How do you interpret Endoscopic Ultrasonography (EUS) images?

Interpreting Endoscopic Ultrasonography (EUS) Images

Endoscopic ultrasonography (EUS) is the modality of choice for evaluating gastrointestinal lesions, providing superior characterization of lesion origin, layer involvement, and enabling tissue acquisition for definitive diagnosis. 1

Understanding the Five-Layer Pattern

EUS imaging of the gastrointestinal tract wall typically reveals 5 distinct layers (numbered from the lumen outward):

1. Layer 1: Interface echo between superficial mucosa and acoustic coupling medium
2. Layer 2: Deep mucosa (including muscularis mucosa)
3. Layer 3: Submucosa plus acoustic interface between submucosa and muscularis propria
4. Layer 4: Muscularis propria
5. Layer 5: Serosa or adventitia (subserosal fat)

2

Key Parameters for EUS Image Interpretation

1. Layer of Origin

• Identifying the layer of origin is crucial for narrowing differential diagnosis:
  • Layer 2 lesions: Often lipomas, carcinoids, or pancreatic rests
  • Layer 3 lesions: Typically varices, cysts, lipomas
  • Layer 4 lesions: Commonly GISTs or leiomyomas 2, 1

2. Echogenicity

• Anechoic (black): Fluid-filled structures like cysts, varices, lymphangiomas
• Hypoechoic (dark): GISTs, leiomyomas, neuroendocrine tumors, lymphoma
• Hyperechoic (bright): Lipomas, fibrolipomas
• Mixed echogenicity: Pancreatic rest, malignant mesenchymal tumors, abscesses 2, 1

3. Margins and Borders

• Smooth, well-circumscribed borders: Typically benign
• Irregular margins with invasion: More likely malignant
• Disruption of adjacent layers: Suggests invasive process 2, 1

4. Homogeneity

• Homogeneous: Uniform appearance throughout the lesion
• Heterogeneous: Variable appearance suggesting complex pathology 2

5. Size

• Larger lesions (>2cm) more likely to have malignant potential
• Size affects diagnostic accuracy of sampling (71% for <2cm vs 95-100% for >4-5cm) 2, 1

Advanced EUS Techniques

Contrast-Enhanced EUS

• Helps distinguish GISTs (hyperenhancement) from leiomyomas (hypoenhancement)
• Accuracy >95% for differentiating these entities 2, 1

EUS Elastography

• Evaluates tissue stiffness/elasticity
• Provides additional information about lesion characteristics 1, 3

Digital Image Analysis

• Objective assessment of EUS images using texture analysis and brightness values
• Parameters like mean brightness (echogenicity) and standard deviation (heterogeneity) can help differentiate GISTs from benign mesenchymal tumors with 90.8% accuracy 4, 5

Common Pitfalls and Limitations

1. Operator Dependence: EUS interpretation is highly subjective with variable interobserver agreement 1, 4

2. Limited Diagnostic Accuracy: Overall sensitivity and specificity of EUS in predicting malignant potential are only 64% and 80%, respectively 2

3. Technical Challenges:

   • Difficult scope positioning in certain anatomical locations
   • Challenging visualization in obstructing lesions 2, 1

4. Sampling Limitations:

   • Small lesions (<1cm) may have insufficient yield
   • Needle selection impacts diagnostic success (22-gauge or 25-gauge needles more maneuverable in fundus) 2, 1

When to Pursue Tissue Sampling

• Hypoechoic masses in layers 3 or 4 should undergo tissue sampling as they may represent malignant or potentially malignant lesions
• EUS-guided FNA/FNB provides diagnostic accuracy of 46-93%
• FNB needles generally provide better tissue acquisition than FNA needles 2, 1

Integration with Other Imaging

• CT/MRI cannot identify histologic layers but are useful for defining extent of large extramural masses and evaluating for metastatic spread
• Combined approach using EUS with CT improves efficiency and structure identification 2, 6

By systematically evaluating these parameters during EUS examination, clinicians can more accurately characterize gastrointestinal lesions and guide appropriate management decisions to improve patient outcomes.