Abdominal Abscess

How an abdominal abscess forms

The bowel contains huge numbers of bacteria. When the bowel wall is breached by inflammation, perforation or surgery, bacteria leak into the abdominal cavity. The body's defenses, including the omentum (a fatty apron in the abdomen) and inflamed bowel loops, wall off the infection to stop it spreading. This creates a contained pocket of pus. Antibiotics struggle to penetrate an abscess, which is why drainage is usually needed.

Abscesses are named by location:

• Pelvic abscess: low in the pelvis, after appendicitis, diverticulitis or gynecologic infection
• Subphrenic abscess: under the diaphragm, often after upper abdominal surgery
• Paracolic abscess: beside the colon, typically from diverticulitis
• Organ abscesses: in the liver, spleen or pancreas
• Psoas abscess: in the muscle at the back of the abdomen, from Crohn's disease or spinal infection

See also intra-abdominal abscess.

Causes and risk factors

• Appendicitis that has perforated
• Diverticulitis: abscesses form in a significant minority of acute attacks
• Crohn's disease: inflamed bowel can form fistulas and abscesses
• Abdominal surgery, especially bowel surgery with a leak at the join (anastomotic leak). See postoperative infection
• Bowel perforation from ulcers, injury or cancer
• Pelvic inflammatory disease (tubo-ovarian abscess)
• Pancreatitis with infected fluid collections
• Liver abscess from biliary infection, bowel infection spreading through the bloodstream, or amoebic infection after travel

Risk is higher with diabetes, steroid use, immune suppression, obesity and older age.

Symptoms

• fever, often spiking and with chills or sweats
• abdominal pain, usually localized to one area and worse with movement
• tenderness and sometimes a palpable mass
• loss of appetite, nausea and vomiting
• diarrhea or a frequent urge to pass stool (especially with pelvic abscesses)
• shoulder-tip pain or hiccups (subphrenic abscess)
• hip or back pain and limping (psoas abscess)
• a slow recovery after surgery, with ongoing fever and poor appetite

Diagnosis

1. Blood tests: raised white cell count and inflammatory markers (CRP), blood cultures, kidney and liver function.
2. CT scan with contrast: the main test; it shows the size, location and number of collections and helps plan drainage.
3. Ultrasound: useful for liver abscesses, pelvic collections and in children or pregnancy.
4. MRI: for pelvic and perianal abscesses in Crohn's disease.
5. Fluid sampling: pus obtained during drainage is sent to the lab to identify bacteria and guide antibiotics.

Treatment

Antibiotics

Broad-spectrum intravenous antibiotics covering gut bacteria are started promptly, then tailored to culture results. Very small abscesses (generally under about 3 cm) may be treated with antibiotics alone. Treatment usually continues for about 4 days after good drainage in uncomplicated cases, longer for liver abscesses or if drainage is incomplete.

Percutaneous drainage

For most abscesses, a radiologist uses CT or ultrasound guidance to insert a needle through the skin into the abscess under local anesthetic and sedation. A thin drain tube is left in place to let pus flow out. This avoids open surgery in most cases. Drains are flushed regularly and removed once output stops and a scan confirms the abscess has resolved.

Surgery

Surgery (laparoscopic or open) is needed when:

• the abscess cannot be reached safely with a needle
• there are multiple collections
• there is widespread peritonitis or a persistent leak
• drainage fails

After a diverticular or appendix abscess has settled, surgery to remove the affected bowel may be offered later in selected patients.

Supportive care

Fluids, pain relief, nutrition support and control of blood sugar aid recovery.

Complications

• sepsis and septic shock
• spread to cause generalized peritonitis
• fistulas (abnormal connections between bowel and skin, bladder or other organs)
• recurrence
• bowel obstruction from scar tissue

Outlook

With prompt drainage and antibiotics, most people recover well, typically feeling better within 48 to 72 hours. Recovery is slower in older adults, people with multiple abscesses or weakened immunity. Follow-up imaging confirms the abscess has gone. If the underlying cause is diverticulitis or Crohn's disease, a colonoscopy or specialist follow-up is usually arranged.

Frequently asked questions

What are the symptoms of an abdominal abscess?

The main symptoms are fever, chills, belly pain and tenderness in one area, loss of appetite, nausea and feeling generally unwell. Pelvic abscesses can cause diarrhea or urgency to pass stool. Symptoms often appear days to weeks after appendicitis, diverticulitis or surgery.

How is an abdominal abscess treated?

Most are treated with antibiotics and drainage. A radiologist inserts a thin tube through the skin into the abscess using CT or ultrasound guidance to drain the pus. Small abscesses may respond to antibiotics alone. Surgery is needed when drainage is not possible or fails.

Can an abdominal abscess go away on its own?

Very small abscesses sometimes resolve with antibiotics alone, but most need drainage. An untreated abscess can rupture, cause peritonitis or lead to sepsis, which can be life-threatening. Any suspected abscess needs medical assessment.

How long does it take to recover from an abdominal abscess?

Most people feel better within 2 to 3 days of drainage. Drains often stay in for 1 to 3 weeks, and full recovery can take several weeks, depending on the cause, the size of the abscess and overall health.

Why do abscesses form after abdominal surgery?

Bacteria from the bowel can contaminate the abdomen during surgery, or a join in the bowel can leak afterward. The body walls off the infection, forming an abscess. Fever and worsening pain several days after surgery are typical warning signs.