Anorectal Abscess (Crypto- glandular Disease)
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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
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
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.
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
(3) Anteriorly - The fossa is limited by the posterior border of the
(4) Posteriorly - (a) Lower border of the gluteus maximus and (b) sacrotuberous
(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.
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
(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 -
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
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.
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.