A subepithelial lesion (SET) is defined as a lesion, bulge or impression visible within the lumen of the gastrointestinal tract that is covered by normally appearing mucosa and usually found incidentally during routine endoscopy. Such a lesion could be either an intramural mass or an impression caused by extramural structures. The old terminology has recently been replaced by the term “subepithelial lesion” because intramural lesions may arise and can be located in any layer of the GI wall underneath the epithelium. The most common SELs are gastrointestinal stromal tumors (GISTs), leiomyomas, lipomas, granular cell tumors (GCTs), pancreatic rests and carcinoid tumors. The prognosis varies from benign to potentially malignant. While the majority of the lesions are considered benign, some tumors such as GISTs and carcinoids have a strong propensity for malignant transformation. Endoscopic ultrasonography (EUS) is the most accurate diagnostic method for distinguishing between extraluminal compressions and intramural lesions and plays a critical role in the detection and management of SELs. This is because EUS can reveal the precise sonographic nature of the lesion even though sometimes there are complex cases, which are difficult to diagnose by EUS alone. Performing routine biopsies and obtaining tissue samples for diagnosis can be difficult because SELs are located beneath the normal epithelial layer. Mostly, EUS allows the practitioner to extract an optimal tissue sample since it allows fine-needle aspiration (FNA) and fine-needle biopsy (FNB) both of which provide good results. With immunocytochemical staining, all these techniques increase the accuracy of the diagnosis. Evaluation of subepithelial lesions by means of EUS imaging will provide further characterization of the lesion to help guide us in appropriate differential diagnosis and further management. In this chapter, we provide a systematic EUS-guided approach to the diagnosis, management and later surveillance for SELs, as well as presenting updated diagnostic techniques that may help physicians to appropriately manage these subepithelial lesions.
Part of the book: Endoscopic Ultrasound