Teaching Case

An 80-year-old man was being studied for persistent anemia. Upper digestive endoscopy and colonoscopy were unremarkable. An abdominal CT was performed.

Post contrast CT revealed a well-circumscribed expansive solid lesion, with a lobulated contour and scattered calcifications. The leading point was the wall of the third portion of the duodenum, revealing a predominantly exophytic growth making a slight impression on the mesenteric vessels and the uncinate process of the pancreas, with no infiltrative characteristics. It measured 80 x 40 mm and showed an intense heterogeneous enhancement in the arterial phase with internal hypodense areas, due to necrosis.
By its characteristics and location the first diagnostic hypothesis was a gastrointestinal stromal tumour (GIST).
A partial duodenectomy (D3 and D4) plus a lateral duodenal-jejunal anastomosis (Latero-Lateral mechanics) was performed. Histological result of the resected tumour was consistent with a malignant GIST with positive imunohistochemical markers (CD117, CD134 and actine).

GISTs are rare mesenchymal gastrointestinal tumors, ranking in third in prevalence behind adenocarcinomas and lymphomas.
Historically, GISTs were thought to be muscle or nerve tumors, but recent research indicates that GISTs originates in cells found in the walls of the gastrointestinal tract (GI), called Cajal cells; these cells express KIT (CD117) protein and are GI pacemaker cells, responsible for initiating and coordinating GI motility. Mutations in c-kit proto-oncogene are thought to be responsible for these tumors [1].
GISTs are submucosal lesions, which can grow endophytically, although most of the times they manifest as an exophytic extraluminal mass. Most GISTs (60-70%) originate in the stomach while 20-30% arise from the small bowel. Lesions are rare in the colon and rectum (5-10%). Omentum, mesentery and retroperitoneum GISTs have been reported but are very uncommon [1].
GISTs have no racial prevalence, no sex predilection and are most commonly diagnosed in the sixth/seventh decades of life [3].
These tumors are usually benign (70-90%) [1]. GISTs often grow quite large before they are discovered, and on occasions might produce symptoms. When they are first discovered, symptoms depend on the localization and include abdominal discomfort, early satiety, weight loss, nausea and vomiting or secondary symptoms resulting from tumor bleeding, such as anemia [1].
At CT, GISTs appear as solid, large and well-circumscribed masses arising from the gastrointestinal tract. They enhance moderately, with a heterogeneously enhancing rim, surrounding low attenuation areas in the centre (necrosis, hemorrhage or cystic formation) [2]. Calcifications in GIST occur in 10% of the cases[4].
CT features that may suggest malignancy include: diameter exceeding 5 cm; ill-defined margins; heterogeneous attenuation before and after contrast-administration; central necrosis; invasion of surrounding structures; hepatic metastasis and peritoneal dissemination. Metastatic lymphadenopathy is uncommon [5].
For localized primary GISTs, surgical resection is the mainstay of therapy. In case of metastasis, the secondary tumors may also be surgically removed. Unlike treatments for other types of cancer, radiation therapy and chemotherapy are generally ineffective[3]. Imatinib has now been shown to be a uniquely effective therapeutic agent with a remarkable response and a prolonged survival, by competing for the ATP binding site on the target kinase, inhibiting the tyrosine kinase, thus reducing cellular proliferation [6].
At contrast-enhanced CT, a successful response to Imatinib is characterized by rapid transition to a homogeneously cystic pattern, with resolution of the enhancing tumor. Development of an enhancing nodule within the treated tumor indicates recurrence, regardless of changes in tumor size [6].