Anorectal abscesses
In 60 percent of cases the pus from the
abscess yields a pure culture of Escherichia
coli; in 23 per cent a pure culture of Staphylococcus
aureus is obtained. In diminishing frequency, pure cultures of Bacteroides,
a Streptococcus or Proteus strain
are found. In many cases the infection is mixed. In a high percentage of cases
— some estimate it as high as 90 per cent —the abscess commences as an
infection of an anal gland (Figs 61.34 and 61.35). Other causes are penetration
of the rectal wall, e.g. by a fish bone, a blood-borne infection or an extension
of a cutaneous boil. Underlying rectal disease, such as neoplasm and
particularly Crohn’s disease, may be the cause. Similarly patients with
generalised disorders, such as diabetes and more recently AIDS, may present with
an anorectal abscess. The latter patients usually have abscesses which run an
aggressive course.
A
large percentage of anorectal abscesses coincides with a fistula in ano. For
this reason, anorectal abscess becomes a highly important subject. Moreover, as
antibiotics cannot reach the contents of an abscess in adequate concentration,
no reliance can be placed on antibiotic therapy alone. A fistula is much more
likely if bacterial culture of the pus discloses bowel (as opposed to skin)
organisms (Grace).
Differential
diagnosis
The only conditions with which an anorectal
abscess is likely to be confused are an abscess connected with a pilonidal
sinus, Bartholin’s gland or Cowper’s gland.
Classification
A clear understanding of suppuration in this
area is dependent on a concise knowledge of the anatomy (Figs 61.34 and
61.35). There are four main varieties: perianal, ischiorectal, submucous and
pelvirectal.
Perianal (60
per cent)
This usually occurs as the result of
suppuration in an anal gland, which spreads superficially to lie in the region
of the subcutaneous portion of the external sphincter (Fig.
61.35a).
It may also occur as a result of a thrombosed
external pile. If the haematoma is not evacuated, it may become infected and
Treatment.
No time should be lost in evacuating the pus.
Operation.
Thorough drainage is achieved by making a cruciate incision over the abscess and
excising the skin edges
Ischiorectal
abscess (30 per cent)
Commonly, this is due to an extension
laterally through the external sphincter of a low intermuscular anal abscess (Fig.
61.35b). Rarely, the infection is either lymphatic or blood borne. The
fat, which fills the ischiorectal fossa (Fig. 61.36), is particularly vulnerable
because it is poorly vascularised; consequently it is not long before the whole
space becomes involved. 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.
Should an internal opening into the anal canal ensue, a ‘horseshoe’ abscess
develops enveloping the whole of the posterior part of the circumference of
the anal canal (cf. horseshoe fistula).
An
ischiorectal abscess gives rise to a tender, brawny induration palpable on the
corresponding side of the anal canal and the floor of the fossa. Constitutional
symptoms are severe, the temperature often rising to 38—390C. Men
are affected more often than women.
Treatment.
Operation should be undertaken early — as soon as it is certain that an abscess is present in
this area — remembering that antibiotic therapy often masks the general signs.
Operation.
Stage 1.
A cruciate incision (Fig. 61.37 inset) is made into the abscess. A
portion of skin is sometimes excised (Fig. 61.37) but deroofing is not necessary
in every case.
Stage 2. As soon as the acute infection has
subsided, the wound should be re-examined, preferably under general anaesthesia.
A careful search is made for a fistulous opening communicating with the anal
canal. If such is found, the treatment should be as for fistula. If no fistula
is found, the cavity should be lightly packed with gauze wrung out in any weak
antiseptic favoured by the operator. A T-bandage is applied. When the cavity has
become covered with granulation tissue, skin grafting may help to expedite final
epithelialisation.
Submucous
abscess
Submucous abscess (5 per cent) occurs above the dentate line (Fig.
61.35c). When it
occurs after the injection of haemorrhoids, it always resolves. Otherwise, it
can be opened with sinus forceps when adequately displayed by a proctoscope.
Pelvirectal
abscess
Pelvirectal abscess is situated between the
upper surface of the levator ani and the pelvic penitoneum (Fig.
61.35d). It is
nothing more or less than a pelvic abscess and, as such, is usually secondary to
appendicitis, salpingitis, diverticulitis or parametritis. Abdominal
Crohn’s disease is an important cause of pelvic disease that can present as
perianal sepsis (cf. fistula in ano). A relevant point to remember is that,
rarely, a supralevator abscess/fistula may be due to overenthusiastic attempts
to drain an ischiorectal abscess or to display a fistula, when a probe is forced
through the levator ani/rectal wall from below.
Fissure abscess
This is the name given to a subcutaneous
abscess lying in immediate association with an anal fissure. Drainage is
achieved at the same time as the fissure is treated by sphincterotomy.