(Radiographics. 2001;21:1557-1560.)
© RSNA, 2001
Best Cases from the AFIP
Gastrointestinal Stromal Tumor1
Rebecca M. Sharp, MD,
Howard J. Ansel, MD and
Suzanne B. Keel, MD
1 From the Department of Radiology, University of Minnesota—Veterans Affairs Medical Center, 420 Delaware St SE Box 292, Minneapolis, MN 55455. Received June 28, 2001; revision requested August 10 and received August 27; accepted August 28. Address correspondence to R.M.S., 2835 Century Hills Ln NE, Rochester, MN 55906 (e-mail: sharp019@hotmail.com).
Index Terms: Gastrointestinal stromal tumor (GIST), 70.30, 72.30 • Gastrointestinal tract, neoplasms, 70.30, 72.30 • Stomach, neoplasms, 72.30
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History
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A 67-year-old man presented with intermittent odynophagia and dysphagia with both liquids and solids. Physical examination findings were normal. No laboratory tests were performed.
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Imaging Findings
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A double-contrast upper gastrointestinal barium study demonstrated a round, smooth submucosal mass 3 cm in diameter arising from the greater curvature of the stomach (Fig 1). The remainder of the examination was normal. Contrast material–enhanced computed tomography (CT) demonstrated a large mass with central low attenuation arising from the greater curvature of the gastric wall. The majority of the mass projected inferiorly into the peritoneum, and a small portion protruded into the gastric lumen (Fig 2).
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Figure 1. Image from a double-contrast barium study demonstrates a round, smooth submucosal mass protruding into the gastric lumen along the greater curvature. The overlying mucosa appears to be intact.
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Pathologic Evaluation
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The patient underwent a subtotal distal gastrectomy. Gross examination revealed a well-defined, firm, lobulated, 7.5 x 7.2 x 3.8-cm tan to hemorrhagic mass arising from the gastric wall. The majority of the mass was exterior to the gastric lumen, with only a small, rounded portion protruding into the lumen (Fig 3a). At analysis of the cut section, the mass was seen to contain areas of cystic degeneration filled with straw-colored, semiviscous fluid (Fig 3b). In addition, an anterior gastric wall nodule measuring 0.4 x 0.3 x 0.2 cm was submitted. This nodule was not detectable at imaging.
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Figure 3a. (a) Photograph of the resected specimen reveals a large, lobulated mass that is primarily extraluminal in location. Only a small portion of the mass protrudes into the gastric lumen. The overlying mucosa is intact. (b) Photograph of the cut section reveals internal degenerative cystic changes in the mass, accounting for the central low attenuation seen at CT (cf Fig 2).
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Figure 3b. (a) Photograph of the resected specimen reveals a large, lobulated mass that is primarily extraluminal in location. Only a small portion of the mass protrudes into the gastric lumen. The overlying mucosa is intact. (b) Photograph of the cut section reveals internal degenerative cystic changes in the mass, accounting for the central low attenuation seen at CT (cf Fig 2).
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Microscopic examination demonstrated the tumor to be composed primarily of fascicles of spindle cells with oblong nuclei and a moderate amount of eosinophilic cytoplasm (Fig 4). The majority of the tumor was hypocellular. In cellular areas, up to two mitoses per 50 high-power fields were identified. No necrosis was seen.
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Figure 4a. (4a) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) demonstrates a cellular focus of tumor composed of spindle cells that are somewhat haphazardly arranged. (4b) Higher-power photomicrograph (original magnification, x200; hematoxylin-eosin stain) shows that the spindle cells contain a moderate amount of eosinophilic cytoplasm. Necrosis is not present.
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Figure 4b. (4a) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) demonstrates a cellular focus of tumor composed of spindle cells that are somewhat haphazardly arranged. (4b) Higher-power photomicrograph (original magnification, x200; hematoxylin-eosin stain) shows that the spindle cells contain a moderate amount of eosinophilic cytoplasm. Necrosis is not present.
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Immunohistochemical staining demonstrated the tumor cells to be positive for CD34 protein, vimentin, and actin (Fig 5). The tumor cells were negative for desmin, keratin, and S-100 protein. The histologic features and staining pattern were consistent with a gastrointestinal stromal tumor (GIST). The immunohistochemical stain for the c-kit (CD117) protein was not available at our institution at the time of diagnosis. The smaller gastric wall nodule had the same microscopic and immunohistochemical properties, consistent with a metastasis. The large size of the mass, the metastasis, and the slightly increased mitotic rate were all indicative of a malignant GIST.
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Discussion
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Gastrointestinal stromal tumor is a relatively new term that refers to gastrointestinal mesenchymal tumors arising from a common precursor cell. It has been suggested that this precursor cell is either the interstitial cell of Cajal (an intestinal pacemaker cell) or a more primitive stem cell from which both Cajal cells and smooth muscle cells arise (1). GISTs display spindle cell or epithelioid morphologic characteristics and specific immunohistochemical properties. The most specific and important immunohistochemical marker is the c-kit (CD117) protein, a tyrosine kinase growth factor receptor (1). Most GISTs also express CD34 protein. Other possible markers include vimentin, actin, S-100 protein, and desmin (1). Many tumors previously diagnosed as leiomyomas, leiomyoblastomas, or leiomyosarcomas have been found to be positive for CD117 and are now considered GISTs. This includes tumors involving most sites in the gastrointestinal tract except the esophagus, where true leiomyomas are more common than GISTs (1,2). Schwannomas, true leiomyomas, and true leiomyosarcomas are not GISTs because they are not derived from the GIST precursor cell and do not meet the specific immunohistochemical criteria (1).
GISTs may occur anywhere along the gastrointestinal tract. Approximately 60%–70% of GISTs occur in the stomach, and 20%–30% arise in the small intestine (1). Less commonly, they may arise in the rectum, colon, esophagus, mesentery, or omentum (1). GISTs are usually solitary tumors. They most often occur in middle-aged to older individuals and are rare in individuals under 40 years of age (1,3). Patients may present with pain, dysphagia, weight loss, gastrointestinal bleeding, bowel obstruction, or a palpable abdominal mass (1,3).
GISTs account for about 2.5% of all gastric tumors (3); 10%–30% of GISTs are malignant (1,5). The risk of malignancy increases with an extragastric location, a size greater than 5 cm, extension into adjacent organs, and more than one mitosis per 50 high-power fields (2,4). In a study by DeMatteo et al (4) of 200 patients with malignant GISTs, 47% presented with metastatic disease. The liver is the most common site of metastatic disease, followed by the peritoneum (3,4). Lung, bone, and lymph node metastases can also be seen (3,4).
Barium examinations and CT are commonly used to diagnose gastric GISTs. Barium studies classically show a smooth, discrete submucosal mass, usually with intact overlying mucosa (5). Tumors greater than 2 cm, whether benign or malignant, may ulcerate, giving the lesion a typical "bull’s-eye" appearance (5). As in this case, actual tumor size may be underestimated at barium studies because often there is a substantial extraluminal component that is seen only at cross-sectional imaging (4,6). At CT, benign GISTs are usually homogeneous with attenuation values similar to those of muscle (6). Aggressive GISTs are often heterogeneous with central areas of low attenuation reflecting cystic degeneration or necrosis (7). GISTs infrequently calcify (5,6).
Radiologic signs of malignancy include extrinsic mass effect on the stomach, central necrosis, intratumoral gas, "ulceration that communicates with the stomach by a fistulous tract" (4), adjacent organ invasion, and metastatic disease (4,6). Low-attenuation liver metastases and peritoneal spread may be demonstrated at CT (6). Liver metastases may be hypervascular (7).
At microscopy, 70%–80% of GISTs are composed of spindle cells, and 20%–30% have epithelioid morphologic features (1). These cells can be arranged in a wide variety of histologic patterns (2). As mentioned earlier, the tumor must meet specific immunohistochemical criteria to be classified as a GIST, the most important of which is the presence of the c-kit protein (1).
Until recently, the only therapy that proved effective for GISTs was surgical resection. In April 2001, Joensuu et al (8) published a case report about a nonresectable, widely metastatic GIST that showed a very dramatic response to a tyrosine kinase inhibitor, STI571 (Gleevec; Novartis, East Hanover, NJ). This drug acts on the c-kit growth factor receptor, which, as discussed earlier, is the most important diagnostic marker of GISTs. This dramatic therapeutic effect provides exciting new hope for a cure for GISTs.
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Footnotes
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Abbreviation: GIST = gastrointestinal stromal tumor
Editor’s Note.—Everyone who has taken the course in radiologic pathology at the Armed Forces Institute of Pathology (AFIP) remembers bringing two beautifully illustrated cases for accession to the Institute. In recent years, the staff of the Department of Radiologic Pathology has judged the "best cases" by organ system, and recognition is given to the winners on the last day of the class. Beginning with the July 2001 issue of RadioGraphics, one of these cases is published with each issue of the Journal, written by the winning resident. Radiologic-pathologic correlation is emphasized, and the causes of the imaging signs of various diseases are illustrated.
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References
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Miettinen M, Lasota J. Gastrointestinal stromal tumors: definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Archiv 2001; 438:1-12.[Medline]
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Miettinen M, Sarlomo-Rikala M, Lasota J. Gastrointestinal stromal tumors: recent advances in understanding of their biology. Hum Pathol 1999; 30:1213-1220.[Medline]
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Davis GB, Blanchard DK, Hatch GF, et al. Tumors of the stomach. World J Surg 2000; 24:412-420.[Medline]
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DeMatteo RP, Lewis JJ, Leung D, Mudan SS, Woodruff JM, Brennan MF. Two hundred gastrointestinal stromal tumors: recurrence patterns and prognostic factors for survival. Ann Surg 2000; 231:51-58.[Medline]
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Levine MS. Benign tumors of the stomach and duodenum. In: Gore RM, Levine MS, eds. Textbook of gastrointestinal imaging. 2nd ed. Philadelphia, Pa: Saunders, 2000; 584-587.
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Koehler RE, Memel DS, Stanley RJ. Gastrointestinal tract. In: Lee JKT, Heiken JP, Sagel SS, Stanley RJ, eds. Computed body tomography with MRI correlation. 3rd ed. Philadelphia, Pa: Lippincott-Raven, 1998; 649-653.
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Levine MS, Megibow AJ. Other malignant tumors of the stomach and duodenum. In: Gore RM, Levine MS, eds. Textbook of gastrointestinal imaging. 2nd ed. Philadelphia, Pa: Saunders, 2000; 645-648.
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Joensuu HR, Sarlomo-Rikala M, Andersson LC, et al. Effect of tyrosine kinase inhibitor STI571 in a patient with metastatic gastrointestinal stromal tumor. N Engl J Med 2001; 344:1038-1042.[Abstract/Free Full Text]
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Boggino HE, Fernandez MP, Logrono R. Cytomorphology of gastrointestinal stromal tumor: diagnostic role of aspiration cytology, core biopsy and immunochemistry. Diagn Cytopathol 2000; 23:156-160.[Medline]
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