Colonic abscess
Synonyms and keywords: diverticular abscess, intestinal abscess, abscess of colon, colonic diverticular abscess.
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# Overview
Colonic abscess is defined as a localized collection of pus within the wall of the colon that may cause necrosis and destroy tissue. Colonic abscess is a rare entity and mostly develops as a complication of diverticulitis. If the abscess is small and remains within the wall of the colon, it is treated alone with antibiotics. If the abscess is large (> 5cms), or unresponsive to medical therapy, it must be drained using a catheter facilitated by sonography.

# Pathophysiology
- The primary process is thought to be an erosion of the diverticular wall by increased intraluminal pressure or inspissated food particles.
- Inflammation and focal necrosis ensue, resulting in the abscess formation.

### Gross Pathology
- The serosal surface of the colon looks pale with rough edges and yellowish exudate along with hyperemia

### Microscopic findings
- A focally necrotic debris is seen in the mucosal wall.
- Intravascular fibrin is seen in medium-sized blood vessels.
- Clusters of neutrophils are seen on the serosal aspect.

# Causes
Natural gut flora which includes gram-negative and anaerobic bacteria play a major role in the development of colonic abscess.

# Differentiating Colonic abscess from other diseases

# Epidemiology and Demographics

### Incidence
- Incidence rates of colonic abscess among age groups 18 to 44 is 15.1 to 25.1 per 100,000 population.
- Incidence rates of colonic abscess among age groups  45 to 64 years of age is 65.9 to 77.7 per 100,000 population.

### Gender
- At young age (<50 years), males are more commonly affected with diverticulosis than females.
- At older age, women are more frequently affected with diverticulosis than males.

### Race
- Caucasian individuals are at higher risk of developing diverticulosis compared with Asian and non-African Black individuals.

# Risk factors
Risk factors in the development of colonic abscess include same as that of diverticular diseases of the colon, such as advanced age, chronic constipation, connective tissue diseases (such as Marfan syndrome or Ehlers-Danlos syndrome), lows dietary fiber intake, high intake of fat and red meat, and obesity.

# Screening
Screening for colonic abscess is not recommended in the general population.

# Natural history, Complications and Prognosis

## Natural history
If left untreated colonic abscess will rupture through the wall, and this may eventually lead to death if peritonitis develops.

## Complications
- Peritonitis
- Septicemia
- Hemorrhage
- Death

## Prognosis
- Majority of the patients with colonic abscess recover quickly with drain and IV antibiotics, but complications can occur if treatment is delayed or if peritonitis occurs.
- It usually takes between 10 and 28 days to recover completely.
- Typical abscess responds quickly to antibiotics and percutaneous drain and resolves spontaneously.

# History and symptoms
The most common symptom of colonic abscess is left lower quadrant abdominal pain along with fever and chills. The most common sign is tenderness around the left side of the lower abdomen. Nausea, vomiting, chills, cramping, diarrhea and constipation may occur as well. The severity of symptoms depends on the extent of the infection.

# Laboratory findings
Hematologic parameters suggestive of infection like, leukocytosis, anemia, abnormal platelet counts, and abnormal liver function frequently are present in patients with colonic abscess, although patients who are debilitated or elderly often fail to mount reactive leukocytosis or fever. Blood cultures indicating persistent polymicrobial bacteremia strongly implicate the presence of an abscess.

# CT Abdomen
- CT abdomen is the preferred diagnostic modality for colonic abscess.
- Findings include colonic and paracolic inflammation in the presence of underlying diverticula (diverticula are identified on CT scans as outpouchings of the colonic wall).
- Symmetric thickening of the colonic of approximately 4-5 mm is common.
- Enhancement of the colonic wall is commonly noted. This usually has inner and outer high-attenuation layers, with a thick middle layer of low attenuation.
- Free diverticular perforation results in the extravasation of air and fluid into the pelvis and peritoneal cavity.
- Air in the bladder in the presence of a nearby segment of diverticulitis is suggestive of a colovesical fistula.

# Medical therapy
Antibiotics should be started immediately once the diagnosis of abscess is made and is the only treatment of choice if abscess is less than 5 cms. Preoperative antibiotics have been associated with lower rates of wound and intra-abdominal infections. 
- 1 Emperic therapy:
- 1.1 Single agent:
- Preferred regimen (1): Imipenem-Cilastatin 500 mg IV q6h OR 1 g q8h
- Preferred regimen (2): Meropenem 1 g IV q8h
- Preferred regimen (3): Doripenem 500 mg IV q8h
- Preferred regimen (4): Piperacillin-tazobactam 3.375 g IV q6h
- 1.2 Combination:
- Preferred regimen (1): Cefepime 2 g  q812 h AND Metronidazole 500 mg IV q812 h or 1500 mg q24h
- Preferred regimen (2): Ceftazidime 2 g q8h AND Metronidazole 500 mg IV q812 h or 1500 mg q24h
- Preferred regimen (3): Ciprofloxacin 400 mg q12h AND Metronidazole 500 mg IV q812 h or 1500 mg q24h
- Preferred regimen (4): Levofloxacin  750 mg q24h AND Metronidazole 500 mg IV q812 h or 1500 mg q24h
- Note: Antimicrobial therapy of established infection should be limited to 47 days, unless it is difficult to achieve adequate source control. Longer durations of therapy have not been associated with improved outcome.

# Surgery

## Indications
- Unresponsive to medical treatment
- Large abscess (>5cms)

## Percutaneous drainage
Percutaneous drainage can be performed under ultrasound or CT guidance, using either the Seldinger or trocar technique. Ultrasound is limited if the abscess is small, obscured by other structures, or if precise placement is required because of nearby vessels or organs. In these cases, CT is the optimal imaging modality. When an abscess is deep in the pelvis, depending on the specific location of the fluid collection, access may be obtained via transgluteal, transvaginal, or transrectal approaches. If the fluid collection is sterile, a transgluteal approach is preferred because it allows for sterile technique. Depending on the location of abscess, patient is placed in prone or supine position on the CT table. Localization scan using CT allows in selecting a safe window of access into the collection. A coaxial micropuncture introducer set is advanced into the abscess under CT guidance. An Amplatz guidewire is advanced through the sheath and coiled within the abscess. After serial dilatation of the tract with a dilator, a pigtail drain is advanced over the guidewire and deployed.

# Prevention
Dietary fiber and a vegetarian diet may reduce the incidence of symptomatic diverticular disease by decreasing intestinal inflammation and altering the intestinal microbiota..
Vigorous physical activity appears to reduce the risk of diverticulitis and diverticular bleeding..