What is the role of Endoscopic Ultrasonography (EUS) in diagnosing gastrointestinal conditions?

Role of Endoscopic Ultrasonography (EUS) in Gastrointestinal Diagnosis

EUS is the most accurate imaging modality for evaluating gastric subepithelial masses, determining the layer of origin within the GI wall, and performing locoregional staging of gastrointestinal malignancies, with the critical advantage of enabling tissue diagnosis through fine-needle aspiration. 1

Primary Diagnostic Applications

Gastric Subepithelial Masses

EUS should be performed before any biopsy is taken when a subepithelial lesion is identified on endoscopy. 1 The key diagnostic capabilities include:

• Differentiating intramural lesions from extrinsic compression with sensitivity of 89-98%, far superior to endoscopy alone (29-64% specificity) 1
• Determining the exact layer of origin within the five-layer gastric wall structure, which narrows the differential diagnosis significantly 1
• Characterizing echogenicity patterns (hyperechoic, hypoechoic, or anechoic) and morphologic features (homogeneous vs. heterogeneous, smooth vs. irregular margins) 1
• Identifying lipomas by their intensely hyperechoic appearance from the submucosal (third) layer, which combined with the endoscopic "pillow sign" has 98% specificity 2

Tissue Diagnosis Requirement

For hypoechoic masses in the third or fourth echo layer, tissue sampling should be strongly considered because these lesions carry malignant potential (gastrointestinal stromal tumors, carcinoid tumors, lymphomas, metastases). 1 EUS-guided fine-needle aspiration achieves diagnostic accuracy of 46-93% for subepithelial lesions, with immunocytochemistry helping distinguish between potential causes. 3

Gastric Cancer Staging

Early Gastric Cancer

EUS is formally indicated for selecting patients for endoscopic treatment of early gastric cancer (EGC), particularly in discriminating T1a from T1b lesions. 1 This distinction is critical because:

• T1a lesions (mucosal stage) meeting specific criteria can undergo endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) 1
• EUS improves diagnostic accuracy for T-stage determination, though current accuracy rates are variable (46.2% for T category, 66.7% for N category) 3

Advanced Gastric Cancer

EUS is a helpful tool to identify infiltrated regions of the gastric wall in advanced disease, though it is not strictly necessary when CT shows clearly advanced forms. 1 The National Comprehensive Cancer Network recommends EUS for early-stage disease detection, acknowledging that more reliable sonographic markers are needed. 3

Comparative Imaging Advantages

EUS is superior to CT and MRI for intramural lesions because cross-sectional imaging cannot identify the histologic layers of the gut wall. 1 Specific advantages include:

• CT and MRI are adequate only for large extramural masses and detecting metastatic spread of malignant GISTs 1
• When cross-sectional imaging shows only normal structures, EUS must confirm whether the endoscopic "mass" represents external compression or an intramural lesion not identified on CT/MRI 1
• Contrast-enhanced EUS can differentiate gastrointestinal stromal tumors from leiomyomas with >95% accuracy 3

Emerging Technologies

The National Comprehensive Cancer Network supports several technological advances:

• High-frequency EUS miniprobes may improve staging accuracy for early gastric cancer 3
• Artificial intelligence algorithms for automated interpretation can reduce operator dependency and improve staging accuracy 3
• Elastography in EUS potentially improves diagnostic accuracy beyond conventional EUS for characterizing subepithelial lesions 3

Clinical Decision Algorithm

For subepithelial gastric masses discovered on endoscopy:

1. Perform EUS before biopsy to determine if the lesion is intramural or extrinsic compression 1
2. If extrinsic compression is confirmed, no further evaluation is typically needed 1
3. If intramural and hyperechoic from the third layer with "pillow sign," diagnose as lipoma and observe if asymptomatic 2
4. If hypoechoic mass from third or fourth layer, perform EUS-guided FNA to exclude malignancy 1, 3
5. For symptomatic lesions, proceed to endoscopic or surgical resection regardless of imaging findings 1

Critical Limitations

EUS imaging alone is insufficient to provide accurate diagnosis of hypoechoic intramural masses and cannot determine the true malignant potential of individual gastrointestinal stromal tumors. 1 This is why tissue sampling through EUS-guided FNA is essential for these lesions rather than relying on imaging characteristics alone. 1, 3