MRCP Recognition Pattern

Systematic approach to interpreting MRCP with biliary anatomy variants, pathological patterns, and protocol optimization

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1. MRCP Protocol

A. Standard Sequences

• • Heavily T2-weighted:
  - Single-shot FSE/TSE
  - TE: 800-1200ms
  - Slice thickness: 3-5mm (thicker for MIP)
• • 3D FRFSE:
  - Isotropic acquisition (1-2mm)
  - Multiplanar reformats
  - Better for small ducts

B. Supplemental Sequences

• • T2-weighted fat-sat:
  - Pancreatic parenchyma
  - Periampullary region
• • T1-weighted pre/post-contrast:
  - Tumor detection
  - Liver evaluation

2. Biliary Anatomy

A. Normal Measurements

Duct

Normal Diameter

Abnormal Threshold

Common bile duct

≤6mm (≤8mm post-chole)

>8mm (>10mm post-chole)

Common hepatic duct

≤5mm

>6mm

Intrahepatic ducts

≤2mm or "too small to see"

>3mm or visible in periphery

B. Common Variants

• • Ductal confluence:
  - Normal (70%): Right + Left → Common
  - Triple confluence (12%)
  - Right posterior drains into left (18%)
• • Cystic duct insertion:
  - Low medial (50%)
  - Parallel course (25%)
  - High lateral (15%)

3. Biliary Obstruction

A. Level Determination

Level

Dilated Structures

Common Causes

Intrahepatic

IH ducts only

PSC, metastases, cholangitis

Hilar (Klatskin)

IH + CHD

Cholangiocarcinoma, stones

Pancreatic

IH + CHD + CBD

Pancreatic CA, pancreatitis

B. Stone vs Tumor

• • Choledocholithiasis:
  - Round/oval filling defect
  - Dependent position
  - "Meniscus" sign
• • Cholangiocarcinoma:
  - Irregular stricture
  - Shouldered margins
  - Ductal wall thickening

4. Pancreatic Duct Evaluation

A. Normal Variants

• • Ductal configuration:
  - Normal: Gradual taper
  - Divisum: Dominant dorsal duct
  - Ansapanscreaticus: Loop configuration

B. Pathological Patterns

Condition

Duct Features

Chronic pancreatitis

Irregular dilation, strictures, calculi

IPMN

Segmental dilation, mural nodules

Pancreatic CA

Abrupt cutoff, "double duct" sign

5. Post-Surgical Anatomy

A. Common Procedures

Procedure

Expected Findings

Complications

Cholecystectomy

Absent gallbladder

Bile leak, retained stones

Whipple

Pancreaticojejunostomy

Anastomotic stricture

Liver transplant

Duct-to-duct anastomosis

Ischemic cholangiopathy

6. Reporting Template

• 1. Technique: Sequences, contrast use
• 2. Biliary tree:
  - Dilation level/pattern
  - Filling defects/strictures
• 3. Pancreatic duct:
  - Caliber, configuration
  - Communication with cysts
• 4. Parenchyma:
  - Pancreatic atrophy/fibrosis
  - Liver lesions
• 5. Post-surgical (if applicable)

Always correlate with LFTs and clinical history. For stone detection, review source images as small calculi may be obscured on MIPs. In PSC, document dominant strictures and ductal dilation pattern. For IPMN, measure main duct diameter and note worrisome features (nodules, rapid growth). Post-liver transplant patients require careful evaluation of anastomotic sites. Consider secretin-enhanced MRCP for pancreatic duct evaluation when available.

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