A subepithelial mass or a bulge encountered during an endoscopy can arise from within any layer of the gastrointestinal tract wall (intramural) or outside of the wall (extramural). They are usually found incidentally during routine imaging with barium contrast radiography or endoscopy. The differential diagnosis includes a number of benign and malignant non-epithelial gastric wall tumors, intramural vessels, and extrinsic compression from extramural structures.
Endoscopy alone cannot accurately distinguish between intramural and extramural lesions . By contrast, endoscopic ultrasonography (EUS) has provided a major breakthrough for characterizing such masses. This topic review will provide an overview of the most common subepithelial lesions that can be identified endosonographically. Discussions on the individual lesions are also available on the corresponding topic reviews.
GENERAL PRINCIPLES FOR IMAGING
EUS provides a number of methods for characterizing subepithelial lesions:
- It provides an understanding of whether the lesion arises from the bowel wall (intramural) or from a structure outside the bowel wall (extramural) compressing the gastrointestinal wall. Extramural lesions may be a normal adjacent structure (eg, spleen, aorta, gallbladder) or pathologic structures (eg, splenic artery aneurysm, cyst, tumor). Rarely, the distinction between an intra- and extramural lesion may be difficult when there is invasion into the gastrointestinal wall.
- It can determine the originating layer of intramural lesions, an important clue for achieving a diagnosis (table 1). Stromal cell tumors, for example, can typically be seen as evolving from the muscularis propria or muscularis mucosa, whereas lipomas typically evolve from the submucosa.
- The echogenicity, vascularity, margins, size of the lesion, and absence or presence of adjacent lymph nodes also help to narrow the differential diagnosis.
- EUS-guided fine-needle aspiration or trucut biopsy of the lesion may be helpful in some settings. (See "Endoscopic ultrasound-guided fine-needle aspiration biopsy in the gastrointestinal tract" and "Endoscopic ultrasound guided trucut biopsy".)
Technical considerations — The following are basic principles that should be understood by endosonographers attempting to visualize subepithelial lesions.