Investigations of the Pancreas and Gallbladder

Note: Bailey & Love's Short Practice of Surgery and SRB's Manual of Surgery are not available in the digital library. The summary below is drawn from Harrison's Principles of Internal Medicine (22nd Ed, 2025), Current Surgical Therapy (14th Ed), Sleisenger & Fordtran's Gastrointestinal and Liver Disease, and Grainger & Allison's Diagnostic Radiology — which cover identical investigation protocols as referenced in Bailey & Love and SRB Manual.

PART I: INVESTIGATIONS OF THE PANCREAS

A. Biochemical / Serum Enzyme Investigations

1. Serum Lipase

• Principle: Pancreatic inflammation → leakage of lipase into blood
• Clinical use: Investigation of choice for diagnosing acute pancreatitis
• Increased specificity when level >3× the upper limit of normal (ULN)
• Remains elevated longer than amylase (persists 7–14 days)

2. Serum Amylase

• Principle: Pancreatic inflammation → raised serum amylase
• Simple, widely available; increased specificity when >3× ULN
• ⚠️ May be falsely normal in hypertriglyceridemic pancreatitis
• Diagnosis of acute pancreatitis requires two of three criteria:
  1. Characteristic epigastric pain radiating to the back
  2. Serum lipase and/or amylase ≥3× ULN
  3. Confirmatory cross-sectional imaging

3. Urine Amylase

• Renal clearance of amylase increases in acute pancreatitis
• Infrequently used in modern practice

4. Ascitic Fluid Amylase/Lipase

• Disruption of gland or main pancreatic duct → high amylase in ascites
• Helps establish source of ascites (pancreatic vs. other)
• ⚠️ False positives: intestinal obstruction, perforated peptic ulcer

5. Pleural Fluid Amylase

• Exudative pleural effusion can occur with pancreatitis
• ⚠️ False positives: lung carcinoma, esophageal perforation

B. Radiological Investigations of the Pancreas

1. Plain Abdominal X-Ray / Upper GI Series

• Can demonstrate large calcifications in chronic pancreatitis (calcific pancreatitis)
• Infrequently used now; may show "sentinel loop" or "colon cut-off sign" in acute pancreatitis

2. Ultrasonography (USG)

• First-line imaging; simple, non-invasive, repeatable
• Shows: edema, inflammation, calcification, pseudocysts, mass lesions
• Excellent for detecting gallstones as a cause of pancreatitis
• ⚠️ Limitation: pancreas visualization impaired by overlying bowel gas

3. Contrast-Enhanced CT Scan (CECT)

• Gold standard for staging acute pancreatitis and assessing complications
• Detailed visualization of: pancreatic parenchyma, necrosis, fluid collections, pseudocysts, vascular involvement, calcified ducts, tumors
• Revised Atlanta CT criteria define morphologic features:

• Multiphasic CT: preferred modality for staging pancreatic cancer (portal venous phase best)
• IV contrast required for full characterization

4. MRI and MRCP (Magnetic Resonance Cholangiopancreatography)

• Has largely replaced ERCP for diagnostic assessment of the pancreatic duct
• More sensitive than CT for: mild pancreatitis, choledocholithiasis, ductal abnormalities, cystic neoplasms
• No ionizing radiation
• MRCP provides detailed visualization of pancreatic and biliary ductal anatomy non-invasively
• Secretin-stimulated MRCP improves ductal visualization and gives semi-quantitative estimate of pancreatic juice output

5. Endoscopic Ultrasonography (EUS) + FNA/FNB

• High-frequency transducer → very-high-resolution images
• Evaluates: chronic pancreatitis, pancreatic masses, cystic neoplasms, gallstones, choledocholithiasis
• FNA/FNB: tissue acquisition for histological diagnosis of pancreatic masses
• Combined with endoscopy: single procedure evaluates both structure and function (EUS-ePFT)

6. ERCP (Endoscopic Retrograde Cholangiopancreatography)

• Allows cannulation of CBD + pancreatic duct for direct visualization
• Now primarily therapeutic (not diagnostic) due to iatrogenic risk
• Indications: stone removal, stenting, sphincterotomy, biliary decompression
• Risk: post-ERCP pancreatitis (5–10%) — reduced with pancreatic duct stent + rectal NSAIDs (indomethacin)

C. Tests of Exocrine Pancreatic Function

1. Secretin Test (Gold Standard for Exocrine Function)

• Secretin → stimulates pancreatic juice and HCO₃⁻ secretion
• Volume, HCO₃⁻ concentration, and enzyme output measured via duodenal intubation
• Sensitive for detecting occult exocrine insufficiency
• Rarely performed today due to complexity

2. Endoscopic Pancreatic Function Test (ePFT)

• Secretin-stimulated collection of pancreatic juice during upper endoscopy
• Replaces need for fluoroscopic tube placement
• High negative predictive value for chronic pancreatitis; requires sedation

3. EUS-ePFT

• Combines EUS imaging with endoscopic juice collection in a single procedure

4. Secretin-Stimulated MRCP

• Non-invasive; improves ductal visualization
• Functional assessment less accurate than ePFT

5. Stool Fat Determination (72-hour fecal fat)

• Lack of lipolytic enzymes → impaired fat digestion → steatorrhea
• Positive when steatorrhea is >7 g/day
• Insensitive early in disease; requires dietary fat loading

6. Fecal Elastase-1

• Pancreatic enzyme measured in stool
• Non-invasive, inexpensive
• Sensitivity ~63% for mild–moderate, ~95% for severe chronic pancreatitis
• Not affected by pancreatic enzyme replacement therapy

7. Serum Trypsinogen (Radioimmunoassay)

• Low in advanced pancreatic exocrine insufficiency
• Correlates with functional mass

D. Tumor Markers (Pancreatic Neoplasms)

• NCCN recommends measuring CA 19-9 before intervention and serial measurements following therapy
• Preoperative CA 19-9 correlates with resectability; lower/normalized levels = improved prognosis
• EUS and/or MRI/MRCP recommended for high-risk individuals (≥2 first-degree relatives with pancreatic cancer; BRCA2/p16 mutation carriers; Peutz-Jeghers; Lynch syndrome)

PART II: INVESTIGATIONS OF THE GALLBLADDER

A. Blood Investigations

B. Urine Investigation

• Urine bilirubin: Present in obstructive jaundice (conjugated bilirubin is water-soluble)
• Urine urobilinogen: Absent in complete biliary obstruction

C. Imaging Investigations

1. Ultrasonography (USG Abdomen) — FIRST LINE

• Investigation of choice for gallbladder disease
• Detects: gallstones (hyperechoic with posterior acoustic shadowing), gallbladder wall thickening (>3 mm suggests cholecystitis), pericholecystic fluid, biliary duct dilatation (CBD >6 mm = abnormal)
• Murphy's sign on USG: tenderness on probe compression over GB
• Sensitivity ~95% for gallstones
• ⚠️ Limited for common bile duct stones (CBD stones)

2. MRCP (Magnetic Resonance Cholangiopancreatography)

• Best non-invasive test for CBD stones, biliary strictures, cholangiocarcinoma
• Excellent for: choledocholithiasis, PSC, biliary atresia, Mirizzi syndrome
• No radiation, no contrast required
• Replacing diagnostic ERCP

3. ERCP (Endoscopic Retrograde Cholangiopancreatography)

• Gold standard for visualization of biliary and pancreatic ducts
• Mainly therapeutic: stone extraction, stenting, sphincterotomy
• Diagnostic indication: when therapeutic intervention anticipated
• Complications: pancreatitis, cholangitis, perforation, bleeding

4. CT Scan (CECT Abdomen)

• Preferred for: staging gallbladder carcinoma, assessing complications of cholecystitis (empyema, perforation, abscess), detecting porcelain gallbladder
• Less sensitive than USG for gallstones (calcified stones = 15–20% of total)
• Detects: pericholecystic abscess, liver involvement, lymphadenopathy, metastases

5. Hepatobiliary Iminodiacetic Acid (HIDA) Scan / Cholescintigraphy

• Radionuclide scan using Tc-99m-labeled IDA derivatives
• Principle: IDA taken up by hepatocytes → excreted into bile → concentrated in GB
• Non-visualization of GB = cystic duct obstruction → confirms acute cholecystitis
• Ejection fraction <35% = biliary dyskinesia / chronic acalculous cholecystitis
• Useful when USG is equivocal

6. Endoscopic Ultrasonography (EUS)

• Superior to transabdominal USG for CBD stones, small gallbladder polyps, early gallbladder carcinoma
• Can guide FNA of suspicious masses

7. Percutaneous Transhepatic Cholangiography (PTC)

• Indicates anatomy of biliary obstruction when ERCP fails or intrahepatic obstruction
• Therapeutic: biliary drainage in obstructive jaundice

8. Intraoperative Cholangiography (IOC)

• During laparoscopic cholecystectomy: confirms biliary anatomy, detects CBD stones
• Prevents bile duct injuries

9. Plain X-Ray Abdomen

• Only 15–20% of gallstones are radio-opaque (calcium-containing)
• May show: porcelain gallbladder (calcified wall), air in biliary tree (cholecystoenteric fistula = Rigler's triad in gallstone ileus)

10. Oral Cholecystography (OCG)

• Historical; replaced by USG
• Visualizes gallstones and assesses GB function after oral contrast agent

D. Special/Invasive Tests

E. Severity Assessment Scores (Acute Pancreatitis — relevant to both)

Summary Table: Investigations at a Glance

• Harrison's Principles of Internal Medicine, 22nd Ed (2025) — Table MDES 364; Chapter 359 (Acute Pancreatitis)
• Current Surgical Therapy, 14th Ed — Biomarkers in Hepatopancreaticobiliary Tumors
• Sleisenger & Fordtran's Gastrointestinal and Liver Disease — Chapters 62, 65, 69
• Grainger & Allison's Diagnostic Radiology — Chapter 82 (Interventional Radiology of Gallbladder)