Anorectal abscess Summary

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Anorectal abscess
ID: 644
Type: Monograph Standard [en-us]

Topic Synonyms
• Perirectal abscess
• Perianal abscess

Related Topics
• Crohn disease
• Anal fissure
• Hemorrhoids
• Hidradenitis suppurativa
• Pilonidal disease
• Overview of sexually transmitted diseases
• Necrotizing fasciitis

Summary
Key Highlights
• Commonly presents with perianal pain with leukocytosis.
• Usually treated by incision and drainage.
• Adjunctive antibiotics are unnecessary for uncomplicated cases. Antibiotics are indicated for patients
with diabetes, immunocompromise, chronic debilitation, elderly age, history of cardiac valvular disease
or associated extensive cellulitis.

History and Exam, Tests Treatment Options
Diagnostic Factors Other Tests Acute
Key Diagnostic Factors to Consider • all patients
• anal fistula • WBC • surgical drainage of abscess
• hx of Crohn disease count • elderly, immunocompromised, cardiac
• male gender • serum valvular disease, diabetes, or significant
• perianal pain glucose associated cellulitis
• perianal or rectal • serum • broad-spectrum antibiotics with
induration electrolytes anaerobic and gram-negative
• anal coverage
Other Diagnostic l
ta o o r p y
ur s n ga h • elderly, immunocompromised, cardiac
Factors • CT valvular disease, diabetes, or significant
• perianal swelling pelvis associated cellulitis
• low-grade fever • MRI • aminoglycosides
• change in bowel pelvis • unresponsive to initial treatment
habits • re-examination under anesthesia
• rectal bleeding • all patients
• tachycardia • postoperative care
• inability to urinate • elderly, immunocompromised, cardiac
valvular disease, diabetes, or significant
associated cellulitis
• broad-spectrum antibiotics with
anaerobic and gram-negative
coverage

Page 1
• elderly, immunocompromised, cardiac
valvular disease, diabetes, or significant
associated cellulitis
• aminoglycosides
• unresponsive to initial treatment
• re-examination under anesthesia
• all patients
• fistulotomy
• elderly, immunocompromised, cardiac
valvular disease, diabetes, or significant
associated cellulitis
• broad-spectrum antibiotics with
anaerobic and gram-negative
coverage
• elderly, immunocompromised, cardiac
valvular disease, diabetes, or significant
associated cellulitis
• aminoglycosides
• unresponsive to initial treatment
• re-examination under anesthesia

Basics
Basics: Definition
An anorectal abscess is an infection of the soft tissues around the anus.[1] Severe perianal pain and
swelling are the most common presenting complaints. Other symptoms include fever, chills or urinary
retention.[2] Rarely, patients may present with life-threatening sepsis from an associated necrotizing
soft-tissue infection.[3] The diagnosis of an anorectal abscess can usually be made by physical examination,
but occasionally atypical presentations require imaging studies such as CT or MRI.[4] [5]

Basics: Classifications
Clinical anatomic classification[6]
Anorectal abscesses are usually classified clinically, based on the anatomy of the abscess:
• Intersphincteric abscesses are located in the space between the internal and external anal sphincter.
• Perianal abscesses occur in the superficial soft tissues overlying the intersphincteric space.
• Perirectal abscesses are found in the ischiorectal or postanal spaces.
• Supralevator abscesses occur above the anorectal ring in the supralevator space.

Basics: Vignette
Common Vignette
A 32-year-old male presents to the ER complaining of perirectal pain and swelling. The symptoms began
24 hours earlier and have become progressively worse.The patient denies any rectal bleeding and describes
the pain as very severe and localized to the area of the swelling. He relates a subjective history of fever
but denies any change in bowel habits. He also denies any history of recent or chronic medical problems.

Page 2
Basics: Other Presentations
An anorectal abscess can be a manifestation of Crohn disease.[1] While severe perianal pain and swelling
are the most common presenting symptoms, 1 or both symptoms may be absent. Occasionally, patients
with anorectal abscesses will present with urinary retention. This is more common in men with a previous
history of urinary problems.[2] [7] Intersphincteric abscesses are very difficult to diagnose as they produce
little swelling and few perianal signs of infection. In these cases anal pain is the predominant symptom, is
usually described as being up inside the anal area and is so severe that it precludes a digital rectal
examination.[8] Supralevator abscesses may present with abdominal or deep pelvic pain mimicking an
intra-abdominal condition without any obvious perirectal swelling.[9] Rarely, patients with an anorectal
abscess present with life-threatening sepsis from an associated necrotizing soft-tissue infection. This is
most likely in patients with diabetes, the elderly or those who are immunocompromised or chronically
debilitated.[3] [10]

Basics: Epidemiology
Anorectal abscesses are a very common problem, affecting an estimated 0.18% of the general
population.[11] For patients with Crohn disease, an anorectal abscess will develop in approximately one
third of patients. Anorectal abscesses are between 2 and 3 times more common in men than women, with
most abscesses occurring in patients between 20 to 40 years of age. The highest occurrence is during
spring and summer.[12] [13]

Basics: Etiology
The majority of anorectal abscesses result from infections of the anal glands (cryptoglandular infections).
The anal canal has 6 to 14 glands that lie in the plane between the internal and external anal sphincters.
Ducts from these glands pass through the internal sphincters and drain into the anal crypts at the dentate
line. These glands may become infected when a crypt is occluded by impaction of food matter, edema
from trauma secondary to a hard stool or foreign body, or as a result of an adjacent inflammatory process
such as Crohn disease.

Basics: Pathophysiology
If a crypt does not spontaneously drain into the anal canal, an infection of the intersphincteric space may
occur. This infection may spread along the intersphincteric space and result in an intersphincteric, perianal
or supralevator abscess. The infection may also pass through the external anal sphincter and result in a
perirectal abscess.[2] [6]
Anorectal abscesses are associated with anal fistulas in 37% of patients.[14] [15] If these fistulas are not
recognized and treated, perirectal abscesses may recur. Perirectal abscesses are also a common
manifestation of Crohn disease and this diagnosis must be considered in patients with recurrent anorectal
abscesses.[1]

Basics: Risk Factors
Strong
anal fistula
• Multiple recurrent anorectal abscesses are a common clinical manifestation of anal fistulae.
• These recurrent abscesses occur when fistulae become occluded from impaction of food matter in
the fistula tract or from healing of the skin over the external opening of the fistula.
• An anal fistula will occur in 37% of patients with an anorectal abscess.[14] [15] Fistulae result from
the drainage, either surgical or spontaneous, of the anorectal abscess.
Crohn disease
• Anorectal abscesses will develop in approximately one third of patients with Crohn disease.[1]

Page 3
• The majority of anorectal abscesses result from infections of the anal glands (cryptoglandular
infections). The ducts from these anal glands pass through the internal sphincters, draining into the
anal crypts at the dentate line. These anal glands may become infected when a crypt is occluded as
a result of an adjacent inflammatory process such as Crohn disease.
male gender
• Anorectal abscesses are between 2 and 3 times more common in men than women.[12] [13]

Weak
hard stools
• Hard stools are a risk factor for anorectal abscesses, though a diet that contains 25 to 30 g/day of
fiber and 60 to 80 ounces/day of fluid has not been shown to prevent anorectal abscesses.[12]
age 20 to 40 years
• Most anorectal abscesses occur in patients between 20 to 40 years of age.[12]

Basics: Prevention
A diet that contains 25 to 30 g/day of fiber and 60 to 80 ounces of fluid/day has not been shown to prevent
anorectal abscesses but is recommended for the prevention of hard stools, which are a risk factor for
anorectal abscesses.[12]

Diagnosis
Diagnosis: Diagnosis Approach
The diagnosis of an anorectal abscess is usually suspected from a patient's clinical history and confirmed
by physical examination. Laboratory and radiologic studies are not usually needed for the diagnosis of an
anorectal abscess but can be useful in some special situations.
The location of an anorectal abscess affects its diagnosis and management.[6] Intersphincteric abscesses
are difficult to diagnose because they produce little swelling and few perianal signs of infection, but they
are associated with anal pain that is so severe that it precludes digital rectal examination. Anesthesia is
usually required for an adequate examination and diagnosis of the condition.[16] Supralevator abscesses
may present with symptoms that mimic an intra-abdominal condition. Rectal examination usually reveals
a tender, indurated area above the anorectal ring, but imaging with CT or MRI may be required to make
the diagnosis.[9]

History
The presence of key risk factors such as a history of Crohn disease or anal fistula should be elicited. In
addition, it should be noted that anorectal abscesses are more common in men than women.[12] [13]
Patients with anorectal abscesses usually relate a history of localized anal or perianal pain.[2] Pain usually
begins 1 to 2 days before presentation and becomes progressively more severe. Patients frequently
complain of swelling and warmth of the perianal tissues. The patient may occasionally relate the onset to
some precipitating event such as a difficult bowel movement, though pain associated only with defecation
is likely to be due to a fissure. The pain may be exacerbated by movement, coughing, sneezing or bowel
movements. Patients may often try taking warm baths as pain relief, but these fail to improve their pain or
make it worse. Most patients will not report rectal bleeding unless their abscess has spontaneously drained
(usually associated with some decrease in the pain). Fever is common and is usually less than 101.5ºF
(38.6ºC).
Patients with rare supralevator abscesses may describe pain in the lower abdomen or pelvis, mimicking
an intra-abdominal condition.[9] Occasionally patients with anorectal abscesses may complain of being

Page 4
unable to urinate, particularly men with a previous history of difficulties with urination.[2] [7] Symptoms of
inflammation, pain and swelling are frequently absent or diminished in patients with:[2]
• Diabetes
• Immunocompromise
• Debilitation
• Older age
• Associated necrotizing soft-tissue infection.

Physical examination
An adequate anorectal examination can usually be performed in the office or ER, though on occasion this
may be impossible because of pain. Intersphincteric and supralevator abscesses in particular require
anesthesia for full examination.
The most common finding on physical examination is a tender, indurated area immediately adjacent to the
anus, within the anal canal, or above the anorectal ring.[2] The further the indurated area is located from
the anal verge, the less likely it is to be an anorectal abscess. Anal fistulae associated with anorectal
abscesses may have a hard, cord-like structure leading toward the anus and palpable in the soft tissues.
Infected epidermal inclusion cysts are much more likely when the indurated area is more than 3 cm from
the anal verge while pilonidal disease is more common when the induration is located in the intergluteal
area.
Occasionally, the infection can spread to involve both ischiorectal fossae and the postanal space (horseshoe
abscess), though anorectal abscesses are almost always solitary. The induration in horseshoe abscesses
may be more prominent in the ischiorectal fossae and appear to be bilateral abscesses.[17] If multiple
abscesses are present, the diagnosis is much more likely to be multiple infected epidermoid inclusion cysts
or perianal hidradenitis suppurativa.
Induration may be absent or diminished in patients with diabetes, or those who are immunocompromised,
debilitated, or elderly. Detection of low-grade fever and mild tachycardia should also form part of the physical
examination as these are common symptoms of anorectal abscess.

Laboratory studies
Laboratory studies are rarely helpful in the diagnosis and management of anorectal abscesses and need
not be a routine component of the evaluation and management of these patients.[2]
Basic tests include:
• WBC count: will frequently reveal a leukocytosis with an increased proportion of neutrophils. Anorectal
abscesses do not cause anemia or other hematologic abnormalities.
• Blood glucose: may show hyperglycemia, which may or may not be associated with diabetes.
For patients with a necrotizing soft-tissue infection related to their anorectal abscess, serum electrolyte
determination may reveal an elevated BUN and creatinine, decreased bicarbonate and an increased base
deficit (metabolic acidosis).
Abnormal blood chemistry results should generally be evaluated further only after the acute abscess has
been treated, while addressing any urgent treatment considerations acutely (e.g., volume depletion,
hyperglycemia).

Radiologic studies
Radiologic studies are rarely helpful in the diagnosis and management of anorectal abscesses. Occasionally,
for patients with complex or atypical presentations, or those with supralevator or horseshoe abscesses,
anal ultrasonography has been used for evaluation. However, the severe pain associated with the anorectal

Page 5
abscess frequently limits the use of this modality. Other imaging modalities such as CT or MRI may be
more helpful in the evaluation of these patients.[4] [5]

Diagnosis: History and Exam, Diagnostic Factors
Key Diagnostic Factors
anal fistula (common)
• Considered a key risk factor. Multiple recurrent anorectal abscesses are a common clinical
manifestation of anal fistulae. Anal fistulae may also be a complication of anorectal abscesses.
hx of Crohn disease (common)
• Considered a key risk factor. Anorectal abscesses will develop in approximately one third of patients
with Crohn disease.[1]
male gender (common)
• Considered a key risk factor. Anorectal abscesses are more common in men than women.[12] [13]
perianal pain (common)
• Extremely common symptom of an anorectal abscess.[2]
• Anal canal pain occurs more commonly with intersphincteric abscesses and pelvic pain is more
commonly due to supralevator abscesses.
• There are very few conditions that cause anorectal pain. If the pain occurs only during and immediately
after bowel movements and improves with time, the diagnosis is more likely to be an anal fissure
rather than an anorectal abscess.
• Constant pain usually occurs only with thrombosed external hemorrhoids that can be diagnosed by
simple inspection of the anus or an anorectal abscess.
• Pain may be less severe in those with a compromised immune system.
perianal or rectal induration (common)
• The vast majority of patients with anorectal abscesses will have induration in the perianal tissues,
the anal canal or above the anorectal ring.
• This sign may be absent in those with a compromised immune system.

Other Diagnostic Factors
perianal swelling (common)
• Swelling and tenderness of the perianal tissues is a frequent complaint.
• Swelling may be absent in patients with intersphincteric or supralevator abscesses, or those with a
compromised immune system.
low-grade fever (common)
• Most patients with an anorectal abscess have a fever, though this is usually less than 101.5ºF (38.6ºC).
• Fever is usually absent in those with a compromised immune system.
change in bowel habits (uncommon)
• There is seldom any change in bowel habits in patients with anorectal abscesses. A history of chronic
diarrhea may suggest Crohn disease, a risk factor for anorectal abscess.
rectal bleeding (uncommon)
• Usually absent unless the abscess has spontaneously drained.
• The presence of rectal bleeding is more indicative of an anal fissure.
tachycardia (common)

Page 6
• Mild tachycardia is frequently observed.
• The etiology can be multifactorial, including slight volume depletion from inadequate oral intake of
fluids, possibly related to fever and pain.
inability to urinate (uncommon)
• Patients with anorectal abscesses may occasionally complain of being unable to urinate, particularly
men with a history of difficulties with urination.[2] [7]

Diagnosis: Tests
Other Tests to Consider
Test Result
WBC count may be elevated with
• This may be useful in the evaluation of a patient with a suspected increased proportion of
anorectal abscess and helps to confirm this diagnosis. granulocytes (left shift)
• While an elevated WBC count is very sensitive, it is not specific for an
anorectal abscess and the absence of leukocytosis does not exclude
the diagnosis.
serum glucose normal or hyperglycemia
• Useful for the management of diabetic patients with a suspected
anorectal abscess, though it may be difficult to treat the hyperglycemia
prior to drainage of the abscess.
serum electrolytes usually normal; may show
• These are common findings in patients with necrotizing soft-tissue elevated BUN and creatine,
infections and life-threatening sepsis associated with their anorectal decreased bicarbonate
abscess.
• Abnormal blood chemistry results should generally be evaluated further
only after the acute abscess has been treated, while addressing any
urgent treatment considerations acutely (e.g., volume depletion,
hyperglycemia).
anal ultrasonography visualization of anorectal
• Anal ultrasonography is an inexpensive means to diagnose anorectal abscesses
abscesses, though it is not normally needed for diagnosis of
uncomplicated cases.
• Excessive discomfort with this modality also limits its use in the diagnosis
of intersphincteric and supralevator abscesses.
CT pelvis visualization of anorectal
• Most anorectal abscesses are easily visualized with CT. abscesses
• While CT imaging is very sensitive and specific for anorectal abscesses,
with the possible exception of supralevator abscesses, it is seldom
needed to make the diagnosis or determine the appropriate treatment.[4]
• CT may be a very useful adjunct to clinical assessment in patients with
severe perirectal inflammation who are difficult to examine without
anesthesia.[5]
MRI pelvis visualization of anorectal
• Most anorectal abscesses are easily visualized with MRI. abscesses

Page 7
• While MRI imaging is very sensitive and specific for anorectal abscesses,
with the possible exception of supralevator abscesses, it is seldom
needed to make the diagnosis or determine the appropriate treatment.[5]

Diagnosis: Differentials
Condition Sign/Symptoms Differentiating tests
Anal fissure • Pain occurs primarily during bowel movements • Diagnosis is usually clinical.
and may improve in the next few hours. Anal However, MRI or CT pelvis may
fissures are frequently associated with rectal be used in difficult to examine
bleeding. cases to exclude anal fissure
• Physical examination can distinguish between the (both investigations are very
2 conditions although anesthesia will occasionally sensitive and specific for
be needed for an adequate examination. On anorectal abscesses).
physical examination, fissures are located in the
anterior or posterior midline, are without induration
and are tender to palpation. Secondary finding of
an anal fissure may be present (sentinel pile).
Thrombosed • Usually presents with the sudden onset of perianal • Diagnosis is clinical.
hemorrhoid pain and swelling.
• On physical examination, thrombosed hemorrhoids
are swollen, with minimal induration or signs of
inflammation, and are frequently bluish in color.
Pilonidal • Very difficult to distinguish clinically, but physical • MRI or CT pelvis may be used
abscess examination may do so. While anorectal in difficult to examine cases to
abscesses are usually immediately adjacent to the exclude pilonidal abscess (both
anus, pilonidal abscesses are characteristically investigations are very sensitive
located in the intergluteal region and frequently and specific for anorectal
have a visible sinus tract in the midline. abscesses).
Infected • Difficult to distinguish clinically, but physical • MRI or CT pelvis may be used
epidermoid examination can do so in some cases. While in difficult to examine cases to
inclusion cyst anorectal abscesses are usually immediately exclude infected epidermoid
adjacent to the anus, infected epidermoid inclusion inclusion cyst (both
cysts are more commonly >3 cm from the anal investigations are very sensitive
verge. and specific for anorectal
abscesses).
Perianal • The presenting signs and symptoms are the same • Diagnosis is clinical.
hidradenitis as those for anorectal abscesses, but physical
suppurativa examination can often distinguish between the
conditions. Perianal hidradenitis suppurativa is
usually associated with hidradenitis in other areas,
most commonly the axilla and inguinal areas.
While anorectal abscesses are usually single,
abscesses associated with hidradenitis are more
commonly multiple and usually associated with
purulent drainage from multiple sinus tracts.
STDs • History of anal-receptive sex with or without • Rectal swab for microscopy,
immunosuppression (e.g., HIV), rectal discharge, Gram stain, and culture usually
severe anal pain, and malaise may be present. reveals the causative organism
(e.g., Neisseria gonorrhoeae,

Page 8
• Physical examination may reveal systemic fever, Chlamydia trachomatis, Herpes
lymphadenopathy, or anal discharge. In addition, simplex, Treponema pallidum).
rectal examination, usually under anesthesia, will • In addition, stool microscopy
reveal rectal mucosal changes consistent with and culture, serologic testing,
proctitis. and tissue biopsy may help
confirm diagnosis.

Treatment
Treatment: Treatment Approach
The goal of treatment of anorectal abscesses is to achieve adequate drainage of the abscess without
damaging the anal sphincters. Antibiotics are not an alternative to surgical drainage of these abscesses
and should be reserved for patients with diabetes, immunocompromise, chronic debilitation, older age,
history of cardiac valvular disease or significant associated cellulitis.[2] In these circumstances, a broad
spectrum antibiotic with anaerobic and gram-negative coverage would be appropriate. Drainage of the
abscess should be accomplished without undue delay because of the potential for the abscess to spread
into a necrotizing, soft-tissue infection leading to life-threatening sepsis.[10] [18]
External drainage of perianal and perirectal abscess is appropriate, while intersphincteric and supralevator
abscesses should be drained internally into the anal canal and rectum respectively. For patients with
anorectal abscesses associated with Crohn disease, treatment of the underlying condition should be
considered after the acute anorectal sepsis has been treated.[1] [19] The management of an anal fistula
is controversial.[15] [20] [21] [22] [23]

Surgical management
Perianal abscesses can frequently be drained in the office or ER using local anesthesia and drained
externally using an incision that is oriented in a radial fashion relative to the anus. This incision has the
potential to damage the anal sphincters if the incision is extended too far medially, but in those patients
who have an associated anal fistula, it will make subsequent fistula management simpler. Perirectal
abscesses should be drained in the operating room where optimal anesthesia can be achieved.
An alternative for drainage of the abscess is a curvilinear incision that is parallel to the anus. This incision
has a decreased risk to the anal sphincters, but can make subsequent management more challenging for
those patients with an associated anal fistula. Whichever incision is used, either an ellipse of skin can be
removed, or a second, smaller incision can be made perpendicular to the primary incision at its midpoint
(cruciate incision) to prevent reapproximation of the skin edges. A small drainage catheter can be used to
facilitate drainage of deeper infections.
If examination at the time of surgical drainage reveals an associated anal fistula, while controversial,
consideration can be given to managing the fistula at the same time.[20] [22] [23] [e1] If the anal fistula is
superficial and does not involve more than 25% of the sphincter mechanism, some surgeons feel that the
anal fistula can be managed by fistulotomy at that time. Fistulotomy does have a risk of diminished fecal
continence that has been reported to be as high as 45%.[24] [e2] Others would advocate drainage alone
or the placement of a loose, plastic seton to act as a drain in this situation.[15] [21] The seton will reduce
the risk of recurrent anorectal abscess and will allow for sphincter-preserving management of the fistula
after the acute infection has resolved and the fistula tract has matured. If the anal fistula is found to involve
more than 25% of the sphincter mechanism, fistulotomy is not an option but consideration can still be given
to placement of a seton to prevent recurrent anorectal abscess.[18]
If the abscess is being drained outside the operating room or under local anesthesia, it may not be possible
to perform an adequate anal examination or place a seton. In this circumstance, there is a risk of recurrent
anorectal abscess. Intersphincteric and supralevator abscesses frequently require general anesthesia to
allow for an adequate anal examination to make a diagnosis and drain the abscess. These abscesses

Page 9
should be drained internally into the anal canal and rectum respectively.[9] [16] Anal fistulas only rarely
occur after drainage of these abscesses so there is no need to consider fistula management at the time
of abscess drainage.

Postoperative wound care
Postoperatively, patients should begin comfortably warm water baths 2 or 3 times daily to clean the wound
until the complete healing has occurred. Baths should also be used for cleansing after bowel movements.
Absorbent dressings can be used to prevent staining of the underclothes if drainage continues.

Adjunctive antibiotic therapy
Usually reserved for patients with diabetes, immunocompromise, chronic debilitation, older age, history of
cardiac valvular disease or significant associated cellulitis.[2] Broad-spectrum antibiotics with anaerobic
and gram-negative coverage should be started preoperatively and be discontinued within 24 hours of
surgery or after cellulitis has resolved. There is no standardized antibiotic regime in the literature. In general,
some combination of an IV broad-spectrum penicillin (e.g., ampicillin/sulbactam) or a second- or
third-generation cephalosporin (e.g., cefoxitin or cefotetan) is combined with either clindamycin, ciprofloxacin
or metronidazole.
There is no clinical evidence to support triple antibiotic coverage, but some authors also recommend adding
an aminoglycoside (gentamicin or tobramycin) to the regimen. Aminoglycosides are known to cause nephro-
and ototoxicity. If used for more than 24 hours, serum levels need to be monitored.

Treatment failure
Adequate drainage of the abscess should result in a prompt improvement in the symptoms. If not,
re-examination under anesthesia is indicated to ensure complete drainage of the abscess. Inadequate
drainage of the abscess occurs most commonly in patients with horseshoe abscesses when the postanal
or ischiorectal component of the abscess is more prominent and is drained, but the other components of
this abscess are not recognized and treated.[24] [25]
For patients who develop a recurrent anorectal abscess or whose wound from the initial drainage fails to
heal, examination by a general or colorectal surgeon is indicated to exclude an anal fistula as the cause
of these problems.

Treatment: Treatment Options
Acute
Treatment
Patient Group Line Treatment
all patients 1st surgical drainage of abscess
• The appropriate treatment of anorectal abscesses is surgical
drainage of the abscess. Antibiotics are not an alternative to surgical
drainage and should be reserved for patients with diabetes,
immunocompromise, chronic debilitation, older age, history of
cardiac valvular disease or significant associated cellulitis.[2]
• Drainage of the abscess should be accomplished without undue
delay because of the potential for the abscess to spread into a
necrotizing, soft-tissue infection with life-threatening sepsis.[3]
• Perianal abscesses can frequently be drained in the office or ER
using local anesthesia and drained externally using an incision that
is oriented in a radial fashion relative to the anus. This incision has
the potential to damage the anal sphincters resulting in diminished
fecal continence if the incision is extended too far medially. Perirectal

Page 10
abscesses should be drained in the operating room where optimal
anesthesia can be achieved.
• An alternative for drainage of the abscess is a curvilinear incision
parallel to the anus. This incision has a decreased risk to the anal
sphincters, but can make subsequent management more challenging
for those patients with an associated anal fistula. Whichever incision
is used, either an ellipse of skin can be removed, or a second,
smaller incision can be made perpendicular to the primary incision
at its midpoint (cruciate incision) to prevent reapproximation of the
skin edges. A small drainage catheter can be used to facilitate
drainage of deeper infections.
• Intersphincteric and supralevator abscesses frequently require
general anesthesia to allow for an adequate anal examination to
make a diagnosis and drain the abscess. These abscesses should
be drained internally into the anal canal and rectum respectively.[9]
[16]

elderly, plus broad-spectrum antibiotics with anaerobic and gram-negative coverage
immunocompromised, • Broad-spectrum antibiotics with anaerobic and gram-negative
cardiac valvular coverage should be started preoperatively and be discontinued
disease, diabetes, or within 24 hours of surgery or after cellulitis has resolved.
significant associated • There is no standardized antibiotic regime in the literature.
cellulitis • In general, some combination of an IV broad-spectrum penicillin
(e.g., ampicillin/sulbactam) or a second- or third-generation
cephalosporin (e.g., cefoxitin or cefotetan) is combined with either
clindamycin, ciprofloxacin or metronidazole.

Primary Options
• ampicillin/sulbactam: 1 g orally/intravenously every 6 hours or
• Dose refers to ampicillin component.

•cefoxitin: 1 g intravenously every 8 hours or
•cefotetan : 1-2 g intravenously every 12 hours
-- AND --
• metronidazole : 500 mg orally/intravenously every 6 hours or
• ciprofloxacin : 200-400 mg intravenously every 12 hours; 500 mg
orally every 12 hours or
• clindamycin : 600 mg orally/intravenously every 8 hours
adjunct aminoglycosides
• There is no clinical evidence to support triple antibiotic coverage,
but some authors also recommend adding an aminoglycoside
(gentamicin or tobramycin) to the regimen.
• Treatment is for 24 hours or until the cellulitis has resolved.
• Aminoglycosides are known to cause nephro- and ototoxicity. If
used for more than 24 hours, serum levels need to be monitored.

Primary Options
• gentamicin: 80 mg intravenously every 8 hours for 24 hours or until
cellulitis has resolved

Page 11
• tobramycin : 80 mg intravenously every 8 hours for 24 hours or until
cellulitis has resolved
unresponsive to initial plus re-examination under anesthesia
treatment • Adequate drainage of the abscess should result in a prompt
improvement of symptoms. If not, re-examination under anesthesia
is recommended to ensure complete drainage of the abscess.
• Inadequate drainage of the abscess occurs most commonly in
patients with horseshoe abscesses when the postanal or ischiorectal
component of the abscess is more prominent and is drained, but
the other abscess components are not recognized and treated.[17]
• For patients who develop a recurrent anorectal abscess or whose
wound from the initial drainage fails to heal, examination by a
general or colorectal surgeon is indicated to exclude an anal fistula
as the cause of these problems.[14] [15]

all patients plus postoperative care
• Patients should begin baths with comfortably warm water 2 or 3
times daily postoperatively to clean the wound until healed. Warm
water baths should also be used for cleansing after bowel
movements.
• Absorbent dressings can be used to prevent staining of underclothes
if there is drainage.
• A diet containing 25 g to 30 g of dietary fiber/day and 60 to 80
ounces/day of fluid should be considered to prevent hard stools.

Primary Options
• ampicillin/sulbactam: 1 g orally/intravenously every 6 hours or
• Dose refers to ampicillin component.

Page 12
adjunct aminoglycosides
• There is no clinical evidence to support triple antibiotic coverage,
but some authors also recommend adding an aminoglycoside
(gentamicin or tobramycin) to the regimen.
• Treatment is for 24 hours or until the cellulitis has resolved.
• Aminoglycosides are known to cause nephro- and ototoxicity. If
used for more than 24 hours, serum levels need to be monitored.

Primary Options
• gentamicin: 80 mg intravenously every 8 hours for 24 hours or until
cellulitis has resolved
• tobramycin : 80 mg intravenously every 8 hours for 24 hours or until
cellulitis has resolved
unresponsive to initial plus re-examination under anesthesia
treatment • Adequate drainage of the abscess should result in a prompt
improvement of symptoms. If not, re-examination under anesthesia
is recommended to ensure complete drainage of the abscess.
• Inadequate drainage of the abscess occurs most commonly in
patients with horseshoe abscesses when the postanal or ischiorectal
component of the abscess is more prominent and is drained, but
the other abscess components are not recognized and treated.[17]
• For patients who develop a recurrent anorectal abscess or whose
wound from the initial drainage fails to heal, examination by a
general or colorectal surgeon is indicated to exclude an anal fistula
as the cause of these problems.[14] [15]

all patients adjunct fistulotomy
• If examination at the time of surgical drainage reveals an associated
anal fistula (usually with perianal or perirectal abscesses; rarely with
intersphincteric or supralevator abscesses), while controversial,
consideration can be given to managing the fistula at the same
time.[20] [22] [23] [e1] If the anal fistula is superficial and involves
no more than 25% of the sphincter mechanism, some surgeons feel
that the anal fistula can be managed by fistulotomy. Fistulotomy
does have a risk of diminished fecal continence that can be as high
as 45%.[24] [e2] Others would advocate drainage alone or the
placement of a loose, plastic seton to act as a drain in this
situation.[15] [21] The seton reduces the risk of recurrent anorectal
abscess and will allow for sphincter-preserving management of the
fistula after the acute infection has resolved and the fistula tract has
matured. If the anal fistula involves more than 25% of the sphincter
mechanism, fistulotomy is not an option but consideration can still
be given to placement of a seton to prevent recurrent anorectal
abscess.[18]
• If the abscess is being drained outside the operating room or under
local anesthesia, it may not be possible to perform an adequate
anal examination or place a seton. In this circumstance, there is a
risk of recurrent anorectal abscess.

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elderly, plus broad-spectrum antibiotics with anaerobic and gram-negative coverage
immunocompromised, • Broad-spectrum antibiotics with anaerobic and gram-negative
cardiac valvular coverage should be started preoperatively and be discontinued
disease, diabetes, or within 24 hours of surgery or after cellulitis has resolved.
significant associated • There is no standardized antibiotic regime in the literature.
cellulitis • In general, some combination of an IV broad-spectrum penicillin
(e.g., ampicillin/sulbactam) or a second- or third-generation
cephalosporin (e.g., cefoxitin or cefotetan) is combined with either
clindamycin, ciprofloxacin or metronidazole.

Primary Options
• ampicillin/sulbactam: 1 g orally/intravenously every 6 hours or
• Dose refers to ampicillin component.

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Treatment: Treatment Guidelines
Practice parameter for the treatment of perianal abscess and fistula-in-ano[26]
View Guidelines
Published by: American Society of Colon and Rectal Surgeons
Last Published: 2005
Summary
• Anorectal abscesses should be treated in a timely fashion by incision and drainage.
• Antibiotics are an unnecessary addition to incision and drainage of uncomplicated anorectal abscesses.

Followup
Followup: Outlook
Adequate drainage of the abscess should result in a prompt improvement in the symptoms.[17] Recurrence
of the anorectal abscess occurs in less than 2% of patients unless there is an associated anal fistula.[14]
[15]

Recurrence
Anorectal abscesses are associated with an anal fistula in about 37% of patients. A common clinical
manifestation of these anal fistulas is recurrent anorectal abscesses.[14] [15] These recurrent abscesses
occur when the fistula becomes occluded from impaction of food matter in the fistula tract or from healing
of the skin over the external opening of the fistula.

Followup: Complications
Complication LikelihoodTimeframe
recurrent anorectal abscess medium variable
• Recurrence of the anorectal abscess will occur in about 11% of patients, usually
from an unrecognized anal fistula.
• For patients who develop a recurrent anorectal abscess, examination by a
general or colorectal surgeon is indicated to exclude an anal fistula as the
cause.
anal fistula high variable
• An associated anal fistula will be present or develop in about 37% of patients
with an anorectal abscess.[14] [15]
• If examination at the time of surgical drainage reveals an associated anal
fistula, while controversial, consideration can be given to managing the fistula
at the same time.[20] [22] [23] [e1] If the anal fistula is superficial and involves
no more than 25% of the sphincter mechanism, some surgeons feel that the
anal fistula can be managed by fistulotomy.
necrotizing soft-tissue infection low short term
• Necrotizing soft-tissue infections of the perineum (Fournier gangrene) with
life-threatening sepsis may be present or develop in patients with anorectal
abscesses when there is a delay in diagnosis or management.
• This is more likely to occur in patients with diabetes, immunocompromise,
chronic debilitation or older age.[3] [10]

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Followup: Recommendations
Monitoring
Routine postoperative follow-up with perianal examination is needed every 2 to 3 weeks until the surgical
wound has healed. Recurrence of the abscess or persistence of the wound after 6 weeks is strongly
suggestive of an associated anal fistula and in these cases further evaluation is warranted.
Patient Instructions
Postoperatively, patients should be instructed to begin baths with comfortably warm water 2 or 3 times
daily to clean the perianal area until the surgical wound has healed. Warm water baths should also be
used for cleansing after bowel movements. Absorbent dressings can be used to prevent staining of the
underclothes. A diet which contains 25 to 30 g of dietary fiber/day and 60 to 80 ounces/day of fluid should
be considered to prevent hard stools.

Evidence Scores
e1. Decision to perform fistulotomy at time of abscess drainage: medium-quality evidence in the form of
a review of different treatment methods for anal fistula showed no true comparison of different methods
available and that the choice of treatment (e.g., primary or secondary fistulotomy) depends on a
number of factors, including experience of the surgeon, hospital facilities, patient history and local
anatomical structure.[27] Score: B
e2. Symptom improvement: medium-quality evidence in the form of a meta-analysis comparing abscess
drainage alone versus primary sphincter-cutting procedures for anorectal abscess-fistula found
insufficient evidence to favor one option over the other.[28] However, primary sphincter-cutting
procedures were associated with a higher risk of fecal incontinence.Score: B

Key Articles
• Nomikos IN. Anorectal abscesses: need for accurate anatomical localization of the disease. Clin Anat.
1997;10:239-244.[Abstract]
• Gilliland R, Wexner SD. Complicated anorectal sepsis. Surg Clin North Am. 1997;77:115-153. [Abstract]

Referenced Articles
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2. Marcus RH, Stine RJ, Cohen MA. Perirectal abscess. Ann Emerg Med. 1995;25:597-603.[Abstract]
3. Adinolfi MF, Voros DC, Moustoukas NM, et al. Severe systemic sepsis resulting from neglected
perineal infections. South Med J. 1983;76:746-749.[Abstract]
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1986;161:153-157.[Abstract] [Full Text ]
5. Rafal RB, Nichols JN, Cennerazzo WJ, et al. MRI for evaluation of perianal inflammation. Abdom
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6. Nomikos IN. Anorectal abscesses: need for accurate anatomical localization of the disease. Clin Anat.
1997;10:239-244.[Abstract]
7. Godec CJ, Cass AS, Ruiz E. Another aspect of acute urinary retention in young patients. Ann Emerg
Med. 1982;11:471-474.[Abstract]
8. Ramanujam PS, Prasad ML, Abcarian H, et al. Perianal abscesses and fistulas. A study of 1023
patients. Dis Colon Rectum. 1984;27:593-597.[Abstract]
9. Prasad ML, Read DR, Abcarian H. Supralevator abscess: diagnosis and treatment. Dis Colon Rectum.
1981;24:456-461.[Abstract]
10. Salvino C, Harford FJ, Dobrin PB. Necrotizing infections of the perineum. South Med J.
1993;86:908-911.[Abstract]
11. Gilliland R, Wexner SD. Complicated anorectal sepsis. Surg Clin North Am. 1997;77:115-153. [Abstract]

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12. Kovalcik PJ, Peniston RL, Cross GH. Anorectal abscess. Surg Gynecol Obstet.
1979;149:884-886.[Abstract]
13. Read DR, Abcarian H. A prospective survey of 474 patients with anorectal abscess. Dis Colon Rectum.
1979;22:566-568.[Abstract]
14. Hamalainen KP, Sainio AP. Incidence of fistulas after drainage of acute anorectal abscesses. Dis
Colon Rectum. 1998;41:1357-1361.[Abstract]
15. Vasilevsky CA, Gordon PH. The incidence of recurrent abscesses or fistula-in-ano following anorectal
suppuration. Dis Colon Rectum. 1984;27:126-130.[Abstract]
16. Millan M, Garcia-Granero E, Esclapez P, et al. Management of intersphincteric abscesses. Colorectal
Dis. 2006;8:777-780.[Abstract]
17. Onaca N, Hirshberg A, Adar R. Early reoperation for perirectal abscess: a preventable complication.
Dis Colon Rectum. 2001;44:1469-1473.[Abstract]
18. Williams JG, MacLeod CA, Rothenberger DA, et al. Seton treatment of high anal fistulae. Br J Surg.
1991;78:1159-1161.[Abstract]
19. Sangwan YP, Schoetz DJ Jr, Murray JJ, et al. Perianal Crohn's disease. Results of local surgical
treatment. Dis Colon Rectum. 1996;39:529-535.[Abstract]
20. Tang CL, Chew SP, Seow-Choen F. Prospective randomized trial of drainage alone vs. drainage and
fistulotomy for acute perianal abscesses with proven internal opening. Dis Colon Rectum.
1996;39:1415-1417.[Abstract]
21. Schouten WR, van Vroonhoven TJ. Treatment of anorectal abscess with or without primary
fistulectomy. Results of a prospective randomized trial. Dis Colon Rectum. 1991;34:60-63.[Abstract]
22. Cox SW, Senagore AJ, Luchtefeld MA, et al. Outcome after incision and drainage with fistulotomy
for ischiorectal abscess. Am Surg. 1997;63:686-689.[Abstract]
23. Knoefel WT, Hosch SB, Hoyer B, et al. The initial approach to anorectal abscesses: fistulotomy is
safe and reduces the chance of recurrences. Dig Surg. 2000;17:274-278.[Abstract] [Full Text ]
24. Garcia-Aguilar J, Belmonte C, Wong WD, et al. Anal fistula surgery. Factors associated with recurrence
and incontinence. Dis Colon Rectum. 1996;39:723-729.[Abstract]
25. Chrabot CM, Prasad ML, Abcarian H. Recurrent anorectal abscesses. Dis Colon Rectum.
1983;26:105-108.[Abstract]
26. Whiteford MH, Kilkenny J 3rd, Hyman N, et al. Practice parameters for the treatment of perianal
abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48:1337-1342.[Abstract] [Full Text ]
27. Holzheimer RG, Siebeck M. Treatment procedures for anal fistulous cryptoglandular abscess - how
to get the best results. Eur J Med Res. 2006;11:501-515. [Abstract]
28. Quah HM, Tang CL, Eu KW, et al. Meta-analysis of randomized clinical trials comparing drainage
alone vs primary sphincter-cutting procedures for anorectal abscess-fistula. Int J Colorectal Dis.
2006;21:602-609. [Abstract]

Credits
Authors
C. Neal Ellis
Professor of Surgery
University of South Alabama
Mobile
AL
CNE declares that he has no competing interests.

Peer Reviewers
Jan Rakinic
Associate Professor of Surgery
Chief
Section of Colorectal Surgery
Southern Illinois University School of Medicine

Page 17
Springfield
IL
Mark H. Whiteford
Assistant Professor of Surgery
Colon and Rectal Surgery
Gastrointestinal and Minimally Invasive Surgery Division
The Oregon Clinic
Portland
OR
Neil Hyman
Chief
Division of General Surgery
Professor of Surgery
Fletcher Allen Healthcare
Burlington
VT
JR is a co-author of a reference cited in this monograph.
MHW declares that he has no competing interests.
NH declares that he has no competing interests.

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