the fecal matter goes through the main anal canal, and the fistulous con- nection is excised.

Colonic duplication/triplication with two or more imperforate ani terminating with or without a fistula to the genitourinary tract present in early infancy due to colonic obstruction [24]. External genital anomalies are rare in these patients, but varying degrees of associated internal genitourinary anomalies requir- ing treatment are present. The treatment options for these patients are: colostomy followed by definitive repair later, total colectomy, and ileoanal anastomosis.

13.2.5 Management of Associated Anomalies

Associated anomalies occur frequently and are seen in 20–40% of cases and include cleft lip and palate, cardiac anomalies, malrotation, lumbosacral dysgen- esis, renal anomalies, omphalocele, meningomyelo- cele, and early cranial fusions [21–23, 25–27]. The most common associated anomaly is spina bifida.

External genitalia in association with anal duplication may have a varied presentation – double external and internal genitalia, double genitourinary tract.

The urethral duplications may be complete or incomplete. In complete duplications the patient may void with a double stream. Epispadiac duplications are usually associated with significant dorsal curva- ture of the penis. The most common type of urethral duplication is the Y-type, where the duplication arises from the prostatic urethra and the main urethra opens at the anal verge, through which most of the urine passes. The other urethra is very narrow and dysplastic and can not serve the purpose for micturition. There is also a spindle duplication, where the duplication arises from the prostatic urethra and re- joins the urethra at some point along the shaft of the penis.

Most urethral duplications present with a double stream or a leak from the second orifice. Diagnosis is by MCU and panendoscopy, although it is often difficult to catheterize either of the two urethrae. No spe- cific treatment will be required if both the urethrae are normal in caliber and serve their purpose well.

However, as the ventral component is the normal urethra in almost all cases, and opens in the perineum just anterior to the anus, the urethral reconstruction is really technically demanding and requires staged procedures, even under the cover of a colostomy in

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most cases. Still, the neourethra is not only very long, but is also without any urethral resistance (due to absence of corpus spongiosum), and micturition often remains ineffective.

Associated diphallia may occur as a simple bifid glans, a bifid penile shaft with distal duplication, or total penile duplication. The two organs may lie from side to side. The minor anomaly may not require any intervention; however, an ectopic phallus may be excised if the functional result is not affected. Before reconstruction, the genitourinary system should be evaluated fully with MCU and cystoscopy, as each penis may have a functioning urethra draining the bladder. The decision as to which of the organs is retained is a pragmatic one.

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