What are the typical EUS (Endoscopic Ultrasound) features of a gastric neuroendocrine tumor (NET) in an adult patient with a history of gastrointestinal symptoms?

EUS Features of Gastric Neuroendocrine Tumors

Gastric NETs on EUS typically appear as well-defined, hypoechoic masses originating from the deep mucosa or submucosa (third or fourth echo layer), with homogeneous echotexture and smooth borders. 1, 2

Characteristic Sonographic Appearance

Layer of Origin and Echogenicity

• Gastric NETs characteristically arise from the third (deep mucosa/muscularis mucosae) or fourth (submucosa) echo layer of the gastric wall, appearing as hypoechoic (darker than surrounding tissue) lesions 2, 3
• The hypoechoic appearance reflects the solid cellular composition of neuroendocrine tissue, distinguishing them from cystic or inflammatory lesions 2
• Most lesions demonstrate homogeneous internal echotexture without calcifications or necrosis, particularly in smaller tumors 1

Size and Morphology

• Type 1 gastric NETs (associated with chronic atrophic gastritis) are typically small (<2 cm), multiple, and polypoid, appearing as well-circumscribed hypoechoic nodules 4, 2
• Larger tumors (>2 cm) are more likely to be non-functioning and may show signs of malignancy including heterogeneous echotexture, irregular borders, and invasion into deeper layers 1
• The lesions maintain smooth, well-defined margins in benign cases, with loss of this feature suggesting malignant transformation 1, 2

Diagnostic Performance and Clinical Utility

Detection Sensitivity

• EUS achieves 82-93% sensitivity for detecting gastric and pancreatic NETs, significantly superior to CT (57-94%), MRI (74-94%), and conventional ultrasound (17.4%) 1, 5
• EUS is particularly valuable for detecting small tumors (<2 cm) that are frequently missed by cross-sectional imaging, with one study showing 91.6% detection rate for lesions under 20mm 2, 5
• The technique demonstrates 87% accuracy for localizing pancreatic NETs and can identify multiple synchronous lesions in MEN1 syndrome with 92-97% sensitivity 1, 5

Tissue Acquisition

• EUS-guided fine-needle aspiration (FNA) provides tissue diagnosis with close correlation between aspiration cytology and final surgical histology, maintaining a low complication rate 1, 3
• FNA is particularly useful for lesions in the deep submucosa where endoscopic biopsy may be inadequate or risky 3
• The dual capability of visualization and tissue sampling makes EUS the preferred first-line diagnostic modality when gastric NET is suspected 5

Assessment of Invasion and Staging

Depth of Wall Invasion

• EUS accurately evaluates the depth of parietal invasion in 75% of cases, determining whether the tumor is confined to mucosa/submucosa or extends into muscularis propria 5
• This assessment is critical for treatment planning, as tumors crossing into muscularis propria require more extensive resection than simple endoscopic removal 3
• Invasion into the fifth echo layer (serosa) or beyond indicates advanced disease requiring surgical rather than endoscopic management 1

Lymph Node Assessment

• EUS can identify metastatic lymph nodes with 90.9% accuracy, appearing as hypoechoic, rounded structures with loss of normal architecture 5
• Regional lymph node involvement changes management from endoscopic resection to surgical resection with lymphadenectomy 3

Signs of Malignancy

High-Risk Features

• Large size (>2 cm), necrosis, calcification, and invasion/infiltration of surrounding structures indicate malignant potential 1
• Heterogeneous echotexture with irregular borders suggests aggressive behavior requiring more extensive surgical intervention 1
• Loss of the normal layered architecture of the gastric wall indicates transmural invasion 2

Clinical Context and Pitfalls

Type-Specific Considerations

• Type 1 gastric NETs (associated with chronic atrophic gastritis and hypergastrinemia) present as multiple small (<1 cm) polyps in the gastric body/fundus, requiring recognition of the underlying gastritis pattern 4, 6
• These lesions may be subtle on standard endoscopy but are readily apparent on EUS as multiple hypoechoic nodules in the deep mucosa 6

Common Diagnostic Errors

• Avoid relying solely on standard endoscopy for gastric NET detection, as these tumors can be easily missed when small or located in the deep submucosa 6, 3
• Do not confuse gastric NETs with GISTs or leiomyomas; NETs typically arise from more superficial layers (third/fourth) while GISTs originate from the muscularis propria (fourth/fifth layer) 7
• EUS should be performed early in the diagnostic workup rather than after failed conventional imaging, given its superior sensitivity for small lesions 2, 5

Integration with Other Modalities

• While EUS excels at local staging, combine with somatostatin receptor scintigraphy (SSRS) or 68Ga-DOTATOC PET/CT for whole-body staging to detect distant metastases 1
• The combination of EUS and functional imaging increases overall diagnostic sensitivity beyond either modality alone 2
• Reserve CT and MRI primarily for excluding hepatic and distant metastases rather than primary tumor detection 2, 5