Facts About Anal or Rectal Abscess

An anorectal abscess (also referred to as an anal abscess, rectal abscess, perianal abscess, or perirectal abscess depending on its location) is a pus-filled cavity that forms within the furrows of the anal canal (called the anal sinuses). Anorectal abscesses are most often caused by the accumulation of common bacteria ​in vulnerable or compromised tissues. As your body tries to control the infection, white blood cells killed in the battle and other bodily fluids start to collect in the tissue, forming a pocket of pus.

Abscesses can form near or within the anus or develop much higher up in the rectum itself. While an abscess can form spontaneously for no apparent reason, it is commonly associated with gastrointestinal disease, bowel irregularities, immune suppression, and even certain medications.

Anorectal abscesses are usually first recognized because of a dull, throbbing pain in the anus or rectum, often accompanied by sharp pain when defecating. 

Perianal abscesses ("peri-" meaning around) are the most common type and can usually be identified visually as they occur in the upper layers of tissue. When touched, the lump will usually be tender, red, and warm. By contrast, perirectal abscesses tend to form deeper tissues and are often more felt than seen. Of the two types, a perirectal infection tends to be more serious.

As the pus starts to consolidate and form a palpable mass, other symptoms of an anorectal abscess appear, including:

• Fever
• Fatigue
• Constipation
• Rectal discharge and bleeding
• Feeling like you need to go to the bathroom when you don’t
• Increasing and often constant pain, worsening with movement or while sitting

If you experience any of these symptoms, it is important to see a doctor and have a thorough examination. If left untreated, an abscess can lead to the development of an anal fistula, an abnormal tunneling connection between the skin around the anus and the rectal or anal canal through which stool and pus may drain. This may require intensive surgery and a prolonged period of recovery.

If you develop a high fever (over 100.4 degrees), shaking chills, persistent vomiting, the inability to have a bowel movement, or extreme anal or rectal pain (with or without a bowel movement), go to the emergency room without delay. These may indicate a systemic infection that has spread from the site of the abscess into the bloodstream.

Without proper treatment, a systemic infection of this sort can lead to sepsis, toxic shock, and even death.

An anorectal abscess can develop in isolation, often due to the overgrowth of bacteria common in the digestive tract, such as Escherichia coli (E. coli). However, in recent years, there has been an increasing number of cases associated with methicillin-resistant Staphylococcus aureus (MRSA), a difficult-to-treat bacterial strain that can be passed through skin-to-skin contact.

While anyone, young or old, can get an anorectal abscess, there are a number of conditions that can increase your risk. They include:

• Inflammatory bowel diseases (IBD) like Crohn's disease and ulcerative colitis
• HIV and other forms of immune suppression
• Diabetes
• Anal sex
• Chronic or severe constipation or diarrhea
• Steroid drug use, including prednisone
• Chemotherapy
• Sexually transmitted infections of the anus or rectum
• Hidradentis suppurativa, a rare skin condition

Most anorectal abscesses are diagnosed based on your medical history and a physical exam. If an abscess is internalized within the anal canal, your doctor may want to perform an endoscopy, using a flexible, lighted endoscope to get a better look inside.

Less commonly, imaging tests such as computed tomography (CT) scan or a transrectal ultrasound (TRUS) may be used if the abscess is especially deep.

During the physical exam, your doctor will want to ascertain whether the mass is an abscess or hemorrhoid. The two conditions can usually be differentiated by the presentation of symptoms.

With an abscess, the pain will worsen over time and fail to respond to standard hemorrhoid treatment. There may also be generalized symptoms of infection that you would not commonly experience with hemorrhoids, such as fever and nighttime chills.

Other tests may be ordered if IBD, HIV, or diabetes is suspected, including blood tests and colonoscopy.

Anorectal abscesses rarely go away on their own or resolve solely with antibiotic therapy. In most cases, the doctor would need to drain the abscess, a relatively simple in-office procedure that involves a local numbing agent, a scalpel, and a pair of forceps.

If the abscess is especially deep or situated high in the rectum, the procedure needs to be performed in a hospital under general anesthesia. The surgery generally takes around 30 minutes. Some of the extracted pus may be sent to the lab to identify the causal bacterium.

Once the procedure is done, antibiotics are prescribed for around a week to help treat the infection and prevent any further spread. You may also be advised to use a sitz bath, a shallow basin used to soak and clean the anal area. Tylenol (acetaminophen) is sometimes prescribed to help relieve the pain.

During recovery, stool softeners may be needed to reduce abrasion and allow the drained abscess to better heal. After a bowel movement, dab softly with toilet paper and rinse with a squirt bottle filled with warm water. Wash lightly with soap but avoid alcohol or hydrogen peroxide, which can slow healing. If needed, pad the wound with gauze or a maxipad.

You can also ask your doctor about the short-term use of over-the-counter topical creams and gels, which may help soothe anal tissues.

The drainage of an abscess will provide almost immediate relief. While there may some pain after the procedure, it will usually be mild by comparison. However, if you experience excessive rectal bleeding, fever, chills, or vomiting after returning home from the procedure, call your doctor immediately.