Perianal Abscess: Introduction
A perianal abscess represents an infection of the soft tissues
surrounding the anal canal, with formation of a discrete
abscess cavity. The severity and depth of the abscess are
quite variable, and the abscess cavity is often associated with
formation of a fistulous tract. For that reason, along with
perianal abscess, perianal fistula also is discussed in this
article.
Problem
An anorectal abscess originates from an infection arising in
the cryptoglandular epithelium lining the anal canal. The
internal anal sphincter is believed to serve normally as a
barrier to infection passing from the gut lumen to the deep
perirectal tissues. This barrier can be breached through the
crypts of Morgagni, which can penetrate through the internal
sphincter into the intersphincteric space. Once infection
gains access to the intersphincteric space, it has easy access
to the adjacent perirectal spaces. Extension of the infection
can involve the intersphincteric space, ischiorectal space, or
even the supralevator space. In some instances, the abscess
remains contained within the intersphincteric space. The
variety of anatomic sequelae of the primary infection is
translated into variable clinical presentations.
Frequency
The peak incidence of anorectal abscesses is in the third and
fourth decades of life. Men are affected more frequently
than are women, with a male-to-female predominance of 2:1
to 3:1. Approximately 30% of patients with anorectal
abscesses report a previous history of similar abscesses that
either resolved spontaneously or required surgical
intervention.
A higher incidence of abscess formation appears to
correspond with the spring and summer seasons. While
demographics point to a clear disparity in the occurrence of
anal abscesses with respect to age and sex, no obvious
pattern exists among various countries or regions of the
world. Although suggested, a direct relationship between the
formation of anorectal abscesses and bowel habits, frequent
diarrhea, and poor personal hygiene remains unproved.
The occurrence of perianal abscesses in infants also is quite
common. The exact mechanism is poorly understood but
does not appear to be related to constipation. Fortunately,
this condition is quite benign in infants, rarely requiring any
operative intervention in these patients other than simple
drainage.
Etiology
Perirectal abscesses and fistulas represent anorectal
disorders arising predominately from the obstruction of anal
crypts. Infection of the now static glandular secretions results
in suppuration and abscess formation within the anal gland.
Typically, the abscess forms initially in the intersphincteric
space and then spreads along adjacent potential spaces.
Pathophysiology
As mentioned above, perirectal abscesses and fistulas
represent anorectal disorders that arise predominately from
the obstruction of anal crypts. Normal anatomy
demonstrates anywhere from 4-10 anal glands drained by
respective crypts at the level of the dentate line. Anal glands
normally function to lubricate the anal canal. Obstruction of
anal crypts results in stasis of glandular secretions and, when
subsequently infected, suppuration and abscess formation
within the anal gland results. The abscess typically forms in
the intersphincteric space and can spread along various
potential spaces.
Common organisms implicated in abscess formation include
Escherichia coli, Enterococcus species, and Bacteroides
species; however, no specific bacterium has been identified
as a unique cause of abscesses.
Less common causes of anorectal abscess that must be
considered in the differential diagnosis include tuberculosis,
squamous cell carcinoma, adenocarcinoma, actinomycosis,
lymphogranuloma venereum, Crohn's disease, trauma,
leukemia, and lymphoma. These may result in the
development of atypical fistula-in-ano or complicated fistulas
that fail to respond to conventional surgical treatment.
Presentation
The classic locations of anorectal abscesses listed in order of
decreasing frequency are as follows: perianal 60%,
ischiorectal 20%, intersphincteric 5%, supralevator 4%, and
submucosal 1%. These major types are illustrated in the
image below. Clinical presentation correlates with the
anatomic location of the abscess.
Illustration
of the
major
types of
anorectal
abscesses
(submucos
al not
pictured).
Patients with a perianal abscess typically complain of dull
perianal discomfort and pruritus. Their perianal pain often is
exacerbated by movement and increased perineal pressure
from sitting or defecation. Physical examination
demonstrates a small, erythematous, well-defined, fluctuant,
subcutaneous mass near the anal orifice.
Patients with an ischiorectal abscess often present with
systemic fevers, chills, and severe perirectal pain and fullness
consistent with the more advanced nature of this process.
External signs are minimal and may include erythema,
induration, or fluctuancy. On digital rectal examination (DRE),
a fluctuant, indurated mass may be encountered. Optimal
physical assessment of an ischiorectal abscess may require
anesthesia to alleviate patient discomfort that would
otherwise limit the extent of the examination.
Patients with an intersphincteric abscess present with rectal
pain and exhibit localized tenderness on DRE. Physical
examination may fail to identify an intersphincteric abscess.
Although rare, supralevator abscesses present a similar
diagnostic challenge. As a result, clinical suspicion of an
intersphincteric or supralevator abscess may require
confirmation through computed tomography (CT) scanning,
magnetic resonance imaging (MRI), or anal ultrasonography.
Use of the last modality is limited to confirming the presence
of an intersphincteric abscess.
Indications
As a rule, the presence of an abscess is an indication for
incision and drainage. Watchful waiting while administering
antibiotics is inadequate.
Relevant Anatomy
Classification of anorectal abscess
Abscesses are classified based on their anatomic location.
The most commonly described locations are perianal,
ischiorectal, intersphincteric, and supralevator. The image
below illustrates the different anatomic locations of
anorectal abscesses.
Perianal abscesses represent the most common type of
anorectal abscesses, accounting for approximately 60% of
reported cases. These superficial collections of purulent
material are located beneath the skin of the anal canal and
do not transverse the external sphincter.
The next most common types of abscesses, in descending
order of frequency, are ischiorectal, intersphincteric, and
supralevator. An ischiorectal abscess forms when
suppuration transverses the external sphincter into the
ischiorectal space. Intersphincteric abscesses result from
suppuration contained between the internal and external
anal sphincters. A supralevator abscess results either from
primary disease in the pelvis (eg, appendicitis, diverticular
disease, gynecologic sepsis) or from suppuration extending
cranially from an origin in the intersphincteric space, through
the longitudinal muscle of the rectum and reaching above the
levators.
Horseshoe abscesses, while rare, result from circumferential
infiltration of pus within the intersphincteric planes.
The Goodsall rule for perianal fistulas
The Goodsall rule states that the external opening of a
fistulous tract located anterior to a transverse line drawn
across the anal verge is associated with a straight radial tract
of the fistula into the anal canal/rectum. Conversely, an
external opening posterior to the transverse line follows a
curved, fistulous tract to the posterior midline of the rectal
lumen. This rule is important for planning surgical treatment
of the fistula and is illustrated in the images below.
Diagram illustrating
the Goodsall rule for
anorectal fistulas.
Fistulas that exit in
the posterior half of
the rectum generally
follow a curved
course toward the
posterior midline,
while those that exit
in the anterior half
of the rectum usually
follow a radial
course to the
dentate line.
Illustration of the
Goodsall rule for
anorectal
fistulas.
Note the curved
nature
of
the
posterior fistulas and
the radial (straight)
orientation of the
anterior fistulas.
Contraindications
Clinical suspicion of anorectal abscess warrants aggressive
identification and surgical drainage. Delayed surgical
intervention results in chronic tissue destruction, fibrosis,
and stricture formation and may impair anal continence.
Delayed incision and drainage of an anorectal abscess is
contraindicated.
Workup
Laboratory Studies
1. No specific laboratory studies are indicated in the
evaluation of a patient with a perianal or anorectal
abscess.
2. Certain patients, such as individuals with diabetes and
patients who are immunocompromised, are at high risk
for developing bacteremia and possibly sepsis, as a result
of an anorectal abscess. In such cases, complete
laboratory evaluation is important. Laboratory
evaluation of the septic patient is not the focus of this
article.
Imaging Studies
Imaging studies rarely are necessary in the evaluation of
patients with an anorectal abscess; however, clinical
suspicion of an intersphincteric or supralevator abscess may
require confirmation by CT scanning, MRI, or anal
ultrasonography. Use of the last modality is limited to
confirming the presence of an intersphincteric abscess. The
ultrasound can also be used intraoperatively to help identify
a difficult abscess/fistula.
Diagnostic Procedures
1. Digital examination under anesthesia can be helpful in
certain cases, because patient discomfort can
significantly limit physical assessment. For example,
optimal evaluation for an ischiorectal abscess is
performed in this manner. A fistula tract can be injected
with peroxide solution at the time of examination under
anesthesia in order to facilitate the visualization of the
internal opening of the fistula.
2. Evidence suggests that the use of endoscopic
visualization (transrectal and transanal) is an excellent
way to evaluate complex cases of perianal abscess and
fistula. With the endoscopic technique, the extent and
configuration of the abscess and fistulas can be clearly
visualized. The endoscopic visualization has been
reported to be as effective as fistulography. In
experienced hands, endoscopic evaluation is the
preferred diagnostic procedure in patients with
perirectal pathology because of the low risk of bacterial
dissemination and the low incidence of patient
discomfort. Utilizing endoscopic evaluation after
nonsurgical treatment is also effective for the
documentation of the patient's response to therapy.
Treatment
Medical Therapy
In most patients with anorectal abscess, adjuvant medical
therapy with antibiotics generally is not necessary. However,
the presence of a systemic inflammatory response, diabetes,
or immunosuppression justifies the concomitant use of
antibiotics.
Surgical Therapy
Treatment of anorectal abscesses involves early surgical
drainage of the purulent collection.4,5,6,7,8 Primary antibiotic
therapy alone is ineffective in resolving the underlying
infection and simply postpones surgical intervention. Any
delay in surgical drainage of anorectal abscesses prolongs
infection, augments tissue damage, and may impair sphincter
continence function, as well as promote stricture and/or
fistula formation. The ability to drain an anorectal abscess
depends on patient comfort and on the location and
accessibility of the abscess.
Drainage of perianal or superficial abscesses usually can be
accomplished in the office or emergency department, using
local anesthetics. A small incision is made over the area of
fluctuancy in close proximity to the anal verge. Pus is
collected and sent for culture. Hemostasis is achieved with
manual pressure, and the wound is packed with iodophor
gauze. The gauze is removed after 24 hours, and the patient
is instructed to take sitz baths 3 times a day and after bowel
movements. Postoperative analgesics and stool softeners are
prescribed to relieve pain and prevent constipation. The
patient typically will follow up with his/her physician in 2-3
weeks for wound evaluation and inspection for possible
fistula-in-ano. (A short fistula-in-ano coursing through a
minimal amount of external sphincter is best treated with a
fistulotomy.)
A potential complication of anorectal abscess drainage is the
formation of fistulous tracts. Management of fistulas will be
addressed later in this review. The type of organism cultured
from an anorectal abscess is an important predictor of fistula
formation following surgical incision and drainage.
Underlying anal fistulas are present in 40% of abscess
cultures that are positive for intestinal bacteria; however,
cultures growing Staphylococcus species are associated with
perianal skin infections and typically indicate that there is no
subsequent risk that anal fistulas will develop.
Treatment of ischiorectal, intersphincteric, and supralevator
abscesses is performed best under general or regional
anesthesia. In the case of ischiorectal abscess, a cruciate
incision is made at the site of maximal swelling. Pus is
drained and cultured. The ischiorectal fossa is probed with a
finger or hemostat to disrupt loculations and facilitate
drainage. Placement of a drain only is indicated for the
management of complex or bilateral abscesses.
To drain an ischiosphincteric abscess, a transverse incision is
made in the anal canal below the dentate line posteriorly.
The intersphincteric space is identified, and the plane
between the internal and external sphincters is exposed. The
abscess is opened to allow drainage, and a small mushroom
catheter is sutured in situ to assist drainage and prevent
premature wound closure.
Location and etiology determine the drainage technique to
be used for supralevator abscesses. Failure to manage
supralevator abscesses with consideration of the primary
etiology may result in iatrogenic fistula formation. Evaluation
with MRI or CT scanning can exclude intra-abdominal or
pelvic pathology as possible sources.
If the supralevator abscess evolved from the extension of an
ischiorectal abscess, external drainage through the
ischiorectal fossa would be indicated. If the abscess resulted
from an upward extension of an intersphincteric abscess,
appropriate drainage would be created through the rectal
mucosa. In cases of posterior supralevator abscess
collections, a transverse incision is made in the posterior anal
canal below the dentate line. The dissection extends from the
intersphincteric plane through the puborectalis sling and into
the posterior anal space. A mushroom catheter then is
sutured in place to ensure adequate drainage.
Anterior supralevator abscesses are superficial and are more
common in women than in men. Surgical drainage may be
approached using an anteriorly directed transanal incision or
by a transvaginal approach entering the posterior cul-de-sac.
A mushroom catheter is placed to ensure adequate drainage
of the abscess collection. Patients with systemic signs of
toxicity are admitted to the hospital and treated with
intravenous antibiotics. If the patient does not improve
clinically over the next 24-48 hours, reevaluation of the
supralevator abscess by CT scan or reoperation may be
indicated. In the face of recurrent, severe supralevator
abscesses, some patients may require a diverting colostomy
for optimal management.
The anal fistula is a common surgical ailment that has been
reported since the time of Hippocrates, but little systematic
evidence exists on its management. Different treatment
modalities have been evaluated in 443 reported trials.
Examples of various research studies include the following:
1. Treatment with fistulotomy versus the use of
fistulectomy
2. Seton treatment
3. Marsupialization
4. Glue therapy
5. Anal flaps
6. Radiosurgical approaches
7. Fistulotomy/fistulectomy at time of abscess incision
8. Intraoperative anal retractors
Two reported meta-analyses evaluated the use of incision
and drainage alone vs the employment of incision +
fistulotomy. Evidence suggests that following fistulotomy,
marsupialization reduces bleeding and permits faster healing.
Results from small trials indicate that healing rates after flap
repair may be no worse than those following fistulotomy,
although this has not yet been proven.11 Failure rates may
increase in cases in which flap repair has been combined with
fibrin glue treatment of fistulas.12 Radiofrequency fistulotomy
results in less pain on the patient's first postoperative day
and may permit faster healing.13 However, a great deal is not
yet understood about the surgical treatment of anal fistulas. 7
Preoperative Details
Because of the acute nature of anorectal abscesses,
preoperative bowel preparation is not possible and typically
is unnecessary.
Intraoperative Details
Decisive management of anal fistulas relies on therapeutic
interventions. Healing rarely is spontaneous, and failure to
achieve adequate treatment often results in recurrent
abscess, persistent drainage, and even malignancy. The main
paradigms to follow in the management of anorectal fistulas
include the following:
1. Determine the anatomy of the fistula
2. Provide adequate drainage
3. Eradicate the fistula tract
4. Prevent recurrence
5. Preserve sphincter function - Preservation of sphincter
function relies on maintaining the integrity of the
anorectal ring.
Once the external opening of the anorectal fistula has been
identified and the surrounding tissue has been palpated,
probing of the fistula tract is warranted. Aggressive probing
of the fistula is discouraged to prevent formation of false
channels. Using a blunt probe (eg, a small lachrymal probe),
the internal origin of a primary fistula can be identified in the
majority of cases.
When searching for a fistula tract's opening in the anal canal,
the Goodsall rule is an excellent guideline. This rule states
that an external opening anterior to a transverse line drawn
across the anal verge is associated with a straight radial tract
into the canal. An external opening posterior to the
transverse line follows a curved fistulous tract to the
posterior midline rectal lumen. Horseshoe fistulas
occasionally are associated with anterior and posterior
openings in the anal canal.
Treatment options for the management of fistulas are aimed
at providing definitive therapy while minimizing the
morbidity of the procedure. For example, 2 widely accepted
treatment
interventions
include
fistulectomy
and
fistulotomy. Studies have demonstrated that removal of the
entire fistula tract along with the surrounding scar tissue (ie,
fistulectomy) unnecessarily results in a larger wound,
prolonged healing time, and higher risks of incontinence. As a
result, the more conservative approach of unroofing the tract
without excising all surrounding tissue (fistulotomy) usually is
preferred and decreases the risk of incontinence and fistula
recurrence; fistulotomy also shortens wound healing time.
A fistulotomy is performed as a primary procedure for
superficial fistulas that require minimal dissection of the
fistula from the surrounding sphincter musculature. In
contrast, simple fistulotomy for repair of high-level fistulas is
contraindicated as the primary treatment.
The use of loose setons is warranted in high-level fistulas (ie,
transsphincteric and suprasphincteric) to reduce the risk of
incontinence or in cases in which poor wound healing is
anticipated. Setons may also be used as temporary initial
intervention in the management of a fistula. A seton is a
nonabsorbable nylon or silk suture that is guided through the
fistula tract and tied exteriorly, in this way compressing and
maintaining suture placement in the tract. Other material
frequently used for seton placement include soft vessel loop.
The seton suture must be left in place for a prolonged period
of time (weeks to months).
The ischemic compression by the seton and the local
inflammatory reaction of adjacent tissues initiates fibrosis.
Once fibrosis of the surrounding tissue develops, it helps to
maintain the integrity of the sphincter musculature during
subsequent fistulotomy. Setons often are used in patients
with fistulas secondary to inflammatory bowel disease (IBD).
In addition, the seton allows epithelialization of the fistulous
tract, thereby preventing secondary closure and facilitating
the drainage of abscesses.
Another commonly used type of seton is the cutting seton,
which can be used to gradually transect the anal sphincter
musculature underlying the fistula by externally tightening
the suture to induce pressure necrosis. Typically, retightening
the seton over a period of several days is necessary (this can
be performed in the outpatient setting). The cutting seton
may eliminate the need for subsequent fistulotomy. While
the cutting seton is used as an effective therapeutic option
for high-level fistulas, it is contraindicated in patients with
IBD.
Other treatment modalities include resection with coverage
using advancement tissue flaps (used for more complex
cases) and bioprosthetic fistula plug (made of surgisis porcine
submucosa). The plug technique is indicated in selected cases
with long fistulous tracts. The success rate is variable (5070%).
Patients with anal fissures can be treated with nifedipine gel
(calcium channel blocker - topical use) and Botox injections.
Occasionally, sphincterotomy (lateral internal anal sphincter
muscle) may be necessary.
Postoperative Details
Postoperatively, administer analgesics for pain, stool bulking
agents, and stool softeners to prevent constipation. Followup evaluation of an incised anorectal abscess is important not
only for determining whether healing is adequate, but also
for assessing the potential development of anorectal fistulas.
The patient typically will follow up with his/her physician in
2-3 weeks for wound evaluation and inspection for possible
fistula-in-ano.
Antibiotics are used as adjuncts to surgical therapy for
patients with a comorbidity, such as diabetes, valvular heart
disease, or immunodeficiency.
Follow-up
The patient typically will follow up with his/her physician in
2-3 weeks for wound evaluation and inspection for possible
fistula-in-ano.
Complications
Anorectal fistulas
Anorectal fistulas occur in 30-60% of patients with anorectal
abscesses. The intersphincteric glands lie between the
internal and external anal sphincters and are associated most
commonly with abscess formation. Anorectal fistulas arise
through obstruction of anal crypts and/or glands and are
identified by purulent drainage from the anal canal or from
the surrounding perianal skin. Other etiologies of anorectal
fistulas are multifactorial and include diverticular disease,
IBD,14 malignancy, and complicated infections, such as
tuberculosis and/or actinomycosis.
The Parks classification system defining the 4 major types of
anorectal fistulas in order of decreasing frequency is as
follows15 : intersphincteric (70%), transsphincteric (23%),
extrasphincteric (5%), and suprasphincteric (2%). An
intersphincteric fistula is found between internal and
external sphincters. A transsphincteric fistula extends
through the external sphincter into the ischiorectal fossa. An
extrasphincteric fistula passes from the rectum to the skin
through the levator ani. Lastly, the suprasphincteric fistula
extends from the intersphincteric plane through the
puborectalis muscle, exiting the skin after traversing the
levator ani.
The Goodsall rule states that an external opening of a
fistulous tract that is anterior to a transverse line drawn
across the anal verge is associated with a straight radial tract
of the fistula into the anal canal/rectum. Conversely, an
external opening that is posterior to the transverse line
demonstrates a curved fistulous tract to the posterior midline
rectal lumen. This rule, which is important for the planning of
surgical treatment of the fistula, is illustrated below.
Approximately two thirds of patients with rectal abscesses
who are treated by incision and drainage or by spontaneous
drainage will develop a chronic anal fistula.
The recurrence rate of anorectal fistulas after fistulotomy,
fistulectomy, or the use of a seton is about 1.5%. The success
rate of primary surgical treatment with fistulotomy appears
to be fairly good.16
The overall incidence of major fecal incontinence after the
surgical management of complex suprasphincteric fistulas is
estimated to be approximately 7%.
Future and Controversies
Some surgeons advise performing a complementary
colostomy to facilitate the management of complex anal
fistulas. This may be of some benefit in selected cases, but
the perirectal infection may continue despite a diverting
colostomy. Adequate drainage of the abscess is the most
important factor in controlling progressive perirectal
infection.