An anal, or rectal, abscess occurs when a cavity in the anus becomes filled with pus. It causes extreme pain, fatigue, rectal discharge, and fever. In some cases, anal abscesses can result in painful anal fistulas. This occurs when the abscess doesn’t heal and breaks open on the surface of the skin. If an anal abscess doesn’t heal, it can cause a lot of pain and may require surgery. Diagnosis of anorectal abscess includes:

Clinical evaluation
Sometimes examination under anesthesia or rarely CT

Patients who have a pointing cutaneous abscess, a normal digital rectal examination, and no signs of systemic illness do not require imaging. CT scan is useful when a deep abscess or Crohn disease are suspected. Higher (supralevator) abscesses require CT to determine the intra-abdominal source of the infection. Those with any findings suggestive of a deeper abscess or complex perianal Crohn disease should have an examination under anesthesia at the time of drainage.