Intra-abdominal abscess

Gastroenterology (12%) Core Clinical Conditions

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Definition Aetiology Pathophysiology Sign and Symptoms Investigations Management

An intra-abdominal abscess, also known as an abdominal abscess, is a localised collection of pus that forms within the abdominal cavity. It occurs as a result of bacterial infection, usually arising from a perforated organ, inflammation, or postoperative complications. This type of abscess can develop in various areas within the abdomen, including the liver, spleen, appendix, gallbladder, or intestines. The formation of an intra-abdominal abscess typically follows an initial insult to the abdominal cavity, such as appendicitis, diverticulitis, Crohn's disease, or gastrointestinal perforation. When bacteria invade the abdominal space due to these conditions, they can multiply rapidly and lead to the accumulation of infected fluids and debris.

1. Postoperative Complications: One of the most common causes of intra-abdominal abscesses is postoperative complications following abdominal surgery. Surgical procedures, such as appendectomy, cholecystectomy, or bowel resection, may disrupt the normal anatomy and introduce bacteria into the abdominal cavity. These bacteria can then cause infection and lead to abscess formation.
2. Diverticulitis: Abscesses can also develop as a complication of diverticulitis, which refers to the inflammation or infection of small pouches (diverticula) that form in the walls of the colon. When these pouches become infected, they can cause localised pockets of pus to form, resulting in an intra-abdominal abscess.
3. Acute Pancreatitis: In some cases, intra-abdominal abscesses can occur as a complication of acute pancreatitis. The inflammation of the pancreas can lead to the development of pseudocysts or necrotic tissue, which can become infected and form an abscess. This condition requires prompt medical attention due to the potential for severe complications.
4. Perforated Viscus: When there is a perforation or rupture of an abdominal organ, such as the stomach, small intestine, or colon, it can lead to the formation of an intra-abdominal abscess. Conditions such as peptic ulcers, perforated diverticulitis, or perforated appendicitis can cause these perforations, allowing bacteria to enter the abdominal cavity and trigger abscess formation.
5. Foreign Body: In rare cases, the presence of a foreign body within the abdominal cavity can lead to the development of an abscess. This can occur when a foreign object, such as a surgical sponge or mesh, is accidentally left inside the body during surgery. These foreign bodies can act as a nidus for bacterial growth, resulting in abscess formation.
6. Immunocompromised Individuals: Individuals with weakened immune systems, such as those with HIV/AIDS, undergoing chemotherapy, or on long-term immunosuppressive therapy, are at an increased risk of developing intra-abdominal abscesses. Their reduced ability to fight off infections and control bacterial growth makes them more susceptible to abscess formation.

Pathophysiology of Intra-abdominal Abscess

Intra-abdominal abscess refers to the localised collection of pus within the abdominal cavity, typically caused by a bacterial infection. To comprehend the pathophysiology of an intra-abdominal abscess, it is essential to understand the underlying mechanisms that lead to its formation.

Infection and Inflammation

The primary cause of an intra-abdominal abscess is an initial bacterial infection within the abdominal cavity. This can occur due to conditions such as appendicitis, diverticulitis, perforated viscus, or after abdominal surgery. Bacteria can gain access to the peritoneal cavity through various routes, including direct extension from infected organs or through blood circulation.

Once bacteria enter the peritoneal cavity, they provoke an immune response, leading to inflammation. This inflammatory response is characterised by the release of inflammatory mediators such as cytokines, chemokines, and prostaglandins. Inflammation serves as the body's defence mechanism to eliminate the invading pathogens and initiate the healing process.

Formation of Abscess

During the early stages of infection, inflammation triggers an increase in blood flow to the infected site, attracting immune cells to clear the infection. Neutrophils are the predominant immune cells involved in combating the infection. These cells release various enzymes and chemicals to neutralise bacteria and destroy infected tissues. As the infection progresses, local tissue necrosis occurs due to the aggressive nature of the immune response and bacterial toxins.

The necrotic tissues, bacteria, and immune cells accumulate, forming a localised collection of pus, known as an abscess. Abscesses contain a mixture of dead tissue, bacteria, immune cells, and fluid. The abscess wall forms as a result of surrounding inflamed tissues attempting to seal off the infection, preventing the spread of infection to other areas of the abdomen.

Clinical Manifestations

The symptoms and clinical manifestations of an intra-abdominal abscess may vary depending on its location, size, and the patient's general health. Common clinical features include abdominal pain, tenderness, fever, chills, nausea, and vomiting. In some cases, an abscess can exert pressure on adjacent organs, leading to additional symptoms such as altered bowel movements or difficulty urinating.

1. Abdominal Pain: One of the most significant symptoms of an intra-abdominal abscess is persistent and severe abdominal pain. The pain is usually localised to the affected area and may gradually worsen over time. It can be described as a dull ache or a sharp stabbing sensation.
2. Fever and Chills: Intra-abdominal abscesses often lead to an elevated body temperature, resulting in fever and chills. The fever can range from mild to high-grade, accompanied by intensified sweating and shivering.
3. Gastrointestinal Disturbances: Patients with an intra-abdominal abscess may experience a variety of gastrointestinal symptoms. These can include nausea, vomiting, diarrhoea, constipation, and a generalised feeling of indigestion or discomfort.

4. Loss of Appetite and Weight Loss: As a consequence of the abdominal pain and associated symptoms, individuals suffering from an intra-abdominal abscess often experience a reduction in appetite leading to significant weight loss. This loss of nourishment and energy can further weaken the immune system.

5. Abdominal Swelling and Tenderness: The affected area may become swollen and tender to touch due to the inflammation caused by the abscess. The swelling might be localised or involve a larger abdominal area, depending on the size and location of the abscess.

6. Changes in Bowel Habits: In some cases, the presence of an intra-abdominal abscess can cause alterations in bowel movements. This can manifest as increased gas, bloating, or changes in stool consistency, such as diarrhoea or bloody stool.

7. Malaise and Fatigue: The continuous infection and presence of an abscess can lead to a general feeling of malaise and fatigue. Patients may experience a decreased level of energy, weakness, and a reduced ability to perform daily activities.

1. Clinical Assessment:
A comprehensive clinical evaluation is the initial step in diagnosing an intra-abdominal abscess. The patient's medical history, presenting symptoms, and physical examination findings can provide valuable clues. Symptoms such as abdominal pain, fever, nausea, vomiting, and altered bowel movements are typically observed. On physical examination, tenderness, rigidity, or palpable masses in the abdomen may be noted.
2. Laboratory Tests:
Routine laboratory investigations play a supportive role in the diagnosis of intra-abdominal abscesses. Blood tests, including full blood count (FBC), liver function tests (LFTs), and inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), can indicate the presence of infection and inflammation. Elevated white blood cell (WBC) count is a common finding.
3. Imaging Studies:
Imaging plays a pivotal role in diagnosing and characterising intra-abdominal abscesses. Different modalities can be utilised based on the suspected location and size of the abscess. These may include:

• Ultrasound (US): This non-invasive imaging technique is often employed as the first-line investigation for intra-abdominal abscesses. US provides real-time images and is particularly useful in detecting fluid collections. It helps in guiding the needle for aspiration or drainage procedures, providing additional diagnostic and therapeutic benefits.

• Computed Tomography (CT) Scan: CT scan with intravenous contrast is considered the gold standard imaging modality for diagnosing intra-abdominal abscesses. It provides detailed cross-sectional images, facilitating the identification of the abscess location, size, and extent. CT scan also helps in evaluating the surrounding structures, determining the aetiology and possible complications, and guiding therapeutic intervention.

• Magnetic Resonance Imaging (MRI): In certain situations, such as when CT scan is contraindicated or further characterization of the abscess is required, MRI may be used. MRI offers excellent soft tissue contrast and can provide valuable information about the abscess and its relationship with neighbouring organs.

• Abdominal X-ray.

Intervention

The management of intra-abdominal abscesses typically involves a combination of medical therapy, percutaneous drainage, and surgical intervention. The choice of intervention depends on several factors, including the patient's clinical condition, abscess size, location, and underlying cause.

Medical Therapy

Medical therapy plays an essential role in treating intra-abdominal abscesses. It comprises broad-spectrum antibiotics targeting the suspected pathogens. Empirical antibiotic therapy should cover a wide range of aerobic and anaerobic bacteria until culture and sensitivity results are obtained. The duration of antibiotic therapy varies but is typically continued for 7 to 14 days, depending on the response and source control achieved.

Percutaneous Drainage

Percutaneous drainage is a minimally invasive procedure that involves the insertion of a catheter or needle into the abscess cavity under radiological guidance. It can be used as first-line therapy for stable patients with accessible abscesses, especially when there is no evidence of generalised peritonitis. The drainage procedure can be repeated as needed until complete resolution is achieved. Regular monitoring of patients undergoing percutaneous drainage is essential to ensure adequate abscess drainage and resolution.

Surgical Intervention

Surgical intervention is reserved for patients who do not respond to or are not candidates for percutaneous drainage. It is also indicated in the presence of generalised peritonitis, signs of hemodynamic instability, bowel perforation, or inadequate drainage with percutaneous methods. Surgical options include open surgical drainage, laparoscopic drainage, or a combination of both. During the procedure, the abscess is drained, and any underlying pathology, such as removal of the perforated viscus, is addressed.

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