**2.2 Endoscopic ultrasound**

The endosonographic morphology of SETs is based on size, layer of origin, echogenicity, echotexture, vascularity and lymph nodes [2]. The procedure is difficult in cases of large lesions or inaccessible regions like the jejunum, ileum or, sometimes, the fourth part of the duodenum.

Size should be reported in two orthogonal planes. There are five layers visible when examining the digestive tract. The first layer (hyperechoic) is the interface of the superficial mucosa with the contrast medium. The second layer (hypoechoic) is the deep part of the mucosa, containing the muscularis mucosae and lamina propria. The third layer (hyperechoic) is the submucosa and the interface between the submucosa and the muscularis propria. The fourth layer (hypoechoic) is the muscularis propria. The fifth layer is the serosa and the interface with adjacent structures. In addition, an SET described at EGD, as mentioned before, can actually be an extrinsic compression, originating beyond all layers. The relation with adjacent layers and structures has to be described. Are the layers immediately above and below distinguishable? Do they present ulcerations or irregularities? Can the neighboring structures be clearly distinguished or is there invasion? All these questions should be answered in a correctly redacted EUS result. The echogenicity of the tumor has to be noted. It can be anechoic (compare to the water in the lumen), hypoechoic (compare to muscularis propria), hyperechoic (compare to submucosa). The texture can also give useful information, as inhomogeneous lesions can raise suspicions of malignancy, as can irregular margins. For further description one can also mention the adjacent vascularization, presence of regional lymph nodes, hepatic lesions or free liquid in the peritoneum. Of all the characteristics mentioned, the most important are layer of origin and echogenicity (**Table 2**).

EUS without histological examination has a high diagnostic yield in duodenal SETs. Xu et al. reported an efficiency of up to 93.3% in a group of 75 duodenal SETs that had a later histological diagnosis [4]. However, diagnostic efficiency seems to be size related, as Brugge et al. reported a correct diagnosis in 45% of gastric lesions less than 2 cm in size and proposed, naturally, EUS with fine-needle aspiration (EUS-FNA) as the gold


**Table 2.**

*Main ultrasonographic characteristics of duodenal lesions.*

standard [10]. As literature regarding duodenal SETs is scarce, there is no consensus about when to perform EUS-FNA, but as previously mentioned, EUS can perform poorly in diagnosing small lesions, so biopsies should be performed in all lesions that are considered suspicious (possible malignant or with malignity potential). All lesions of the fourth layer (muscularis propria) should be biopsied, as most gastrointestinal mesenchymal tumors (GIMTs) have these characteristics. Techniques to obtain deep biopsies, like "jumbo" or "buttonhole" biopsies, may have better outcomes than EUS-FNA in submucosal lesions, but carry high risk of hemorrhage [9, 11].
