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From the Archives of the AFIP

Gastrointestinal Stromal Tumors: Radiologic Features with Pathologic Correlation¹

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).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Clinical Features Pathologic Features Radiologic Features Prognosis and Therapy Conclusions References

 
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

	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.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Clinical Features Pathologic Features Radiologic Features Prognosis and Therapy Conclusions References

 
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.

	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.

	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).

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   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.

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.

View larger version (195K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (200K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (191K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (226K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (195K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (195K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (207K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (208K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (179K): [in this window] [in a new window] [Download PPT slide]   Figure 5.  Photomicrograph of a small intestinal GIST (original magnification, x80; H-E stain) shows eosinophilic skeinoid fibers (arrow).

View larger version (200K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (209K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (224K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (188K): [in this window] [in a new window] [Download PPT slide]   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.

	Radiologic Features

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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.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   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.

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).

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   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.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   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).

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 19a.  CT features of small intestinal GISTs. (a) Unenhanced CT scan of a 77-year-old man shows an intraluminal polypoid small intestinal mass (arrow) that was incidentally discovered when he was being evaluated for an abdominal aortic aneurysm. (b) Contrast-enhanced CT scan of a 62-year-old woman with melena shows a heterogeneously enhancing mass in the posterior pelvis (arrow) that is arising from the distal ileum. (c) Contrast-enhanced CT scan of a 67-year-old man who presented with melena and a history of gastrointestinal bleeding shows a soft-tissue attenuation mass in the distal jejunum. The mass has an intraluminal component (arrow) and an extraluminal component, which invades an adjacent segment of small intestine. (d) Contrast-enhanced CT scan of a 66-year-old man with abdominal pain shows a cavitary mass in the right side of the midabdomen that contains air, debris, and oral contrast material.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 19b.  CT features of small intestinal GISTs. (a) Unenhanced CT scan of a 77-year-old man shows an intraluminal polypoid small intestinal mass (arrow) that was incidentally discovered when he was being evaluated for an abdominal aortic aneurysm. (b) Contrast-enhanced CT scan of a 62-year-old woman with melena shows a heterogeneously enhancing mass in the posterior pelvis (arrow) that is arising from the distal ileum. (c) Contrast-enhanced CT scan of a 67-year-old man who presented with melena and a history of gastrointestinal bleeding shows a soft-tissue attenuation mass in the distal jejunum. The mass has an intraluminal component (arrow) and an extraluminal component, which invades an adjacent segment of small intestine. (d) Contrast-enhanced CT scan of a 66-year-old man with abdominal pain shows a cavitary mass in the right side of the midabdomen that contains air, debris, and oral contrast material.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 19c.  CT features of small intestinal GISTs. (a) Unenhanced CT scan of a 77-year-old man shows an intraluminal polypoid small intestinal mass (arrow) that was incidentally discovered when he was being evaluated for an abdominal aortic aneurysm. (b) Contrast-enhanced CT scan of a 62-year-old woman with melena shows a heterogeneously enhancing mass in the posterior pelvis (arrow) that is arising from the distal ileum. (c) Contrast-enhanced CT scan of a 67-year-old man who presented with melena and a history of gastrointestinal bleeding shows a soft-tissue attenuation mass in the distal jejunum. The mass has an intraluminal component (arrow) and an extraluminal component, which invades an adjacent segment of small intestine. (d) Contrast-enhanced CT scan of a 66-year-old man with abdominal pain shows a cavitary mass in the right side of the midabdomen that contains air, debris, and oral contrast material.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 19d.  CT features of small intestinal GISTs. (a) Unenhanced CT scan of a 77-year-old man shows an intraluminal polypoid small intestinal mass (arrow) that was incidentally discovered when he was being evaluated for an abdominal aortic aneurysm. (b) Contrast-enhanced CT scan of a 62-year-old woman with melena shows a heterogeneously enhancing mass in the posterior pelvis (arrow) that is arising from the distal ileum. (c) Contrast-enhanced CT scan of a 67-year-old man who presented with melena and a history of gastrointestinal bleeding shows a soft-tissue attenuation mass in the distal jejunum. The mass has an intraluminal component (arrow) and an extraluminal component, which invades an adjacent segment of small intestine. (d) Contrast-enhanced CT scan of a 66-year-old man with abdominal pain shows a cavitary mass in the right side of the midabdomen that contains air, debris, and oral contrast material.

Anorectum
Six (9%) of the 64 GISTs in our series were located in the anorectal region. Anorectal GISTs are most commonly mural masses that expand the rectal wall. As a result, a focal well-circumscribed mural mass is the most common finding on CT images (Fig 20). Mucosal ulceration may be present. External spread frequently occurs with extension of the mass into the ischiorectal fossa, prostate, or vagina (Fig 21) (35). The least common appearance is a focal intraluminal polypoid mass (22).

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.  Rectal GIST in a 69-year-old woman with pelvic pain and hematochezia. (a) CT scan shows a mural mass along the left anterolateral rectal wall (arrow). (b) Photograph of the opened abdominoperineal resected specimen and bivalved GIST shows the tumor in the distal rectum. Multiple foci of hemorrhage are present within the tumor.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.  Rectal GIST in a 69-year-old woman with pelvic pain and hematochezia. (a) CT scan shows a mural mass along the left anterolateral rectal wall (arrow). (b) Photograph of the opened abdominoperineal resected specimen and bivalved GIST shows the tumor in the distal rectum. Multiple foci of hemorrhage are present within the tumor.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 21.  Rectal GIST in a 55-year-old man with rectal pain. CT scan shows a 5-cm mass (arrows) arising from the posterior rectal wall and extending into the ischiorectal fossa.

The differential diagnosis for anorectal GISTs includes both epithelial and nonepithelial neoplasms of the anorectal region. Rectal adenocarcinoma, anal squamous cell carcinoma, lymphoma, malignant melanoma, carcinoid, leiomyoma, and leiomyosarcoma may have imaging appearances similar to that of GISTs, although leiomyosarcoma may have a dominant polypoid intraluminal component (22). Carcinomas tend to have irregular margins and may be associated with perirectal lymphadenopathy, whereas GISTs tend to have well-defined margins and lack perirectal adenopathy. GISTs that have significant perirectal extension may be mistaken as tumor arising from adjacent structures such as prostatic adenocarcinoma or sarcomas of the prostate and perineum. Anorectal lymphoma is seen in patients with AIDS (acquired immunodeficiency syndrome) and manifests radiographically as an eccentric or annular mural mass that may be associated with mucosal ulceration or perianal fistulization.

Colon
Primary colonic GISTs are much less common than gastric, small intestinal, and anorectal GISTs, although GISTs metastatic from other sites commonly involve the external aspect of the colon. We had only one case of a colonic GIST in our series. In the literature, they are described as transmural tumors that involve the intraluminal and extraserosal surfaces of the colon (9). They may be smooth or multinodular in contour and may contain central areas of hemorrhage, cystic change, necrosis, or calcification. A circumferential growth pattern with aneurysmal dilatation of the affected colonic segment has been observed in a colonic GIST (9).

The radiographic and cross-sectional imaging appearances of colonic GISTs are similar to those of leiomyosarcomas (37). Small lesions are typically confined to the wall of the colon and appear as mural or submucosal masses at barium examination. Mucosal ulceration may be present. The lesion in our series was a 10-cm homogeneously enhancing mass that extended beyond the serosal surface of the colon on CT images (Fig 22).

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   Figure 22a.  Colonic GIST in a 47-year-old woman with a small bowel obstruction. (a) CT scan shows a lobulated 10-cm mass obstructing the ascending colon (arrow). The mass shows heterogeneous enhancement with intravenous contrast material. There are dilated, fluid-filled segments of small intestine, and a small amount of fluid is in the adjacent right paracolic gutter. (b) Photograph of the right hemicolectomy specimen shows the GIST at the level of the hepatic flexure (arrows). C = cecum, TI = terminal ileum.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 22b.  Colonic GIST in a 47-year-old woman with a small bowel obstruction. (a) CT scan shows a lobulated 10-cm mass obstructing the ascending colon (arrow). The mass shows heterogeneous enhancement with intravenous contrast material. There are dilated, fluid-filled segments of small intestine, and a small amount of fluid is in the adjacent right paracolic gutter. (b) Photograph of the right hemicolectomy specimen shows the GIST at the level of the hepatic flexure (arrows). C = cecum, TI = terminal ileum.

Esophagus
Esophageal GISTs are relatively uncommon, and we had only one case of an esophageal GIST in our series. GISTs accounted for approximately 25% of esophageal mesenchymal neoplasms studied by Miettinen et al (6). In contrast, leiomyomas are the most common mesenchymal neoplasm of the esophagus (75% of cases) and occur in a younger population (median age, 35 years) compared with GISTs (for whom the median patient age is 63 years) (6).

To our knowledge, there have been no reports of the radiologic appearance of esophageal GISTs. The one esophageal GIST in our series had radiologic features similar to tumors reported as esophageal leiomyosarcomas (38,39).

Esophageal GISTs are reported to range up to 25 cm in size and are most commonly located in the distal third of the esophagus (6). The single esophageal GIST in our series measured 16 cm in size and manifested as a middle mediastinal mass on chest radiographs (Fig 23). Barium studies of the esophagus may show a smooth intramural mass or a large, ulcerative mass that extends into the esophageal lumen. Distal lesions may extend into the proximal stomach. On CT images, these lesions may be homogeneous or heterogeneous in attenuation. They may contain central areas of low attenuation from hemorrhage, necrosis, or cystic degeneration.

View larger version (85K): [in this window] [in a new window] [Download PPT slide]   Figure 23a.  Esophageal GIST in a 71-year-old man who presented with upper gastrointestinal tract bleeding. (a) Lateral chest radiograph shows a retrocardiac mass. (b) Barium esophagram shows the distal esophageal mass that distorts and widens the esophageal lumen. (c) Unenhanced CT scan shows a 16-cm soft-tissue attenuation mass involving the esophagus.

View larger version (51K): [in this window] [in a new window] [Download PPT slide]   Figure 23b.  Esophageal GIST in a 71-year-old man who presented with upper gastrointestinal tract bleeding. (a) Lateral chest radiograph shows a retrocardiac mass. (b) Barium esophagram shows the distal esophageal mass that distorts and widens the esophageal lumen. (c) Unenhanced CT scan shows a 16-cm soft-tissue attenuation mass involving the esophagus.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 23c.  Esophageal GIST in a 71-year-old man who presented with upper gastrointestinal tract bleeding. (a) Lateral chest radiograph shows a retrocardiac mass. (b) Barium esophagram shows the distal esophageal mass that distorts and widens the esophageal lumen. (c) Unenhanced CT scan shows a 16-cm soft-tissue attenuation mass involving the esophagus.

GISTs that extend into the esophageal lumen may simulate a polypoid mass so that lesions of mucosal origin may occasionally be considered in the differential diagnosis. Papilloma, adenoma, inflammatory polyp, fibrovascular polyp, and carcinoma manifest as intraluminal polypoid masses. Large, highly aggressive GISTs that extend into the mediastinum have radiologic appearances similar to those of advanced stage carcinoma, malignant melanoma, lymphoma, and leiomyosarcoma.

Mesentery and Omentum
Primary GISTs may occur in any of the mesenteric or omental structures within the peritoneum. We had a single case in our series that originated in the small bowel mesentery. In the series reported by Miettinen et al (4), the median size of primary omental and mesenteric GISTs was 16.5 cm. The presence of hemorrhage, necrosis, and cystic change in these tumors results in the appearance of a complex mass on cross-sectional images. Our case was characterized as a well-circumscribed, multilobulated mass containing areas of low attenuation (Fig 24). The cystic component of the tumor may be the dominant feature. The peripheral solid portions of the tumor enhance during intravenous contrast material administration.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 24a.  GIST arising from the small bowel mesentery in a 65-year-old man with abdominal pain. (a) Intravenous contrast-enhanced CT scan shows a 15-cm mass in the small bowel mesentery that contains areas of contrast enhancement and low attenuation (white arrows). There are adjacent metastatic lesions in the mesentery (black arrows). (b) CT scan through the upper abdomen shows liver metastases and intraperitoneal spread of tumor (arrow).

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 24b.  GIST arising from the small bowel mesentery in a 65-year-old man with abdominal pain. (a) Intravenous contrast-enhanced CT scan shows a 15-cm mass in the small bowel mesentery that contains areas of contrast enhancement and low attenuation (white arrows). There are adjacent metastatic lesions in the mesentery (black arrows). (b) CT scan through the upper abdomen shows liver metastases and intraperitoneal spread of tumor (arrow).

GISTs from the gastrointestinal tract may metastasize to the omentum and mesentery; however, they typically result in multiple masses throughout the peritoneal cavity. In these instances, the differential diagnosis includes peritoneal carcinomatosis, lymphomatosis, and the benign condition leiomyomatosis peritonealis disseminata; the latter typically manifests as innumerable small nodules measuring only a few millimeters each (42).

	Prognosis and Therapy

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Clinical Features Pathologic Features Radiologic Features Prognosis and Therapy Conclusions References

 
Tumor size and mitotic rate (mitoses per consecutive 50 high-power fields) are the most common criteria used by pathologists to assess benign versus malignant biologic behavior. Anatomic site alone has been demonstrated to be an independent prognostic factor (43), and the significance of size is also site dependent (28).

A small number of GISTs recur or metastasize despite a histologically benign appearance (ie, small size and absence of mitoses or low mitotic rate). Therefore, some authors support stratifying GISTs into very low-, low-, intermediate-, and high-risk categories rather than classifying them as benign or malignant (23,27). Currently, it is recommended that all patients with GISTs be carefully monitored for an indefinite period because patients with recurrence have a poor prognosis (27).

The conventional therapy for patients with GISTs has been surgical resection of the primary disease. Malignant GISTs typically recur and metastasize to the liver and peritoneal surface. Lymph node metastasis is very uncommon. Conventional systemic and intraperitoneal chemotherapeutic agents, arterial chemoembolization, surgery, and irradiation have been ineffective in treating patients with metastatic and recurrent disease.

In 2001, Hirota et al (44) described a small series of patients with GISTs containing activating mutations in exon 11 of the KIT gene. Such mutations cause increased enzymatic activity of the KIT tyrosine kinase. Tuveson et al (45) showed that inhibition of the mutant KIT by STI-571 leads to growth arrest and death of the tumor cells. KIT mutation is not present in all GISTs; the reported frequency of the mutation ranges from 52% to 85% (46,47). Current studies show that 59%–69% of patients respond to therapy with STI-571, 19%–26% stabilize, and in 11%–13% disease progresses (48,49). The exact role of STI-571 has not yet been established; it may prove useful in neoadjuvant and adjuvant treatment or in combination with conventional therapy (49).

	Conclusions

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Clinical Features Pathologic Features Radiologic Features Prognosis and Therapy Conclusions References

 
GISTs most commonly involve the muscularis propria of the stomach or intestinal wall and extend to involve extramural, mural, and intraluminal surfaces of the stomach and small intestine. The extramural component of GISTs may be extensive such that the bulk of the tumor is outside the organ of origin. GISTs occurring in the gastrointestinal tract and mesentery characteristically have hemorrhage, necrosis, or cyst formation that appears as focal areas of low attenuation on CT 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.

	Footnotes

 
See also the drawing by Cooper (p 456) in this issue .

Abbreviations: GIST = gastrointestinal stromal tumor, H-E = hematoxylin-eosin

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official nor as reflecting the view of the Departments of the Army or Defense.

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Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Clinical Features Pathologic Features Radiologic Features Prognosis and Therapy Conclusions References

 

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