DOI: 10.1148/rg.232025146
(Radiographics. 2003;23:283-304.)
© RSNA, 2003
From the Archives of the AFIP
Gastrointestinal Stromal Tumors: Radiologic Features with Pathologic Correlation1
Angela D. Levy, LTC, MC, USA,
Helen E. Remotti, MAJ, MC, USAR,
William M. Thompson, MD,
Leslie H. Sobin, MD and
Markku Miettinen, MD
1 From the Departments of Radiologic Pathology (A.D.L., W.M.T.), Hepatic and Gastrointestinal Pathology (H.E.R., L.H.S.), and Soft Tissue Pathology (M.M.), Armed Forces Institute of Pathology, 6825 16th St NW, Washington, DC 20306-6000; Department of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md (A.D.L.); and Department of Radiology, Duke University, Durham, NC (W.M.T.). Received August 30, 2002; revision requested October 3 and received October 11; accepted October 16. Address correspondence to A.D.L. (levya@afip.osd.mil).
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Abstract
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Gastrointestinal stromal tumors (GISTs) are unique neoplasms that occur throughout the gastrointestinal tract, mesentery, omentum, and retroperitoneum. They are the most common mesenchymal neoplasm of the gastrointestinal tract and are defined by their expression of KIT (CD117), a tyrosine kinase growth factor receptor. The expression of KIT is important to distinguish GISTs from other mesenchymal neoplasms such as leiomyomas, leiomyosarcomas, schwannomas, and neurofibromas and to determine the appropriateness of KIT-inhibitor therapy. The series described herein was accumulated over 2 years and includes 64 pathologically proved GISTs (28 gastric, 27 small intestinal, six anorectal, one colonic, one esophageal, and one from the small bowel mesentery). Radiologic features of GISTs vary depending on tumor size and organ of origin. Since most GISTs arise within the muscularis propria of the stomach or intestinal wall, they most commonly have an exophytic growth pattern and manifest as dominant masses outside the organ of origin. Dominant intramural and intraluminal masses are less common radiologic manifestations. GISTs occurring in the gastrointestinal tract and mesentery characteristically have hemorrhage, necrosis, or cyst formation that appears as focal areas of low attenuation on computed tomographic images. Although the radiologic features of GISTs are often distinct from those of epithelial tumors, criteria to separate GISTs radiologically from other nonepithelial tumors have not yet been fully developed.
© RSNA, 2003
Index Terms: Gastrointestinal stromal tumor (GIST), 70.30 • Gastrointestinal tract, neoplasms, 70.30 • Intestinal neoplasms, 74.30 • Stomach, neoplasms, 72.30
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:
- Identify the clinical and pathologic features of GISTs.
- Describe the radiologic appearances of GISTs.
- Discuss the differential diagnosis of GISTs throughout the gastrointestinal tract and abdomen.
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Introduction
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Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. The term gastrointestinal stromal tumor defines a unique group of mesenchymal neoplasms that are distinct from true smooth muscle and neural tumors. The histogenesis of GISTs has been debated for over 50 years (1). Older medical literature referred to these tumors as smooth muscle tumors, leiomyomas, leiomyosarcomas, epithelioid leiomyosarcomas, and leiomyoblastomas because these tumors were believed to originate from the smooth muscle layers of the wall of the gastrointestinal tract. This variable nomenclature has led to considerable diagnostic confusion and is indicative of the diverse radiologic and histologic manifestations of mesenchymal neoplasms.
The best defining feature of GISTs is the expression of KIT (CD117), a tyrosine kinase growth factor receptor. Immunoreactivity for KIT distinguishes GISTs from true leiomyomas, leiomyosarcomas, schwannomas, and neurofibromas (2,3). The expression of KIT by GISTs has led several authors to postulate that GISTs arise from primitive stem cells that phenotypically resemble the native KIT-positive gut pacemaker cell or interstitial cell of Cajal (4,5). Not only is KIT immunoreactivity of useful diagnostic utility in diagnosing GISTs, but also more important, ligand-independent constitutive activation of KIT is central to the pathogenesis of GISTs. Pharmacologically targeting this receptor with a KIT-tyrosine kinase inhibitor (STI-571, Imatinib [Gleevec]; Novartis, Basel, Switzerland) has been shown to be of clinical utility in treating patients with GISTs.
GISTs, leiomyomas, and leiomyosarcomas are distinctly different neoplasms that arise with variable frequency throughout the gastrointestinal tract. GISTs are the most common and may occur from the esophagus to the anus. They may also occur primarily in the omentum, mesentery, and retroperitoneum. The esophagus is the only site where leiomyomas predominate (75% of esophageal mesenchymal tumors are leiomyomas; 25% are GISTs) and leiomyosarcomas are rare (6). In the stomach, small intestine, colon, and anorectum, GISTs account for almost all mesenchymal tumors, as leiomyomas and leiomyosarcomas in these sites are very rare (7–9).
The clinical manifestation of GISTs is highly variable. In some patients, small benign GISTs are discovered incidentally during radiologic evaluation or surgery for another condition. In contrast, other patients present with profound symptoms that reflect large or highly aggressive GISTs that invade adjacent organs and metastasize. As a result, GISTs have a wide spectrum of radiologic appearances. This article summarizes the current literature and our recent experience with 64 cases of GIST (28 gastric, 27 small intestinal, six anorectal, one colonic, one esophageal, and one from the small bowel mesentery) accessioned into the Radiologic Pathology Archives at the Armed Forces Institute of Pathology from April 1998 to May 2002. The clinical, pathologic, and radiologic spectrum of GISTs throughout the gastrointestinal tract, omentum, and mesentery is presented.
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Clinical Features
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The exact prevalence of GISTs is difficult to determine. Miettinen and Lasota (8) estimate the frequency of GISTs as 10–20 cases per million persons. No association between geographic location, ethnicity, race, or occupation has been established (10). Most individuals are over 50 years of age at the time of presentation, and GISTs are rarely seen in patients younger than 40 years of age (11). Although some studies in the literature show a slight male predominance, others show no gender predilection (12–14). Patients with neurofibromatosis type 1 (NF1) have an increased prevalence of GISTs. Classically, patients with NF1 have multiple small intestinal GISTs (15, 16). GISTs are likely a feature of the Carney triad, which is a rare condition referring to the association of an epithelioid leiomyosarcoma with paraganglioma and pulmonary chondroma (17). Patients with KIT germ line mutations have an increased prevalence of GISTs (18).
Presenting signs and symptoms depend on the size and anatomic location of the tumor. GISTs most frequently occur in the stomach (70% of cases), followed by the small intestine (20%– 30%), anorectum (7%), colon, and esophagus (8). The most common clinical manifestation for symptomatic GISTs in the stomach, small intestine, colon, and anorectum is gastrointestinal bleeding from mucosal ulceration (19). Patients may present with hematemesis, melena, hematochezia, or signs and symptoms of anemia caused by occult bleeding. Other signs and symptoms include nausea, vomiting, abdominal pain, weight loss, abdominal distention, and intestinal obstruction. Occasionally, small asymptomatic GISTs are discovered incidentally during a radiologic evaluation or surgical procedure performed for other reasons. Asymptomatic anorectal tumors may be discovered as a palpable mass during routine digital rectal examination. The most common clinical manifestation for patients with esophageal GISTs is dysphagia (6). Less common manifestations for esophageal lesions include cough, gastrointestinal bleeding, and the incidental discovery of a posterior or middle mediastinal mass on chest radiographs.
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Pathologic Features
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Gross Pathologic Features
GISTs of the hollow gastrointestinal tract most commonly involve the muscularis propria of the intestinal wall. Mesenchymal tumors that involve the muscularis mucosae most frequently arise in the colon and occur as polyps. Such tumors are thought to uniformly represent true leiomyomas (20). Because GISTs usually involve the outer muscular layer, they have a propensity for exophytic growth (Fig 1a). Therefore, the most common appearance is that of a mass arising from the intestinal wall and projecting into the abdominal cavity (19). Often, a component of the tumor distends to the mucosal surface of the involved segment of intestine. Mucosal ulceration is seen on the luminal surface of the tumor in up to 50% of cases (Fig 1c) (19).
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Figure 1a. Gross pathologic features of GISTs. (a) Photomicrograph (actual size [1:]; hematoxylin-eosin [H-E] stain) of resected jejunum from an 82-year-old man with gastrointestinal bleeding shows an intramural GIST with its origin in the muscularis propria (solid arrows). There is intact overlying normal small intestinal mucosa (open arrow). (b) Intraoperative photograph of the serosal surface of the ileum in a 70-year-old man who presented with melena shows a 6.0-cm pedunculated GIST. (c) Photograph of resected and opened jejunum from a 67-year-old man who presented with melena shows a 4.0-cm hemorrhagic GIST protruding into the intestinal lumen. The mucosa overlying the tumor is ulcerated (arrow). (d) Photograph of a bivalved resected 18-cm GIST from the ileum of a 66-year-old man who presented with weight loss shows a central cavity containing hemorrhage.
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Figure 1b. Gross pathologic features of GISTs. (a) Photomicrograph (actual size [1:]; hematoxylin-eosin [H-E] stain) of resected jejunum from an 82-year-old man with gastrointestinal bleeding shows an intramural GIST with its origin in the muscularis propria (solid arrows). There is intact overlying normal small intestinal mucosa (open arrow). (b) Intraoperative photograph of the serosal surface of the ileum in a 70-year-old man who presented with melena shows a 6.0-cm pedunculated GIST. (c) Photograph of resected and opened jejunum from a 67-year-old man who presented with melena shows a 4.0-cm hemorrhagic GIST protruding into the intestinal lumen. The mucosa overlying the tumor is ulcerated (arrow). (d) Photograph of a bivalved resected 18-cm GIST from the ileum of a 66-year-old man who presented with weight loss shows a central cavity containing hemorrhage.
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Figure 1c. Gross pathologic features of GISTs. (a) Photomicrograph (actual size [1:]; hematoxylin-eosin [H-E] stain) of resected jejunum from an 82-year-old man with gastrointestinal bleeding shows an intramural GIST with its origin in the muscularis propria (solid arrows). There is intact overlying normal small intestinal mucosa (open arrow). (b) Intraoperative photograph of the serosal surface of the ileum in a 70-year-old man who presented with melena shows a 6.0-cm pedunculated GIST. (c) Photograph of resected and opened jejunum from a 67-year-old man who presented with melena shows a 4.0-cm hemorrhagic GIST protruding into the intestinal lumen. The mucosa overlying the tumor is ulcerated (arrow). (d) Photograph of a bivalved resected 18-cm GIST from the ileum of a 66-year-old man who presented with weight loss shows a central cavity containing hemorrhage.
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Figure 1d. Gross pathologic features of GISTs. (a) Photomicrograph (actual size [1:]; hematoxylin-eosin [H-E] stain) of resected jejunum from an 82-year-old man with gastrointestinal bleeding shows an intramural GIST with its origin in the muscularis propria (solid arrows). There is intact overlying normal small intestinal mucosa (open arrow). (b) Intraoperative photograph of the serosal surface of the ileum in a 70-year-old man who presented with melena shows a 6.0-cm pedunculated GIST. (c) Photograph of resected and opened jejunum from a 67-year-old man who presented with melena shows a 4.0-cm hemorrhagic GIST protruding into the intestinal lumen. The mucosa overlying the tumor is ulcerated (arrow). (d) Photograph of a bivalved resected 18-cm GIST from the ileum of a 66-year-old man who presented with weight loss shows a central cavity containing hemorrhage.
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GISTs range in size from several millimeters to greater than 30 cm (19). They are typically well-circumscribed masses that compress adjacent tissue and lack a true capsule. Cut sections of specimens have a pink, tan, or gray surface (Fig 1c). Focal areas of hemorrhage, cystic degeneration, and necrosis may occur, particularly in large lesions. Cavities form from extensive hemorrhage or necrosis and may communicate with the intestinal lumen (Fig 1d). Aneurysmal dilatation of the involved segment of the colon is an uncommon feature of colonic GISTs (9).
Histologic Features
GISTs can be histologically classified by their predominant cell morphology, either spindle cell or epithelioid. The spindle cell morphology is present in 70%–80% of gastric GISTs, with the remaining 20%–30% having the epithelioid morphology (Fig 2) (11). In the older literature, the tumors with an epithelioid morphology were referred to as leiomyoblastomas or epithelioid leiomyosarcomas.
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Figure 2a. Cytologic features of GISTs. (a) Photomicrograph (original magnification, x40; H-E stain) of a spindle cell GIST shows uniform cigar-shaped cells with elongated nuclei. (b) Photomicrograph (original magnification, x40; H-E stain) of an epithelioid GIST shows round cells with centrally placed nuclei. (c) Photomicrograph (original magnification, x40; H-E stain) shows the signet ring appearance from prominent cytoplasmic vacuolization in a GIST.
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Figure 2b. Cytologic features of GISTs. (a) Photomicrograph (original magnification, x40; H-E stain) of a spindle cell GIST shows uniform cigar-shaped cells with elongated nuclei. (b) Photomicrograph (original magnification, x40; H-E stain) of an epithelioid GIST shows round cells with centrally placed nuclei. (c) Photomicrograph (original magnification, x40; H-E stain) shows the signet ring appearance from prominent cytoplasmic vacuolization in a GIST.
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Figure 2c. Cytologic features of GISTs. (a) Photomicrograph (original magnification, x40; H-E stain) of a spindle cell GIST shows uniform cigar-shaped cells with elongated nuclei. (b) Photomicrograph (original magnification, x40; H-E stain) of an epithelioid GIST shows round cells with centrally placed nuclei. (c) Photomicrograph (original magnification, x40; H-E stain) shows the signet ring appearance from prominent cytoplasmic vacuolization in a GIST.
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Spindle cell GISTs are composed of cigar-shaped cells with elongated nuclei and eosinophilic to basophilic cytoplasm (Fig 2a). Epithelioid GISTs are composed of round or polygonal cells with centrally placed nuclei (Fig 2b) (19). Fixation artifact may cause clear perinuclear halos or cytoplasmic vacuolization. Prominent cytoplasmic vacuolization may create a signet ring cell appearance caused by displacement of the nuclei to the periphery of the cell (Fig 2c). GISTs may display a variety of architectural patterns. Spindle cell GISTs may be arranged in bundles of interlacing fascicles resembling smooth muscle tumors or a nuclear palisading pattern resembling nerve sheath tumors (Fig 3a, 3b). GISTs may also display a pattern with prominent vascularity (Fig 3c). Occasionally, GISTs are composed of uniform small round cells that display a nesting organoid pattern that resembles neuroendocrine tumors. The stromal portions of the tumor may show extensive perivascular or stromal hyalinization, myxoid change, or hemorrhage (Fig 4).
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Figure 3a. Architectural patterns of GISTs. (a) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a pattern of interlacing fascicles. (b) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a nuclear palisading pattern. (c) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows an angiomatoid pattern with large blood-filled vascular spaces within the tumor.
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Figure 3b. Architectural patterns of GISTs. (a) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a pattern of interlacing fascicles. (b) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a nuclear palisading pattern. (c) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows an angiomatoid pattern with large blood-filled vascular spaces within the tumor.
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Figure 3c. Architectural patterns of GISTs. (a) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a pattern of interlacing fascicles. (b) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows a nuclear palisading pattern. (c) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows an angiomatoid pattern with large blood-filled vascular spaces within the tumor.
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Figure 4a. Stromal features of GISTs. (a) Photomicrograph (original magnification, x10; H-E stain) shows a GIST that has extensive myxoid stroma with interspersed tumor cells. (b) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows perivascular hyalinization.
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Figure 4b. Stromal features of GISTs. (a) Photomicrograph (original magnification, x10; H-E stain) shows a GIST that has extensive myxoid stroma with interspersed tumor cells. (b) Photomicrograph (original magnification, x10; H-E stain) of a spindle cell GIST shows perivascular hyalinization.
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Small intestinal GISTs are most often spindle cell tumors. They often contain extracellular collagenous skeinoid fibers (Fig 5) (21). Although the majority of anorectal, colonic, and esophageal GISTs are of the spindle cell type, epithelioid GISTs may occasionally be seen in these sites (6,9,22). Tumors may show an admixture of spindle and epithelioid elements.
In general, malignant GISTs are larger, more highly cellular, and more mitotically active than their benign counterparts (Fig 6). In the stomach, benign GISTs are three times more common than malignant ones (8). It is generally accepted that gastric GISTs less than 5 cm in largest dimension and with five or fewer mitoses per 50 consecutive high power fields (HPF) have low risk for metastasis and are probably benign. Gastric GISTs larger than 10 cm and with more than five mitoses per 50 HPF are considered malignant, whereas those that fall between these categories have uncertain malignant potential or intermediate risk for metastasis or recurrence. GISTs with marked mitotic activity (more than 50 mitoses per 50 HPF) are considered high-grade malignancies with an extremely aggressive clinical behavior (23). Small intestinal GISTs may have a more aggressive course compared with that of gastric GISTs of the same size. Therefore, the size threshold for estimating recurrent or metastatic risk in small intestinal GISTs may be smaller than that for gastric GISTs. The majority of esophageal, colonic, and anorectal GISTs are malignant.
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Figure 6a. Cytologic features as a reflection of biologic potential. (a) Photomicrograph (original magnification, x40; H-E stain) of a low-risk or probably benign GIST shows bland-appearing tumor cells and absent mitotic activity. (b) Photomicrograph (original magnification, x40; H-E stain) of an intermediate-risk or low-grade malignant GIST shows a more cellular tumor with higher nuclear-cytoplasmic ratio. (c) Photomicrograph (original magnification, x40; H-E stain) of a high-risk or highly malignant GIST shows increased cellularity, high nuclear-cytoplasmic ratio, and numerous mitoses (arrows).
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Figure 6b. Cytologic features as a reflection of biologic potential. (a) Photomicrograph (original magnification, x40; H-E stain) of a low-risk or probably benign GIST shows bland-appearing tumor cells and absent mitotic activity. (b) Photomicrograph (original magnification, x40; H-E stain) of an intermediate-risk or low-grade malignant GIST shows a more cellular tumor with higher nuclear-cytoplasmic ratio. (c) Photomicrograph (original magnification, x40; H-E stain) of a high-risk or highly malignant GIST shows increased cellularity, high nuclear-cytoplasmic ratio, and numerous mitoses (arrows).
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Figure 6c. Cytologic features as a reflection of biologic potential. (a) Photomicrograph (original magnification, x40; H-E stain) of a low-risk or probably benign GIST shows bland-appearing tumor cells and absent mitotic activity. (b) Photomicrograph (original magnification, x40; H-E stain) of an intermediate-risk or low-grade malignant GIST shows a more cellular tumor with higher nuclear-cytoplasmic ratio. (c) Photomicrograph (original magnification, x40; H-E stain) of a high-risk or highly malignant GIST shows increased cellularity, high nuclear-cytoplasmic ratio, and numerous mitoses (arrows).
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Immunohistochemical Features
By definition, GISTs are positive for KIT (CD117) (Fig 7). KIT (CD117) is a transmembrane receptor for a growth factor called stem cell factor that is normally expressed on hematopoietic stem cells, germ cells, mast cells, melanocytes, and the myenteric plexus of the normal adult gastrointestinal tract (3,24). Approximately 70% of GISTs coexpress CD34 (2,3). CD34 is a hematopoietic progenitor cell antigen that is typically expressed in normal and neoplastic endothelial cells and in some fibroblasts and their neoplasms (25,26). GISTs may also be positive for smooth muscle actin and rarely for desmin and S-100 protein. The current consensus opinion of pathologists working in the field is that the term GIST applies only to gastrointestinal mesenchymal neoplasms with KIT immunoreactivity, with only rare exceptions (27).
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Figure 7. KIT immunoreactivity. Photomicrograph (original magnification, x20; KIT [CD117] stain) of a GIST shows that the cytoplasm of the tumor cells stains brown, indicating immunoreactivity.
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Radiologic Features
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Stomach
The stomach is the most common location for GISTs, which make up 2%–3% of all gastric tumors. In our series of 64 GISTs, 28 (44%) were located in the stomach. Four (14%) of our cases were confined to the cardia and fundus of the stomach, 21 (75%) were located in the body, and three (11%) were in the antrum. The tumors ranged from 4 to 25 cm in maximal dimension. The mean tumor dimension was 10.8 cm. On the basis of recently published criteria on tumor size and mitotic rate (28), three cases were classified as probably benign, nine uncertain malignant potential, and 16 malignant. No correlation between radiologic appearance and malignant potential could be established with regard to the degree of necrosis, hemorrhage, cyst formation, or contrast material enhancement on computed tomographic (CT) images.
Abdominal radiography may show a nonspecific soft-tissue mass indenting or displacing the gastric air shadow (Fig 8). Rarely, calcification may occur and be visible on abdominal radiographs. In barium studies of the stomach, GISTs have the classic features of submucosal masses, similar to those of leiomyomas and leiomyosarcomas (29). The margin of the lesion forms obtuse or right angles with the gastric wall when viewed in profile, and the masses are smoothly circumscribed when viewed en face (Fig 9). They have a smooth mucosal surface when coated with barium, and the overlying mucosal surface is generally intact with the exception of focal areas of ulceration, which can be seen in 60% of cases (29). A focal intraluminal polypoid mass resembling a mucosal polyp is the least common appearance of GISTs on barium images of the stomach. A polypoid intraluminal component was present in only four (14%) of our cases.
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Figure 8a. GIST arising from the stomach in a 66-year-old woman with left-sided upper abdominal pain. (a) Chest radiograph shows elevation of the left hemidiaphragm and a mass of soft-tissue opacity that displaces an irregular gas collection away from the diaphragm (arrow). (b, c) Contrast material-enhanced CT scans (c obtained at a lower level than b) show the subdiaphragmatic cavitary mass of heterogeneous attenuation. The cavity (*) is air-filled. The mass originates from the gastric wall (arrow). There is a metastatic lesion within the liver.
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Figure 8b. GIST arising from the stomach in a 66-year-old woman with left-sided upper abdominal pain. (a) Chest radiograph shows elevation of the left hemidiaphragm and a mass of soft-tissue opacity that displaces an irregular gas collection away from the diaphragm (arrow). (b, c) Contrast material-enhanced CT scans (c obtained at a lower level than b) show the subdiaphragmatic cavitary mass of heterogeneous attenuation. The cavity (*) is air-filled. The mass originates from the gastric wall (arrow). There is a metastatic lesion within the liver.
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Figure 8c. GIST arising from the stomach in a 66-year-old woman with left-sided upper abdominal pain. (a) Chest radiograph shows elevation of the left hemidiaphragm and a mass of soft-tissue opacity that displaces an irregular gas collection away from the diaphragm (arrow). (b, c) Contrast material-enhanced CT scans (c obtained at a lower level than b) show the subdiaphragmatic cavitary mass of heterogeneous attenuation. The cavity (*) is air-filled. The mass originates from the gastric wall (arrow). There is a metastatic lesion within the liver.
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Figure 9a. Features of GISTs seen during upper gastrointestinal tract series. (a) Anteroposterior view of the stomach from a barium study in a 67-year-old man shows a smoothly circumscribed mass in the body of the stomach viewed en face (arrows). (b) Oblique view of the stomach from a barium study in a 67-year-old woman shows a smoothly marginated, mural-based mass that forms obtuse angles with the gastric wall.
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Figure 9b. Features of GISTs seen during upper gastrointestinal tract series. (a) Anteroposterior view of the stomach from a barium study in a 67-year-old man shows a smoothly circumscribed mass in the body of the stomach viewed en face (arrows). (b) Oblique view of the stomach from a barium study in a 67-year-old woman shows a smoothly marginated, mural-based mass that forms obtuse angles with the gastric wall.
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CT showed an intramural component in all 28 cases of gastric GIST that we reviewed. Extragastric extension was present in 86% of cases. Extension may occur into the gastrohepatic ligament, into the gastrosplenic ligament, or posteriorly into the lesser sac. In many cases, the bulk of the tumor will be in an extragastric location, which makes it difficult to appreciate the origin of the tumor from the gastric wall on CT images. The tumor may be attached to the gastric wall by a thin pedicle. Careful evaluation of the gastric wall in these cases may reveal subtle wall thickening that will help establish the stomach as the origin of the mass (Fig 10).
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Figure 10a. GIST arising from the stomach in a 65-year-old man with left-sided upper abdominal pain. (a) Contrast-enhanced CT scan shows a large mass arising from the posterior gastric wall (arrow) that extends into the gastrosplenic ligament. There are areas of low attenuation within the mass. (b) Photograph of the cut surface of the resected specimen shows areas of hemorrhage and necrosis within the tumor.
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Figure 10b. GIST arising from the stomach in a 65-year-old man with left-sided upper abdominal pain. (a) Contrast-enhanced CT scan shows a large mass arising from the posterior gastric wall (arrow) that extends into the gastrosplenic ligament. There are areas of low attenuation within the mass. (b) Photograph of the cut surface of the resected specimen shows areas of hemorrhage and necrosis within the tumor.
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A peripheral enhancement pattern was present in the majority (92%) of our cases on intravenous contrast-enhanced CT images. Correlation of this appearance with gross pathologic findings demonstrates that this pattern represents enhancement of peripheral areas of viable tumor. Central areas of low attenuation correspond to hemorrhage, necrosis, or cyst formation (Fig 10) (30). Homogeneous enhancement was present in a minority (8%) of cases. Lesions with extensive hemorrhage or necrosis may form large cystic spaces or cavities. The cavities may communicate with the gastric lumen and contain air, air-fluid levels, or oral contrast media (Fig 11) (31). Calcification is an unusual feature of GISTs, seen in only one (3%) of our gastric cases. It may occur in a mottled pattern or be present extensively throughout the tumor (Fig 12). CT may also demonstrate evidence of adjacent organ invasion, ascites, omental and peritoneal spread of tumor, or liver metastasis. Metastatic lymphadenopathy is not a feature in patients with GISTs.
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Figure 11a. GIST arising from the lesser curvature of the stomach in a 55-year-old man with melena and hematemesis. (a, b) Contrast-enhanced CT scans (b obtained at a lower level than a) show a cavitary mass that extends into the gastrohepatic and gastrosplenic ligaments. The cavity contains air (solid straight arrow) and oral contrast material (curved arrow). Low-attenuation areas in the tumor (open arrow) represent hemorrhage. (c) Photograph of the bivalved resected specimen shows a cavity (*) and areas of hemorrhage (arrow) in the solid portions of the tumor.
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Figure 11b. GIST arising from the lesser curvature of the stomach in a 55-year-old man with melena and hematemesis. (a, b) Contrast-enhanced CT scans (b obtained at a lower level than a) show a cavitary mass that extends into the gastrohepatic and gastrosplenic ligaments. The cavity contains air (solid straight arrow) and oral contrast material (curved arrow). Low-attenuation areas in the tumor (open arrow) represent hemorrhage. (c) Photograph of the bivalved resected specimen shows a cavity (*) and areas of hemorrhage (arrow) in the solid portions of the tumor.
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Figure 11c. GIST arising from the lesser curvature of the stomach in a 55-year-old man with melena and hematemesis. (a, b) Contrast-enhanced CT scans (b obtained at a lower level than a) show a cavitary mass that extends into the gastrohepatic and gastrosplenic ligaments. The cavity contains air (solid straight arrow) and oral contrast material (curved arrow). Low-attenuation areas in the tumor (open arrow) represent hemorrhage. (c) Photograph of the bivalved resected specimen shows a cavity (*) and areas of hemorrhage (arrow) in the solid portions of the tumor.
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Figure 12a. GIST arising from the posterior stomach in a 72-year-old woman with back pain. Contrast-enhanced CT scans (b obtained at a lower level than a) show a soft-tissue attenuation mass arising from the posterior wall of the stomach (straight arrow). The mass extends into the gastrosplenic ligament and contains extensive dense calcification (curved arrow).
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Figure 12b. GIST arising from the posterior stomach in a 72-year-old woman with back pain. Contrast-enhanced CT scans (b obtained at a lower level than a) show a soft-tissue attenuation mass arising from the posterior wall of the stomach (straight arrow). The mass extends into the gastrosplenic ligament and contains extensive dense calcification (curved arrow).
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Magnetic resonance (MR) imaging features of gastric GISTs are variable. The degree of necrosis and hemorrhage greatly affects the signal-intensity pattern. The solid portions of tumor are typically low signal intensity on T1-weighted images, are high signal intensity on T2-weighted images, and enhance after administration of gadolinium. Areas of hemorrhage within the tumor will vary from high to low signal intensity on both T1- and T2-weighted images, depending on the age of the hemorrhage (32). MR imaging is a useful adjunct to CT, particularly in the evaluation of large tumors. The multiplanar capability of MR imaging may be helpful in determining the organ of origin in large tumors and the relationship of the tumor to other organs and major blood vessels (Fig 13).
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Figure 13a. Gastric GIST in a 66-year-old woman with left-sided upper abdominal pain. (a) Axial T1-weighted MR image shows a subdiaphragmatic hypointense mass containing a cavity (*) in the left side of the upper abdomen. (b) On the T2-weighted image, the mass increases in signal intensity. Areas of focal high-signal-intensity hemorrhage are present within the mass (arrow). (c) Coronal T2-weighted image shows that the mass originates from the gastric fundus (arrow).
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Figure 13b. Gastric GIST in a 66-year-old woman with left-sided upper abdominal pain. (a) Axial T1-weighted MR image shows a subdiaphragmatic hypointense mass containing a cavity (*) in the left side of the upper abdomen. (b) On the T2-weighted image, the mass increases in signal intensity. Areas of focal high-signal-intensity hemorrhage are present within the mass (arrow). (c) Coronal T2-weighted image shows that the mass originates from the gastric fundus (arrow).
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Figure 13c. Gastric GIST in a 66-year-old woman with left-sided upper abdominal pain. (a) Axial T1-weighted MR image shows a subdiaphragmatic hypointense mass containing a cavity (*) in the left side of the upper abdomen. (b) On the T2-weighted image, the mass increases in signal intensity. Areas of focal high-signal-intensity hemorrhage are present within the mass (arrow). (c) Coronal T2-weighted image shows that the mass originates from the gastric fundus (arrow).
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The differential diagnosis for gastric GISTs includes other mesenchymal neoplasms such as true leiomyomas, leiomyosarcomas, schwannomas, neurofibromas, and neuroendocrine neoplasms (eg, solitary gastric carcinoids). Because all of these neoplasms arise in the gastric wall, their imaging features may be similar to those of GISTs. True leiomyomas and leiomyosarcomas occur infrequently in the stomach. Likewise, schwannomas occur in the stomach with much less frequency than GISTs but have similar radiologic features (Fig 14). Schwannomas are histologically characterized by bundled spindle-shaped cells and often have a distinctive lymphoid cuff that may contain germinal centers (Fig 14d). They stain positive for S-100 protein. Solitary gastric carcinoids are most commonly seen in the antrum and characteristically have a central ulceration.
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Figure 14a. Gastric schwannoma in a 69-year-old woman with postprandial epigastric pain. (a) Image from an upper gastrointestinal tract series shows a mural-based mass along the lesser curvature of the stomach (arrows). (b) Contrast-enhanced CT scan shows the homogeneous low-attenuation gastric mass (S) extending into the gastrohepatic ligament. (c) Photograph of the cut surface of the resected specimen shows a yellow tumor in the gastric wall with no evidence of hemorrhage or necrosis. Scale is in centimeters. (d) Photomicrograph (original magnification, x2; H-E stain) shows the tumor, which is composed of spindle-shaped cells arising from the muscularis propria. There is a peripheral lymphoid cuff (arrows) within the tumor.
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Figure 14b. Gastric schwannoma in a 69-year-old woman with postprandial epigastric pain. (a) Image from an upper gastrointestinal tract series shows a mural-based mass along the lesser curvature of the stomach (arrows). (b) Contrast-enhanced CT scan shows the homogeneous low-attenuation gastric mass (S) extending into the gastrohepatic ligament. (c) Photograph of the cut surface of the resected specimen shows a yellow tumor in the gastric wall with no evidence of hemorrhage or necrosis. Scale is in centimeters. (d) Photomicrograph (original magnification, x2; H-E stain) shows the tumor, which is composed of spindle-shaped cells arising from the muscularis propria. There is a peripheral lymphoid cuff (arrows) within the tumor.
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Figure 14c. Gastric schwannoma in a 69-year-old woman with postprandial epigastric pain. (a) Image from an upper gastrointestinal tract series shows a mural-based mass along the lesser curvature of the stomach (arrows). (b) Contrast-enhanced CT scan shows the homogeneous low-attenuation gastric mass (S) extending into the gastrohepatic ligament. (c) Photograph of the cut surface of the resected specimen shows a yellow tumor in the gastric wall with no evidence of hemorrhage or necrosis. Scale is in centimeters. (d) Photomicrograph (original magnification, x2; H-E stain) shows the tumor, which is composed of spindle-shaped cells arising from the muscularis propria. There is a peripheral lymphoid cuff (arrows) within the tumor.
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Figure 14d. Gastric schwannoma in a 69-year-old woman with postprandial epigastric pain. (a) Image from an upper gastrointestinal tract series shows a mural-based mass along the lesser curvature of the stomach (arrows). (b) Contrast-enhanced CT scan shows the homogeneous low-attenuation gastric mass (S) extending into the gastrohepatic ligament. (c) Photograph of the cut surface of the resected specimen shows a yellow tumor in the gastric wall with no evidence of hemorrhage or necrosis. Scale is in centimeters. (d) Photomicrograph (original magnification, x2; H-E stain) shows the tumor, which is composed of spindle-shaped cells arising from the muscularis propria. There is a peripheral lymphoid cuff (arrows) within the tumor.
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Gastric adenocarcinoma and lymphoma rarely demonstrate marked exophytic growth. However, they may occasionally have a radiologic appearance similar to that of GISTs—that is, a predominantly mural location or an intraluminal component. Advanced gastric carcinomas and lymphomas commonly have associated perigastric, hepatoduodenal ligament, and celiac lymphadenopathy, which are not seen in malignant GISTs. Lymphoma may be associated with bulky adenopathy or adenopathy that extends into the lower abdomen and pelvis. Adenopathy is not usually observed in cases of gastric GISTs.
Small Intestine
GISTs may occur throughout the small intestine. Of the 27 small intestinal GISTs in our series, eight were located in the duodenum, 12 in the jejunum, six in the ileum, and one at the jejunoileal junction. The tumors ranged from 2.2 to 21 cm in maximal dimension, with a mean size of 8.6 cm.
In those patients who presented with signs and symptoms of small intestinal obstruction, abdominal radiography showed evidence of small intestinal dilatation or a soft-tissue mass (Fig 15). Irregular gas collections were evident on abdominal radiographs in those patients who had cavitary masses containing air (Fig 16).
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Figure 15a. Small intestinal GIST in a 93-year-old woman with acute abdominal pain. (a) Abdominal radiograph shows a small bowel obstruction and a mass of soft-tissue opacity in the right lower quadrant. Intestinal gas is absent. (b) Unenhanced CT scan shows dilated segments of small intestine and the well-circumscribed, low-attenuation mass in the right side of the pelvis. (c) Intraoperative photograph shows the 20-cm mass arising from the jejunum that had undergone torsion, which resulted in small bowel obstruction.
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Figure 15b. Small intestinal GIST in a 93-year-old woman with acute abdominal pain. (a) Abdominal radiograph shows a small bowel obstruction and a mass of soft-tissue opacity in the right lower quadrant. Intestinal gas is absent. (b) Unenhanced CT scan shows dilated segments of small intestine and the well-circumscribed, low-attenuation mass in the right side of the pelvis. (c) Intraoperative photograph shows the 20-cm mass arising from the jejunum that had undergone torsion, which resulted in small bowel obstruction.
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Figure 15c. Small intestinal GIST in a 93-year-old woman with acute abdominal pain. (a) Abdominal radiograph shows a small bowel obstruction and a mass of soft-tissue opacity in the right lower quadrant. Intestinal gas is absent. (b) Unenhanced CT scan shows dilated segments of small intestine and the well-circumscribed, low-attenuation mass in the right side of the pelvis. (c) Intraoperative photograph shows the 20-cm mass arising from the jejunum that had undergone torsion, which resulted in small bowel obstruction.
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Figure 16. Small intestinal GIST in a 54-year-old woman with a palpable abdominal mass. Abdominal radiograph obtained with the patient supine shows a soft-tissue mass in the left side of the midabdomen. The mass contains an irregular collection of air (arrows).
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Barium studies of the small intestine may reveal an intraluminal or submucosal mass. The margins are typically sharply defined. However, the mucosal surface may show luminal irregularity or focal ulceration (Fig 17). As with gastric GISTs, many intestinal tumors often have an extraserosal component. These tumors may exhibit significant mass effect on the affected segment of intestine or adjacent segments. Cavity and fistula formation may occur, resulting in luminal enlargement and communication of the cavity or fistula with the intestinal lumen (Fig 18).
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Figure 17a. Small intestinal GIST in a 28-year-old man who presented with melena. (a) Image from an enteroclysis study shows a smoothly circumscribed, 3-cm mural mass with central ulceration in the proximal jejunum (arrow). (b) Photograph from enteroscopy shows the ulcerated mass in the proximal jejunum (arrows).
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Figure 17b. Small intestinal GIST in a 28-year-old man who presented with melena. (a) Image from an enteroclysis study shows a smoothly circumscribed, 3-cm mural mass with central ulceration in the proximal jejunum (arrow). (b) Photograph from enteroscopy shows the ulcerated mass in the proximal jejunum (arrows).
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Figure 18a. Small intestinal GIST in a 56-year-old man who presented with fatigue, weight loss, and melena. (a) Image from a barium study of the small intestine shows barium extending from the intestinal lumen into a cavity (arrows). There is mass effect on adjacent segments of small intestine. (b) Contrast-enhanced CT scan shows a cavitary mass in the pelvis that contains air and oral contrast material (arrows).
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Figure 18b. Small intestinal GIST in a 56-year-old man who presented with fatigue, weight loss, and melena. (a) Image from a barium study of the small intestine shows barium extending from the intestinal lumen into a cavity (arrows). There is mass effect on adjacent segments of small intestine. (b) Contrast-enhanced CT scan shows a cavitary mass in the pelvis that contains air and oral contrast material (arrows).
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The intraluminal, mural, and extraserosal components of small intestinal GISTs are well depicted on CT images. GISTs may appear as an intramural mass or intraluminal polyp (Fig 19) (33). Six (22%) of the small intestinal GISTs in our series were primarily in an extraserosal location such that a small bowel origin was not readily evident at CT. Following intravenous administration of contrast media, GISTs are typically enhancing masses with areas of low attenuation from hemorrhage, necrosis, or cyst formation (34). A homogeneous pattern of attenuation is less common and was present in four of our cases. Extension into the adjacent small bowel mesentery and encasement of noncontiguous segments of small intestine, colon, bladder, ureter, and abdominal wall may occur (Fig 19c) (14). Patients with malignant GISTs may present with metastases to the liver, omentum, and peritoneum (14). The MR imaging appearance of small intestinal GISTs is very similar to that of gastric GISTs. The pattern of signal intensity is variable depending on the degree of hemorrhage and necrosis. Gadolinium enhancement in areas of viable tumor helps delineate areas of necrosis.
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Abstract
LEARNING OBJECTIVES FOR TEST...
