Is a CT (Computed Tomography) scan with or without contrast indicated for diagnosing pancreatitis?

CT for Pancreatitis: With or Without Contrast

Contrast-enhanced CT (CECT) is the imaging modality of choice for diagnosis, staging, and detection of complications in acute pancreatitis, particularly for identifying and quantifying pancreatic necrosis, with optimal timing being 72-96 hours after symptom onset. 1

Initial Diagnostic Approach

• Ultrasound (US) should be performed first on admission to determine the etiology of acute pancreatitis, particularly to identify biliary causes 1, 2
• In the majority of patients with acute pancreatitis, CT is not required initially 1
• When diagnosis is uncertain, CT should be considered, especially to rule out secondary perforation peritonitis or mesenteric ischemia 1

When to Use Contrast-Enhanced CT (CECT)

CECT is indicated in the following scenarios:

• Patients with severe acute pancreatitis
• When diagnosis is uncertain
• Clinical deterioration
• Suspected complications
• Failure to improve within 72-96 hours 1, 2

Optimal Timing for CECT

• The extension of pancreatic necrosis may be detected with CECT after 72 hours from the onset of acute pancreatitis 1
• Early CT scan (within first 72 hours) will not show necrotic/ischemic areas completely and will not modify clinical management during the first week of illness 1
• CECT has been shown to yield an early overall detection rate of 90% with close to 100% sensitivity after 4 days for pancreatic necrosis 1

CT Protocol

For optimal imaging of the pancreas in acute pancreatitis:

• Patients should receive approximately 500 ml of oral contrast
• An initial scan without intravenous contrast allows identification of pancreatic levels and demonstrates the extent of peripancreatic change
• Post-contrast series should be obtained after bolus intravenous injection of non-ionic contrast (100 ml delivered at 3 ml/s)
• Images through the pancreatic bed should use thin collimation (5 mm or less) starting approximately 40 seconds after injection
• A second series beginning at 65 seconds (portal venous phase) provides information about patency of main peripancreatic veins 1

CT Without Contrast: When Appropriate

CT without contrast is appropriate in:

• Patients with allergy to iodinated contrast
• Patients with renal impairment/insufficiency
• When MRI is not available for these patient groups 1

However, non-contrast CT provides suboptimal information about the pancreas and should generally be avoided when assessing for pancreatic necrosis 1

CT Severity Index

The CT Severity Index (CTSI) helps predict outcomes in acute pancreatitis:

CT Severity Index	Complications	Mortality
0-3	8%	3%
4-6	35%	6%
7-10	92%	17%

This index combines CT grade (0-4) and necrosis score (0-6) 1, 2

Follow-up CT

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

Concerns About Contrast Use

While concerns have been raised about post-contrast acute kidney injury (AKI), a recent meta-analysis with over 100,000 participants found no evidence supporting an association between contrast and AKI, renal replacement therapy, or mortality. However, caution should still be applied in patients with severe acute pancreatitis or sepsis 1

Alternative Imaging Modalities

• MRI is preferable to CECT in patients with contrast allergy, renal impairment, and in young or pregnant patients
• MRI is better for identifying non-liquefied material (debris or necrotic tissue)
• CT is more sensitive than MRI for detecting gas in fluid collections 1
• MRCP or endoscopic ultrasound should be used to screen for occult choledocholithiasis when US doesn't show gallstones, sludge, or biliary obstruction 1, 2

Avoiding Unnecessary CT Scans

Reducing overuse of CT scans in uncomplicated acute pancreatitis can decrease healthcare expenditure and radiation exposure to patients. Clinical and biochemical diagnosis (using Ranson's Criteria and BISAP score) can identify uncomplicated acute pancreatitis with 99.5% accuracy, often making initial CT unnecessary 3