What is the most likely diagnosis in a patient with right upper‑quadrant/epigastric pain, CT showing peripancreatic fat stranding and intra‑hepatic bile‑duct dilation, and elevated transaminases, alkaline phosphatase and bilirubin?

Most Likely Diagnosis: Acute Gallstone Pancreatitis with Choledocholithiasis

The most likely diagnosis is acute gallstone pancreatitis secondary to choledocholithiasis (common bile duct stones), given the combination of right upper quadrant/epigastric pain, peripancreatic fat stranding on CT, intrahepatic bile duct dilation, and the cholestatic pattern of liver enzyme elevation.

Diagnostic Reasoning

Key Clinical Features Present

The clinical presentation combines three critical findings that point toward a biliary-pancreatic process:

• Peripancreatic fat stranding on CT indicates pancreatic inflammation 1
• Intrahepatic bile duct dilation suggests biliary obstruction
• Elevated transaminases, alkaline phosphatase, and bilirubin demonstrate both hepatocellular injury and cholestasis

Why Gallstone Pancreatitis with Choledocholithiasis

This constellation of findings is pathognomonic for a gallstone impacted at or near the ampulla of Vater, causing both biliary obstruction and pancreatic inflammation. The peripancreatic fat stranding confirms acute pancreatitis 1, while the bile duct dilation and cholestatic liver enzymes indicate concurrent common bile duct stone (CBDS) obstruction 2.

Laboratory Pattern Analysis

The liver enzyme pattern is particularly informative:

• Elevated transaminases (ALT/AST): Among patients with acute calculous cholecystitis (ACC) and CBDS, 90% have elevated ALT 2. In choledocholithiasis specifically, transaminase elevation is the most common laboratory abnormality 3
• Elevated alkaline phosphatase and bilirubin: This cholestatic pattern has high specificity for biliary obstruction. At ALP >125 IU/L, sensitivity is 92% for CBDS 2
• Combined elevation: The presence of all three markers (transaminases, ALP, and bilirubin) strongly suggests CBDS with 77% having raised ALP, 60% abnormal bilirubin, and 90% elevated ALT 2

Imaging Correlation

The CT findings are diagnostic:

• Peripancreatic fat stranding: This finding on CT is associated with worse outcomes in acute pancreatitis and can be demonstrated even on non-contrast scans 1
• Intrahepatic bile duct dilation: While common bile duct dilation alone is insufficient to diagnose CBDS 2, intrahepatic duct dilation indicates more proximal and significant obstruction

Important Caveats

Elevated LFTs Are Not Diagnostic Alone

Do not rely solely on elevated liver function tests to diagnose CBDS 2. In patients with ACC, 15-50% show LFT elevation without CBDS due to acute inflammation of the gallbladder and biliary tree rather than direct obstruction. However, when combined with imaging findings of bile duct dilation and peripancreatic inflammation, the diagnosis becomes much more certain.

Timing of CT Assessment

Early CT (within first 4 days) may underestimate the severity of pancreatic necrosis, as the full extent of necrotic process takes at least 4 days to develop 1. The peripancreatic fat stranding visible on this CT suggests the inflammatory process is already established.

Next Steps for Confirmation

While the diagnosis is highly likely based on current findings, definitive confirmation requires:

1. Direct visualization of CBD stone: Ultrasound visualization of a stone in the common bile duct would be confirmatory 2, though sensitivity ranges from 0.32 to 1.00
2. MRCP or EUS: If ultrasound is non-diagnostic, these modalities can definitively identify stones 4, 5
3. Severity assessment: Apply Glasgow score at 48 hours and measure C-reactive protein to assess pancreatitis severity 1

The combination of clinical presentation, laboratory cholestasis, and CT findings of both pancreatic inflammation and biliary obstruction makes gallstone pancreatitis with choledocholithiasis the diagnosis until proven otherwise.