An anal abscess is a localised collection of pus in the anal region, most commonly caused by a bacterial infection involving the anal glands. These small structures, located within the anal canal, may become obstructed, creating an environment that encourages bacterial growth. This leads to an accumulation of purulent material in the surrounding tissues, causing inflammation, swelling and local pain, which is often severe.
Classification of anal abscesses
Anorectal abscesses are classified according to the anatomical site affected by the infection. Correct identification of their location is essential, as it influences both diagnosis and surgical treatment. The perianal abscess is the most common and generally the easiest form to recognise: it develops close to the anal opening and is often associated with pain, redness and visible swelling. However, there are also deeper and more complex forms, closely related to the sphincter muscles, which are essential structures for faecal continence and for controlling the passage of gas and stool. The main anatomical variants include:
- Ischiorectal abscess: affects the deep spaces, crosses the sphincter and extends into the ischiorectal fossa, beneath the levator ani muscle. In some cases, it may also spread to the opposite side, forming the characteristic “horseshoe abscess”.
- Intersphincteric abscess: located between the internal and external anal sphincters. It is considered a particularly insidious type of abscess, as the purulent collection is deep and often not visible on external examination, making diagnosis more challenging.
- Pelvirectal abscess (or supralevator abscess): a rarer but more complex form. The infection develops deep above the levator ani muscle and may extend towards the peritoneum or nearby abdominal organs, potentially leading to severe clinical conditions.
Causes and risk factors
The main cause of an anal abscess is usually the penetration of bacteria or foreign material into the anal glands. This obstruction leads to impaired glandular drainage, stagnation, subsequent infection and abscess formation. However, several diseases, factors and conditions may contribute to the development of an anal abscess:
- local trauma;
- changes in stool consistency;
- proctocolitis and proctitis;
- chronic inflammatory bowel diseases (such as Crohn’s disease or ulcerative colitis);
- surgical complications;
- sexually transmitted infections;
- reduced immune defences.
Symptoms
The symptoms of an anal abscess vary depending on the location and depth of the infection. Deep abscesses may present with fewer obvious local signs but more pronounced systemic symptoms, including general malaise, fatigue, fever and abdominal or pelvic pain. Perianal abscesses, on the other hand, usually present with a more typical and easily recognisable clinical picture. The main symptoms include:
- intense, throbbing and persistent pain in the anal region;
- a local burning sensation;
- swelling near the anus;
- redness of the surrounding skin;
- difficulty walking, sitting or passing stools.
In the early stages, the patient may not immediately notice the swelling, as the purulent collection and tissue enlargement often represent the final stage of the infectious process. Pain, by contrast, tends to appear early and progressively worsen over hours or days, eventually becoming constant throughout the day. Symptoms typically worsen during defecation due to increased pressure in the anal region and may significantly affect the patient’s quality of life.
Diagnosis and treatment
When symptoms of an anal abscess appear, it is essential to consult a proctology specialist promptly in order to properly assess the extent of the condition and establish the most appropriate treatment. Diagnosis is initially based on a clinical assessment, including digital rectal examination and anoscopy, which allows visualisation of the anal canal and identification of inflammatory signs or purulent collections. In more complex cases, or when deep abscesses are suspected, the doctor may request further diagnostic investigations, including endoanal ultrasound, MRI scan, CT scan, colonoscopy and blood tests.
The main treatment consists of surgical incision and drainage of the purulent material. The procedure may be performed under local or general anaesthesia, depending on the depth and extent of the lesion, and is essential to rapidly resolve the infection and relieve pain. In specific situations, such as high fever, diabetes, marked cellulitis, immunosuppression or risk of systemic spread, antibiotic therapy is combined with surgical treatment. Prompt and appropriate intervention is crucial to prevent possible complications, including the formation of anal fistulas or the spread of inflammation to surrounding tissues.
❗The contents of this page are for informational purposes only and should in no way replace the advice, diagnosis, or treatment prescribed by your physician. Responses to the same treatment may vary from patient to patient. Always consult your doctor regarding any information related to diagnoses and treatments, and meticulously follow their instructions.
