Gastrointestinal stromal tumor (GIST) of the small bowel

CLINICAL HISTORY
An 85-year-old woman complained of long-term mild abdominal pain. Abdominal examination revealed a palpable mass in the left paraumbilical region.

FINDINGS
FIGURE 1. Transverse abdominal ultrasound of left lower quadrant shows a large heterogeneous mass with necrotic central areas. Lesion ulcerates penetrating adjacent small bowel loop wall, confirming its origin in the gut (*).
FIGURE 2. Axial abdominal CT with iodinated oral and intravenous contrast shows a large heterogeneous, enhancing mass, with a low-attenuation necrotic central portion. The mass arises from an adjacent segment of the small intestine. Wall ulceration and direct communication with the intestinal lumen are identified.
FIGURE 3. Coronal T2-weighted MRI shows the round heterogeneous mass with a large draining vessel at its upper pole.
FIGURE 4. Axial diffusion-weighted MRI (b = 1000) shows tumor restriction causing decreased signal on the video-inverted images.

DIAGNOSIS
Small bowel gastrointestinal stromal tumor (GIST).

DIFFERENTIAL DIAGNOSIS
Primary and metastatic small intestinal neoplasms. Adenocarcinoma is the most common primary malignancy of the small bowel. Lymphoma produces large masses within the small intestine that may ulcerate, cavitate, and extend into the adjacent mesentery. Lymphoma may be indistinguishable from GIST on radiological images. Mesenteric fibromatosis (desmoid tumor), leiomyomas, carcinoids, in¬flammatory pseudotumor, sclerosing mesenteritis, and metastatic disease may also simulate GIST.

DISCUSSION
Stromal tumors are the most common mesenchymal neoplasms of the gastrointestinal tract. They may occur from the esophagus to the anus. The tumor is frequently found in the stomach (70%) and the small intestine (20% to 30%) and, less commonly, in the omentum, mesentery, and retroperitoneum. Patients are typically over 50 years old at the time of presentation. GIST is rarely seen in patients younger than 40 years old.

The most specific diagnostic criterion for GIST is the expression of the tyrosine kinase growth factor receptor KIT (CD117). Clinical manifestations are highly variable, and depend on the location and size of the tumors. Small, benign GIST may be discovered incidentally. Other patients will present with profound symptoms that reflect large or highly aggressive tumors invading adjacent organs. The most common clinical manifestation for symptomatic GIST is gastrointestinal bleeding from mucosal ulceration.

Abdominal contrast-enhanced CT typically shows a large, hypervascular, enhancing mass (Figure 2). The mass is often heterogeneous owing to necrosis, hemorrhage, or cystic degeneration. Ulceration and fistulization to the gastrointestinal lumen are also common features.

Malignancy is characterized by local invasion and metastases (Figure 4). Malignant GISTs are larger, more highly cellular, and more mitotically active than benign tumors. GIST metastases are most frequently found in the liver and peritoneum. Metastases to the lymph nodes are extremely rare.

Surgical resection has been the conventional therapy for patients with GIST. Malignant GISTs typically recur, metastasizing to the liver and peritoneal surface. Chemotherapy, chemoembolization, and irradiation have been ineffective in treating patients with metastatic and recurrent disease. A new molecularly targeted tyrosine kinase receptor blocker (Imatinib mesylate) is proving to be highly effective.

Bibliography
Burkill GJ, Badran M, Al-Muderis O, et al. Malignant gastrointestinal stromal tumor: distribution, imaging features, and pattern of metastatic spread. Radiology 2003;226(2):527-532. Hong X, Choi H, Loyer EM, et al. Gastrointestinal stromal tumor: role of CT in diagnosis and in response evaluation and surveillance after treatment with imatinib. Radiographics 2006;26(2):481-495. Levy AD, Remotti HE, Thompson WM, et al. Gastrointestinal stromal tumors: Radiologic features with pathologic correlation. Radiographics 2003;23(2):283-304. Lupescu IG, Grasu M, Boros M, et al. Gastrointestinal stromal tumors: retrospective analysis of the computer-tomographic aspects. J Gastrointestin Liver Dis 2007; 16(2):147-151.

Case submitted by Dr. Paula Bartumeus Martínez, resident in radiology, and Dr. Luis Martí-Bonmatí, head of the MR and radiology sections, both at the Dr. Peset University Hospital in Valencia, Spain.