Version May 2024
INTRODUCTION — A subepithelial mass or a bulge encountered during an endoscopy can arise from within any layer of the gastrointestinal (GI) tract wall (intramural) or outside of the wall (extramural). They are usually found incidentally during endoscopy or routine imaging with barium contrast radiography, magnetic resonance imaging (MRI), or computed tomography (CT). The differential diagnosis includes a number of benign and malignant nonepithelial tumors, intramural vessels, and extrinsic compression from extramural structures.
Endoscopy alone cannot accurately distinguish between intramural and extramural lesions [1]. By contrast, endoscopic ultrasonography can characterize such masses and determine if the lesion is intramural or extramural (or both), identify the GI wall layer(s) of origin, and guide tissue acquisition for studies that include histology, cytology, immunohistochemistry, and flow cytometry. The pathology combined with lesion size, location, and sonographic morphology can help distinguish between benign (the majority of subepithelial lesions) and malignant (or potentially malignant) lesions (algorithm 1).
This topic review will provide an overview of common subepithelial lesions that can be identified endosonographically. This discussion is generally consistent with society guidelines [2]. Further information on the individual lesions is also available:
●(See "Clinical presentation, diagnosis, and prognosis of gastrointestinal stromal tumors".)
●(See "Benign lesions of the esophagus".)
●(See "Epidemiology, clinical features, and types of small bowel neoplasms".)
GENERAL PRINCIPLES FOR IMAGING — Endoscopic ultrasound (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 (GI) wall or both. 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 GI wall.
●It can determine the originating layer of intramural lesions, an important clue for making a diagnosis (algorithm 1). Stromal cell tumors, for example, can typically be seen as evolving from the muscularis propria or less commonly from the muscularis mucosa, whereas lipomas typically evolve from the submucosa. Determining the layer of origin will have a significant impact on management (surgical, endoscopic, or no treatment) and the endoscopic approach. (See 'General principles of tissue sampling' below and "Overview of endoscopic resection of gastrointestinal tumors".)
●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 (FNA) or fine needle biopsy (FNB) of the lesion is helpful in some settings. (See "Endoscopic ultrasound-guided fine needle aspiration in the gastrointestinal tract" and "Endoscopic ultrasound-guided fine needle biopsy in the gastrointestinal tract".)
Technical considerations — The following are basic principles that should be understood by endosonographers attempting to visualize subepithelial lesions.
●The lesions should be localized endoscopically or by cross-sectional imaging (CT, MRI, abdominal ultrasound) prior to endosonographic evaluation.
●The GI tract wall echo structure, five layers of alternating bright (hyperechoic) and dark (hypoechoic) lines of approximately 3 to 4 mm thickness, should be understood (figure 1).
●EUS imaging should be performed adjacent to the lesion. Water instillation may be helpful to provide adequate acoustic coupling while achieving a focal distance that permits optimal imaging. The focal length for a 7.5 MHz transducer is approximately 2 cm. Imaging can be optimized by using a minimally inflated, water-filled balloon and instilling water to distend the lumen while providing a medium to transmit the ultrasound waves without reflection.
●For small (<1 cm) or flat lesions, imaging with through-the-scope, high-frequency catheter ultrasound probes ("miniprobes") may be technically easier than using a dedicated echoendoscope. Miniprobes are approximately 3 mm in diameter and operate at 12 and 20 MHz frequencies, permitting more detailed imaging of the GI wall compared with the lower-frequency standard echoendoscopes. However, they have relatively shallow depth of penetration, limiting visualization of large tumors and surrounding lymph nodes. The miniprobes can be introduced through the working channel of a diagnostic endoscope and directed to the lesion endoscopically.
Description of the lesion's characteristics — Primary characteristics that should be determined include the layer of origin or extramural origin, size, echogenicity, and vascularity (algorithm 1). Echogenicity has been described as the following:
●Anechoic – The echogenicity of water or clear fluid (ie, black with no internal echoes). Anechoic lesions are typically associated with acoustic enhancement, which is a brighter echo located behind a fluid-filled structure. Common examples are cysts, vessels, and the gallbladder.
●Hypoechoic – Echogenicity that is equivalent or lower than that of the second (lamina propria) and fourth wall layers (muscularis propria). Common examples include leiomyomas, GI stromal tumors (GIST), or mucin/debris-filled cysts.
●Hyperechoic – Echogenicity that is equivalent to or higher than the first (superficial mucosa), third (submucosa), and fifth layers (serosa). The most common example is a lipoma.
●Isoechoic – Echogenicity that is equivalent or nearly equivalent to the involved layer of the lesion. This appearance can be somewhere in between hyperechoic and hypoechoic.
General principles of tissue sampling — A number of methods are available for obtaining tissue samples.
●Standard forceps biopsy – Specimens obtained by standard endoscopic forceps have a low diagnostic yield due to their superficial sampling. Taking a biopsy within the site of a previous biopsy ("bite-on-bite," "tunnel," or "well" biopsies) has not been shown to significantly increase the yield [3].
●Jumbo forceps biopsy – "Bite-on-bite" jumbo biopsy has been reported with mixed results, although jumbo forceps have nearly twice the jaw volume of standard forceps. In one study, jumbo biopsies using the bite-on-bite technique in 22 subepithelial lesions was found to be diagnostic in 18 of 22 cases; however, another study of jumbo biopsies from submucosal lesions found the diagnostic yield to be only 17 percent [4,5].
A retrospective study compared the use of jumbo forceps biopsy with EUS-guided FNA (average lesion size 15±9.3 mm, location primarily in the upper GI tract), and the methods were similar with regard to making a definitive diagnosis (59 versus 45 percent) [6]. However, significant bleeding requiring hemostasis occurred in nearly 35 percent of patients undergoing jumbo forceps biopsy. Jumbo forceps had the greatest utility in diagnosing lesions that arose from the submucosal layer of the GI tract wall, whereas FNA was more accurate for muscularis propria lesions.
●Single-incision needle-knife (SINK) biopsy – The diagnostic yield of a tissue biopsy can be improved by resecting the overlying mucosa or a portion of the lesion using a snare or needle knife, a maneuver that creates access to deeper tissue. This technique has been referred to as "SINK" or "unroofing." Various approaches are used to facilitate SINK, including the use of a double-channel endoscope, band ligation, and a cap attachment. A prospective study comparing biopsy and SINK techniques showed a marked increase in diagnostic yield between the two modalities (17 versus 87 percent, respectively) [5]. Another study reported a 94 percent yield for diagnosis and assessment of risk for malignancy using the SINK technique in subepithelial tumors originating from the muscularis propria on EUS [7].
In a study of 49 patients who had SINK biopsies of subepithelial lesions, a definitive diagnosis was made in 42 cases (86 percent), and 40 of 44 biopsy specimens (91 percent) were adequate for immunohistochemistry when it was required [8].
●Ligation prior to SINK – To prevent complications such as bleeding and perforation [9], ligation using bands and endoloops has been proposed prior to SINK biopsy [10-12]. Ischemia resulting from ligation may result in therapeutic ablation.
●Fine needle aspiration (FNA) – Several needles are available for performing EUS-guided FNA, and they range in size from 19- to 25-gauge. EUS-guided FNA may be used to obtain a tissue sample for cytology and is often used in conjunction with immunohistochemistry staining, such as for c-kit (CD 117). EUS-guided FNA is discussed in more detail separately. (See "Endoscopic ultrasound-guided fine needle aspiration in the gastrointestinal tract".)
●Fine needle biopsy (FNB) – Specialized needles have been designed to acquire larger "core" specimens that preserve tissue architecture for a histologic diagnosis and immunohistologic staining, and this method is discussed separately. (See "Endoscopic ultrasound-guided fine needle biopsy in the gastrointestinal tract".)
●Endoscopic snare resection – Small (<20 mm) lesions arising superficial to the muscularis propria can usually be resected with a snare using the endoscopic mucosal resection (EMR) technique (with or without prior band or loop ligation).
●Endoscopic submucosal dissection (ESD) – ESD with a dissecting knife has been primarily used for the treatment of mucosal gastric and esophageal cancers [13-15], but has been increasingly described for the resection of subepithelial tumors [16,17]. Resection success rates are over 90 percent for patients with neuroendocrine (carcinoid) tumors [18] and granular cell tumors [19]. In a study of 144 patients treated with ESD for subepithelial gastric lesions arising from the muscularis propria, 134 of 145 lesions (92 percent) were resected completely, with no local recurrence or distal metastasis during a mean follow-up of 19 months [20]. Perforation occurred in 21 of 144 patients (14 percent), but all perforations were managed endoscopically.
ESD requires an advanced level of operator skill, is time consuming, and is associated with significant complication rates, especially bleeding and perforation. As a result, ESD should be reserved for centers specialized in this advanced procedure. (See "Overview of endoscopic resection of gastrointestinal tumors", section on 'Endoscopic submucosal dissection'.)
●Endoscopic full-thickness resection – Advantages of full-thickness resection are the ability to completely resect lesions arising from the muscularis propria, resect larger tumors (up to 4 cm), and resect at difficult locations such as the fundus and the proximal body. However, closure of the gastric wall defect must be effective. This can be performed using standard or over-the-scope clips, endoscopic suturing, and endoloops [21-23].
●Submucosal "tunneling" – Tunneling may improve the safety of tissue acquisition and endoscopic resection of subepithelial tumors [24-26]. The technique involves performing a mucosal incision proximal to the lesion, followed by scope advancement into the submucosal space, and dissection in the submucosa up to the lesion. Enucleation of the lesion can be performed with ESD techniques and the lesion retrieved through the tunnel. Mucosal closure of the tunnel is then performed. Theoretical advantages of submucosal tunneling are the preservation of mucosal integrity and lower risks of peritonitis or mediastinitis.
ACCURACY — Multiple studies have evaluated the accuracy of EUS in characterizing subepithelial lesions [27]. Studies focusing on specific lesions are presented below. As a general rule, the ability of EUS alone to distinguish among subepithelial lesions is variable. As a result, histology is still considered to be the "gold standard."
Some representative studies have shown the following:
●A prospective study evaluating the accuracy of EUS in characterizing 100 patients with subepithelial lesions found that EUS findings alone correctly predicted the specific lesion type in only 48 percent of cases where biopsy confirmation had been obtained [1]. Most misclassifications occurred in hypoechoic lesions in the third and fourth layers, which include neuroendocrine (carcinoid) tumors, gastrointestinal stromal tumors, aberrant pancreas, and granular cell tumors.
●In a second study, the results of endoscopic resection or biopsies after unroofing in 54 submucosal lesions were compared with the EUS findings [28]. The overall accuracy of EUS in determining the layer of origin and location of lesion was 80 percent; six lesions were located deeper in the GI wall than estimated by EUS and five were more superficial. EUS and pathology findings coincided in 74 percent of lesions.
●In a third study, 22 patients underwent EUS prior to endoscopic resection of gastric subepithelial lesions [29]. EUS alone correctly diagnosed 10 (46 percent) of the lesions. The types of lesions that were incorrectly diagnosed included pancreatic rests and gastritis cystica profunda.
EXTRAMURAL LESIONS — Typical anatomic structures and extraluminal benign and malignant tumors can compress the gastrointestinal (GI) tract and mimic an intramural tumor. Incidental lesions are being detected more commonly with the increasing use of total body scans in healthy patients. EUS can assist in further characterizing such findings.
Endoscopic appearance — Extramural lesions are commonly seen as a bulge located in the GI tract with normal overlying mucosa, usually with a smooth border and no significant irregularity (picture 1).
Endosonographic findings — The five-layer GI wall structure is seen interposed between the lesion and the bowel lumen. Specific echo features vary depending upon the type of structure identified. As an example, the splenic vessels appear as an anechoic structure that can be followed longitudinally. The spleen may appear to have a homogeneous echogenicity. A pancreatic pseudocyst originates from a region of the pancreas and is commonly hypoechoic or anechoic.
Diagnosis — An understanding of expected EUS findings is required to determine if a structure is atypical. Common extrinsic structures include the splenic artery, spleen, gallbladder, left lobe of the liver, and the pancreas [30]. EUS examination may identify abnormalities such as pancreatic pseudocysts, enlarged lymph nodes, aneurysms, omental metastasis, and hepatic, pancreatic, and renal tumors. One group reported 100 percent accuracy in distinguishing extramural from intramural structures [30].
GASTROINTESTINAL STROMAL TUMORS — The nomenclature of gastrointestinal (GI) mesenchymal tumors is evolving with an increased understanding of molecular, histologic, and clinical features that distinguish different types of tumors [31-34]. The most common mesenchymal tumor in the GI tract, gastrointestinal stromal tumors (GISTs), were initially thought to be of smooth muscle origin, however, a more complete understanding of their molecular markers and biologic behavior has demonstrated that they encompass a heterogeneous group of tumors with respect to cell of origin (eg, interstitial cells of Cajal), cellular differentiation, and prognosis.
GISTs are most frequently diagnosed in older individuals, in whom they are most common in the stomach (40 to 60 percent), small intestine (25 to 30 percent), colon/rectum (15 percent), and esophagus (<1 percent) [33]. The differential diagnosis includes a multitude of lesions that can occupy the submucosal layers. These include leiomyomas, leiomyosarcomas, schwannomas, inflammatory myofibroblastic tumors in pediatric patients, lipomas, liposarcomas, metastatic tumors, and desmoid tumors. Distinction from these other tumors is made based upon clinical, histologic, and molecular features.
A distinguishing molecular feature of GISTs is that they are positive for c-kit (a stem cell factor receptor referred to as CD117) in the majority of patients. This immunohistochemical stain distinguishes GIST from other kinds of spindle cell tumors [35]. Other tumors that are positive for c-kit (such as angiosarcomas and metastatic melanomas) can usually be distinguished based upon clinical and histologic features. Additional markers found in GISTs include DOG-1 [36], CD34, and smooth muscle actin (table 1) [33].
It was previously thought that some GISTs (less than 1 to 2 cm in size and with a low mitotic rate) were benign. However, virtually all GISTs, especially those greater than 1 cm, have malignant potential. The main factors associated with prognosis are tumor size, mitotic rate, and primary location (with small intestinal GISTs being more aggressive than those in the stomach). The clinical features, diagnosis, and prognosis of GISTs are discussed in detail separately. (See "Clinical presentation, diagnosis, and prognosis of gastrointestinal stromal tumors".)
Endoscopic appearance — A GIST commonly appears as a bulge located in the GI tract with normal overlying mucosa and can vary in size from several millimeters to over 30 centimeters. It usually has a smooth and regular appearance without major mucosal irregularities. In some cases, the overlying mucosa can be ulcerated or appear inflamed.
Endosonographic findings in GISTs — GISTs are typically hypoechoic, homogeneous lesions with well-defined margins, although they can rarely have irregular margins and ulcerations. Most GISTs originate from within the muscularis propria (fourth layer of the GI tract); small lesions may originate from the muscularis mucosa (second layer). Infrequently, the tumors are inhomogeneous, which has been attributed to liquefaction necrosis, connective tissue, and cystic and hyaline degeneration [37,38].
Specific endosonographic characteristics can be helpful for identifying features of malignant transformation. Large tumors with a heterogeneous echo texture are more likely to be leiomyosarcomas and leiomyoblastomas.
Histopathology — A definitive diagnosis of a GIST requires an adequate tissue specimen for immunohistochemistry. Standard endoscopic forceps biopsies are unlikely to reach the lesion. The use of jumbo forceps has shown diagnostic yields for fourth-layer lesions of 40 percent but has also been found to be associated with a 35 percent significant bleeding rate requiring endoscopic hemostasis [6].
EUS-guided tissue sampling with fine needle aspiration (EUS-FNA) is limited by scant sample size that may be nondiagnostic in nearly 40 percent of patients [39,40]. Use of next generation fine needle biopsy (FNB) was associated with higher diagnostic yield results [41,42]. In a study including 147 patients with a suspected GIST, tissue sampling with EUS-FNB was associated with higher cytopathology yield (92 versus 46 percent), higher immunohistochemistry yield (89 versus 41 percent), and higher diagnostic yield (89 versus 37 percent) compared with EUS-FNA [42]. (See "Endoscopic ultrasound-guided fine needle biopsy in the gastrointestinal tract".)
The single-incision needle-knife biopsy technique has been used to obtain endoscopic biopsies of subepithelial tumors originating in the muscularis propria. In one report, this technique resulted in a 94 percent yield for diagnosis and assessment of risk for malignancy [7]. Performing loop ligation before unroofing appears to reduce the risk of procedural bleeding and perforation [11,12]. (See 'General principles of tissue sampling' above.)
Management — Local treatment options for patients with GIST vary according to size, and these issues are discussed in detail separately. (See "Local treatment for gastrointestinal stromal tumors, leiomyomas, and leiomyosarcomas of the gastrointestinal tract".)
LEIOMYOMAS AND LEIOMYOSARCOMAS — Most leiomyomas are located in the esophagus, and are rarely found in other parts of the gastrointestinal (GI) tract. Ninety percent of esophageal leiomyomas are located in the lower and middle esophagus because of the muscular composition of the esophagus, with predominantly smooth muscle in the lower esophagus, and mixed with striated muscle in the middle portion.
EUS is the most accurate method for diagnosing leiomyomas and distinguishing them from other submucosal lesions, including duplication cysts and leiomyosarcomas (image 1). These lesions arise from the fourth and rarely the second gastric wall layer. Immunohistochemical studies on aspirates are positive for smooth muscle actin and desmin and negative for c-kit (CD 117). (See "Clinical presentation, diagnosis, and prognosis of gastrointestinal stromal tumors".)
The epidemiology, clinical presentation, diagnosis, and surgical management of leiomyomas and leiomyosarcomas are discussed in detail elsewhere. (See "Clinical presentation, diagnosis, and prognosis of gastrointestinal stromal tumors" and "Local treatment for gastrointestinal stromal tumors, leiomyomas, and leiomyosarcomas of the gastrointestinal tract".)
LIPOMAS — Lipomas are benign intramucosal tumors of mature lipocytes that are commonly incidental findings on colonoscopy and endoscopy. They can be seen in any part of the gastrointestinal (GI) tract, although they are most common in the lower GI tract. Lipomas are rarely symptomatic, but may result in hemorrhage, abdominal pain, and intestinal obstruction [43]. They have no malignant potential.
Endoscopic appearance — A lipoma commonly appears as an isolated solitary bulge located in the GI tract with normal overlying mucosa, a yellowish hue, and a smooth regular appearance. When probed, they are soft and usually collapse to create an indentation known as the "pillow or cushion sign." Biopsy forceps may grasp the overlying mucosa to create the "tenting sign" by pulling the mucosa away from the submucosal growth. They are commonly small (less than 4 centimeters). In one report of seven lesions (six of which were proven to be a lipoma by EUS) a pillow sign on endoscopy had low sensitivity (40 percent) but high specificity (99 percent) [1].
Endosonographic findings — The five layers of the GI tract should be easily identified using low-frequency imaging. Lipomas are hyperechoic, homogeneous lesions with regular margins arising from the submucosa (third layer of the GI tract) (image 2).
Diagnosis and treatment — The diagnosis is almost always made by a characteristic endoscopic and endosonographic appearance. Biopsies usually show only normal mucosa. However, a tissue diagnosis may be made by either fine needle aspiration or tunnel biopsy.
Lipomas found incidentally should be followed expectantly. Endoscopic and endosonographic surveillance are not necessary. Local excision is advised for symptomatic lipomas or when the lesion cannot be distinguished from a malignant neoplasm (such as a liposarcoma). Endoscopic snare resection using polypectomy technique has been described [44,45]. However, snare excision may be associated with perforation and hemorrhage, the risk of which is particularly increased for lesions greater than 2 cm in diameter [44,45]. To reduce the risk, endoloop ligation prior to resection has been reported [10]. Endoloop ligation as stand-alone therapy (without resection) has also been reported [46]. This approach was successful in a series of 10 patients with pedunculated submucosal tumors [47], six of whom had lipomas, with no reported complication. However, a drawback was the lack of a reliable surgical specimen for pathology. Patients were instructed to retrieve specimens from stool, but this was successful in only 60 percent of cases.
NEUROENDOCRINE (CARCINOID) TUMOR — Neuroendocrine (carcinoid) tumors (NETs) are rare intramucosal tumors of endocrine cell origin with malignant potential and are commonly asymptomatic. They are usually discovered incidentally during endoscopy, surgery, or autopsy. In the United States, NETs are most commonly found in the appendix, rectum, and ileum, while in Japan they are often located in the stomach, rectum, and duodenum [45,48]. Rare complications include hemorrhage, abdominal pain, intestinal obstruction, and endocrine syndromes due to secretion of functionally active substances (particularly when they metastasize to the liver). (See "Clinical characteristics of well-differentiated neuroendocrine (carcinoid) tumors arising in the gastrointestinal and genitourinary tracts" and "Staging, treatment, and post-treatment surveillance of non-metastatic, well-differentiated gastrointestinal tract neuroendocrine (carcinoid) tumors".)
●Endoscopic appearance – NETs appear as small, round sessile or polypoid lesions with normal overlying mucosa that rarely ulcerate [49]. They range in size from a few millimeters to a few centimeters. Gastric and ileal NETs are commonly multiple, while those arising elsewhere are typically solitary (picture 2).
●Endosonographic appearance – NETs are homogeneous hypo- or isoechoic with regular margins. They arise from the mucosa/lamina propria (second layer of the gastrointestinal [GI] tract) and can invade the submucosal layer (third layer) (image 3) [50].
●Diagnosis and treatment – The diagnosis and treatment of NETs are discussed separately. (See "Staging, treatment, and post-treatment surveillance of non-metastatic, well-differentiated gastrointestinal tract neuroendocrine (carcinoid) tumors" and "Clinical characteristics of well-differentiated neuroendocrine (carcinoid) tumors arising in the gastrointestinal and genitourinary tracts".)
GRANULAR CELL TUMOR — Granular cell tumors (GCTs) are rare submucosal tumors of Schwann cell origin that are usually incidental findings on endoscopy and colonoscopy. They are most common in the oropharynx, skin, subcutaneous tissue, or breasts, but they can involve any part of the intestinal tract and the biliary tree [51-54]. Most intestinal tract lesions are found in the middle to lower third of the esophagus. Immunostaining is usually positive for the S-100 protein. (See "Benign lesions of the esophagus".)
GCTs are considered benign, although malignant GCTs have been reported in less the two percent of cases, particularly when larger than 4 cm [53]. These lesions are rarely associated with complications such as bleeding and lumen obstruction [55,56].
●Endoscopic appearance – GCTs usually appear as small, isolated nodules or polyps located in the gastrointestinal (GI) tract with normal overlying mucosa and a yellowish hue. The majority are small (<4 cm) and solitary, although multifocal lesions have been described (picture 3).
●Endosonographic findings – GCTs are usually hypoechoic, homogeneous lesions with smooth margins arising from the mucosa (majority) and/or submucosa (second or third layer of the GI tract) (picture 3) [57].
●Diagnosis and treatment – Surveillance endoscopy is recommended for asymptomatic GCTs. GCTs that are not excised should be monitored by EUS for an increase in size every one to two years [45].
Symptomatic or larger lesions (>10 mm) are removed with en bloc resection using endoscopic mucosal resection for lesions ≤20 mm or endoscopic submucosal resection for lesions >20 mm [58]. Alternatives to endoscopic resection include surgical resection.
DUPLICATION CYSTS — Duplication cysts (DCs) are benign, rare anomalies that arise during early embryonic development. They are most frequently found in the proximal small intestine, although they can also be found in the esophagus, stomach, and colon. There are two general types: those that are adjacent to the lumen (having lost communication to the gastrointestinal [GI] wall), and those that are tubular and communicate directly with the lumen [59,60]. DC are lined with stratified, ciliated, or columnar epithelium and contain a mucoid fluid [60,61].
The cysts are typically discovered incidentally on endoscopy or radiologic imaging since they only uncommonly cause symptoms. Complications are rare but may include dysphagia, abdominal pain, bleeding, and pancreatitis when located near the ampulla of Vater [61]. While they are believed to have a low malignant potential, case reports have described malignant transformation [62].
Endoscopic appearance — DCs can appear as a bulge with normal overlying mucosa, or as a diverticulum that can vary in size from several millimeters to over 5 cm. They have a smooth and regular appearance without mucosal irregularities. They are most commonly diagnosed by CT scan or MRI since they are infrequently seen endoluminally (picture 1).
Endosonographic findings — DCs are usually anechoic homogeneous lesions with regular margins arising from the submucosal (third layer) or extrinsic to the GI wall. Their walls can be characterized by three- or five-layer structures. They also can contain septae, fluid levels, or echogenic material consisting of layering debris or mucin (image 4). Occasionally, a cyst appears as a solid lesion on CT scan due to the higher density elicited from debris particles within a cyst. EUS is helpful in discriminating a DC from a solid mass.
Diagnosis and treatment — The diagnosis can usually be made by the characteristic endoscopic and endosonographic appearance. We do not typically perform fine needle aspiration (FNA) because it is not necessary and is associated with increased risk of infection [63,64].
Management of asymptomatic cysts is usually expectant, but resection has been recommended based upon their potential for complications, including malignant transformation. However, prospective studies evaluating the natural history of DCs are lacking. When symptomatic, DCs can be treated surgically or endoscopically [65]. Successful endoscopic management of endoluminal cysts has been described using FNA, needle-knife cystostomy, and, when small, snare excision [60].
PANCREATIC REST — A pancreatic rest (also known as ectopic pancreas, aberrant pancreas, and heterotopic pancreas) refers to ectopic pancreatic tissue. These rare submucosal tumors most commonly consist of cystically dilated exocrine cells. Endocrine pancreatic tissue or a combination of exocrine and endocrine cell types may also be seen [66].
Pancreatic rests are most frequently found in the distal stomach, duodenum, or proximal jejunum, but have also been reported within a Meckel's diverticulum, the gallbladder, bile ducts, and the minor and major papillae [67]. They are typically discovered incidentally during endoscopy, surgery, or autopsy. They are also occasionally found on CT scan. CT findings that may help differentiate pancreatic rests from other submucosal lesions identified in one study included [68]:
●A flat-ovoid shape (long diameter to short diameter ratio of greater than 1.4)
●Location of the lesion in the antrum, pylorus, or duodenum
●An endoluminal growth pattern
●An ill-defined border
●Prominent enhancement of the overlying mucosa
The study found that the presence of at least two of the above findings had a sensitivity of 100 percent and a specificity of 82.5 percent for diagnosing a pancreatic rest in the upper GI tract [68]. The specificity increased to 100 percent if three of the above findings were present.
However, while pancreatic rests may be detected with CT scan, if a submucosal lesion is noted on upper endoscopy, we suggest EUS for further evaluation, as small lesions may be missed on CT scan. (See 'General principles of tissue sampling' above.)
While most patients with pancreatic rests are asymptomatic, some patients may develop abdominal pain, GI bleeding, intestinal obstruction, or pancreatitis related to the lesion [66,69,70]. Rare cases of malignant transformation have also been reported, but the incidence is <1 percent [71,72].
Endoscopic appearance — A pancreatic rest appears as a submucosal nodule, usually with a central umbilication that corresponds to a draining duct.
Endosonographic findings — Pancreatic rests are hypoechoic or intermediate echogenic heterogeneous lesions with indistinct margins. They most commonly arise from the third or fourth layer, or a combination of the two layers of the GI tract. Anechoic areas within the lesion correlate with ductal structures [66]. In a national registry of over 24,000 EUS procedures, 575 endosonographic examinations were performed for suspected subepithelial lesions of the upper GI tract, and 63 of these (11 percent) were cases of pancreatic rest [73]. In over 50 percent of the cases of pancreatic rest, the endosonographic appearance was described as heterogeneous, and in nearly 90 percent of cases, the layer of origin was identified.
Diagnosis and treatment — The diagnosis of pancreatic rest can be made based on endoscopic appearance. (See 'Endoscopic appearance' above.)
If the diagnosis is uncertain, it can be established histologically from tissue obtained by biopsy forceps, especially if the biopsy forceps is directed into the central umbilication. Additional techniques include snare excision, although techniques to obtain deeper biopsies (using jumbo biopsy forceps, tunnel biopsy, unroofing, or fine needle aspiration) may be required [66]. The management strategy should be guided by symptoms and suspicion for malignancy. Asymptomatic lesions can be followed expectantly. Endoscopic resection can be performed by standard snare, band ligation-assisted, or cap-assisted polypectomy technique [74]. Ligation-induced ischemia using a 20-mm loop deployed through an 18-mm cap attachment was reported as an alternative approach to treat three patients with symptomatic pancreatic rests [12]. Surgical resection is preferred to endoscopic resection when the muscularis propria is involved.
VARICES — Varices are blood vessels that distend as a result of a hypertensive portal or splenic venous system.
Endoscopic appearance — Varices can be visualized in the esophagus, stomach, duodenum, and rectum. They typically appear as bluish enlarged vessels that are commonly tortuous and easily compressed with instrumental pressure. Gastric varices may be confused with thickened folds or a submucosal lesion.
Endosonographic findings — Varices are round anechoic structures arising from the lamina propria or submucosa. Color Doppler can be used to detect blood flow, which will immediately confirm a vascular structure, distinguishing a varix from other anechoic subepithelial lesions such as a cyst. A potential problem using a dedicated echoendoscope to image small varices is the tendency to compress the varix by the instrument or with inflation of the transducer balloon. This can be overcome by using a catheter ultrasound probe (miniprobe) inserted through the working channel of an endoscope. The miniprobe permits precise endoscopic targeting of the varix with a small diameter (approximately 3 mm) transducer that will not compress the varix. However, miniprobes lack Doppler capability.
Diagnosis and treatment — The diagnosis is based on the typical endoscopic and endosonographic features. It is important never to obtain endoscopic biopsies if varices are in the differential, as this will provoke massive bleeding. Treatment depends upon the clinical context. (See "Overview of the management of patients with variceal bleeding" and "Endoscopic variceal ligation" and "Methods to achieve hemostasis in patients with acute variceal hemorrhage".)
UNCOMMON LESIONS — A variety of uncommon submucosal lesions can be seen endosonographically, including esophageal fibrovascular polyps, inflammatory fibroid polyps, pneumatosis cystoides, thickened folds, fibromas, Brunner's gland nodules, gastrointestinal (GI) wall hematomas, esophageal hemangiomas, and GI wall metastasis. However, their endosonographic descriptions have been heterogeneous and scarce [75]. Thus, use of EUS to diagnose these lesions should be made on an individual case basis.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Gastrointestinal stromal tumors".)
SUMMARY AND RECOMMENDATIONS
●General principles – Endoscopic ultrasound (EUS) can characterize subepithelial lesions by identifying the layer of origin and by guiding tissue acquisition for cytohistology, immunohistochemistry, or flow cytometry. The pathology combined with lesion size, location, and sonographic morphology can help distinguish between benign (the majority of subepithelial lesions) and malignant lesions (algorithm 1). (See 'Introduction' above.)
●Accuracy – In general, the ability of EUS alone to distinguish among subepithelial lesions is variable. As a result, histology is regarded as the "gold standard." The sonographic appearances of some lesions are highly suggestive of the diagnosis, while for others, EUS provides complementary information to other diagnostic modalities. Hypoechoic lesions in the third and fourth layers are most prone to misclassification. (See 'Accuracy' above.)
●Tissue sampling – When indicated, tissue sampling can be performed by a number of methods, including fine needle aspiration or fine needle biopsy under EUS guidance or by endoscopic biopsy after unroofing. (See 'General principles of tissue sampling' above.)
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