An Unusual Cause of a Pancreatic Head Tumor

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• Answer to the Clinical Challenges and Images in GI Question: Image 3: Extragastrointestinal Stromal Tumor of the Pancreas
• References
• Copyright

Question: A 58-year-old man presented with a 3-month history of weight loss and dysuria. Urinalysis and blood investigations including the complete blood count, liver function test, carcinoembryonic antigen, carbohydrate antigen 19-9, and prostate-specific antigen were within normal limits. A cystoscopy was performed, which revealed findings suspicious for a colovesical fistula or bladder diverticulum. Computed tomography (CT) performed demonstrated an incidental finding in the pancreas (Figures A and B). What is the diagnosis?

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Answer to the Clinical Challenges and Images in GI Question: Image 3: Extragastrointestinal Stromal Tumor of the Pancreas 

CT scan demonstrated a large, 8.9 × 6.6 × 7.7 cm, cystic mass with solid components arising from the head of the pancreas. At surgery, a large tumor was found in the head of pancreas without evidence of metastases, for which a pancreaticoduodenectomy was performed (Figure C). Microscopic examination revealed that the tumor involved the subserosal layer of the duodenum but no continuity with the muscularis propria of the bowel could be demonstrated. The tumor was composed of sheets and fascicles of spindle cells that showed cytologic atypia with a mitotic count of >10 per 50 high-power field (Figure D). On immunohistochemistry, the tumor was positive for CD117 but negative for CD34, S100, smooth muscle actin, desmin, and vimentin, which is compatible with gastrointestinal stromal tumor (GIST). The patient was followed up with 6 monthly CT scans and remained disease-free after 5 years.

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GISTs are the most common mesenchymal tumors of the gastrointestinal tract. Recently, mesenchymal tumors with clinicopathologic and molecular genetic profiles similar to GISTs but arising from extragastrointestinal sites such as the retroperitoneum, omentum and mesentery have been reported in the literature.¹, ², ³ These have been termed extragastrointestinal stromal tumors (EGISTs). To date, only a few cases of EGISTs have been reported to arise from the pancreas.², ³

Presently, the origin of EGISTs remains controversial. Some have proposed that EGISTs may be the result of extensive extramural growth of mural GISTs, resulting in minimal or even complete loss of contact with the muscularis propria.¹ Others have suggested that ICC may not be the actual cell of origin, but that GISTs actually arise from a common precursor cell of ICC and smooth muscle, which accounts for their growth within and outside the gastrointestinal tract; ICCs have not been convincingly demonstrated outside the gastrointestinal tract.¹ However, recently ICCs have been reported to occur in the pancreas² and this may account for the occurrence of pancreatic EGISTs.²

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References 

1. Agaimy A, Wunsch PH. Gastrointestinal stromal tumours: a regular origin in the muscularis propria, but an extremely diverse gross presentation (A review of 200 cases to critically re-evaluate the concept of so-called extra-gastrointestinal stromal tumours). Langenbecks Arch Surg. 2006;391:322–329
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2. Showalter SL, Lloyd JM, Glassman DT, et al. Extra-gastrointestinal stromal tumor of the pancreas (Case report and a review of the literature). Arch Surg. 2008;143:305–308
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3. Yang F, Long J, Fu DL, et al. A giant cystic lesion in the epigastric region. Gut. 2008;57:1494;1636
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