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Anorectal Abscess (Crypto- glandular Disease)

Dr.Barin Bose.
Email : askbarin@rediffmail.com
Jabalpur (M.P)


Cellulitis leading to abscess formation is relatively common in the tissues surrounding the anal canal and lower rectum. Anorectal abscess or Crypto - Glandular disease because infection of the anal crypts followed by infection of the anal glands leads to the abscess formation . Cryptogandular disease in acute stage presents as anorectal abscess while in chronic sages it presents as fistula in ano. According to Ellis in 1958, it is usually due to Staphylococci, Streptococci, Ecoli or Proteus. Now a days it was shown that anaerobes such as clostridium welchii and bacteroides are frequently responsible for these abscess. Sometimes tubercle bacillus is found but in association with a mixed pyogenic infection. Whitehead in 1982 shown that gut specific organisms particularly bacteroides were found more frequently in abscess which had an obvious fistulous connection with the anal canal than in those unassociated with a fistula. He believe that the isolation of gut specific organisms from the pus evacuated from a perianal abscess should suggest that a fistula may be present and lead to a careful review of the case from that point of view.

Grace had suggested that cutaneous organisms such as S.aureus were isolated from nonfistulous perirectal abscess and their presence could be regarded as an help in exclusion of the existence of fistula. Whitehead found that cutaneous organism were found with equal frequency in fistulous and nonfistulous abscesses, he disregarded the diagnostic value of such organisms in this matter.

Surgical Anatomy of Anal Canal

This short passage though onty 3 cms long is of greatest surgical importance because of its role in the mechanism of rectal continence and because it is prone to certain diseases. The anatomical anal canal extends from the anal valve to the anal verge and is 2 cms in length . The surgical anal canal is 4 cms in length and extends from anorectal ring to the anal verge.In a normal living subjects the anal canal is completely collapsed due to the tonic contration of the anal sphincters. Posteriorly the anal canal is related to the coccyx with some amount of fibrous, fatty and muscular tissue intervening. Laterally there is the two ischiorectal fossas on either sides. Anteriorly in males lies the bulbous part of the urethra and posterior border of the urogenital diaphragm. In females the canal is related to the perineal body and lowest part of posterior vaginal wall.

The mucocutaneous lining of the anal canal - The lining of the anal canal consists of an upper mucosal and a lower cutaneous part the junction of the two part is marked by the lining of anal valves which is 2 cms from the anal verge. This line is also called as pectinate or dentate line because of the serrated fringe produced by the valves.The pectinate line marks the junction of postallantoic gut and the protodium. The valves themselves representing as the reminent of proctodeal membrane. Above each valve is a little pit or pocket known as anal sinus or crypt or sinus of Morgagni. These sinus may be of some surgical significance as some foreign body may lodge in them with resulting infection or trauma may be inflicted by hard stools. It was believed by Ball that anal fissure was due to tearing down of one of the anal valves , but this theory is no longer accepted.
Above the pectinate line the mucosa is thrown into 8 to 14 longitudinal folds known as Anal column of Morgagni. The two adjacent column being connected below at he pectinate line by anal valves.The mucosa immediately above the valve is lined by epithelium consists of layers of cuboidal cells . One cm below the pectinate line the anal canal is lined by a modified skin which is devoid of hairs, sebaceous and sweat glands and closely adherent to the underlying tissue (that is why the perianal abscesses in this region are very painful).Traced further inferiorly the lining becomes thicker and just outside the anal orifice acquires the hair follicles, glands and histological features of normal skin.
Anal intermuscular glands - There are apparently four to eight of these glands in the normal anal canal. Each has a direct opening into the apex of an anal crypt and occasionally two glands open into the same crypt. About half of the crypts have no gland communicating with them. Traced outwards from its cryptal opening,the gland has a short tubular portion in the submucosa which quickly branches into a racemose structure of widely ramifying ducts. Some glands remain confined entirely to the submucosa but two third of them, one or more branches entre the internal sphincter. One half of their branches crosses the sphincter completely to reach the intersphincteric longitudinal layer. The direction of the gland is outwards and downwards, but practically never upwards above the anal valve.

As a result the anal glands are always confined to the submucosa, internal sphincter or longitudinal layer of the lower half of the anal canal. Parks shown that the glands never proceed beyond the longitudinal intersphincteric muscles. The epithelial lining of the glands are stratified columnar type.
It is highly doubtful whether the glands have any secretory function, they appears to be blind outgrowth of the anal crypts.Their surgical significance lies in the fact that they may provide a route of infection from the anal canal to the submucosa and intersphincteric space. They may also be the site of origin of an adenocarcinoma as was pointed out by Dukes and Galvin.



The Musculature

Internal anal sphincter- It is continuous with the circular muscle coat of the rectum and inferiorly it ends with a well defined rounded edge 6 to 8 mm above the level of the anal orifice . A remarkable feature of the muscle is the manner in which its constituent muscle fibres are disposed. These are grouped into discrete elliptical bundles which in the upper part of the sphincter lie obliquely with their transverse axis running internally and downwards giving them an imbricated arrangement. These obliquity become progressively less as the internal sphincter is traced downwards so that in the lower part of the muscle the bundle lie horizontally and some of the lower ones even inclined slightly upwards. The internal sphincter consists of plain (unstriped) muscle fibres.

External anal Sphincter- The external anal sphincter extend further downwards than the internal sphincter.The lowermost portion curves medially to occupy a position below the lower round edge of the internal sphincter and close to the skin of the anal oricice. The lowermost portion of it which lies below the internal sphincter is traversed by a fan shaped expansion of the longitudinal muscle fibre of the anal canal which splits it up into 8 to 12 discrete muscle bundles. The upper end of the external sphincter fuses with the puborectalis part of the levator ani muscle, Both muscles are made up of striped muscle fibres.

Longitudinal muscle fibres - The longitudinal fibres in the anal canal is seen to lie between the internal and external sphincters. The layer consists of nonstriped muscle fibres mixed with elastic tissue. Traced upwards it is continuous with the longitudinal muscle layer of the rectal wall.Traced downwards it breaks up opposite the lower border of the internal sphincter into a number of septa which diverge fanwise and passes radially through the lowermost part of external sphincter. Some of these fibres are ultimately attached to the skin of the anal and perianal region.

Levatro ani muscles - It is a broad thin muscle attached peripherally to the inner surface of the side of the pelvis and united medially with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It is seen to consists of three parts -
1. The illeococcygeus.
2. The pubococcygeus.
3. The puborectalis.
The puborectalis arise from the back of symphysis pubis and runs backwards to join with its fellow member behind the bowel to form a strong U shaped loop which slings the rectum to the pelvis.


The anorectal ring - The functionally important ring of muscle which surrounds the junction of the rectum and anal canal . This is composed of the upper border of the internal and external sphincters,which completely encircle the junction, and on the posterior and lateral aspects the strong puborectalis sling . As a consequence the ring is stronger posteriorly and laterally than it is anteriorly . Recognition of the anorectal ring is of great importance in the treatment of abscess and fistulas in the anal region, for its division always results in rectal incontinence while its preservation despite the sacrifice of all the rest of the sphincter musculature at least ensures no gross lack of control though minor degree of incontinence may results.
Ischiorectal space - Is a wedge shaped space situated one on either side of the anal canal.below the pelvic diaphragm. Its base is directed downwards towards the surface, and the apex upwards. It contains ischiorectal pad of fat.
Boundries - (1) Base is formed by the skin.
(2) Apex is formed by the line of meeting of the obturator fascia with the inferior fascia of the levator ani (pelvic diaphragm). The line corresponding to the origin of the levator ani from the lateral pelvic diapgragm.
(3) Anteriorly - The fossa is limited by the posterior border of the urogenital diaphragm.
(4) Posteriorly - (a) Lower border of the gluteus maximus and (b) sacrotuberous ligament.
(5) Lateral wall - Is vertical and is formed by (a) obturator internus with its obturator fascia and (b) medial surface of the ischial tuberosity below the attachment of obturator fascia.
(6) Medial wall - Slopes upwards and laterally and is formed by (a)external anal sphincter with fascia covering it in the lower part and (b) levator ani and its fascial covering in the upper part.


Aetiology

The portal of entry of infection is obvious - In 20% of cases the portal of entry of the infective organism is obvious. For example perianal abscess may develop after -
¢ Dorsal anal fissure.
¢ Anal hematoma.
¢ Prolapsed thrombosed internal haemorrhoids.
¢ Following injection of a anaesthetic solution or alcohol in perianal or ischeorectal space in the treatment of perianal pain.
¢ Following injection of internal haemorrhoids is less frequent complication but may lead to abscess formation.
¢ Injury to anal or rectal mucosa by nozzle of enema syringe.
¢ As a complication of haemorrhoidectomy operation.

When no obvious portal of entry of infection was found - In majority of cases of anorectal abscess there is no evidence of pre existing lesion that provide an entry of micro organisms into the tissue space. Under these circumstances some of the mechanism that suggested the entry of organisms into the tissue are - (1)Abrasion or tearing of the lining of the anal canal or of the perianal skin It is possible that minute abrasion or tear of the anal canal produced by (a) hard stools or hard objects such as bone in the faeces (b) Abrasion of the perianal skin cuased by friction of rough underclothes. The breach of the surface lyning thus produced provide the entry of organisms into the subcutaneous tissue resulting in cellulitis and abscess formation.
(2) Infection from an anal crypt via an anal gland . This theory has recently accured greater acceptance. According to this theory the first step in the pathogenesis of an anal abscess or fistula is the formation of an intersphincter abscess , due to infection of anal gland which lyes between the internal sphincter and the longitudinal intersphincteric muscle fibres . Fig - 6.1 . Subsequetly the pus may force its way downwards along the longitudinal fibres to emerge at the anal orifice as perianal abscess. Fig 6.2 . Laterally it may pass through the longitudinal muscles and external sphincter to enter the ischiorectal fossa to give rise to ischiorectal abscess, or it may track upwards in the intersphincteric space to produce a high intermuscular abscess. If the pus tracks still higher in the intersphincteric space it gives rise to pelvirectal abscess. The pelvi rectal space is the space lying between the levator ani and the pelvic peritoneum.
(3) Blood Borne Infection - In septicaemic conditions abscess may arise in perianal region as else where due to blood borne infection. Patient suffering from diabetes or leukaemia appears to be more prone to develop anorectal abscess.
(4) Additional aetiological factors - Three additional aetiological factors which are frequently found in cases of anorectal abscess and if present require special consideration in planning the treatment. They are Crohn's disease, Ulcerative colitis and tuberculosis. The aetiological factors of a pelvirectal abscess is due to abdominal sepsis, which may be due to appendicitis , salpingitis and diverticulitis.

Incidence - More commoner in males than in females . This differences this is due to (a) Anal cleanliness (b) Rougher type of undergarments causing greater friction on the perineal skin (c) Increase sweating in the anal region .

Classification - Anal abscess are generally classified according to their site of origin in different tissue spaces as -
¢ Perianal.
¢ Ischeorectal.
¢ Submucous.
¢ Pelvirectal.

But with time the inflammatory process may spread, thus an abscess originating in perianal space may extend into the ischiorectal space or vice versa and a supralevator abscess may burst through the levator ani muscles and present as ischiorectal abscess. The most common abscess is the perianal abscess which accounts for 60% of the cases , then the ischiorectal abscess which is seen in 30% of the cases rest are rarer forms.

 

Clinical Features

Perianal and Ischiorectal abscess - The initial symptoms with these abscesses is acute pain in the anal reagion , which is throbbing in nature and is aggravated by sitting, caughing, sneezing and defaecation. By the time patient presents at hospital he has swelling near the anus which is extremely tender on touching. Occasionally the abscess burst and the patient report that following discharge of pus his pain was much relieved. Small perianal abscess are not associated with much constitutional disturbances, but large ischiorectal abscess produce a moderate fever and constitutional disturbances.
On examination a perianal abscess shows a red , tender localised , round or oval swelling close to anus . At a later stage fluctuation can be elicited in the swelling . Digital examination of the rectum reveals a tender , indurated bulge on the corresponding aspect of the anal canal above the anal swelling.
An ischiorectal abscess produce a diffused perianal swelling on one side of the anus. A rectal examination with a finger will elicit a similar tender indurated bulge into the anal canal on that side . At times an ischiorectal abscess arising higher up in the ischiorectal space may produce no obvious external signs . The only signs of inflammation may be little tender and induration on palpation of the apical part of the fossa between finger and thumb . The patient presents with pyrexia of obscure origin without pain of any kind. The ischiorectal fossa communicates with that of the opposite side via the postsphincteric space and if an ischiorectal abscess is not evacuated early, involvement of the contralateral fossa is not uncommon thus giving rise to a bilateral ischiorectal abscess with these above signs evident on both sides. The fat which fills the ischiorectal fossa is particularly vulnerable to infection because it has a poor blood supply.
Submucous abscess - It occurs in 5% of the cases, above the dentate line in the submucous plain. It may occur as complication after injection of haemorrhoids. It is treated by opening the abscess by a sinus forceps when after adequately displayed by a proctoscope.
Pelvirectal abscess - It is an abscess situated between the upper surface of levator ani muscle and the pelvic peritonium. It is more or less like a pelvic abscess which is secondary to appendicitis, salpingitis , diverticulitis or parametritis. Abdominal Crohn's disease is an important cause of pelvic abscess that can present as perianal abscess.At times a pelvirectal abscess may be due to an over enthusiastic attempt to drain a ischiorectal abscess or to display a fistula when a probe is forced through the levator ani muscle from below.


Diagnosis - In great majority of cases of anorectal abscess the diagnosis is obvious but some times the distinction between the types of abscess in not easy. Then ultrasound examination using an endorectal probe is of great help.


Differential diagnosis -

(1) Abscess in connection with pilonidal sinus .
(2) Periurethral abscess - will give previous history of urethritis, urethral stricture and urethral instrumentation in past is important.
(3) Tuberculous anorectal abscess - Here the discharge is usually thinner and more watery than in pyogenic abscess. The patient may have known pulmonary tuberculosis. This may be shown by radiological examination and examination of the sputum.


Treatment

Once a diagnosis is confirmed operation will be required and that the sooner it is carried out the better.No time should be lost in evacuating the pus. For perianal and ischiorectal abscess drainage is achieved by making a cruciate incision over the abscess and excising the skin edges . This completely removes the roof of the abscess.
Later as soon as the acute infection is subsided the wound should be examined under general anaesthesia. A careful search is made for fistulous opening communicating with the anal canal. If such is found the treatment should be as fistula in ano. If no fistulous tract is found the cavity should be packed with gauze soaked in a weak antiseptic solution and dressed. With daily dressing the cavity will be covered with granulation tissue from below and subsiquently heals.