Should you perform a computed tomography (CT) scan in patients with acute on chronic pancreatitis?

CT Scanning in Acute on Chronic Pancreatitis

CT scanning should not be performed routinely in the early stages of acute on chronic pancreatitis but should be reserved for patients with predicted severe disease or when complications are suspected. 1

When to Perform CT in Acute on Chronic Pancreatitis

Early CT Scanning (First Week)

• CT scanning is not recommended as routine practice during the first week of illness unless specific management decisions are required 1
• Early CT may underestimate the final severity of the disease as the full extent of necrosis takes at least four days to develop after symptom onset 1
• Concerns exist about potential extension of necrosis and exacerbation of renal impairment following intravenous contrast media 1
• Early CT has low yield and rarely alters clinical management in the first days of acute pancreatitis 2

Indications for CT Scanning

• Perform contrast-enhanced CT in patients with predicted severe disease (APACHE II score >8) 1
• CT should be performed in patients with evidence of organ failure during the initial 72 hours 1
• A dynamic CT scan should be performed in all severe cases between three and 10 days after admission 1
• CT is indicated when there is diagnostic uncertainty or to exclude other potential intraabdominal pathologies 3
• Consider CT when the patient's clinical status deteriorates or fails to show continued improvement 1
• CT is appropriate when C-reactive protein exceeds 150 mg/L 4

CT Protocol for Acute Pancreatitis

Optimal Technique

• Spiral or multislice CT is required for assessment of acute pancreatitis 1
• Patients should receive approximately 500 ml of oral contrast by mouth or nasogastric tube 1
• An initial scan without intravenous contrast should be performed 1
• Post-contrast series should be obtained after bolus intravenous injection of 100 ml of non-ionic contrast delivered at 3 ml/s 1
• Images through the pancreatic bed should use thin collimation (5 mm or less) commencing approximately 40 seconds after injection start 1
• CT without intravenous contrast enhancement gives suboptimal information and should be avoided 1

Timing of CT

• Optimal timing for the first contrast-enhanced CT assessment is 72-96 hours after onset of symptoms 1
• The most recent guidelines recommend against early CT (within first 72 hours) unless specific management decisions are required 1

CT Severity Assessment

CT Severity Index

• The CT severity index as proposed by Balthazar should be used for severity grading 1
• The index combines CT grade (based on pancreatic and extrapancreatic inflammation) with extent of necrosis 1
• Higher CT severity index scores correlate with increased morbidity and mortality:
  • Scores 0-3: 8% complications, 3% mortality 1
  • Scores 4-6: 35% complications, 6% mortality 1
  • Scores 7-10: 92% complications, 17% mortality 1

Follow-up CT

• Patients with mild pancreatitis (CT severity index 0-2) require further CT only if clinical status changes suggesting new complications 1
• For patients with CT severity index 3-10, additional follow-up scans are recommended only if clinical status deteriorates or fails to improve 1
• Some experts advise a single further scan before hospital discharge in patients who make an uncomplicated recovery to detect asymptomatic complications such as pseudocyst or arterial pseudoaneurysm 1

Special Considerations

Alternative Imaging Modalities

• MRI and MRCP may be superior to CT for detecting subtle ductal changes, especially in early or mild disease 3
• Endoscopic ultrasound can be used to diagnose parenchymal and ductal changes during early stages of the disease 3
• Transabdominal ultrasound should be performed on admission to look for cholelithiasis or choledocholithiasis 1

Pitfalls and Caveats

• Relying solely on early CT may lead to underestimation of disease severity 1
• Low and moderately raised Ranson and Imrie scores fail to identify all patients with pancreatic necrosis with sufficient sensitivity 5
• CT findings should be correlated with clinical assessment and laboratory markers (C-reactive protein, APACHE II score, Glasgow score) for comprehensive evaluation 1
• Repeated CT scans increase radiation exposure and should be avoided unless clinically indicated 2