Carcinoma is the most important and the most common tumor of the stomach. Most gastric carcinomas are adenocarcinomas. Predisposing conditions include atrophic gastritis, pernicious anemia, adenomatous polyps, dietary nitrates, and Japanese heritage. The tumors show a predilection for the lesser curvature of the antropyloric region.
Grossly, adenocarcinomas of the stomach can be divided generally into three forms:
- exophytic or polypoid, projecting into the lumen;
- ulcerated, with a shallow or deeply erosive crater;
- diffusely infiltrative (linitis plastica).
Gastric cancer may spread hematogenously to the liver and lung, contiguously to adjacent organs, lymphatically to regional and remote lymph nodes, and/or intraperitoneally to the abdominal lining, mesentery, and serosa.
The goals of MRI in patients with gastric cancer are to demonstrate the primary tumor, assess the depth of invasion, and detect extra gastric disease. Adequate distention is necessary for surveying the gastric wall. On T1-weighted sequences, gastric adenocarcinoma is isointense to normal stomach wall and may be apparent as focal wall thickening. On T2-weighted images, tumors usually are slightly higher in signal intensity than adjacent normal wall except diffusely infiltrative carcinoma (linitis plastica carcinoma), which tends to be lower in signal intensity than normal adjacent wall because of its desmoplastic nature (Auh et al. 1994).
Tumors show heterogeneous enhancement that may be decreased or increased relative to the gastric wall on early, late, or both sets of images (Marcos and Semelka 1999). Linitis plastica carcinoma enhances only modestly after intravenous contrast.
Gadolinium-enhanced fat-suppressed GE imaging aids in identification of transmural spread including peritoneal disease, tumor involvement of lymph nodes and metastases particularly if it is dynamic.