ConditionDigestive system
Perirectal Infection (Perirectal and Perianal Abscess)
A perirectal infection is a bacterial infection in the tissues around the anus and lower rectum. Most start in a small gland inside the anal canal that becomes blocked and forms a pocket of pus (an anorectal abscess). It causes constant, throbbing pain near the anus, swelling and often fever. The main treatment is surgical drainage, not antibiotics alone. About a third of people later develop an anal fistula, and rare deep or spreading infections can be life-threatening.
Also called: Perirectal abscess, perianal abscess, anorectal abscess, ischiorectal abscess
At a glance
- What it is
- A pus-filled infection next to the anus or rectum, usually starting in an anal gland.
- Key symptoms
- Constant throbbing pain, a tender lump, fever, and pain when sitting or passing stool.
- Who gets it
- Most often men aged 20 to 60; more common with Crohn's disease, diabetes and weak immunity.
- Treatment
- Incision and drainage, with antibiotics for some people.
- Main complication
- An anal fistula in roughly 1 in 3 people.
When to get help
Call 911 or go to the ER
- Rapidly spreading redness, blackened or crackling skin, or severe pain around the anus, scrotum or groin (possible Fournier gangrene)
- Fever with confusion, fast heart rate, low blood pressure or feeling extremely unwell (possible sepsis)
- Inability to pass urine with severe rectal pain
See a doctor within a day or two
- A painful, hot, tender lump beside the anus
- Deep rectal pain and fever without a visible lump (possible deep abscess)
- Any anal abscess in someone with diabetes, a weakened immune system, chemotherapy or Crohn's disease
- An abscess that has burst but pain and fever continue
Book a routine appointment
- Recurring boils or abscesses in the same area
- Persistent discharge of pus or blood from an opening near the anus after an abscess (possible fistula)
What a perirectal infection is
The anal canal has 6 to 10 small glands that open into the lining at the dentate line, about 2 cm inside the anus. If one becomes blocked, bacteria from stool multiply and the infection tracks outward into the fatty tissue around the anus and rectum, forming an abscess. This is the cryptoglandular theory, and it explains about 90% of cases.
Doctors name the abscess by where the pus collects:
| Type | Location | How it shows |
|---|---|---|
| Perianal | Just under the skin at the anal edge | Visible red, tender lump; the most common type |
| Ischiorectal (ischioanal) | Deeper, in the fat beside the rectum | Large, diffuse buttock swelling, fever |
| Intersphincteric | Between the two anal sphincter muscles | Deep rectal pain with little visible outside |
| Supralevator | Above the pelvic floor muscles | Pelvic or rectal pain, fever, sometimes urinary retention |
| Horseshoe | Spreads around both sides behind the anus | Pain and swelling on both sides |
A perianal abscess is the surface form. "Perirectal" is often used for all of these, and especially for the deeper ones.
Symptoms
- constant, throbbing pain near the anus, worse when sitting, coughing or passing stool
- a tender, warm, red swelling beside the anus
- fever, chills and feeling unwell, more common with deep abscesses
- pus or blood draining if the abscess bursts, often with sudden pain relief
- constipation from pain, and sometimes difficulty passing urine
Deep abscesses can cause fever and rectal pain with nothing visible on the skin, so they are easy to miss.
Causes and risk factors
- blocked anal glands (most cases)
- Crohn's disease, which causes complex and recurring abscesses and fistulas
- diabetes and obesity
- weakened immunity: HIV, chemotherapy, steroids, low white cell counts
- anal sex, trauma or foreign bodies
- less commonly tuberculosis, sexually transmitted infections, cancer or radiation
Diagnosis
Most perianal abscesses are diagnosed by looking and gently feeling the area. A rectal exam may reveal a tender, swollen area for deeper abscesses. Imaging is used when the abscess is deep, recurrent or linked to Crohn's disease:
- CT scan for suspected deep or spreading infection
- pelvic MRI, the best test to map abscesses and fistula tracts
- endoanal ultrasound as an alternative
- blood tests, including white cell count, blood sugar and blood cultures if sepsis is suspected
- examination under anesthesia in the operating room for complex cases
Treatment
Incision and drainage
Drainage is the essential treatment. Antibiotics alone do not cure an abscess because they cannot penetrate the pus pocket. Small superficial abscesses are drained under local anesthetic; deeper ones need surgery under general or spinal anesthesia. The surgeon may leave a small drain or a loose thread (seton) if a fistula is found.
Antibiotics
Antibiotics are added for people with diabetes, weak immunity, heart valve problems, spreading skin infection (cellulitis) or signs of sepsis.
Aftercare
- Soak in a warm sitz bath 2 to 3 times a day and after bowel movements.
- Take pain relief following the label dose.
- Use stool softeners and fiber to avoid straining.
- Wear a pad to absorb drainage for a few days to weeks.
- Most wounds heal within 3 to 4 weeks.
Complications
- Anal fistula: a tunnel between the inside of the anal canal and the skin, causing persistent discharge. It needs surgery to heal.
- Recurrence, especially if drainage was incomplete or a fistula is present.
- Necrotizing soft tissue infection (Fournier gangrene): a rare, rapidly spreading infection that needs emergency surgery. People with diabetes are at greater risk.
- Sepsis.
- Damage to the sphincter muscles from infection or repeated surgery, causing leakage of stool.
Outlook
Most people recover fully after drainage, with pain improving within a day or two. Recurrence or fistula formation affects a significant minority, so persistent discharge after healing should be checked by a colorectal surgeon.
Frequently asked questions
What causes a perirectal infection?
Most start when one of the small glands inside the anal canal becomes blocked and infected by bacteria from stool. Crohn's disease, diabetes, weakened immunity and anal injury raise the risk. It is not caused by poor hygiene.
What does a perirectal abscess feel like?
It usually causes constant, throbbing pain near the anus that gets worse when you sit, move or pass stool. There may be a hot, red, tender lump and a fever. Deep abscesses may cause only rectal pain and fever.
Can a perirectal abscess heal without drainage?
Sometimes a small abscess bursts and drains by itself, which relieves pain. It may still need medical review to check that drainage is complete and to look for a fistula. Most abscesses need to be drained by a clinician, and antibiotics alone rarely cure them.
How long does it take to recover after abscess drainage?
Pain usually eases within 1 to 2 days of drainage. The wound typically heals in 3 to 4 weeks with sitz baths and gentle care. Most people return to desk work within a few days.
Is a perirectal abscess the same as a hemorrhoid?
No. A thrombosed hemorrhoid is a painful bluish lump caused by a blood clot in a vein at the anal edge. An abscess is an infection with pus, causes increasing throbbing pain, warmth and often fever, and needs drainage. A doctor can tell them apart quickly on examination.
Sources
This guide was written from current patient and clinical guidance, including:
- American Society of Colon and Rectal Surgeons: Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula
- MedlinePlus: Anorectal abscess
- NHS: Anal fistula
- American Society of Colon and Rectal Surgeons: Abscess and fistula expanded information
- Merck Manual Professional Version: Anorectal abscess