Gastrointestinal stromal tumor (GIST) is the most common subepithelial neoplasm that can be found throughout the gastrointestinal tract, but most of them occur in the stomach. GIST consists of spinde cells or epithelioid cells, therefore they were misdiagnose as leiomyoma or leiomyosarcoma before their immunohistochemical properties were discovered (1). The uniqueness of CD117 positive can distinguish GIST from other neoplasm with similar optical microscopical appearance (2). There are several subepithelial neoplasms of the stomach which can exhibit similar CT and MRI features as GIST. This review seeks to illustrate CT and MR manifestations of GIST of the stomach.
GIST of stomach
60-70% of GIST occurs in the stomach. They arise from interstitial cells of Cajal, which are pacemaker cells for gut movement (3). Therefore, GIST usually arises from the muscularis propria and exhibit characteristics of subepithelial neoplasms (Figure 1). The tumors can be extraluminal, intraluminal or mixed (dumbbell-shaped) pattern, while 79% of them are exophytic growth (4). GIST typically grows into a well-defined exophytic mass (Figures 1,2), but intraluminal masses can also be seen (Figure 3). Small tumors are often of homogeneous density or signal and large tumors tend to show irregular lobulated margins, mucosal ulceration, central necrosis, hemorrhage, cavitation, and heterogeneous enhancement (3) (Figures 4,5). Extensive necrosis can result in fistula formation with air-fluid level or oral contrast materials in the cavity (Figure 6). Mucosal ulceration can lead to gastrointestinal bleeding. Gastric GIST often has a better survival than small intestinal GIST (5). Large size, hepatic metastasis and presence of wall invasion often suggest a high-grade GIST and predict poor outcome (6) (Figure 7). Malignant GIST commonly metastasizes to the liver or peritoneum, whereas metastases to the lymph nodes and extra-abdominal metastases are rare.
Leiomyoma originates from either the muscularis mucosae or muscularis propria. They are composed of well-differentiated smooth muscle cells and are rare in the stomach. Although they show similar optical microscopy appearances with GIST, positive staining for a-smooth muscle actin and desmin and negative staining for CD117, CD34, and s100 proteins can distinguish them from GIST at immunohistochemical examination. Leiomyoma appears as subepithelial masses with enhancement at CT and MRI (Figure 8). Because their imaging findings overlap with GIST, it is impossible to distinguish the two entities. The final diagnosis is established by immunohistochemical examination.
Nerve sheath tumors
Gastric schwannoma arises from the Schwann cells of the neural plexus within the stomach wall. They manifest as subepithelial masses with minimal enhancement during the arterial phase and delayed enhancement during the equilibrium phase (Figure 9). Malignant nerve sheath tumors may show necrosis and heterogeneous enhancement (Figure 10).
Most neuroendocrine tumors occur in the appendix, followed by small bowel, but more gastric neuroendocrine tumors are founded recently due to endoscopic examinations. These entities manifest as subepithelial masses with avid enhancement after iv contrast materials (Figure 11).
Gastric lymphomas account for 1-5% malignant tumors involving the stomach (7). Due to the characteristic of submucosal spread, gastric lymphomas often appears as abnormally thickened gastric walls with perigastric lymph adenopathy (8). Sometimes, gastric lymphoma can form a focal mass which mimics a subepithelial tumor (Figure 12).
Castleman disease, solitary fibrous tumor (SFT), inflammatory myofibroblastic tumor, and schwannomas from peritoneal or retroperitoneal, as well as GIST arising from the mesentery and omentum can be adjacent to the stomach and can mimic extraluminal gastric GIST. Tumors from liver or spleen can invade or compress the stomach, which can also mimic gastric GIST (Figures 13,14)
When a mass of the stomach without characteristics of epithial tumors is encountered at CT or MRI, GIST should be considered first in the differential diagnosis. Majority of gastric GIST manifests as an extramural growth soft tissue mass. Moderate to intense enhancement can be found after iv contrast materials. Small masses often appear as homogeneous textures or enhancement, while large masses tend to show heterogeneous texture or enhancement. Extensive necrosis, even fistula between gastric lumen and necrosis cavity, can be seen. Unlike the epithial tumors, GIST seldom causes GI tract obstruction, ascites and metastasis to lymph nodes. Malignant GIST often metastasizes to the liver and mesentery. Several gastric subepithelial tumors may mimic GIST and their imaging manifestations overlap. Due to their benign biological characteristics, GIST tends to grow into a large mass when the mass products symptom and the patient seeks medical services. Therefore, when a large subepithal mass of the stomach is found at CT or MRI, it more like to be a GIST, especially when it poses extensive necrosis, fistula formation and hepatic or/and mesentery metastasis without ascites, lymph node enlargement and GI tract obstruct sign.
Disclosure: The authors declare no conflict of interest.
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