Br. J. Surg. Voi. 64 (1977) 525-528

Congenital anal duplication : a cause of para-anal sinus R . E. B. T A G A R T ” SUMMARY

Four cases of recurringpara-anal sinus originating, it is suggested, as congenital duplication of the anal canal, are described. The diagnosis depends upon the finding of columnar mucus-secreting epithelium in a sinus track which does not communicate with the bowel lumen. The sinus may or may not penetrate the levator ani muscle. Treatment should be by excision of the sinus, rather than by laying it open into the anal canal. If the sinus is superficial, the latter operation will result only in delayed healing and prolonged convalescence, but if it runs deep, there is a danger of causing incontinence or an extra-sphincteric fistula. Untreated lesions may eventually be the site of malignant change. This complication was not encountered in the present series.

THATanal infection should occur is not surprising since the locality teems with potentially pathogenic organisms. What is less easy to explain’isthe fact that an anal abscess, even after surgical drainage which, by ordinary standards, was adequate, is sometimes followed by the formation of a chronic fistula or para-anal sinus. Foreign bodies, peritoneal infection which tracks down through the levator ani muscles and specific conditions such as Crohn’s disease are primary causes. The successful treatment of these conditions will result in cure of the anal infection and they are not considered in this paper. Parks (1961) came to the conclusion that in 7-9 fistulas out of 10, the infection originated in the plane between the internal and external sphincters of the anus and that it reached this plane by way of the anal gland ducts which lie between the two muscle layers. These ducts penetrate the internal sphincter to open into the anal canal. Later, Parks et al. (1976) described in considerable detail the various ways in which infection may spread into and around the anus and lower rectum. They implied that infection in an anal gland is still the most common initiating cause. Goligher et al. (1967) were not wholly convinced on the latter point. They found that in 29 cases of anal abscess there was connection with a crypt (the normal level at which the duct of an anal gland opens into the anal canal) in only 5, while dissection of 34 cases of anal fistula disclosed the presence of an abscess in the intersphincteric plane in only 9. There seems, therefore, to be room for more speculation about the origin of anal infections, and the following case reports suggest a cause which may not be rare, since the patients presented within 1 year to a general surgical practice only partly orientated towards proctology. The condition has been described but the pathology is not, perhaps, as well known as it might be. Knowledge of the pathology provides a logical basis for simple, quick and effective treatment. Case reports Case 1:A housewife, aged 35 years, presented with a history of a recurrent chronic sinus to the right of the anus which had

been present since the drainage of a ‘gluteal abscess’ when she was 8 years old. By the time she was seen in early July 1974, pus was discharging from the sinus at approximately 2-weekly intervals. At operation a ‘collar stud‘ abscess was found. Part of the wall of the abscess was excised. No communication with the rectum or the anal canal was found. Four days later more of the ‘abscesscapsule’ was excised. Failure of the sinus to heal prompted further surgical exploration on two occasions in January 1975. She was then referred to the author. The sinus was 9cm deep. A barium enema examination showed no abnormality. A sinugram (Fig. 1) showed a deep cavity. Operation in May 1975 revealed what appeared to be a squamous-lined cavity of an estimated diameter of 5 cm. This cavity lay above the levator ani muscle and to the right of, and behind, the rectum. No communication with the anal canal or rectum was found. As much as possible of its wall, which lay in very close contact with the rectum, was excised, and the wound was left open to heal by second intention. By November 1975 the skin was completely healed. Pathology report (J. H. Dean) : Microscopic examination showed anal epithelium with underlying fat, connective tissue and smooth and striated muscle, in which there were a number Of small cysts. These were lined by a complex epithelium, partly columnar mucus-secreting and containing some goblet cells and partly stratified squamous. The contents were largely of much with some squamous cells and polymorphonuclear leucocytes. As the columnar epithelial components were clearly not of accessory skin, they must, in this situation, have derived from colonic epithelial elements. Also, below the surface anal epithelium were a number of epithelial clefts, mainly lined by squamous epithelium, but including some columnar epithelium. Case 2 : Amale sales representative,aged45 years, presented with a 5-year history of recurrent inflammation on the right side of the anus. On examination the opening of a sinus was found about 2 cm from the right side of the anal orifice. Exploration under anaesthesia revealed that it was 3 cm deep and that the track inclined medially towards the anal canal, which, however, it did not approach closely. The track was steadied with a probe and excised completely. The wound was left open and was healed in 3 months. Pathology report (J. H. Deun) : Macroscopic examination showed an elongated piece of fibrofatty tissue (3 cm longx 0.8 cm in diameter) containing a fistulous track for half its length. Microscopic examination revealed fibromuscular tissue with a central fistulous track lined by chronic purulent inflammatory granulation tissue, which at one level in addition had a layer of mucus-secreting columnar epithelium. Elsewhere there were bundles of smooth muscle cut transversely and at one level a well-formed lymphoid follicle was present. The presence of mucus-secreting columnar epithelium in this specimen clearly pointed to a colonic origin, and this was supported by the accompaniment of rudimentary smooth muscle bundles and a lymphoid follicle. Stratified columnar epithelium was also present (Fig. 2). A few fields away and in continuity was mucosa of typical colonic type (Fig. 3). It therefore seemed a possibility that the surgical specimen under discussion represented a developmental abnormality. Case 3 :A male infant aged 11 months presentedwith a history of recurring right-sided anal infection. He was also known to have a small ventricular septal defect in the heart. On examination a sinus opening was found to the right of the anus and an indurated track could be felt leading medially towards the anus (Fig. 4). Examination under anaesthesia revealed that the sinus penetrated the levator ani muscle. It did not approach the

* Newmarket and West Suffolk Hospitals.

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Fig. 1. Case 1. Sinugram showing a large pararectal cavity.

Fig. 4. Case 3. Sinus opening to the right of the anus.

Fig. 2. Case 2. Cleft lined by stratified cubical and columnar cells and containing pus. (HE. x 260.)

Fig. 5. Case 3. Mucus-secreting stratified columnar epithelium from a para-anal sinus. (HE. x 112.)

Fig. 3. Case 2. Mucus-secreting columnar epithelium in a para-anal sinus. Much appears black. ( x 233.)

rectal wall at all closely. The sinus was completely excised and the wound left open. It was completely healed in 3 weeks. Pathology report (J. H . Dean): Skin with underlying fat, smooth and striated muscle was seen. Transverse sections revealed the superficial part of the sinus to be lined by cbronic purulent inflammatory granulation and at a deeper level by rather distorted squamous epithelium. At the deepest level was a small cleft. The last was lined by complex epithelium predominantly and, next to the lumen, by stratiEed mucus-secreting columnar epthelium (Fig. 5). Deep to the surface layer the epithelium was stratilied and thought to be squamous. Case 4: A 38-year-old male sales representative presented with a 2-year history of recurring anal pain. For 3 months there had

Congenital anal duplication been intermittent swelling and discharge from the left of the anus. On examination there was a scar to the right of the anus. A sinus opening was present 3 cm from the anus in the left anterior quadrant. An indurated track led from the opening towards the anus. Proctoscopy and sigmoidoscopy to 20 cm were normal. At operation the sinus was excised; it went very close to the anal mucous membrane but did not penetrate it, neither did it penetrate deep to the levator ani. The wound, which was deep and narrow, was packed to control bleeding. The pack was removed on the second day and replaced by a flat dressing. With this dressing and daily baths the wound was healed in 3 weeks. Pathology reporf (J. H. Dean): Macroscopic examination showed a portion of fatty tissue (3.5 cm long x up to 0.9 cm in diameter). Within the structure was a dark, central, clearly defined area (0.2 cm in diameter). Microscopic examination revealed that in the majority of the levels of section the sinus was lined by chronic purulent inflammatory granulation tissue, but at 3 of the 11 levels there was a lining, or partial lining, of tall columnar mucus-secreting epithelium. Also at these levels externally there was a significant striated muscle componentpresumably implying a relationship of the sinus with the levator ani or external anal sphincter.

Discussion These reports are, it is suggested, of congenital duplication of the anal canal, a condition quite distinct from anal gland infection. Dukes and Galvin (1956) reported 10 cases, in 8 of which malignant change had occurred. They set out clearly their reasons for identifying the lesion. They considered the possibility that these tracks might arise from the anal intermuscular glands, but rejected it because of the very different nature of the cells of the lining epithelium. Certainly, in the cases reported here, although the sinus tracks in some ran very close to the anal epithelium, they did so at a level well above that at which the anal glands are known to lie. There is usually, but not always, a long history or the condition manifests itself early in life. The other feature essential for the diagnosis is the presence of columnar mucus-secreting epithelium in tracks which do not communicate with the anal or rectal lumen. The other epithelial tissues which line the anal canal are squamous and stratified columnar epithelium. It could be argued that squamous epithelium in a paraanal sinus is present as a result of growth inward from the skin opening, but such an argument does not hold good in the case of columnar mucussecreting epithelium. That these duplications do not usually appear to communicate with the upper anal canal or rectum at the deep end is fortunate, because if they did, extrasphincteric fistula (Parks et al., 1976), a very serious clinical problem, would not be as rare as it is. It is important that the condition be recognized for what it is and that injudicious or overvigorous probing, resulting in the creation of a fistula where none previously existed, be avoided. If the sinus does not penetrate beyond the level of the upper anal canal, this mistake will result merely in delayed healing and unnecessarily prolonged morbidity. If, however, a false passage is made into the rectum, a nearincurable extra-sphincteric fistula may be created. The tendency for all tracks near the anus to be called fistulas sometimes leads surgeons to convert a sinus into a fistula in order to carry out the standard treatment of laying open the latter into the anal canal. Avoidance of semantic confusion shouId reduce the occurrence of this error.

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Table 1: CLINICAL. FEATURES OF PARA-ANAL SINUS DUE TO ANAL DUPLICATION Relationship Healing Length to time Case of anal canal Depth of after No. Sex Age history or rectum sinus excision 1 F 35yr 27 yr Very close Penetrated 6111th levator ani 5 yr Not close Superficialto 3 mth 2 M 45 yr levator ani M 11 mth Short Not close Penetrated 3 wk 3 levator ani 4 M 38 yr 2 yr Very close Superficialto 3 wk levator ani

Table Z summarizes the clinical features and operative findings in the cases reported here. Other possible cases were encountered in the period under review. In one, a male in his thirties, the sinus track was laid open into the anal canal after it had inadvertently been converted into a fistula by injudicious probing. Fortunately, the false passage was low in the anal canal and, although healing took longer than necessary, there was no impairment of continence. In another, a child of 7 years, recurrent abscesses in the right buttock and a persistent discharge did not cease until the sinus track had been completely excised. Unfortunately, a detailed microscopic examination of the removed tissue was not made. Other sinuses which were excised and did not contain columnar epithelium showed either a foreign body type of reaction or simply non-specific inflammatory changes.

Treatment Complete cure of the lesion is necessary both to relieve symptoms and to forestall the eventual probability of malignant change. If the condition first presents as an anal abscess, the cavity should be drained by simple laying open at a first operation. A sinus, when encountered either at the first consultation or as a sequel to the drainage of an abscess, should be carefully excised in order to eradicate completely mucus-secreting epithelium, the persistent presence of which will result in recurrence. The track is first carefully probed, along the line of induration leading towards the anus, in order to exclude the possibility of its being a fistula. If a fistula is found, it is laid open into the anal canal in the usual manner. Once the absence of an internal opening has been established, the probe is left in position and steadied by an assistant. After the skin opening has been excised by knife dissection, scissor dissection into the ischiorectal fossa is started. It is essential that a finger of the free hand is kept in the anal canal so that perforation of the anal or rectal mucous membrane is avoided. The operation may be simple or it may be made very difficult by postinflammatory fibrosis or by the track running very close to the anal or rectal mucous membrane. The excision wound, which may be narrow and deep, is packed, if necessary, to control haemorrhage. The pack is removed and replaced by a flat surface dressing on the second or third postoperative day and the wound left open to heal by second intention. In most cases this takes only 2 or 3 weeks but dense fibrosis due to repeated infection or previous operations may prolong the healing time.

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Conclusion The case for anal gland infection being the most common cause of chronic anal fistula is strong. However, anal abscess probably has other causes, direct infection of excoriated anal skin and infection of an anal haematoma being among these. Abscesses which recur or are followed by the formation of a chronic sinus may well have the aetiology described here. Acknowledgements I am indebted not only to Dr J. H. Dean of Newmarket and Addenbrooke’s Hospitals for the pathology reports, but also

to Mr Peter Haslam of the John Bonnett Laboratories, Addenbrooke’s Hospital, for the photomicrographs.

References c. E. and GALVIN c. (1956) Colloid carcinoma arising within fistulae in the ano-rectal region. Ann. R . Coll. Surg. Engl. 18,246-261. COLIGHER J. c. (1967) Surgery vf the Anus, Rectum and Colon. London, BalliBre, Tindall & Cassell. PARKS A. G. (1961) Pathogenesis and treatment of fistula-in-ano. Br. Med. J . 1, 463469. PARKS A. G . , GORDON P. H. and HARDCASTLE J. D. (1976) A classification of fistula-in-ano. Br. J . Surg. 63, 1-12. DUKES

Congenital anal duplication: a cause of para-anal sinus.

Br. J. Surg. Voi. 64 (1977) 525-528 Congenital anal duplication : a cause of para-anal sinus R . E. B. T A G A R T ” SUMMARY Four cases of recurring...
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