History and exam
Key diagnostic factors
common
anal fistula
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.
history of Crohn's disease
Considered a key risk factor. Anorectal abscesses will develop in approximately one third of patients with Crohn's disease.[1]
perianal pain
Extremely common symptom of an anorectal abscess.[2]
Anal canal pain occurs more commonly with inter-sphincteric abscesses and pelvic pain is more commonly due to supra-levator 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 haemorrhoids 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
The vast majority of patients with anorectal abscesses will have induration in the perianal tissues, in the anal canal, or above the anorectal ring.
This sign may be absent in those with a compromised immune system.
Other diagnostic factors
common
perianal swelling
Swelling and tenderness of the perianal tissues is a frequent complaint.
Swelling may be absent in patients with inter-sphincteric or supra-levator abscesses, or those with a compromised immune system.
low-grade fever
Most patients with an anorectal abscess have a fever, though this is usually <38.6ºC (101.5ºF).
Fever is usually absent in those with a compromised immune system.
tachycardia
Mild tachycardia is frequently observed.
The aetiology can be multi-factorial, including slight volume depletion from inadequate oral intake of fluids, possibly related to fever and pain.
uncommon
change in bowel habits
There is seldom any change in bowel habits in patients with anorectal abscesses. A history of chronic diarrhoea may suggest Crohn's disease, a risk factor for anorectal abscess.
rectal bleeding
Usually absent unless the abscess has spontaneously drained.
The presence of rectal bleeding is more indicative of an anal fissure.
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.
Between 30% to 70% of anorectal abscesses present with concomitant fistula, and around 30% to 50% of patients with anorectal abscesses develop an anal fistula in the months or years following drainage.[4] Fistulae result from the drainage, either surgical or spontaneous, of the anorectal abscess.
Crohn's disease
Anorectal abscesses will develop in approximately one third of patients with Crohn's disease.[1]
The majority of anorectal abscesses result from infections of the anal glands (cryptoglandular infections).[12] 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's disease.
male sex
Anorectal abscesses are about 2 times more common in men than women.[14]
weak
hard stools
Hard stools are a risk factor for anorectal abscesses, though a diet that contains 25 to 30 g/day of fibre and 60 to 80 ounces/day of fluid has not been shown to prevent anorectal abscesses.[15]
age 21 to 40 years
Most anorectal abscesses occur in patients between 21 to 40 years of age.[14]
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