Fistula in ano
A fistula in ano is a track, lined
by granulation tissue, which connects deeply in the anal canal or rectum and
superficially on the skin around the anus. It usually results from an anorectal
abscess which burst spontaneously or was opened inadequately (Fig.
61.34). The
fistula continues to discharge and, because of constant reinfection from the
anal canal or rectum, seldom, if ever, closes permanently without surgical aid.
An anorectal abscess may produce a track, the orifice of which has the
appearance of a fistula, but it does not communicate with the anal canal or
the rectum. By definition this is not a
fistula, but a sinus.
Types of anal
fistulae
These are divided into two groups, according
to whether their internal opening is below or above the anorectal ring.
Low-level
fistulae open into the anal canal below the
High-level
fistulae open into the anal canal at or above the
As
an alternative to the common anatomical classification illustrated in Fig.
61.38, Parks produced another based on the origin of the fistula from an abscess
in an anal gland situated in the plane between the internal and external
sphincters (the ‘anal intersphincteric plane’) (Fig.
61.39).
The
importance of deciding whether a fistula is a low or a high-level type is that
a low-level fistula can be laid open usually without fear of permanent
incontinence (from damage to the anorectal bundle), while a high-level fistula
can be treated only by ‘staged’ operations, often with the use of a
protective colostomy to prevent septic complications and to shorten healing time
between the stages.In probing a high fistulous track, great care must be taken
not to create an internal opening into the rectum where none existed previously.
Such a disaster could convert a relatively straightforward
‘intersphinctenic’ track into a high ‘pelvirectal’ fistula that might
prove very difficult to cure.
By
the standard classification, a high fistula
refers to both a high anal [Fig. 61.38(4)] and a pelvirectal fistula
[Fig. 61.38(5)]. By the Parks’ classification, both a high trans sphinctenic and a
supralevator fistula would qualify as high, with the intersphincteric falling
into either category depending on whether an internal opening was present at
all, and at what level it entered the anal canal [see Fig.
61.38(1)].
Low-level
fistulae
Clinical features. Commonly, the principal
symptom is a persistent seropurulent discharge that irritates the skin in the
neighbourhood and causes discomfort. Often the history dates back for years. So
long as the opening is large enough for the pus to escape, pain is not a
symptom, but if the orifice is occluded pain increases until the discharge
erupts. Frequently, there is a solitary external opening, usually situated
within 3.5—4 cm of the anus, presenting as a small elevation with granulation
tissue pouting from the mouth of the opening. Sometimes superficial healing
occurs, pus accumulates and an abscess reforms and discharges through the same
opening or a new opening. Thus there may be two or more external openings,
usually grouped together on the right or left of the midline but, occasionally,
when both ischiorectal fossas are involved, an opening is seen on each side, in
which case there is often intercommunication between them (Fig.
61.40). As a
rule there is much induration of the skin and subcutaneous tissues around the
fistula.
Goodsall’s rule. Fistulae with an external opening in relation to the anterior half of
the anus tend to be of the direct type (Fig. 61.41). Those with an external
opening or openings in relation to the posterior half of the anus, which are
much more common, usually have curving tracks, and may be of the horseshoe
variety. Note that posteriorly situated fistulae may have multiple external
openings which always connect to a solitary internal orifice, usually midline (Fig.
61.41).
Digital
examination. Not infrequently an internal opening can be felt as a nodule on the
wall of the anal canal. Irrespective of the number of external openings, there
is almost invariably only one internal opening.
Proctoscopy
sometimes will reveal the internal opening of the fistula. A hypertrophied
papilla is suggestive that the internal orifice lies within the crypt related to
the papilla (Fig.
The injection of lipiodol, or other opaque medium, along the sinus, before radiography has little to recommend it. The radiographs thus obtained are seldom illuminating, and the procedure is likely to cause a recrudescence of inflammation. Endoluminal ultrasonography and magnetic resonance imaging are being developed as techniques for ‘mapping’ complex fistulae.
Radiography
of the thorax should be undertaken and the possibility of pulmonary tuberculosis
considered, despite the fact that today it will be found in only a small
proportion of patients with fistula in ano — usually of Asian origin (see
below).
I—
Special clinical types of fistulae in ano
Fistula connected with an anal fissure. Unlike
the usual fistula in ano, pain (due to the fissure) is a leading symptom. The
fistula is very near the anal orifice, usually posterior, and the external
opening is often hidden by the sentinel pile.
Fistula
with an internal opening above the anorectal ring is due, almost invariably, to
penetration by a foreign body or probing and interference with a high abscess.
A supralevatot fistula arising spontaneously will be seen only once or at most
twice in a surgical career.
Granulomatous
infections and Crohn’s disease. If induration around a fistula is lacking, if
the opening is ragged and flush with the surface, if the surrounding skin is
discoloured and the discharge is watery, or if the external openings are
multiple, tuberculous or Crohn’s disease should be considered. In more than 30
per cent of patients suffering from pulmonary tuberculosis, virulent tubercle
bacilli are present in the rectum. About 2—3 per cent of fistulae in the UK
are due to Crohn’s disease or tuberculosis. In Asian communities, the
incidence of tuberculosis is higher. Crohn’s disease should also be
suspected if there are other stigmata, and a small bowel meal may be necessary.
If tuberculosis is suspected, a chest radiograph and sputum cultures are
mandatory. However, the diagnosis can usually only be made on histological
examination of biopsy material from the track. If due to tuberculosis, the
fistula will usually respond to antituberculous drugs alone..
Fistulae
with many external openings may arise from tuberculous proctitis, Crohn’s
disease of colon or ileum, bilharziasis and lymphogranuloma inguinale with a
fibrous rectal stricture. Crohn’s disease is the most frequent cause seen in
this country from this group.
Carcinoma
arising within perianal flstulae. Colloid carcinoma may complicate fistulae in
ano and a colloid carcinoma of the rectum is notoriously liable to be
complicated by perianal fistulae. In some instances, the fistulous condition,
with its discharge of colloid material, overshadows the primary carcinoma, and
not a few unfortunate patients have had their condition diagnosed for a time as
an inflammatory fistula in ann. If a primary tumour is present in the rectum,
usually it can be detected and its nature established by biopsy. Dukes
established conclusively that colloid carcinomatous fistulae can develop without
a primary neoplasm in the rectum. He regarded such cases as examples of colloid
carcinoma developing in a reduplicated portion of the intestinal tract. Both adenocarcinoma and squamous-cell carcinoma are known to arise within chronic
fistulous tracks. The former can develop from the anal granular tissue; the
latter is an example of true malignant change of squamous epithelium lining the
wall of the track.
Hidradenitis
suppurativa. This is a chronic infection of apocrine glands around the anal
margin giving rise to numerous sinuses. The mons pubis and groin can also be
affected. After excision of the area, granulation and healing ate accelerated by
using Silastic foam dressing (Hughes).
Treatment.
That the
fistulous track must be laid open from its termination to its source was a
rule promulgated by John of Arderne more than 600 years ago.
The
operation can best be described in stages:
Step 1. Preoperative cleaning enemas are necessary. When the patient has been
anaesthetised, he or she is placed in the lithotomy position or in the prone jack-knife position, according
to the preference of the operator. Using bidigital palpation under anaesthesia,
it is often possible to obtain more information concerning a fistula than can be
learned from probing; it is surprisingly easy to push a probe through the wall
of the track. Unfortunately, many inexperienced operators find it more
reassuring
to create a false passage than to risk criticism for not being able to
demonstrate the internal opening. Careful bidigital palpation of the perianal
tissue will often reveal a cord-like induration, representing the track, which
will lead the intra anal finger towards the proximal opening. Rather than
insert a probe through the distal orifice at this stage, it is better to
endeavour to find the internal opening via a proctoscope. If the internal
opening still cannot be seen, the insertion of a probe termgradely into an
anal crypt, especially one with a nearby hypertrophied papilla, often reveals
the internal portion of the track (Fig. 61.42). The injection of dilute
methylene blue or other dye into the external mouth of the fistula to establish
the site of the internal opening is occasionally necessary, but is not
recommended as a routine.
Step 2. A probe-pointed director (Fig. 61.43) is inserted into the distal
orifice, and it is advanced delicately until it reaches a point where it does
not pass readily. The track is opened along the director and bleeding is
controlled.
Step 3. If it is not at once evident in which direction the track passes,
granulations are wiped away with gauze (it is seldom necessary to use a
curette). Often this will leave a granulation-filled spot at one site only.
Gentle probing at this spot frequently will give the clue to the continuation of
the fistula. The director is reinserted, and again followed with the knife for a
short distance. This procedure is repeated until the entire track, and any side
channels, are laid open. As far as possible, all muscle is divided at right
angles to its fibres. In the rare event of the track passing above the anorectal
ring, cutting should cease at the level of the dentate line, and from
thenceforth the operation is conducted as suggested below. In most instances,
probing and laying open the track can be repeated until the entire track is laid
open. Pursuing this course, if there is no internal opening, the track will
become bereft of granulations on wiping it. As a rule, the internal opening can
be demonstrated either by direct inspection through a proctoscope, or by a bent
probe inserted into an anal crypt. In the latter circumstance, the internal
portion of the track is excised in continuity.
Step 4. The edges of the track are trimmed, 1—3 mm of tissue being removed —
a step that makes postoperative packing unnecessary after the first 24—36
hours. Hughes advocated primary split skin grafting of the wound resulting from
fistulotomy. The grafts are taken from the inner aspect of the thigh and applied
to the anal wound, being stitched to the skin edges and to each other in the
depths of the wound. Tulle gras is then superimposed and a firm pack of cotton
wool applied. The first dressing is done on the 5th postoperative day.
When
skin grafting is not employed, digital dilatation of the anus, or the passage of
a St Mark’s Hospital3 dilator every other day, prevents pocketing
or bridging of the granulating wound.
Biopsy.
Always send a piece of track for biopsy.
High-level
fistulae
The treatment
of these cases is difficult. If the track is laid open as for low-level
fistulae, incontinence will follow. There are four types (Parks).
Supralevator
fistula — secondary to local disease [Fig.
61.39(3)]. It occurs as a result of
Crohn’s disease, ulcerative colitis, carcinoma, a foreign body perforating the
rectal ampulla from above or trauma. This fistula is quite unrelated to the
ordinary type and the treatment is that of the cause. A traumatic fistula
usually needs a colostomy. None of these fistulae requires to be laid open,
which would in any case cause incontinence.
Trans-sphincteric
fistula [Fig. 61.39(2)] with perforating
secondary track. The condition starts as an intersphincteric track [Fig. 61.39(1)], often with a high secondary
track in the ischiorectal fossa up to the levator ani. Here lies the danger.
Although the anal opening may be low, during exploration of the high secondary
track, unless great care is taken, the probe can be pushed through the levator
ani into the rectal ampulla, thus converting a low fistula into a high-level
type. Treatment should first of all be directed to the low trans-sphinctenic
flstula and healing of the upper track may follow. If it fails to do so, or if
the opening into the rectum is of any size or near the anorectal bundle, a
colostomy must sometimes be done before sound healing will take place. High
tracks often require staged operations.
A
seton — a time-honoured device — (i.e. a ligature of silk,
nylon, silastic or linen) is helpful when the internal opening is near the
anorectal ring. Insertion of a seton and subsequent re-examination of the
patient without anaesthesia will establish whether the internal opening is
situated so near to the anorectal ring that incontinence would result if the
track were laid open. Under these conditions, a staged operation and a covering
colostomy would be the proper treatment. While the seton remains in situ it acts as a wick/drain and allows the acute inflammatory
reaction around the track to subside: this can greatly simplify subsequent
surgery. In expert hands, primary repair of divided sphincter muscle can
preserve continence when a high-level track is laid open.
Intersphincteric
fistula. The track starts as a primary anal gland abscess (Fig.
61.34a), and it
runs between the internal and external sphincter along the plane of the
longitudinal muscle fibres (see Fig. 61.39, Type 1). It may have an opening into
the rectum above the anorectal ring and below at the site of a perianal abscess
(Fig. 61.34b). Providing it is recognised it is easy to treat. The internal
sphincter is divided and the whole track is laid open without fear of
incontinence.
Suprasphincteric
flstula. Occasionally, the intersphincteric track passes over the top of the
sphincter before passing down again in the ischiorectal fossa. Treatment of this
type is very difficult and is sometimes best done by an indwelling seton.