The stomach is the alimentary reservoir for the mixing and enzymatic digestion of food. It is divided into the cardia, fundus, body, antrum, and pylorus; each with its own specific function.

The cardia is the portion of the stomach surrounding the esophageal orifice and the site where the lesser and greater curvatures meet. The fundus is the most cephalic part of the stomach and touches the left hemidiaphragm. The body is the main portion of the stomach and the principal site of acid production. The antrum is the prepyloric part of the stomach. The pylorus is the sphincter that controls emptying into the duodenum; it is formed by thickening of the middle layer of smooth muscle and a thin fibrous septum.

The gastric wall consists of 3 layers of smooth muscle; the outermost is the longitudinal muscle layer, the middle is the circular muscle layer, and the inner is the oblique muscle layer. The middle circular muscle layer is the thickest component.

Gastric rugae are the redundant folds of gastric mucosa that are most prominent when the stomach is collapsed. The reservoir and mixing functions of the stomach demand a thick, expansile, muscular vessel which characterizes gastric morphology.

Gastric mucosa is composed of columnar epithelium. Gastric glands vary in prevalence in different parts of the stomach. These produce mucin (to line and protect the gastric mucosa), pepsinogen (a precursor to pepsin needed for digestion), and hydrochloric acid (which activates digestive enzymes and assists with the breakdown of food).

The stomach has a rich vascular supply, with the lesser curve supplied by branches of the left and right gastric arteries that run within the lesser omentum. Numerous collateral pathways arising from branches of the celiac and superior mesenteric arteries make the stomach and duodenum resistant to ischemic injury, as well as difficult to control by catheter embolotherapy in the setting of acute upper gastrointestinal hemorrhage.

The greater curve is supplied by the left and right gastroomental (gastroepiploic) arteries that run within the greater omentum. In planning for partial gastrectomy, surgeons try to ensure an intact arterial supply from at least 1 of its 2 sources, preferably the gastroepiploic vessels.

Venous drainage is into the portal system through the left and right gastric veins and via the splenic and superior mesenteric veins. All of these have collateral connections that become important in the event of venous occlusion or portal hypertension, when gastric varices may become prominent and hemorrhage.

Lymphatic drainage follows the course of the arteries, then to celiac nodes via efferent lymphatic ducts. Inspection of these nodal groups is important in staging gastric malignancies. The rich lymphatic and venous drainage of the stomach accounts for the high prevalence of metastatic disease at the time of diagnosis of gastric carcinoma.

The vagus nerve carries parasympathetic stimuli to the stomach, stimulating peristalsis and acid secretion. Surgical interruption of the vagus nerve has been used extensively to treat acid-peptic disease, especially in the era before effective medical control. In order to prevent gastric retention, a vagotomy must be accompanied by some form of gastric emptying procedure, such as partial gastrectomy or pyloroplasty.

Gastric diverticula occur with some regularity (though in less than 1%) and are likely to be mistaken for more significant abnormalities. These congenital, true diverticula usually arise near the gastric cardia. They often have only a thin connection to the stomach, and it may not be apparent on CT or MR. A completely fluid-filled diverticulum is often mistaken for an adrenal mass, while one containing both gas and fluid might be misdiagnosed as an abscess.

Fluoroscopic barium studies are complementary to endoscopy and CT for most cases of dyspepsia and abdominal pain, and they are superior to endoscopy in the evaluation of functional abnormalities (e.g., reflux, delayed gastric emptying).

In many radiology practices, the main role of barium studies is in the pre-/postoperative evaluation of patients undergoing gastric surgical procedures, such as esophagectomy with gastric pull-through, fundoplication for gastroesophageal reflux disease (GERD), partial gastrectomy for cancer, or some form of bariatric surgery. Radiologists must become familiar with the range of expected alterations following various surgical procedures, as well as the numerous complications that may result. Since clinical signs and symptoms are often lacking or nonspecific in these patients, radiologists are often the 1st to recognize adverse results of surgery.

CT has become the principal means of staging primary and metastatic tumors involving the stomach. CT is complementary to upper GI series and endoscopy in diagnosing gastritis and gastric ulcers, especially with complications such as perforation. CT has a primary role in diagnosing inflammatory processes that affect the stomach secondarily, such as pancreatitis.

Endoscopy is the most accurate means of diagnosing gastric carcinoma and primary inflammatory conditions, such as gastritis. However, endoscopy may fail to detect submucosal gastric masses, such as lymphoma or GI stromal tumors, in which the overlying mucosa is often normal.

The presence of “thickened folds” on an upper GI series is a finding of limited value in isolation because so many intrinsic and extrinsic processes, inflammatory or malignant, may result in this finding.

CT findings help to narrow the differential diagnosis by allowing characterization of the nature of the wall thickening. As with the small bowel and colon, inflammatory processes (such as gastritis) result in submucosal edema, which appears as a layer of hypodensity (near water attenuation) between the mucosa and serosa. Soft tissue density within the wall is more likely to be of neoplastic origin.

CT may also allow distinction among the various gastric neoplasms. Primary carcinoma usually produces nodular, irregular wall thickening with limited distensibility, often with evidence of metastatic spread to the liver, regional nodes, ± omentum.

Gastric lymphoma often causes massive nodular thickening of folds but uncommonly limits distensibility or causes gastric outlet obstruction. Lymphoma and gastric metastases are often accompanied by extragastric sites of tumor.

A gastric GIST (stromal tumor) usually appears as a submucosal, mostly exophytic gastric mass. While the mucosa is intact over a small GIST, large lesions often have ulcerated mucosa, which, along with central cavitation of the tumor, may be evident as a large perigastric mass containing gas, fluid, and enteric contrast medium.

The “global view” allowed by CT often provides other clues to the etiology of thickened folds, such as evidence of pancreatitis, the presence of an islet cell tumor in Zollinger-Ellison syndrome, or cirrhosis and signs of portal hypertension in a patient with gastric varices.