Pancreatic Abscess

Etiology

A pancreatic abscess is defined as a circumscribed intraabdominal collection of pus that is typically in the vicinity of the pancreas and contains little pancreatic necrosis. Infection is thought to occur via colonic translocation of bacteria. It usually develops in patients with pancreatic pseudocyst that become infected. Hence, its causative organisms are usually gram-negative flora bacteria, especially Escherichia coli, Klebsiella, and Pseudomonas, although gram-positive bacteria are also seen, most commonly Enterococcus. Patients that present with pancreatitis that do not improve after initial management and start developing systemic inflammatory response syndrome should increase the suspicion of some form of intraabdominal infection, especially of the pancreas.

Other causes might include penetrating peptic ulcers, gallstones, and excessive alcohol consumption because they increase the risk and the number of pancreatitis episodes. In rare cases, medications, blunt trauma, and the extension of abscesses from nearby structures can occur.

Epidemiology

Acute pancreatitis is one of the most frequent gastrointestinal causes for hospital admission in the US. The annual incidence of acute pancreatitis ranges from 13 to 45/100,000 persons.[1][2] A pancreatic abscess is a complication that occurs mostly in patients with acute pancreatitis, however, the exact epidemiology of this disease is not known.

Pathophysiology

Acute necrotizing pancreatitis usually presents as fluid collections in the pancreatic and peripancreatic regions, which may present as an acute necrotic collection (ANC) that does not have a definitive wall, or when they are more organized with well-defined wall-off necrosis (WON). These fluid collections initially are sterile but can become infected to develop a pancreatic abscess.

Histopathology

Histology review of patients diagnosed with pancreatic abscesses revealed that 65% were due to chronic pancreatitis, 22% from biliary tract disease, 5% were from duodenal diseases, and the remainder was from other causes.[3]

History and Physical

History taking plays a major role in the diagnosis of pancreatic abscess. A pancreatic abscess usually occurs in patients with a history of pancreatitis or in patients prone to develop pancreatitis. Patients with pancreatitis usually present with abdominal pain, located in the epigastric region radiating to the back, that gets worse after consumption of a meal. They may present with nausea and vomiting as well. Keeping in mind the different causes of pancreatitis will guide the history. 

Causes of pancreatitis include:[4][5][6]

• Idiopathic 
• Gallstones
• Ethanol 
• Trauma 
• Steroids 
• Mumps
• Autoimmune pancreatitis
• Hypercalcemia 
• Hypertrygliceredemia 
• Post-ERCP (endoscopic retrograde cholangiopancreatography)
• Medications (ACE inhibitors, macrolides, mesalamine, fibrates, etc.)[7]

Persistent fevers, worsening abdominal pain, and failure to improve despite appropriate initial management may all be suggestive of superimposed infection of the pancreas. Infection should be suspected in patients who do not improve after 7 to 10 days of hospitalization and supportive care, and in those who rapidly deteriorate. Although the development of systemic inflammatory response syndrome can be attributed to pancreatitis itself, a superimposed infection should be suspected.

Physical examination findings in patients with pancreatic infections generally mimic the symptoms of acute pancreatitis but are usually more severe and often occur after 7 to 10 days of hospitalization. Abdominal pain is located in the mid-epigastric region. An associated mass may or may not be palpable. In severe pancreatitis, patients are often dehydrated on presentation. Hypotension and hypoxia may indicate progression to shock. Fevers can result from underlying infection but also occur in the setting of ongoing pancreatic inflammation.

Evaluation

Several laboratory tests can be sent if an infectious process in the pancreas is suspected. However, none are specific to the condition. A complete blood count (CBC) with differential, basic metabolic panel (BMP), liver function test (LFT), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), lactate dehydrogenase and blood cultures should be obtained in patients presenting with pancreatitis and not improving despite conservative management. CRP greater than 150 has been associated with the detection of the presence of pancreatic necrosis with a 100% sensitivity and 81.4% specificity.[8] A hematocrit of higher than 44% has been established to be a risk factor for pancreatic necrosis and the development of an abscess.

Imaging studies are also required when the patient fails to improve within 72 hours of treatment.

Abdominal computed tomography (CT) scan with contrast and contrast-enhanced magnetic resonance imaging (MRI) are both options for assessment of pancreatic necrosis and abscesses, although CT is more commonly used. On imaging, the presence of extraluminal gas in the pancreatic and/or peripancreatic tissues is consistent with an underlying infection.

Treatment / Management

A suggested approach to pancreatic abscess: 

• CBC with differential 
• Blood cultures 
• CT scan with contrast or MRI with gadolinium. (MRI without contrast can be used in patients with renal failure)
• Broad-spectrum antibiotics should be initiated if cultures are positive, or there are systemic signs of infections. IV imipenem 500 mg IV q8h for 14 days is the drug of choice.[9] Combination therapy with metronidazole and fluoroquinolone is a reasonable alternative in patients that can not tolerate carbapenems.[10]
• Consider CT-guided fine-needle aspiration if a collection is visualized on imaging and infection is suspected.

Treatment 

1. For hemodynamically unstable patients, surgical debridement is the treatment of choice. 
2. For hemodynamically stable patients, minimal-invasive methods of necrosectomy and drainage can be performed using endoscopy.

The resolution of tachycardia, fevers, hypotension, as well as improvement in the patients' abdominal pain, are all markers of clinical improvement. However, they are not specific to the pancreatic abscess.

Daily CBC should be performed to ensure that the leukocytosis is resolving. For patients with diagnosed pancreatic abscess and bacteremia, serial blood cultures should be obtained to confirm the eventual clearance of the infection.

Differential Diagnosis

• Pancreatic pseudocysts
• Pancreatic necrosis without associated infection
• Gastric ulcer
• Ascending cholangitis
• Acute cholecystitis
• Mesenteric ischemia
• Bowel obstruction
• Perforated viscus

Prognosis

The prognosis depends on the severity of the infection. It is a potentially severe complication that may result in the death of the patient if the appropriate management is not given. Patients are at risk of multiple organ failure and sepsis, and in cases in which the infected abscess is not removed either surgically or endoscopically, the mortality rate can reach 100%.

Complications

• Multiple abscesses 
• Enlargement of abscess
• Sepsis 
• Septic shock 
• Multiorgan failure 
• Fistula formation 
• Death