Endoscopic image of<unk>  in fundus of stomach, seen on retroflexion. Same<unk>  seen on forward view of the endoscope showing overlying clot. CT scanning is often undertaken (see the radiology section). The definitive diagnosis is made with a biopsy, which can be obtained endoscopically, percutaneously with CT or ultrasound guidance or at the time of surgery. A biopsy sample will be investigated under the microscope by a pathologist physician. The pathologist examines the histopathology to identify the characteristics of<unk> s (spindle cells in 70-80%, epitheloid aspect in 20-30%). Smaller tumors can usually be confined to the muscularis propria layer of the intestinal wall. Large ones grow, mainly outward, from the bowel wall until the point where they outstrip their blood supply and necrose (die) on the inside, forming a cavity that may eventually come to communicate with the bowel lumen. When<unk>  is suspected—as opposed to other causes for similar tumors—the pathologist can use immunohistochemistry (specific antibodies that stain the molecule CD117 also known as c-kit —see below). 95% of all<unk> s are CD117-positive (other possible markers include CD34, DOG-1, desmin, and vimentin). Other cells that show CD117 positivity are mast cells. If the CD117 stain is negative and suspicion remains that the tumor is a<unk> , the newer antibody DOG-1 (Discovered On<unk> -1) can be used. Also sequencing of Kit and PDGFRA can be used to prove the diagnosis. Imaging The purpose of radiologic imaging is to locate the lesion, evaluate for signs of invasion and detect metastasis. Features of<unk>  vary depending on tumor size and organ of origin. The diameter can range from a few millimeters to more than 30 cm. Larger tumors usually cause symptoms in contrast to those found incidentally which tend to be smaller and have better prognosis. Large tumors tend to exhibit malignant behavior but small<unk> s may also demonstrate clinically aggressive behavior. gastric cardia. The lesion appears submucosal, is hypervascular and protrudes intraluminally. Upper GI bleeding led to endoscopy, finding an ulcerated mass. Non-enhanced CT image of a small<unk>  in the posterior stomach wall (arrow). The lesion appears subserosal. Incidental finding. Plain radiographs are not very helpful in the evaluation of<unk> s. If an abnormality is seen, it will be an indirect sign due to the tumor mass effect on adjacent organs. On abdominal x-ray, stomach<unk> s may appear as a radiopaque mass altering the shape of the gastric air shadow. Intestinal<unk> s may displace loops of bowel and larger tumors may obstruct the bowel and films will show an obstructive pattern. If cavitations are present, plain radiographs will show collections of air within the tumor. Calcification is an unusual feature of<unk>  but if present can be visible on plain films. Barium fluoroscopic examinations and CT are commonly used to evaluate the patient with abdominal complaints. Barium swallow images show abnormalities in 80% of<unk>  cases. However, some<unk> s may be located entirely outside the lumen of the bowel and will not be appreciated with a barium swallow. Even in cases when the barium swallow is abnormal, an MRI or CT scan must follow since it is impossible to evaluate abdominal cavities and other abdominal organs with a barium swallow alone. In a CT scan, abnormalities may be seen in 87% of patients and it should be made with both oral and intravenous contrast. Among imaging studies, MRI has the best tissue contrast, which aids in the identification of masses within the GI tract (intramural masses). Intravenous contrast material is needed to evaluate lesion vascularity. Preferred imaging modalities in the evaluation of<unk> s are CT and MRI, and, in selected situations, endoscopic ultrasound. CT advantages include its ability to demonstrate evidence of nearby organ invasion, ascites, and metastases. The ability of MRI to produce images in multiple planes is helpful in determining the bowel as the organ of origin (which is difficult when the tumor is very large), facilitating diagnosis. Small<unk> s Since<unk> s arise from the bowel layer called muscularis propria (which is deeper to the mucosa and submucosa from a luminal perspective), small<unk>  imaging usually suggest a submucosal process or a mass within the bowel wall. In barium swallow studies, these<unk> s most commonly present with smooth borders forming right or obtuse angles with the nearby bowel wall, as seen with any other intramural mass. The mucosal surface is usually intact except for areas of ulceration, which are generally present in 50% of<unk> s. Ulcerations fill with barium causing a bull's eye or target lesion appearance. In contrast-enhanced CT, small<unk> s are seen as smooth, sharply defined intramural masses with homogeneous attenuation. Large<unk> s As the tumor grows it may project outside the bowel (exophytic growth) and/or inside the bowel (intraluminal growth), but they most commonly grow exophytically such that the bulk of the tumor projects into the abdominal cavity. If the tumor outstrips its blood supply, it can necrose internally, creating a central fluid-filled cavity with bleeding and cavitations that can eventually ulcerate and communicate into the lumen of the bowel. In that case, barium swallow may show an air, air-fluid levels or oral contrast media accumulation within these areas. Mucosal ulcerations may also be present. In contrast enhanced CT images, large<unk> s appear as heterogeneous masses due to areas of living tumor cells surrounding bleeding, necrosis or cysts, which is radiographically seen as a peripheral enhancement pattern with a low attenuation center. In MRI studies, the degree of necrosis and bleeding affects the signal intensity pattern. Areas of bleeding within the tumor will vary its signal intensity depending on how long ago the bleeding occurred. The solid portions of the tumor are typically low signal intensity on T1-weighted images, are high signal intensity on T2-weighted images and enhance after administration of gadolinium. Signal-intensity voids are present if there is gas within areas of necrotic tumor. Features of malignancy Malignancy is characterized by local invasion and metastases, usually to the liver, omentum and peritoneum. However, cases of metastases to bone, pleura, lungs and retroperitoneum have been seen. In distinction to gastric adenocarcinoma or gastric/small bowel lymphoma, malignant lymphadenopathy (swollen lymph nodes) is uncommon (5 cm), heterogeneous enhancement after contrast administration and ulcerations. Also, overtly malignant behavior (in distinction to malignant potential of lesser degree) is less commonly seen in gastric tumors, with a ratio of behaviorally benign to overtly malignant of 3-5:1. Even if radiographic malignant features are present, these findings may also represent other tumors and definitive diagnosis must be made immunochemically.
Gastrointestinal stromal tumor
Ectopic pancreas
Krukenberg tumor
Signet ring cell carcinoma
Lipoblastoma
Nesidioblastoma
Angiomyofibroblastoma
Myxoid cyst