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286 The ASCRS Manual of Colon and Rectal Surgery
D streptococcus. Consequently, infections are successfully
controlled with a third-generation cephalosporin combined
with anaerobic coverage or an extended spectrum penicillin
in combination with an aminoglycoside and an anti-anaerobic
antibiotic. This combination has been associated with an 88%
success rate.
• Because appropriate antibiotic coverage has been found to
control infection successfully, surgery has generally been
recommended only if there is obvious fl uctuation, progression of soft tissue infection, or persistent sepsis after a trial of
antibiotic therapy.
Anorectal Sepsis in the Patient Positive for the Human Immunodefi ciency Virus
• Patients who are human immunodefi ciency virus (HIV) positive and present with abscesses require drainage either by
incision and drainage or use of catheter drainage.
• Because these patients are immunosuppressed, adjunctive
antibiotics should be used.
• Efforts should be directed at keeping wounds small because these
patients are at risk of poor wound healing. An increased incidence
of perianal sepsis may be observed in HIV-positive patients.
C. Fistula-in-Ano
Pathophysiology
Etiology
• A fi stula is defi ned as an abnormal communication between any
two epithelium-lined surfaces. A fi stula-in-ano is an abnormal
tract or cavity communicating with the rectum or anal canal by
an identifi able internal opening. Most fi stulas are thought to
arise as a result of cryptoglandular infection.
Classifi cation
• The most helpful yet complicated classifi cation of fi stula-inano is that described by Parks et al. (Table 13.2 ). It has been
13. Benign Anorectal: Abscess and Fistula 287
Table 13.2. Classifi cation of fi stula-in-ano.
Intersphincteric
Simple low tract
High blind tract
High tract with rectal opening
Rectal opening without perineal opening
Extrarectal extension
Secondary to pelvic disease
Transsphincteric
Uncomplicated
High blind tract
Suprasphincteric
Uncomplicated
High blind tract
Extrasphincteric
Secondary to anal fi stula
Secondary to trauma
Secondary to anorectal disease
Secondary to pelvic infl ammation
suggested that its use is particularly applicable to the treatment
of recurrent fi stulas.
Intersphincteric Fistula-in-Ano
• This fi stula is the result of a perianal abscess. The tract passes
within the intersphincteric space (Fig. 13.7a ). This is the most
common type of fi stula and accounts for approximately 70%
of fi stulas.
Transsphincteric Fistula-in-Ano
• In its usual variety, this fi stula results from an ischioanal
abscess and constitutes approximately 23% of fi stulas seen.
The tract passes from the internal opening through the internal
and external sphincters to the ischioanal fossa (Fig. 13.7b ).
• One form of transsphincteric fi stula is the rectovaginal fi stula.
This is discussed further in Chap. 14.
Suprasphincteric Fistula-in-Ano
• This fi stula results from a supralevator abscess and accounts
for approximately 5% of fi stulas in some series (Fig. 13.7c ).
288 The ASCRS Manual of Colon and Rectal Surgery
Fig. 13.7. Classifi cation of fi stula-in-ano. ( a ) Intersphincteric. ( b ) Transsphincteric.
( c ) Suprasphincteric. ( d ) Extrasphincteric.
Extrasphincteric Fistula-in-Ano
• This constitutes the rarest type of fi stula and accounts for 2%
of fi stulas (Fig. 13.7d ).
Evaluation and Treatment
Symptoms
• A patient with a fi stula-in-ano will often recount a history of
an abscess that has been drained either surgically or spontaneously. Patients may complain of drainage, pain with defecation,
bleeding caused by the presence of granulation tissue at the
internal opening, swelling, or decrease in pain with drainage.
• Additional bowel symptoms may be present when the fi stula is
secondary to proctocolitis, Crohn’s disease, actinomycosis, or
anorectal carcinoma. Systemic diseases such as HIV, carcinoma,
and lymphoma should be entertained.
13. Benign Anorectal: Abscess and Fistula 289
Physical Examination
• The external or secondary opening may be seen as an elevation
of granulation tissue discharging pus. This may be elicited on
digital rectal examination.
• In most cases, the internal or primary opening is not apparent.
• The number of external openings and their location may be
helpful in identifying the primary opening. According to Goodsall’s rule (Fig. 13.8 ), an opening seen posterior to a line drawn
transversely across the perineum will originate from an internal
opening in the posterior midline. An anterior external opening
will originate in the nearest crypt. Generally, the greater the
distance from the anal margin, the greater the probability of a
complicated upward extension.
• Cirocco and Reilly found that Goodsall’s rule was accurate
in describing the course of anal fi stulas with a posterior external opening. It was inaccurate in patients with anterior external
openings because 71% of these fi stulas tracked to a midline
anterior primary opening. This was especially true in women
in whom fi stulas with anterior external openings tracked in a
radial manner in only 31%.
Fig. 13.8. Goodsall’s rule.
290 The ASCRS Manual of Colon and Rectal Surgery
• Digital rectal examination may reveal an indurated cord-like
structure beneath the skin in the direction of the internal opening with asymmetry between right and left sides. Internal
openings may be felt as indurated nodules or pits leading to an
indurated tract.
• Posterior or lateral induration may be palpable indicating fi stulas deep in the postanal space or horseshoe fi stulas.
Investigations
• Anoscopy should be done before operation in an attempt to
identify the primary opening.
• Sigmoidoscopy should be performed to locate a proximal
internal opening and to exclude underlying pathology such as
proctitis or neoplasia.
• Colonoscopy or barium enema and a small bowel series are
indicated in patients who have symptoms suggestive of infl ammatory bowel disease and in patients with multiple or recurrent
fi stulas.
• Although anal manometry is not generally required, it may
be useful as an adjunct to planning the operative approach in
women with previous obstetric trauma, in an elderly patient,
a patient with Crohn’s disease or AIDS, or in a patient with a
recurrent fi stula.
• The role of preoperative imaging is to demonstrate clinically
undetected sepsis, to serve as a guide at the time of the initial
surgery, to determine the relationship of the fi stula tract to the
sphincter mechanism, and to reveal the site of sepsis in a recurrent fi stula, all serving to decrease recurrence rates associated
with fi stula surgery. Imaging may take the form of fi stulography, computed tomography (CT) scan, endoanal ultrasound,
and magnetic resonance imaging (MRI).
Fistulography
• Fistulography, which involves cannulation of the external
opening with a small feeding tube and injection of water-soluble
contrast may be useful in the evaluation of recurrent fi stulas or
in Crohn’s disease where previous surgical forays or disease
may have altered anorectal anatomy.
13. Benign Anorectal: Abscess and Fistula 291
• Fistulography is invasive and potentially may result in the dissemination of sepsis.
CT Scan
• CT scanning performed with intravenous and rectal contrast is
a noninvasive method used to assess the perirectal spaces. Its
use may be to distinguish an abscess requiring drainage from
perirectal cellulitis. It does not permit visualization of tracts in
relation to the levators.
Endoanal Ultrasound
• The role of endoanal ultrasound is to establish the relation of the
primary tract to the anal sphincters, to determine if the fi stula is
simple or complex with extensions, and to determine the location
of the primary opening. It may aid in the identifi cation of complex
fi stulas and may serve as an adjunct in the evaluation of complex suppuration to assess the adequacy of drainage (Fig. 13.9a ).
• Although this investigative modality is rapid and well tolerated,
it is operator dependent and scars or defects caused by previous
sepsis, surgery, or trauma will confuse ultrasonographic interpretation and make delineation of fi stula tracts diffi cult. The
concomitant use of hydrogen peroxide (Fig. 13.9b ) or Levovist™ at the time of ultrasound examination has been found to
improve its accuracy.
Fig. 13.9. ( a ) Anal endosonogram; arrows indicate fi stula tract; ( b ) with hydro-
gen peroxide; arrows indicate better delineation of fi stula tract. (Courtesy
Dr. Julio Faria.)
292 The ASCRS Manual of Colon and Rectal Surgery
Magnetic Resonance Imaging
• MRI in the form of endoanal coil, body coil, and phase array
coil (Fig. 13.10 ) may be of value in the assessment of patients
with complex fi stulas and in those with anatomic distortion
resulting from previous surgery.
• MRI has been found to accurately delineate the presence and
course of a primary fi stulous tract but also demonstrates the
site and presence of any secondary extensions. It also provides
the most accurate imaging technique of localizing the site of the
internal opening because its location can be inferred from the
proximity of the tract in the intersphincteric space.
• The use of the endoanal coil has been found to be superior to
external MRI for the identifi cation of complex sphincter anatomy especially in the demonstration of the morphology of the
internal and external sphincters; however, defi nition may fall
off outside the sphincter and may fail to show the tracts that lie
beyond its range. It is also painful.
Fig. 13.10. Phase array MRI. ( a ) White arrowhead indicates levators; black
arrowhead indicates fi stula tract to rectum; black arrow shows tract crossing
levator. ( b ) Arrowhead indicates tract going to skin.
13. Benign Anorectal: Abscess and Fistula 293
Treatment
General Principles
1. The principles of fi stula surgery are to eliminate the fi stula,
prevent recurrence, and preserve sphincter function. Success
is usually determined by identifi cation of the primary opening
and dividing the least amount of muscle possible.
2. Several methods have been proposed to identify the primary
opening in the operating room:
– Passage of a probe or probes from the external opening to
the internal opening or vice versa.
– Injection of a dye such as dilute solution of methyl-
ene blue, milk, or hydrogen peroxide, and noting their
appearance at the dentate line. Although methylene blue
may stain surrounding tissues, diluting it with saline or
hydrogen peroxide will obviate this problem.
– Following the granulation tissue present in the fi stula tract.
– Noting puckering of an anal crypt when traction is placed
on the tract. This may be useful with simple fi stulas but is
less successful in the more complicated varieties.
Operative Management
Lay-Open Technique
• A probe is inserted from the external opening along the tract
to the internal opening at the dentate line. The tissue overlying
the probe is incised and the granulation tissue curetted and sent
for pathologic evaluation.
• If desired, the wound may be marsupialized on either edge
by sewing the edges of the incision to the tract with a running locked absorbable suture. There is no need to insert
packing if an adequate unroofi ng has been accomplished
(Fig. 13.11a – c ).
Seton
• The problem of preserving anal continence and treating the fi stula is more complicated when managing high transsphincteric
fi stulas.
294 The ASCRS Manual of Colon and Rectal Surgery
Fig. 13.11. Technique of laying open.
( a ) Insertion of probe and incision of
tissue overlying probe. ( b ) Curettage of
granulation tissue. ( c ) Marsupialization
of wound edges.
13. Benign Anorectal: Abscess and Fistula 295
• If the tract is seen to cross the sphincter muscle at a high level,
the use of the lay-open technique in combination with insertion
of a seton is safer.
• A seton may be any foreign substance that can be inserted into
the fi stula tract to encircle the sphincter muscles. Materials frequently used include silk or other nonabsorbable suture material, Penrose drains, rubber bands, vessel loops, and silastic
catheters.
• The lower portion of the internal sphincter is divided along with
the skin to reach the external opening and a nonabsorbable suture
or elastic suture is inserted into the fi stulous tract. The ends of the
suture or elastic are tied with multiple knots to create a handle for
manipulation (Fig. 13.12 ). This form of seton, known as a cutting seton, is tightened at regular intervals to slowly cut through
the sphincter. This allows the tract to become more superfi cial,
converting a high fi stula into a low one. The proximal fi stulotomy subsequently heals by stimulating fi brosis behind it reestablishing continuity of the anorectal ring to prevent separation
of the sphincter muscle at a second-stage repair 8 weeks later
when the remaining external sphincter is divided.
Fig. 13.12. Seton.
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