Images In Gastroenterology

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1 Images In Gastroenterology Thong-Ngam D, et al. THAI J GASTROENTEROL 2005 Vol. 6 No. 2 May - Aug Imaging of Gastrointestinal Stromal Tumors Pornpim Fuangtharnthip, M.D. Narumol Hargroove, M.D. ABSTRACT Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasm in the gastrointestinal tract. GIST is a group of mesenchymal tumors that predominantly exhibit an altered oncogene, KIT (CD 117). There are imaging features and pattern of spreading be suggestive of GISTs diagnosis such as the appearances of a large exophytic bowel mass with necrosis or hemorrhage, hypervascular liver metastases, and smooth low-density mesenteric masses. Adenopathy, concentric bowel involvement, large-volume ascites, and spiculated mesenteric masses suggest an alternative diagnosis. The radiologic appearances can change dramatically after therapy which solid hypervascular masses previously may become completely cystic on CT even within 1 month of treatment. After initial successful treatment; tumor enlargement, new sites of tumor, and/or a new nodule within a stable masses are indicators of progression of disease. Key words : imaging, gastrointestinal stromal tumors, GISTs [Thai J Gastroenterol 2005; 6(2): ] INTRODUCTION Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasm in the gastrointestinal tract. The recent reclassification of mesenchymal tumors which based on a better understanding of the genetics and immunophenotype of gastrointestinal stromal tumor, they are defined as spindle cell, epithelioid and occasionally pleomorphic mesenchymal tumors with expression of the KIT protein, a tyrosine kinase growth factor receptor (also called KIT receptor or CD 117) (1-2). 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. Radiologic Features Radiologic features of GISTs vary depending on tumor size and organ of origin. In this article, we describe their radiologic features as primary tumor, metastatic disease and appearance after treatment. Primary Tumor at Presentation Most GISTs are large heterogeneously enhancing exophytic masses, usually between 3 and 10 cm (Figure 1). Hemorrhage may be seen in large tumors (Figure 2). Small GISTs may show intense enhancement with IV contrast administration which is a less common finding in the small bowel GIST because of tendency of larger and more malignant at presentation. An intraluminal component can occasionally be seen Department of Radiology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.

2 THAI J 106 GASTROENTEROL 2005 A Simple Rat Model of Chronic Helicobacter pylori Infection for Research Study Figure 1 Coronal (a) and axial (b) contrast-enhanced CT scans demonstrate heterogenous enhancing exophytic masses (arrow) that arising from the stomach (ST) with liver metastasis (arrow head). The mass proved to be a malignant GIST at surgery. Figure 3 Gastric gastrointestinal stromal tumor. Upper GI study (a) reveals smooth well-defined submucosal mass (M) and axial contrast-enhanced CT scan (b) demonstrate intraluminal mass (arrrow head) with pocket of air or oral contrast material within the mass (arrow). The pocket of air are better seen on CT images. Figure 2 Axial contrast-enhanced CT scan show fluid-fluid level in tumor mass (M) with multiple liver metastases (LM); representing hemorrhage Figure 4 Mucosal ulceration in gastric GIST arising from stomach: Upper GI study on air contrast (a) and barium-contrast (b) at fundus reveals an ulcer (arrow) within the large submucosal mass.

3 THAI J GASTROENTEROL 2005 Vol. 6 No. 2 May - Aug Thong-Ngam D, et al. as submucosal lesion overlying intact mucosa on upper GI study and endoluminal mass on CT (Figure 3a). Mucosal ulceration occurs in 50% of gastric tumors (Figure 3b, 4) shown by the presence of air or oral contrast material within the mass(3,4). Cavity and fistula formation may occur, resulting in luminal enlargement(3) (Figure 5). Unlike carcinoid tumors, the me- 107 senteric GIST is usually large, well-defined mass with a smooth surface and do not show spiculation of mesentery (Figure 6). Like lymphoma, GIST can also show aneurysmal dilation of the bowel. Calcification was not seen in any tumor at presentation but was occasionally seen in metastases after specific chemotherapy (Figure 7). Figure 5 A 54-year-old women with malignant gastrointestinal stromal tumor. Noncontrast-enhanced (a), contrast-enhanced (b) CT scan and GI follow through (c) showed large mass (M, arrow) arising from small bowel, causing aneurysmal dilatation of bowel with fistula formation Figure 6 Differentiation of small-bowel GIST (a) and carcinoid tumor (b). Axial contrast-enhanced CT scans demonstrate well-defined mass with presence of central air within the mass (a, arrow) and spiculated mesenteric mass (b, arrow) of carcinoid tumor

4 THAI J 108 GASTROENTEROL 2005 A Simple Rat Model of Chronic Helicobacter pylori Infection for Research Study Figure 7 Calcification in the treated jejunal GIST. Axial unenhanced CT scan (a, b) demonstrated coarse calcification (arrow) within masses. Figure 8 Gastric gastrointestinal stromal tumors with post-operative resected gastric tumors. Axial contrast-enhanced CT demonstrates two large mesenteric masses (a) in peritoneal cavity. Another patient (b) shows large mesenteric mass also. Note that differentiation from unopacified bowel is difficult. Metastatic Disease Lymph node metastases are uncommon, unlike adenocarcinoma or lymphoma. The presence of significant adenopathy should raise the possibility of other diagnosis(4). Mesenteric metastases are common on recurrent disease (Figure 8). These may be related to peritoneal spill of tumor content at surgery. However, they can also be found at presentation in large enteric tumors. Many mesenteric masses have a low-density center, even when the primary tumor is hypervascular. Large mesenteric masses may grow around the mesenteric vessels but do not tend to cause distal venous thrombosis. Omental disease is seen less frequently than mesenteric disease. O mental masses are usually small (<2 cm) and homogeneously enhancing. Omen- tal caking was not often seen. Despite a high risk of solid mesenteric metastases, ascites is rare and is more likely to be a result of chemotherapy. Small liver metastases are usually hypervascular on CT and MRI before chemotherapy. However, not all metastases have similar vascularity. In the same liver, there may be hypo- and hypervascular masses(4,5) ( Figure 9), possibly indicating different generations of metastases. Necrosis is common in larger masses. Hemorrhage is rare within the liver metastases. Purely cystic metastases are rare before therapy but are a common finding on CT after specific chemotherapy. Lung, brain or bone metastases are extremely rare in GISTs, even in the presence of extensive liver and peritoneal metastases.

5 Thong-Ngam D, et al. THAI J GASTROENTEROL 2005 Vol. 6 No. 2 May - Aug Figure 9 A 67-year-old male with small-bowel gastrointestinal tumor. Axial contrast enhanced CT scan demonstrate a) large liver metastasis (M) and a smaller hypovascular metastasis (arrowhead). b. multiple hypo- (arrow head) and hypervascular metastases (arrow) Figure 10 Gastric gastrointestinal tumor with liver metastases. Axial contrast-enhanced CT scan of the liver showed well-defined cystic masses (M), which were treated metastases, simulating simple cysts.

6 110 THAI J GASTROENTEROL 2005 A Simple Rat Model of Chronic Helicobacter pylori Infection for Research Study Figure 11 Recurrent tumor. Axial contrast-enhanced CT scan demonstrate new omental metastasis (OM) and a new nodule (arrow) within stable cystic mass after 18-month treatment. Features after Treatment The pattern of tumor response Mesenteric and liver metastatic diseases become hypovascular and, in some cases, completely cystic on CT, even after 1 month of targeted chemotherapy (6) (Figure 10). The pattern of tumor recurrence The indicators of progression of disease during imatinib mesylate therapy may be tumor enlargement, new sites, and/or a new nodule within a stable masses after imatinib mesylate treatment successfully, at least initially (7) (Figure 11). CONCLUSION GIST is a group of mesenchymal tumors that predominantly exhibit an altered oncogene, KIT (CD 117). There are imaging features and pattern of spreading be suggestive of GISTs diagnosis such as the appearances of a large exophytic bowel mass with necrosis or hemorrhage, hypervascular liver metastases, and smooth low-density mesenteric masses. Adenopathy, concentric bowel involvement, large-volume ascites, and spiculated mesenteric masses suggest an alternative diagnosis. The radiologic appearances can change dramatically after therapy which solid hypervascular masses previously may become completely cystic on CT even within 1 month of treatment. After initial successful treatment; tumor enlargement, new sites of tumor, and/or a new nodule within a stable masses are indicators of progression of disease. REFERENCES 1. Miettinen M, Lasota J. Gastrointestinal stromal tumors: definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch 2001; 438: Fletcher CD, Berman JJ, Cordless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol 2002; 33: Levy AD, Remotti HE,Thompson WM, et al. From the archives of the AFIP gastrointestinal stromal tumors: radiologic features with pathologic correlation. Radiographics 2003; 23: Burkill GJ, Badran M, Al-Muderis O, et al. Malignant gastrointestinal stromal tumor: distribution, imaging features, and pattern of metastatic spread. Radiology 2003; 226: Kim H-C, Lee JM, Kim KW, et al. Gastrointestinal stromal tumors of the stomach: CT findings and prediction of malignancy. Am J Roentgenol 2004; 183: Sandrasegaran K, Rajesh A, Rydberg J, et al. Gastrointestinal stromal tumors: clinical, radiologic, and pathologic features. Am J Roentgenol 2005; 184: Shankar S, vansonnenberg E, Desai J, et al. Gastrointestinal stromal tumor: new nodule-within-a-mass pattern of recurrence after partial response to imatinib mesylate. Radiology 2005; 235: