الفهرس 
ANATOMY OF THE STOMACHOnly 14 pages are availabe for public view
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Abstract
Multidetector computed tomography (CT) offers new opportunities in imaging of the gastrointestinal tract. When thin collimation is used, near isotropic imaging of the stomach is possible, allowing high quality multiplanar reformation and three dimensional reconstruction of gastric images. Proper distention of the stomach and optimally timed administration of intravenous contrast material are required to detect and characterize disease. In contrast to gastroscopy and double contrast studies of the stomach, CT provides information about both the gastric wall and the extragastric extent of disease. Preoperative staging of gastric carcinoma appears to be the main clinical indication for multidetector CT. In addition, multidetector CT allows detection of other gastric malignancies (lymphoma, carcinoid tumors, metastases, gastrointestinal stromal tumors) and benign gastric tumors (neural tumors, polyps).
Adenocarcinoma is the most common gastric malignancy and typically appears as focal or segmental wall thickening or a discrete mass. Gastric lymphoma can have a CT appearance similar to that of adenocarcinoma. Both gastric adenocarcinoma and lymphoma may be associated with adenopathy. However severe gastric wall thickening, infrequent gastric outlet obstruction and lymphadenopathy that extends below the renal hilum favor gastric lymphoma over adenocarcinoma. Gastrointestinal stromal tumors (GISTs) tend to appear as well defined masses that arise from the gastric wall and may be exophytic when large. GISTs are usually not associated with significant adenopathy.
Approximately 90% of gastric tumors are benign. The majority of these are hyperplastic polyps. Adenomas are much less common. Both appear as a soft tissue density round mass arising from the mucosa. Neural tumors include neuromas and schwannomas, they appear as an intramural mass with the same appearance as a small GIST. Gastric lipomas are rare but are readily diagnosed by their fat density on CT. They have no malignant potential.
Virtual gastroscopy is a promising method for detecting EGC despite its limitations. The advantages of virtual gastroscopy are that it has a wider field of view than conventional gastroscopy. However, virtual gastroscopy is limited for detecting superficial flat lesions and some depressed lesions especially those located in the gastric angle.
The duodenum is frequently overlooked during interpretation of abdominal CT examinations. Knowledge about techniques for optimal imaging of the duodenum and about diseases that affect it can result in increased diagnostic yield of abdominal CT.
In the duodenal bulb, 90% of tumors are benign. In the second and third portions of the duodenum, tumors are 50% benign and 50% malignant. In the fourth portion of the duodenum, most tumors are malignant. Adenocarcinomas represent 73-90% of malignant duodenal tumors. Small bowel adenocarcinomas are rare, especially in relation to length of the small bowel, 45% of small bowel adenocarcinomas arise in duodenum & 25% of all malignant small bowel tumors occur in duodenum.
Neoplasms of the small bowel are uncommon and are frequently overlooked because of their vague or nonspecific clinical manifestations. Although a fluoroscopic barium study or evolving bowel enteroscopy is usually used to evaluate patients with possible small bowel neoplasms, CT plays a critical role in the preoperative staging.
Computed tomographic (CT) enterography combines the improved spatial and temporal resolution of multi detector row CT with large volumes of ingested neutral enteric contrast material to permit visualization of the small bowel wall and lumen. Adequate luminal distention can usually be achieved with oral hyperhydration, thereby obviating nasoenteric intubation and making CT enterography a useful, well tolerated study for the evaluation of diseases affecting the mucosa and bowel wall.
CT enteroclysis is a fast, well tolerated, and reliable imaging modality for the depiction of small bowel diseases. This technique provides adequate small bowel distention in a majority of patients. In addition, CT enteroclysis allows the detection of extraluminal disease and provides information relative to the entire abdomen that is not obtained with small bowel follow through or endoscopy.
CT enteroclysis can be performed by using positive enteral contrast material without intravenous contrast material and neutral enteral contrast material with intravenous contrast material. CT enteroclysis has been shown to be superior to other imaging tests such as peroral small bowel examinations, conventional CT, and barium enteroclysis. Although it has disadvantages, experience has shown its value in the investigation of small bowel diseases. The use of multidetector technology and two dimensional reformatting has improved sensitivity of detection and confidence in the addition of cross sectional display and multiplanar reformatting made possible by multidetector row helical CT to enteral volume change and the use of multifunctional naso-intestinal catheters make CTE an important tool in the investigation of small bowel neoplasms.
Benign small intestinal neoplasms are reported to account for approximately 0.5%–2% of all gastrointestinal tract neoplasms. There are a variety of benign small intestinal tumors, of which adenomas and stromal tumors are the most common. Primary malignant small intestinal neoplasms account for less than 2% of primary gastrointestinal malignancies. The most common malignant small bowel tumors are adenocarcinoma, carcinoid tumor, lymphoma, and gastrointestinal stromal tumor. Although any of these tumors may appear as focal intra-luminal masses, focal areas of bowel wall thickening, or areas of increased mural enhancement, certain appearances suggest particular tumors.
In conclusion; MDCT & refined 3D imaging processes can offer a full examination of the stomach and the small intestine and powerful information about the surrounding structures thus making easy, rapid and accurate diagnosis & staging of gastric and small intestinal neoplasms.