Perianal Abscess

Question 1

A perianal abscess is a?

Answer 1

collection of pus within the subcutaneous tissue of the anus that has tracked from the tissue surrounding the anal sphincter.

Question 2

Epidemiology of perianal abscess

Answer 2

They are the most common form of anorectal abscess, making up around 60% of cases;

They are more common in men (M:F 2:1);

The average age of patients is around 40 years.

Question 3

Clinical presentation of perianal abscess

Answer 3

Patients may describe pain around the anus, which may be worse on sitting;

They may have also discovered some hardened tissue in the anal region;

There may be pus-like discharge from the anus;

If the abscess is longstanding, the patient may have features of systemic infection.

Question 4

Causes of perianal abscess

Answer 4

They are generally colonised by gut flora such as E. coli;

Those caused by organisms such as Staph. aureus are more likely to be an infection of the skin rather than originating from the digestive tract.

Question 5

Investigations for perianal abscess?

Answer 5

Most perianal abscesses can be detected through inspection of the anus and digital rectal examination;

When querying the underlying cause, colonoscopy and blood tests such as cultures and inflammatory markers may be of use;

Imaging such as MRI and transperineal ultrasound can be useful tools, with the former being the gold standard in imaging anorectal abscesses. They are however rarely used except for cases where the abscess has complications or is part of a more serious underlying process such as IBD.

Question 6

Associated conditions

Answer 6

Any anorectal abscess can be caused by an underlying inflammatory bowel disorder,
especially Crohn’s;

Diabetes mellitus is a risk factor due to its ability to affect wound healing;

Underlying malignancy can cause these abscesses as well as other anorectal lesions due to the risk of bowel perforation.

Question 7

Treatment of perianal abscess

Answer 7

Treatment is usually surgical, with incision and drainage being first line, usually under local anaesthetic. The wound can then either be packed or left open, in which case it will heal in around 3-4 weeks;

Antibiotics can be of use, but are only usually employed if there is systemic upset secondary to the abscess, as they do not seem to help with healing of the wound after drainage.

Question 8

‘perianal abscess’ refers to a simple abscess of the subcutaneous tissue. There are numerous other anorectal abscesses which can be classified by the layers and planes that they occupy.

Answer 8

Ischiorectal abscesses are found between the obturator internus muscles and the external anal sphincter;

Supralevator abscesses form when infection tracks superiorly from the peri-sphincteric area to above the levator ani;

Intersphincteric abscesses are rare (2-5% of cases) and as their name suggests are sited between the internal and external anal sphincters;