DOI: 10.1148/rg.231025071
(Radiographics. 2003;23:75-87.)
© RSNA, 2003
Current Role of CT in Imaging of the Stomach1
Karen M. Horton, MD and
Elliot K. Fishman, MD
1 From the Department of Radiology, Johns Hopkins Medical Institutions, 601 N Caroline St, Rm 3251, Baltimore, MD 21287. Recipient of a Certificate of Merit award for an education exhibit at the 2001 RSNA scientific assembly. Received April 1, 2002; revision requested May 13 and received June 11; accepted June 12. Address correspondence to E.K.F. (e-mail: efishman@jhmi.edu).
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Abstract
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Recent advances in computed tomographic (CT) technology and three-dimensional (3D) imaging software have sparked renewed interest in using CT to evaluate gastric disease. Multidetector row CT scanners allow thinner collimation, which improves the visualization of subtle tumors as well as the quality of the 3D data sets. When water is used as an oral contrast agent, subtle disease is easier to visualize, especially when a rapid contrast material bolus is intravenously administered. 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. 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. In addition to gastric malignancies, CT can also help detect inflammatory conditions of the stomach, including gastritis and peptic ulcer disease. CT angiography is especially helpful for depicting the gastric vasculature, which may be affected by a variety of disease conditions.
© RSNA, 2003
Index Terms: Computed tomography (CT), multi–detector row • Computed tomography (CT), volume rendering • Gastrointestinal tract, diseases, 70.291 • Gastrointestinal tract, neoplasms, 70.321, 70.34 • Stomach, CT, 72.1211 • Stomach, diseases, 72.291 • Stomach, neoplasms, 72.321, 72.34 Stomach, varices, 72.75
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Introduction
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Recent advances in computed tomographic (CT) technology, including the introduction of multidetector row CT and the development of real-time three-dimensional (3D) imaging systems, have sparked renewed interest in using CT to evaluate the gastrointestinal tract. The same technology that is applied to CT colonography and the generation of 3D and endoluminal images of the colon can be used to perform a detailed CT examination of the stomach. For dedicated gastric imaging, water is used as an oral contrast agent. Water is well tolerated and results in good gastric distention as well as excellent visualization of the enhancing gastric wall. Volume rendering of CT data coupled with interactive 3D and stereoscopic display can then be used to more clearly depict gastric disease.
In this article, we describe and illustrate the use of spiral CT and multidetector row CT as well as 3D imaging in the evaluation of patients with suspected gastric disease, including gastric malignancies and inflammatory conditions. We also provide a detailed discussion of CT scanning protocols and 3D imaging techniques.
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Technique
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Oral Contrast Agent
For dedicated imaging of the stomach, adequate distention is essential. If the entire stomach is not well distended, disease may be overlooked or, conversely, the collapsed gastric wall may mimic disease. Traditionally, high-attenuation contrast agents have been administered to enhance and distend the stomach and gastrointestinal tract. These agents can be categorized as positive contrast agents because they have a CT attenuation greater than that of water. Although these agents are safe, well tolerated, and result in good gastric distention, they may not be optimal when evaluating the gastrointestinal tract and stomach. Occasionally, positive oral contrast material may not mix uniformly with gastric contents, and pseudotumors can be created, on both axial and endoluminal images (1). Because the wall of the gastrointestinal tract can enhance up to 120 HU after the intravenous administration of contrast material (Fig 1), the high-attenuation intraluminal contrast material may mask subtle disease (2). Also, the use of positive contrast agents can complicate 3D imaging and CT angiography: The contrast agent may obscure enhanced vessels, thereby necessitating extensive editing.
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Figure 1. Contrast material-enhanced CT scan obtained with water as an oral contrast agent demonstrates the normal appearance of the stomach. The enhancing gastric wall is well visualized because it is between the intraluminal water and the extragastric fat.
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Recently, there has been interest in using alternative oral contrast agents for CT of the gastrointestinal tract. There is an advantage to using low-attenuation agents with attenuation values similar to those of water. These agents allow better evaluation of the enhancing gastric wall (Fig 1) and may allow better detection of subtle disease (3,4). In addition, low-attenuation agents do not interfere with 3D imaging and CT angiography (3). Oil-based oral contrast agents have been tested and allow adequate depiction of the stomach wall but are not very palatable and result in significant steatorrhea, although newer preparations may be better (5). Whole milk has been proposed as a possible CT oral contrast agent and is routinely used for CT angiography by some groups (6). Milk is emptied from the stomach relatively slowly and has a slower small bowel transit time than water. However, many adults are lactose intolerant and may experience cramping and diarrhea.
We prefer to use water as an oral contrast agent in patients with suspected gastric disease. Water is inexpensive (usually free) and well tolerated (4). It distends the stomach well, allows good visualization of the enhancing wall (Fig 1), and does not interfere with the manipulation of the 3D data sets (Fig 2). When CT is performed specifically to evaluate the stomach, the patient is given 750 mL of water approximately 15 minutes before scanning. An additional 250 mL is given immediately prior to the study. If necessary, air crystals can also be given. Although air crystals are rarely necessary, they can help better distend the gastric cardia and gastroesophageal junction. Some authors have suggested combining prone and supine imaging for optimal distention of all parts of the stomach (7), although we rarely find this necessary in our practice. In addition, in certain cases, decubitus imaging may help distend the gastric antrum and pyloric region.
One disadvantage of using water as an oral contrast agent is that it results in suboptimal distention of the distal small bowel. Some authors have advocated administering positive contrast material initially, followed by water (8). The positive contrast material will fill the distal small bowel loops, and the water will distend the stomach and proximal small bowel (8).
Intravenous Contrast Material
In addition to an oral contrast agent, which allows good gastric distention, intravenous contrast material is essential for complete evaluation of neoplastic and inflammatory diseases of the stomach. We routinely administer 120 mL of nonionic contrast material (Omnipaque 350; Nycomed-Amersham, Princeton, NJ) at a rate of 3 mL/sec.
Scanning Protocol
Gastric imaging has been improved by the introduction of multidetector row CT scanners. We currently use a Siemens Somatom Volume Zoom scanner (Siemens Medical Systems, Iselin, NJ), which can perform up to eight times faster than traditional 1-second single-detector-row spiral CT scanners. Depending on the collimator setting, this scanner can acquire up to four sections per 0.5/sec rotation, which almost completely eliminates motion artifacts. Also, this scanner allows acquisition of thinner sections than do single-detector-row spiral scanners. Sections 0.5 mm in thickness are easily obtainable. This thinner collimation definitely improves the quality of the 3D data set in both gastric imaging and CT angiography. Because the radiation dose to the patient increases when thin collimation is used, it is crucial to monitor exactly what dose the patient receives. Also, newer multidetector row CT scanners have features that help minimize patient radiation exposure by modulating the dose according to the patient’s body habitus.
When imaging a patient with known gastric disease, we use the 4 x 1.0-mm collimator setting. Sections with a 1.25-mm thickness are then generated and reformatted at 1-mm intervals. The resulting overlap improves the quality of the 3D imaging. With this setting, the abdomen (diaphragm to iliac crest) can be scanned in 20 seconds. Multidetector row CT offers considerable flexibility; therefore, although the 1.25-mm sections are used for the 3D images, the data can also be reconstructed with 3–5-mm sections for routine review on film or a workstation. In patients undergoing follow-up CT after gastric surgery, 3-mm sections are usually adequate.
Depending on the indication, dual-phase imaging may be performed. Arterial phase images are acquired 25 seconds after the start of injection, and venous phase images are acquired 50 seconds after the start of injection, both with 1.25-mm sections reformatted at 1-mm intervals. This protocol allows optimal visualization of both the gastric arteries and veins.
Three-dimensional Imaging
Three-dimensional imaging of the gastrointestinal tract, particularly the colon, has gained much attention since it was first proposed in 1993. At that time, 3D imaging was limited by computer speed and performance. Early reports of 3D CT of the stomach (CT gastroscopy) were limited to surface-rendering techniques (shaded surface display [SSD]). However, with improvements in computer technology and speed, most manufacturers now also offer volume rendering. SSD displays only information from the surface of the volume, whereas volume rendering can display all attenuation values throughout the data set (1,9). Therefore, volume rendering is superior to SSD for imaging the stomach and gastric vessels. We currently use the Siemens 3D Virtuoso Imaging package. This software includes real-time volume rendering as well as fly-through capabilities.
At our institution, the data are acquired (1.25-mm sections reformatted at 1-mm intervals) and then transferred over an Ethernet to an Infinite Reality or Onyx workstation with Reality Engine graphics (Silicon Graphics, Mountain View, Calif) or to an O2 workstation for interactive volume rendering. Simple two-dimensional (2D) multiplanar reformatted images of the CT data allow quick visualization of the stomach in the axial, sagittal, and coronal planes. Most radiologists are familiar and comfortable with 2D multiplanar reformatting, which is fast and is available on all workstations. An abnormality detected in one plane can immediately be visualized in the other two planes (Fig 3). The ability to visualize an abnormality in multiple planes increases confidence and helps better characterize the morphologic features of the lesion. It is often helpful to start with 2D multiplanar reformatting and then proceed to 3D imaging. The main advantages of 3D volume rendering over 2D multiplanar reformatting are added perspective and enhanced depth perception. A tortuous vessel or complex mass can be visualized in its entirety with 3D imaging, and its relationship to adjacent structures can be better appreciated.
The 3D volume set can be manipulated with different orientations or cut planes for optimal depiction of the stomach and related disease. In gastric disease, it is often helpful to display the stomach in a coronal or coronal oblique plane if possible. The referring physicians especially appreciate this orientation because the resulting images are similar to an upper gastrointestinal series. This flexibility represents a distinct advantage over traditional axial imaging. In addition to using cut planes, the radiologist can change the transparency of the image, the brightness, and the window width and level. This capability allows the radiologist to accentuate certain structures. For example, when CT angiography is performed, the settings can be optimized to display the vessels, and the adjacent soft tissues will become transparent. In addition, the settings can be altered so that the appearance of the water-filled stomach is similar to that on a traditional CT scan. Alternatively, the parameters can be altered to change the appearance of the gastric wall and intraluminal water. This may help highlight a particular disease (Fig 4).
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Figure 4a. Coronal contrast-enhanced 3D volume-rendered multidetector row CT scans obtained in a patient with gastric cancer depict the mass (arrow). With most 3D software, the imaging parameters (transparency, window width and level) can be altered to change the appearance of the gastric wall and intraluminal water. This capability may help highlight a particular disease. The indistinctness of the wall of the greater curvature of the stomach in b is due to the use of an oblique clip plane.
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Figure 4b. Coronal contrast-enhanced 3D volume-rendered multidetector row CT scans obtained in a patient with gastric cancer depict the mass (arrow). With most 3D software, the imaging parameters (transparency, window width and level) can be altered to change the appearance of the gastric wall and intraluminal water. This capability may help highlight a particular disease. The indistinctness of the wall of the greater curvature of the stomach in b is due to the use of an oblique clip plane.
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In addition, the CT data of the stomach can be manipulated to simulate endoscopic images (virtual gastroscopy). This display technique accentuates the stomach wall and folds (Fig 5). Early studies with this technique were limited, mostly due to computer limitations. In a study by Springer et al (1) of both cadavers and patients, the endoluminal images obtained with SSD correlated well with endoscopic images except for artificial smoothing of surface structures and attenuation limitations created by the SSD technique. The quality of virtual gastroscopy should improve with use of thinner collimation, made possible with multidetector row CT scanners, and volume rendering, which can now be performed easily and in real time. Often, it is not necessary to "travel" through the stomach as in virtual colonoscopy; instead, the radiologist can simply use clip planes and different orientations to visualize the entire stomach.
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Gastric Disease
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Neoplasms
Adenocarcinoma.—
Adenocarcinoma is by far the most common gastric malignancy, representing over 95% of malignant tumors of the stomach (10,11). It is an aggressive tumor with a 5-year survival rate of less than 20% (9). Prognosis is correlated to the stage of the tumor at presentation. Therefore, accurate staging of gastric cancer is essential because surgical resection is the treatment for localized disease. CT is currently the staging modality of choice because it can help identify the primary tumor, assess for local spread, and detect nodal involvement and distant metastases.
Several studies have evaluated the benefit of using water as an oral contrast agent for detection and staging of gastric malignancies (12–14). In a study by Hori at al (13) in which water was used as an oral contrast agent, CT helped detect 95% of advanced carcinomas (with local invasion or metastatic disease), 93% of elevated early carcinomas (no local invasion or metastases), and 18% of early depressed carcinomas. In a similar study by Baert et al (14), 22 of 24 gastric carcinomas (92%) were detected. In a study by Rossi et al (12) in which water was used as an oral contrast agent and glucagon was used for hypotonia, the accuracy for staging gastric cancer was 66%– 77%. The major limitation of the latter study was the difficulty in determining the level of tumor invasion in the gastric wall.
When water is used as an oral contrast agent, gastric tumors appear as segmental or diffuse wall thickening that may demonstrate enhancement unlike that of the normal adjacent gastric wall (Figs 3, 4, 6). These tumors may be subtle but are easier to detect if low-attenuation oral contrast material is used (Figs 7, 8).
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Figure 6a. (a) Coronal contrast-enhanced 3D volume-rendered CT scan obtained in a patient with gastric cancer demonstrates segmental wall thickening (arrows). (b) Axial CT scan obtained in the same patient reveals invasion of the anterior abdominal wall by the mass (arrowhead).
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Figure 6b. (a) Coronal contrast-enhanced 3D volume-rendered CT scan obtained in a patient with gastric cancer demonstrates segmental wall thickening (arrows). (b) Axial CT scan obtained in the same patient reveals invasion of the anterior abdominal wall by the mass (arrowhead).
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Figure 7a. Coronal (a) and axial oblique (b) contrast-enhanced 3D volume-rendered CT scans obtained in a patient with gastric cancer demonstrate focal thickening of the pylorus and distal antrum (arrow).
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Figure 7b. Coronal (a) and axial oblique (b) contrast-enhanced 3D volume-rendered CT scans obtained in a patient with gastric cancer demonstrate focal thickening of the pylorus and distal antrum (arrow).
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Figure 8. Axial oblique contrast-enhanced 3D volume-rendered CT scan obtained in a patient with gastric cancer reveals focal thickening of the pylorus (arrows) that results in gastric outlet obstruction.
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In addition to the use of water as an oral contrast agent for the detection and staging of gastric malignancies, there may be an advantage in performing dual-phase dynamic contrast-enhanced CT. Hundt et al (15) studied 40 patients with gastric malignancies with dual-phase CT (arterial phase and venous phase) and water as an oral contrast agent and were able to detect 39 of 40 cancers (97.5%). CT staging correlated with pathologic staging in 79.4% of cases. The major limitation in staging was the difficulty of accurately depicting tumor invasion of nodes. In a study by Mani et al (16) of 20 patients with gastric cancer, dual-phase CT was performed at 45 seconds and 3 minutes after injection of contrast material. Water was given as an oral contrast agent. The earlier-phase CT was highly accurate in determining the depth of tumor invasion through the wall: The authors correctly determined the depth of tumor invasion in 17 of 20 patients (16). The later-phase CT did not provide any additional information. However, arterial phase CT (usually performed 25 seconds after contrast material injection) was not used in this study. Arterial phase imaging would be beneficial for vascular imaging and often accentuates the differences in appearance between normal gastric wall layers and tumor. Arterial phase imaging also better displays the gastric arterial anatomy, which may be important if there is local extension of tumor. However, the optimal protocol for detection and staging of gastric malignancies (arterial phase, venous phase, and delayed imaging) is still under investigation.
Axial images have always been useful in the staging of gastric malignancies. However, multiplanar reformatted images and 3D images provide valuable additional information and improve the detection and staging of both early and advanced tumors (9,17,18) (Figs 7, 8). In a study by Lee and Ko (17) of 31 patients with early gastric cancer, the tumor detection rate was dramatically higher with 3D imaging (93.5%) than with axial imaging alone (64.5%). In another study by the same authors involving 60 patients with advanced gastric malignancies, a combination of 3D imaging and axial imaging was superior to axial imaging alone in tumor staging accuracy (18). In both studies, SSD techniques were used to create the 3D images. Results may be even better if volume rendering is used because this technique has been shown to be superior to SSD for displaying mucosal detail (19).
In addition to 3D imaging of the stomach, endoluminal imaging is also possible (1,9,20). Endoluminal imaging provides a view similar to the endoscopic view (Fig 5). With this technique, it is possible to simultaneously visualize the primary tumor and extraluminal extension. One limitation of this technique is the difficulty in detecting flat lesions that involve only the mucosa (7,9).
Lymphoma.—
The stomach is the most frequent site of gastrointestinal tract involvement by non-Hodgkin lymphoma (21). At CT, gastric lymphoma typically appears as segmental or diffuse wall thickening (Figs 9, 10). In a 1982 study by Buy and Moss (22) of 12 patients with gastric lymphoma, the average gastric wall thickness was 4.0 cm. In contrast to gastric adenocarcinoma, lymphoma typically involves more than one region of the stomach. With use of water as an oral contrast agent, it may now be possible to detect cases of only minimal thickening of the gastric wall. Because lymphoma is considered to be a "soft" tumor, it is less likely to result in gastric outlet obstruction than is gastric adenocarcinoma.
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Figure 9. Contrast-enhanced CT scan obtained with water as an oral contrast agent demonstrates subtle segmental thickening of the gastric antrum (arrow). Endoscopic biopsy revealed gastric lymphoma.
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Figure 10. Contrast-enhanced CT scan obtained with water as an oral contrast agent demonstrates segmental thickening of the stomach (arrows), a finding that represents gastric lymphoma.
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Perigastric adenopathy is common in patients with gastric lymphoma as well as in those with gastric adenocarcinoma. However, adenopathy that extends below the renal hila favors gastric lymphoma over adenocarcinoma as a diagnosis (22). In addition to helping detect gastric involvement by lymphoma, CT is useful in detecting complications such as perforation, extragastric extension, or fistulization (21).
Mucosa-associated lymphoid tissue (MALT) lymphoma is a low-grade lymphoma that is being recognized with increasing frequency. It is thought to be associated with Helicobacter pylori (23). This tumor differs from the typically high-grade non-Hodgkin gastric lymphoma. In a series by Kessar et al (24) of 40 patients with gastric MALT lymphoma, the most frequent finding was gastric wall thickening. Such wall thickening is usually minimal and may not be detected at CT, especially if the stomach is not maximally distended. Associated adenopathy or extragastric distention is uncommon (23–25).
Because the most frequent CT finding in both gastric lymphoma and gastric MALT lymphoma is wall thickening, careful attention to CT technique is necessary. The stomach should be maximally distended. Again, water may allow better evaluation of the enhancing gastric wall. In some cases, the addition of air may also be helpful. To our knowledge, there have been no studies that address the utility of water as an oral contrast agent or of 3D imaging in the detection or staging of gastric lymphoma. However, we have found this technique to be helpful, especially in subtle or complicated cases. In addition, the referring physicians and surgeons find 3D images useful in treatment planning. In many cases, 3D CT will obviate other radiologic studies such as an upper gastrointestinal series.
Gastrointestinal Stromal Tumors.—
Gastrointestinal stromal tumors (GISTs) are uncommon neoplasms that arise from mesenchymal cells in the wall of the gastrointestinal tract. These tumors demonstrate variability in differentiation and are categorized based on findings from immunohistochemical and ultrastructural studies (26). Stromal tumors can be classified histologically as myogenic tumors (arising from smooth muscle), neurogenic tumors (arising from neural elements), or less differentiated tumors (GISTs). Stromal tumors with smooth muscle differentiation were formerly called leiomyomas or leiomyosarcomas. They account for only 1% of gastric tumors (27) and usually occur in adults. CT is useful in the detection of these neoplasms (28).
At CT, GISTs vary in size and appearance. Ninety percent of gastric leiomyosarcomas occur in the fundus or body of the stomach (29). Small tumors appear as intramural masses (Fig 11). As the tumors grow, they stretch the overlying mucosa and can ulcerate (28). When large (>5 cm), the tumors often appear exophytic and may contain areas of central necrosis or calcification (Figs 12, 13) (27,28). When tumors are large and exophytic, it may be difficult to determine their site of origin, and in such cases 3D imaging can be helpful in better characterizing the mass and determining its origin. Associated adenopathy is uncommon, in contrast with gastric adenocarcinoma or lymphoma.
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Figure 12a. Sagittal (a) and axial oblique (b) contrast-enhanced 3D volume-rendered CT scans demonstrate a round, 5-cm exophytic mass (arrows) that arises from the stomach. The mass proved to be a benign GIST at surgery.
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Figure 12b. Sagittal (a) and axial oblique (b) contrast-enhanced 3D volume-rendered CT scans demonstrate a round, 5-cm exophytic mass (arrows) that arises from the stomach. The mass proved to be a benign GIST at surgery.
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Figure 13. Coronal contrast-enhanced 3D volume-rendered CT scan demonstrates a large, ulcerating exophytic mass (arrows) that arises from the stomach, a finding that is compatible with a malignant GIST.
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Malignant stromal tumors can invade adjacent organs and can metastasize hematogenously, usually to the lung or liver. Metastatic lesions may also appear low in attenuation due to necrosis.
CT cannot usually help differentiate between malignant and benign gastric stromal tumors unless obvious local invasion or metastatic disease is seen. However, small tumors (<4–5 cm) are usually benign. Resection and histologic analysis of mitotic activity and markers is necessary.
Inflammatory Conditions
Gastritis.—
CT is not the imaging modality of choice in patients with suspected peptic ulcer disease. However, it is often performed in patients who present with nonspecific complaints such as abdominal pain and nausea. Therefore, CT may be the first study performed and help suggest the diagnosis.
The most common CT finding in patients with gastritis is thickening of the gastric folds and wall (Fig 14). In severe cases, the gastric wall will demonstrate low attenuation compatible with submucosal edema and inflammation (10). At the same time, the mucosa may enhance due to hyperemia. This enhancement may give the wall a layered appearance, which is most pronounced at arterial phase imaging. This layering or "halo" will help distinguish gastritis from other conditions that cause gastric wall thickening (eg, neoplasms). Neoplasms will not penetrate the layers of the gastrointestinal tract wall and therefore will not create this striated or halo appearance. Gastritis may not involve the stomach diffusely and thus may appear as focal or segmental thickening. H pylori gastritis in particular can simulate a gastric neoplasm because it often results in circumferential antral wall thickening or focal thickening along the greater curvature of the stomach (Fig 15) (30). Other conditions such as adult hypertrophic pyloric stenosis can also manifest as segmental wall thickening (Fig 16). Because the CT appearances of gastritis and tumors can overlap, endoscopy is often necessary for definitive diagnosis. The role of 3D CT in the evaluation of inflammatory conditions of the stomach has not been well studied.
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Figure 14a. Coronal (a) and endoluminal (b) contrast-enhanced 3D volume-rendered CT scans demonstrate moderate fold and wall thickening, findings that are compatible with gastritis.
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Figure 14b. Coronal (a) and endoluminal (b) contrast-enhanced 3D volume-rendered CT scans demonstrate moderate fold and wall thickening, findings that are compatible with gastritis.
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Figure 15. Coronal contrast-enhanced 3D volume-rendered CT scan demonstrates H pylori gastritis, which causes segmental fold thickening (arrow) along the greater curvature of the stomach, thereby simulating a tumor.
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Figure 16a. Coronal (a) and coronal oblique (b) contrast-enhanced 3D volume-rendered CT scans reveal circumferential thickening of the pylorus, a finding that was suspicious for cancer. Partial gastrectomy revealed adult hypertrophic pyloric stenosis, which was thought to result from chronic peptic ulcer disease.
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Figure 16b. Coronal (a) and coronal oblique (b) contrast-enhanced 3D volume-rendered CT scans reveal circumferential thickening of the pylorus, a finding that was suspicious for cancer. Partial gastrectomy revealed adult hypertrophic pyloric stenosis, which was thought to result from chronic peptic ulcer disease.
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Peptic Ulcer Disease.—
In addition to gastritis, gastric ulcers are common in patients with peptic ulcer disease. Most gastric ulcers are not visible at CT because they affect only the superficial layers of the gastric wall (31). However, deep ulcers or ulcers that have penetrated or perforated the gastric wall can be detected. Patients with ulcerous penetration may have inflammatory changes in adjacent soft tissue, in addition to gastric wall thickening (31). Perforation appears as inflammatory changes as well as extraluminal air bubbles or pneumoperitoneum.
Emphysematous Gastritis.—
Emphysematous gastritis is an uncommon entity that is usually caused by invasion of the gastric wall by a gas-producing organism, typically Escherichia coli (10,32). Emphysematous gastritis is a life-threatening condition with a high mortality rate. At CT, the stomach is thickened and there is air within the layers of the wall. Air within the gastric wall may rarely occur after caustic ingestion or gastric infarction. In addition, there is a benign condition called gastric emphysema that may also lead to air within the gastric wall. In fact, gastric emphysema is more commonly seen than emphysematous gastritis in clinical practice. The CT appearance of these two entities can be identical. However, patients with benign gastric emphysema are asymptomatic, and the condition tends to resolve spontaneously (10).
Gastric Varices
Gastric varices can occur in association with esophageal varices in patients with cirrhosis and portal hypertension. In these patients, there is increased resistance to portal flow into the liver. Therefore, blood must find an alternative pathway to the heart, which includes the perigastric and periesophageal vessels. Isolated gastric varices without esophageal varices can also occur in patients with splenic vein thrombosis or occlusion. This finding is typically seen in patients with pancreatitis and splenic vein thrombosis or in patients with pancreatic cancer with invasion and occlusion of the splenic vein (Fig 17).
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Figure 17a. (a) Coronal contrast-enhanced 3D volume-rendered CT scan obtained in a patient with pancreatic cancer reveals a mass (straight arrow) that causes obstruction of the splenic vein (curved arrow). (b) CT angiogram obtained in the same patient demonstrates multiple large gastric varices.
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Figure 17b. (a) Coronal contrast-enhanced 3D volume-rendered CT scan obtained in a patient with pancreatic cancer reveals a mass (straight arrow) that causes obstruction of the splenic vein (curved arrow). (b) CT angiogram obtained in the same patient demonstrates multiple large gastric varices.
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CT is valuable for the detection of gastric varices and identification of the underlying cause (33). Gastric varices appear as enhancing tubular vessels, located primarily along the body and fundus of the stomach (Fig 17). Because they are veins, they will enhance during the portal venous phase and will not typically enhance during the arterial phase. Collateral vessels are also commonly seen along the gastrohepatic ligament and left gastric vein (10). Gastric varices can be mistaken for gastric wall thickening, gastric cancer, or perigastric adenopathy if intravenous contrast material is not administered. In patients with cirrhosis and portal hypertension, esophageal varices will also be present.
CT angiography is useful in the detection of gastric varices. A study by Matsumoto et al (34) of 30 patients with gastric varices demonstrated good correlation between findings at 3D CT and at conventional angiography. In fact, in four patients, posterior gastric veins or short gastric veins were identified at 3D CT but not at conventional angiography. In this study, 3D CT was also used to evaluate patients after balloon occlusion of the varices (34). The unlimited imaging planes that are possible with 3D CT represent a definite advantage in trying to identify the small perigastric vessels. In addition to helping detect gastric varices, CT angiography can routinely help identify the arteries and veins that supply the stomach, as well as anatomic variants (Figs 18, 19) (34,35).
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Figure 18a. Sagittal (a) and axial oblique (b) volume-rendered CT angiograms demonstrate the normal anatomy of the celiac axis. The left gastric artery (arrow) is seen to arise from the celiac axis.
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Figure 18b. Sagittal (a) and axial oblique (b) volume-rendered CT angiograms demonstrate the normal anatomy of the celiac axis. The left gastric artery (arrow) is seen to arise from the celiac axis.
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Conclusions
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Recent advances in CT technology and 3D imaging software have sparked renewed interest in using CT to evaluate gastric disease. Detailed CT examinations of the stomach can routinely be performed when water is used as an oral contrast agent, along with a rapid intravenous contrast material bolus and the thin collimation that is possible with new multidetector row CT scanners. Three-dimensional imaging of the stomach is helpful in the detection and evaluation of gastric malignancies and of a variety of inflammatory conditions that affect the stomach. CT angiography is especially useful for identifying the perigastric vasculature and gastric varices.
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Footnotes
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Abbreviations: GIST = gastrointestinal stromal tumor,
MALT = mucosa-associated lymphoid tissue,
SSD = shaded surface display,
3D = three-dimensional,
2D = two-dimensional
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References
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Abstract
Introduction
