*3.3.2 GISTs*

*Endoscopy in Small Bowel Diseases*

*3.2.4 Pancreatic rest*

**Figure 1.**

preferred [14].

**3.3 Solid lesions**

*3.3.1 Lipomas*

Pancreatic rest, also known as heterotopic pancreatic tissue or ectopic pancreas, is pancreatic tissue located, aberrantly, in the digestive tract wall, most often in the stomach. It is usually asymptomatic and is an incidental finding at EGD or CT scan. Its endoscopic characteristics are irregular overlaying mucosa and a central umbilication. Rests originate from the third and fourth layer (submucosa and muscularis propria) and their sonographic appearance is most often mixed (solid and liquid) but highly variable, depending on the dominant tissue. Type 1 heterotopia consists of both pancreatic acini and ducts. Type 2 consists solely of pancreatic acini, and type 3 of pancreatic ducts. Types 1 and 2 have a hypoechoic, inhomogeneous sonographic appearance, poorly delineated from the surrounding tissue (secondary to the lobulated structure of acinous tissue). Type 3 most often appears as a septated cyst (multiple dilated pancreatic ducts). A characteristic appearance of a pancreatic rest seems to be thickening of the fourth layer behind the mass (muscularis propria) [13]. Asymptomatic lesions should be followed endoscopically for size changes, and the rare cases of symptomatic lesions can be resected endoscopically by snare, band ligation or more advanced resection techniques. If the muscularis propria is involved and the heterotopic tissue must be removed, surgical resection is

*Endoscopic (top row) and ultrasonographic (bottom row) appearance of Brunner's gland hyperplasia.*

Lipomas are the most frequent solid, hyperechoic SETs in the duodenum. They are composed of mature lipocytes and originate from the third layer (the submucosa). They are most common in the colon, but are also in the stomach and small bowel. A characteristic endoscopic appearance, with a yellowish tint and a typical

**78**

GISTs are the most common mesenchymal tumors in the GI tract, most often found in the stomach and much more rarely in the duodenum. They originate from the pacemaker cells of the digestive tract wall, the interstitial cells of Cajal. They are a class of SETs that present the most difficulties in diagnosis and management: hypoechoic SETs that originate from the muscle layers (mainly the muscularis propria, sometimes muscularis mucosae). They are similar in sonographic structure and mesenchymal origin. The molecular particularity of GISTs is a mutation in the gene that codes the c-Kit protein. More than 95% of them are immunohistochemical CD117 positive [15]. All GISTs have malignant potential, with the main factors influencing prognosis being mitotic rate, size and location (small intestinal GISTs seem to have a worse prognosis than gastric ones). The most common first symptom is GI bleeding, but a large number of GISTs are probably asymptomatic, as they are a common finding in postmortem examinations or in gastric resection specimens. GISTs in the small intestine may be more aggressive than those located in the stomach, (40–50% of GISTs in the small intestine are malignant, compared with 20–25% of gastric GISTs) [16].

Endoscopically their appearance is similar to other SETs; a bulge in the wall of the digestive tract with normal overlaying mucosa. Sometimes there is a central ulceration or inflammation of the mucosa. They are hypoechoic, arising from a muscle layer. The large ones most often arise from the fourth layer (the muscularis propria). Leiomyomas and other mesenchymal tumors, like the schwannoma, have a similar appearance, but are benign. Therefore a correct diagnosis is essential before a therapeutic decision. Location can be the best indicator of a hypoechoic SET. In the duodenum they mostly turn out to be neuroendocrine tumors. More rarely they are GISTs or granular cell tumors, and they are almost never leiomyomas.

All GISTs have malignant potential, so even though small GISTs used to be followed endoscopically, the current trend is to remove all GISTs. Differentiating between a GIST and a leiomyoma is difficult, even with EUS-FNA/FNB sometimes, thus contrast enhancement is helpful in such cases.

**Figure 2.** *Endoscopic (left) and ultrasonographic (right) appearance of a duodenal lipoma.*

#### *Endoscopy in Small Bowel Diseases*

There is no specific study on contrast enhancement in case of duodenal SETs. A meta-analysis of gastric and esophageal SETs showed that contrast-enhanced endoscopic ultrasound is able to discriminate between GISTs and benign SETs with a pooled sensitivity of 89% and a specificity of 82%. For differentiating the malignant potential of GISTs, the sensitivity was 96% and the specificity was 53% [17]. An uptake of the contrast with the vascular hilum present suggests a leiomyoma, but a heterogenous vascularity suggests GISTs while irregular vessels suggest malignant GISTs.
