Clinical History
A gastric luminal mass was incidentally discovered in the course of a routine sonographic examination performed on an otherwise asymptomatic 67-year-old woman. An upper barium study and a CT
examination confirmed the finding of a submucosal homogeneous mass with endoluminal growth, that was also visible on the preoperative chest radiography.
Imaging Findings
The patient underwent an ultrasound examination to find the reason for an abnormal liver function test. She had no symptoms of gastric outlet obstruction. A large fusiform and homogeneous mass was
visualized, which had projected into the stomach lumen. It apparently arose from the muscular layer, as the submucosal echogenic line was clearly depicted deep into it. An upper barium study also
showed the mass as a large filling defect arising from the posterior wall of the gastric body, which appeared to spare the mucosal surface. Endoscopy was done, which confirmed the presence of a
submucosal mass and also showed an ulcerated area. Superficial biopsies which were performed only revealed foci of chronic gastritis. A CT scan showed the mass to be homogeneous and slightly
hypodense, in an early portal phase after an intravenous contrast administration. Neither sonography nor CT showed any evidence of metastatic spread. As a point of curiosity, the mass could also be
partially seen as a lobulated filling defect in the air-filled gastric fundus on a preoperative chest X-ray film. A partial gastric resection was performed. The macroscopic examination of the
specimen revealed a mass 320 g in weight, covered by atrophic mucosa, with areas of erosion. Microscopically,monomorphic spindle cells were seen arranged in bundles. The mitotic level was low and no
necrosis was present, although some areas of myxoid and cystic degeneration of the stroma were seen. The immunohistochemical profile of the cells was as follows: actin negative, S-100 protein
negative, CD 34 positive, CD 117 positive. A diagnosis of GIST with no definite features of malignancy (large size but low mitotic level) was made.
Discussion
Gastrointestinal stromal tumor (GIST) is the term designated to an infrequent group of gastrointestinal mesenchymal tumors that histologically, immunohistochemically, and genetically, differ from
typical leiomyomas, leiomyosarcomas and schwannomas (1). Since its first description in 1983 there has been considerable debate regarding its nomenclature, cellular origin, diagnosis and prognosis
(2). GISTs may occur anywhere along the gastrointestinal tract (3). Their cellular origin has been proposed to be the interstitial cells of Cajal (intestinal pacemaker cells), as both the GIST and
there cells share the immunohistochemical marker CD 117 (c-kit protein), and ultrastructural characteristics of both smooth muscle and neural differentiation (2). However, it has recently been
suggested that its origin is from a more primitive stem cell from which both the Cajal and the smooth muscle cells arise (4), based on the presence of tumors which are phenotypically identical to
GISTs, and primarily localized in the omentum and the mesentery. At microscopy, 70%–80% of GISTs are seen to be composed of spindle cells, and 20%–30% are found to have epithelioid
morphological features; These cells can be arranged in a wide variety of histological patterns (3). The most important and specific immunohistochemical marker is the c-kit (CD117) protein, a tyrosine
kinase growth factor receptor (4). They are almost invariably negative for desmin (1) and, unlike schwannomas, for the S-100 protein. They most often occur in middle-aged to older individuals (2).
The most frequent primary site of occurrence of a GIST seems to be the stomach, accounting for between 39% and 70% (2,3) of the cases, the small bowel being the second most common site of origin
(20%–32%). Less commonly, they may arise in the rectum, colon, esophagus, mesentery, or omentum (3). They represent approximately 2.5% of all gastric tumors (3), 0.1%–3% of all
gastro-intestinal neoplasms (5) and about 5% of sarcomas (2). About 10%–30% are malignant, the risk of malignancy increasing with an extragastric location, a size greater than 5 cm, the
extension into adjacent organs, tumor necrosis and more than one mitosis per high-power field (2,3). In our case, there was no definite evidence of malignancy, although the tumor was large in size
and metastases have been reported from mitotically inactive tumors. The imaging features and patterns of the metastatic spread of malignant GISTs have recently been reported (5). Metastases are
present in 47%–61% of the cases by the time of diagnosis (2,5), with hepatic, closely followed by peritoneal involvement being the most common. Lymph node metastases are much less frequent (6%)
as are those to bone (6%) or lung (2%) (2,5). Despite the relative frequency of peritoneal dissemination, the existence of ascites is an infrequent event. There is also only a small tendency towards
intestinal obstruction. At CT, benign GISTs are usually found to be homogeneous with attenuation values similar to those of muscle, whereas the malignant tumors often have low attenuation areas,
reflecting cystic degeneration or necrosis. They may show either endoluminal or extrinsic growth. Although only surgical resection has been proven to be therapeutically effective, an enzymatic
treatment with a tyrosine kinase inhibitor (imatinib), which acts on the c-kit growth factor receptor, has recently been described. It is still under clinical trial but the initial studies are
promising.
Differential Diagnosis List
Gastro-intestinal stromal tumor (GIST).
Final Diagnosis
Gastro-intestinal stromal tumor (GIST).
