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DOI: 10.1148/rg.264055089
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RadioGraphics 2006;26:1101-1116
© RSNA, 2006

EDUCATION EXHIBIT

Imaging of Various Gastric Lesions with 2D MPR and CT Gastrography Performed with Multidetector CT1

Jung Hoon Kim, MD, Hyo Won Eun, MD, Dong Erk Goo, MD, Chan Sup Shim, MD and Yong Ho Auh, MD

1 From the Department of Radiology (J.H.K., D.E.G.) and Digestive Disease Center (C.S.S.), Soonchunhyang University Hospital, 657 Hannam-Dong, Youngsan-Ku, Seoul 140-743, Korea; the Department of Diagnostic Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea (H.W.E.); and the Department of Radiology, Cornell University Weill Medical College, New York, NY (Y.H.A.). Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received April 8, 2005; revision requested June 23; final revision received October 6; accepted October 7. All authors have no financial relationships to disclose. Address correspondence to J.H.K. (e-mail: junghkim{at}hosp.sch.ac.kr).


   Abstract
Top
 Abstract
Introduction
 Imaging Techniques
 Clinical Applications
 Limitations of 2D MPR...
 Conclusions
 References
 
Recent advances in computed tomographic (CT) technology, three-dimensional imaging software, and cheaper data storage capacity have made faster, simpler, and more accurate gastric imaging available. Two-dimensional multiplanar reformation and CT gastrography including virtual gastroscopy and transparency rendering allow multiplanar cross-sectional imaging, gastroscopic viewing, and upper gastrointestinal series imaging in the same data acquisition. Multi–detector row CT allows noninvasive assessment of the gastric wall and the perigastric extent of disease. It is also helpful in detection and evaluation of gastric malignancies and a variety of inflammatory conditions that affect the stomach. Conventional gastroscopy provides the most useful information about the exact location of the lesion and also allows performance of biopsy. Endoscopic ultrasonography (US) provides the most useful information about horizontal extension of the tumor, the depth of mural invasion, and perigastric lymphadenopathy. However, endoscopic US has not been able to replace CT for tumor staging because of its limitations in demonstrating distant lymphadenopathy or metastatic deposits.

© RSNA, 2006


   Introduction
Top
 Abstract
 Introduction
Imaging Techniques
 Clinical Applications
 Limitations of 2D MPR...
 Conclusions
 References
 
Recent advances in computed tomographic (CT) technology including the introduction of multi–detector row CT and the development of three-dimensional (3D) imaging systems have provided the distinct clinical potential for evaluation of various gastric diseases, particularly for the initial staging of gastric cancer (1–13).

Multi–detector row CT allows thinner collimation, which improves the visualization of subtle tumors as well as the quality of the 3D data sets. In contrast to conventional gastroscopy and upper gastrointestinal series (UGIS) images of the stomach, CT provides information about both the gastric wall and the perigastric extent of disease. Endoscopic ultrasonography (US) provides the most useful information regarding tumor location, horizontal extension of the tumor, the depth of mural invasion, and perigastric lymphadenopathy. Endoscopic US allows reliable distinction between an intramural lesion and extrinsic compression (14–20). In comparison with endoscopic US, multi–detector row CT is able to demonstrate not only the immediate vicinity of the stomach but also more distant regions, such as paraaortic lymphadenopathy and abdominal organs.

Two-dimensional (2D) multiplanar reformation (MPR) and CT gastrography, including virtual gastroscopy and transparency rendering performed with the volume rendering technique, are types of interactive 2D and 3D medical imaging tools that combine the features of multiplanar cross-sectional imaging, gastroscopic viewing, and UGIS images (1–13).

By using multi–detector row CT, 3D imaging of the stomach becomes more practical and useful in the detection and evaluation of gastric malignancies and the variety of benign conditions that affect the stomach (10,11). In this article, we describe the clinical applications of 2D MPR and CT gastrography including virtual gastroscopy and transparency rendering performed with multi–detector row CT for imaging various gastric lesions and compare these techniques with conventional gastroscopy and endoscopic US.


   Imaging Techniques
Top
 Abstract
 Introduction
 Imaging Techniques
Clinical Applications
 Limitations of 2D MPR...
 Conclusions
 References
 
Computed Tomography
At our institution, a dedicated CT study of the stomach is usually ordered if the UGIS or conventional gastroscopy shows pathologic findings such as gastric malignancies. Also, CT gastrography is requested in patients with suspected gastric disease including indigestion, epigastric pain, and esophageal reflux. 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. CT is performed after administration of 6 g of effervescent granules (Taejoon Pharmaceuticals, Kyungkido, South Korea) with a small amount of water by mouth to distend the stomach.

The patient is placed in the prone position. A scanogram is obtained to ensure adequate gastric distention. At our institution, CT is performed on a multi–detector row scanner (Sensation 4; Siemens Medical Systems, Forchheim, Germany). CT parameters include 4 x 2.5-mm section detector collimation, 120 kV, 145 mAs, 1.5-mm reconstruction interval, 3-mm reconstruction thickness, 15 mm/sec table speed, and pitch of 6. Scanning covers the entire stomach region. Before scanning in the supine position, gastric distention is again checked with a second scout image and additional effervescent granules may be given orally if the stomach is not adequately distended.

Scanning in the prone position is performed without intravenous contrast enhancement, whereas scanning in the supine position is performed after intravenous injection of 150 mL of ionic contrast material (iopamidol [Iopamiro 300; Bracco, Milan, Italy] or iopromide [Ultravist 370; Schering, Berlin, Germany]) with an injection rate of 3 mL/sec through an 18-gauge angiographic catheter inserted into an antecubital vein. Some institutions have used less contrast material (120 mL) with a more rapid injection rate (4 mL/sec) than our institution (11). Contrast enhancement facilitates better staging for gastric cancer and better evaluation of other abdominal organs. Scanning in the supine position is performed 70 seconds after initiation of the contrast material injection; this timing corresponds with the portal venous phase.

3D Imaging
The reconstructed image data set is networked to the 3D workstation (Leonardo, Siemens Medical Systems; VoxelPlus 2.0, Mevisys, Daejeon, Korea). The image analysis consists primarily of a review of the 2D axial images. When an abnormality is detected on an axial image, the 2D MPR images are evaluated to verify the lesion found in the axial plane. The images from both the prone and supine data sets are reviewed. After that, CT gastrography is performed by using volume rendering. CT gastrography has two 3D reformation algorithms for volume rendering: one is virtual gastroscopy, and the other is transparency rendering. With the same volumetric data acquisition, a different opacity assignment can create simulated gastroscopic images for virtual gastroscopy and UGIS images for transparency rendering (Fig 1). The attenuation data (opacity mapping) are assigned to create virtual gastroscopic and transparency-rendered images. An opacity of 100% indicates complete opacity and is applied in virtual gastroscopy. An opacity of 30%–50% indicates partial transparency and is applied in transparency rendering.


Figure 1
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  		Figure 1a.  Early gastric cancer (type I). (a) Image from conventional gastroscopy shows a polypoid mass in the lower body of the stomach along the greater curvature. (b) Oblique coronal 2D MPR image shows the uniformly enhanced mass (arrows) in the lower body of the stomach. (c) Image from virtual gastroscopy shows the polypoid mass. The volume rendering technique with an opacity of 100% was applied to create virtual gastroscopic images. These images correspond to conventional gastroscopic images. (d) Transparency-rendered image shows the mass (arrows) in the lower body of the stomach. The volume rendering technique with an opacity of 30%–50% was applied to create transparency-rendered images. These images correspond to double-contrast UGIS images.

 

Figure 1
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  		Figure 1b.  Early gastric cancer (type I). (a) Image from conventional gastroscopy shows a polypoid mass in the lower body of the stomach along the greater curvature. (b) Oblique coronal 2D MPR image shows the uniformly enhanced mass (arrows) in the lower body of the stomach. (c) Image from virtual gastroscopy shows the polypoid mass. The volume rendering technique with an opacity of 100% was applied to create virtual gastroscopic images. These images correspond to conventional gastroscopic images. (d) Transparency-rendered image shows the mass (arrows) in the lower body of the stomach. The volume rendering technique with an opacity of 30%–50% was applied to create transparency-rendered images. These images correspond to double-contrast UGIS images.

 

Figure 1
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  		Figure 1c.  Early gastric cancer (type I). (a) Image from conventional gastroscopy shows a polypoid mass in the lower body of the stomach along the greater curvature. (b) Oblique coronal 2D MPR image shows the uniformly enhanced mass (arrows) in the lower body of the stomach. (c) Image from virtual gastroscopy shows the polypoid mass. The volume rendering technique with an opacity of 100% was applied to create virtual gastroscopic images. These images correspond to conventional gastroscopic images. (d) Transparency-rendered image shows the mass (arrows) in the lower body of the stomach. The volume rendering technique with an opacity of 30%–50% was applied to create transparency-rendered images. These images correspond to double-contrast UGIS images.

 

Figure 1
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  		Figure 1d.  Early gastric cancer (type I). (a) Image from conventional gastroscopy shows a polypoid mass in the lower body of the stomach along the greater curvature. (b) Oblique coronal 2D MPR image shows the uniformly enhanced mass (arrows) in the lower body of the stomach. (c) Image from virtual gastroscopy shows the polypoid mass. The volume rendering technique with an opacity of 100% was applied to create virtual gastroscopic images. These images correspond to conventional gastroscopic images. (d) Transparency-rendered image shows the mass (arrows) in the lower body of the stomach. The volume rendering technique with an opacity of 30%–50% was applied to create transparency-rendered images. These images correspond to double-contrast UGIS images.

 
Conventional Gastroscopy and Endoscopic US
Conventional gastroscopy was performed with the patient in the left lateral position after oropharyngeal anesthesia and intravenous sedation. Conventional gastroscopy was performed with a gastroscope (GIF-Q240Z; Olympus, Tokyo, Japan). The advantages of conventional gastroscopy are the ability to determine the exact location of the lesion, appreciate the gross morphology, and visualize subtle color changes due to inflammation. The potential to perform biopsies of a suspicious lesion is an added advantage of conventional gastroscopy. However, conventional gastroscopy is limited in determining the depth of a lesion and evaluating extragastric lesions.

Endoscopic US was performed in selected patients with gastric pathologic conditions at conventional gastroscopy. Endoscopic US was performed with a combination of conventional gastroscopy and a US device. A 12-mm-wide gastroscope was passed to the region of the pylorus, and the US device at the tip of the gastroscope was used to obtain images. During the examination, the stomach was filled with 200–500 mL of deaerated water to create an acoustic window. Endoscopic US provides useful information regarding the depth of mural invasion, the horizontal extension of the lesion, and perigastric lymphadenopathy. Standard endoscopic US images demonstrate five layers of the gastric wall. These alternating hypoechoic and hyperechoic bands correspond to the following anatomic wall layers: superficial mucosa or interface (hyperechoic), deep mucosa (hypoechoic), submucosa (hyperechoic), muscularis propia (hypoechoic), and serosa or outer interface (hyperechoic) (Fig 2).


Figure 2
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  		Figure 2a.  (a) Endoscopic US image shows the normal appearance of the stomach. (b) Magnified view of a shows the normal gastric wall. A standard endoscopic US image demonstrates five layers of the gastrointestinal wall. The alternating hypoechoic and hyperechoic bands correspond to the following anatomic wall layers: the hyperechoic superficial mucosa or inner interface, hypoechoic deep mucosa (arrows), hyperechoic submucosa, hypoechoic muscularis propria (arrowheads), and hyperechoic serosa or outer interface.

 

Figure 2
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  		Figure 2b.  (a) Endoscopic US image shows the normal appearance of the stomach. (b) Magnified view of a shows the normal gastric wall. A standard endoscopic US image demonstrates five layers of the gastrointestinal wall. The alternating hypoechoic and hyperechoic bands correspond to the following anatomic wall layers: the hyperechoic superficial mucosa or inner interface, hypoechoic deep mucosa (arrows), hyperechoic submucosa, hypoechoic muscularis propria (arrowheads), and hyperechoic serosa or outer interface.

 

   Clinical Applications
Top
 Abstract
 Introduction
 Imaging Techniques
 Clinical Applications
Limitations of 2D MPR...
 Conclusions
 References
 
Suggested Guidelines for Clinical Application of 3D CT Techniques
Two-dimensional MPR and CT gastrography, which includes virtual gastroscopy and transparency rendering, provide multiplanar cross-sectional imaging, gastroscopic viewing, and UGIS imaging in the same data acquisition (Table).


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  		Suggested CT Techniques for Imaging of Gastric Lesions

 
These techniques allow noninvasive assessment of the gastric wall and the extragastric extent of disease. Two-dimensional MPR allows accurate staging of gastric cancer and provides extraluminal information such as the presence of lymphadenopathy and distant metastasis. The ability to visualize an abnormality in multiple planes increases confidence and helps better characterize the lesion. Virtual gastroscopy allows detection of subtle mucosal changes and differentiation of mucosal lesions from submucosal lesions in the same way as conventional gastroscopy. It is difficult to see these findings at axial CT. Virtual gastroscopy is helpful in the detection of early gastric cancer and evaluation of a variety of malignant and benign conditions that affect the stomach. Transparency rendering allows global orientation of the focal findings in the stomach in the same way as UGIS imaging, thereby providing useful anatomic information for a surgeon. It provides useful information for preoperative mapping.

Gastric Adenocarcinoma
Adenocarcinoma is the most common gastric malignancy, representing over 95% of malignant tumors of the stomach. The peak prevalence is between 50 and 70 years of age. Prognosis is correlated to the stage of the tumor at presentation. It is an aggressive tumor with a 5-year survival rate of less than 20%. However, early gastric cancers are curable lesions, with 5-year survival rates of more than 90%. Therefore, early detection and accurate staging of gastric cancer are essential because surgical resection is the treatment of choice 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 (21–25).

Early Gastric Cancer.— Early gastric cancer is defined as a tumor confined to the mucosa and submucosa, regardless of nodal and distant metastases. The macroscopic findings of early gastric cancer are classified according to the system of the Japanese Research Society for Gastric Cancer: type I is a polypoid lesion; type IIa is a superficial elevated lesion; type IIb is a superficial flat lesion; type IIc is a superficial depressed lesion; type III is an excavated lesion; and there is a mixed type (26,27). Gastroscopy has great value for the detection of early gastric cancer. CT has been used for the staging of early gastric cancer, but early gastric cancer is not easy to detect with axial imaging. The rate of detection of early gastric cancer at axial CT is low, between 53% and 65% (21–24).

In early gastric cancer, lesion detection is most important. Gastroscopy and UGIS have been used for the detection of early gastric cancer. Virtual gastroscopy is a useful 3D tool for the detection of early gastric cancer (13,14). Virtual gastroscopy performed with multi–detectorrow CT can contribute to the detection and characterization of early gastric cancer. This technique depicts the tumor mass in the same way as does gastroscopy. Virtual gastroscopy shows clubbing, abrupt cutting, and fusion of the converging folds at the margin of the depressed lesion, as seen at gastroscopy (Fig 3). Virtual gastroscopy may demonstrate subtle mucosal lesions that are difficult to see at axial CT. It is excellent for demonstration of elevated and depressed lesions but poor in demonstration of flat lesions and gastric angle tumors (Fig 4).


Figure 3
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  		Figure 3a.  Early gastric cancer (type II a+c). (a) Image from conventional gastroscopy shows a superficially elevated and depressed lesion in the midbody of the stomach on the greater curvature side. (b) Image from virtual gastroscopy shows the superficially elevated and depressed lesion. (c) Endoscopic US image shows thickening of the gastric mucosa with superficial infiltration of the submucosa (arrows). The central depressed lesion is also evident (arrowhead).

 

Figure 3
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  		Figure 3b.  Early gastric cancer (type II a+c). (a) Image from conventional gastroscopy shows a superficially elevated and depressed lesion in the midbody of the stomach on the greater curvature side. (b) Image from virtual gastroscopy shows the superficially elevated and depressed lesion. (c) Endoscopic US image shows thickening of the gastric mucosa with superficial infiltration of the submucosa (arrows). The central depressed lesion is also evident (arrowhead).

 

Figure 3
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  		Figure 3c.  Early gastric cancer (type II a+c). (a) Image from conventional gastroscopy shows a superficially elevated and depressed lesion in the midbody of the stomach on the greater curvature side. (b) Image from virtual gastroscopy shows the superficially elevated and depressed lesion. (c) Endoscopic US image shows thickening of the gastric mucosa with superficial infiltration of the submucosa (arrows). The central depressed lesion is also evident (arrowhead).

 

Figure 4
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  		Figure 4a.  Early gastric cancer (type IIb). (a) Image from conventional gastroscopy shows a superficial flat lesion (arrows) in the lower body of the stomach on the lesser curvature side. (b) Image from virtual gastroscopy does not show the lesion. The flat nature of the tumor is the reason why it was overlooked at virtual gastroscopy. (c) Endoscopic US image shows mucosal thickening (arrows) in the lower body of the stomach.

 

Figure 4
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  		Figure 4b.  Early gastric cancer (type IIb). (a) Image from conventional gastroscopy shows a superficial flat lesion (arrows) in the lower body of the stomach on the lesser curvature side. (b) Image from virtual gastroscopy does not show the lesion. The flat nature of the tumor is the reason why it was overlooked at virtual gastroscopy. (c) Endoscopic US image shows mucosal thickening (arrows) in the lower body of the stomach.

 

Figure 4
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  		Figure 4c.  Early gastric cancer (type IIb). (a) Image from conventional gastroscopy shows a superficial flat lesion (arrows) in the lower body of the stomach on the lesser curvature side. (b) Image from virtual gastroscopy does not show the lesion. The flat nature of the tumor is the reason why it was overlooked at virtual gastroscopy. (c) Endoscopic US image shows mucosal thickening (arrows) in the lower body of the stomach.

 
Although virtual gastroscopy offered more improved results in the evaluation of early gastric cancer, endoscopic US is now established as the diagnostic modality of choice for the preoperative staging of early gastric cancer. Patients are evaluated with a dedicated miniprobe of 12 or 20 MHz (UM-2R/3R; Olympus). The assessment of tumor infiltration depth is based on the generally accepted five-layered structure of the gastric wall. Endoscopic US plays an important role in treatment decisions by allowing identification of early cancers. Early gastric cancer that does not extend beyond the mucosa has only a 5% risk of metastases to lymph nodes and can be resected at endoscopy. Conversely, early gastric cancer that is confined to the submucosa has a 10%–20% risk of metastases and requires surgery (14,16–18). However, endoscopic US has not been able to replace CT in preoperative staging of early gastric cancer due to its limitation for demonstrating distant lymphadenopathy and metastasis.

Advanced Gastric Cancer.— Advanced gastric cancer is the most common primary malignant gastric tumor. It may be classified according to the Borrmann type: type 1 is an intraluminal protruding mass; type 2 is a mass with a central ulcer; type 3 is an infiltrative tumor mass with a central ulcer; and type 4 is a diffuse infiltrative tumor (26,27). Accurate staging of gastric carcinoma is important because treatment plans depend on the stage of the cancer. Although UGIS and gastroscopy have been used to detect gastric cancer, these modalities have limitations in staging. CT has been used for the staging of gastric carcinoma, but the accuracy of CT staging has not been satisfactory. In general, the reported accuracy of CT staging in gastric carcinoma has been about 53%–70% (21–24).

The use of 2D MPR and CT gastrography is a promising method in the preoperative evaluation of gastric cancer. Two-dimensional MPR is expected to improve staging of advanced gastric cancer and provide extraluminal information such as the presence of lymphadenopathy and distant metastasis (13,14). The ability to visualize an abnormality in multiple planes increases confidence. It is often difficult to distinguish adjacent organ invasion or lymphadenopathy on axial CT scans. Coronal or sagittal reformatted images are best suited for the evaluation of adjacent organ invasion or lymphadenopathy. Virtual gastroscopy depicts the tumor in the same way as does gastroscopy (Fig 5). Virtual gastroscopy has a wider field of view than conventional gastroscopy, and the angle of the virtual camera can be adjusted omnidirectionally. Transparency rendering is useful for preoperative mapping. It corresponds to UGIS imaging. These images can be extremely helpful in providing global orientation for the focal findings in the stomach, thereby providing useful anatomic information for a surgeon (Fig 6).


Figure 5
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  		Figure 5a.  Advanced gastric cancer (Borrmann type 2). (a) Image from conventional gastroscopy shows a mass with a central ulcer in the gastric antrum. (b) Oblique coronal 2D MPR image shows the enhanced mass in the antrum with adjacent gastric wall thickening (arrows). (c) Image from virtual gastroscopy shows the mass with a central ulcer. (d) Transparency-rendered image shows the well-defined mass (arrows) with a central ulcer in the antrum. (e) Endoscopic US image shows thickening of the entire gastric wall (arrows) with serosal interruption.

 

Figure 5
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  		Figure 5b.  Advanced gastric cancer (Borrmann type 2). (a) Image from conventional gastroscopy shows a mass with a central ulcer in the gastric antrum. (b) Oblique coronal 2D MPR image shows the enhanced mass in the antrum with adjacent gastric wall thickening (arrows). (c) Image from virtual gastroscopy shows the mass with a central ulcer. (d) Transparency-rendered image shows the well-defined mass (arrows) with a central ulcer in the antrum. (e) Endoscopic US image shows thickening of the entire gastric wall (arrows) with serosal interruption.

 

Figure 5
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  		Figure 5c.  Advanced gastric cancer (Borrmann type 2). (a) Image from conventional gastroscopy shows a mass with a central ulcer in the gastric antrum. (b) Oblique coronal 2D MPR image shows the enhanced mass in the antrum with adjacent gastric wall thickening (arrows). (c) Image from virtual gastroscopy shows the mass with a central ulcer. (d) Transparency-rendered image shows the well-defined mass (arrows) with a central ulcer in the antrum. (e) Endoscopic US image shows thickening of the entire gastric wall (arrows) with serosal interruption.

 

Figure 5
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  		Figure 5d.  Advanced gastric cancer (Borrmann type 2). (a) Image from conventional gastroscopy shows a mass with a central ulcer in the gastric antrum. (b) Oblique coronal 2D MPR image shows the enhanced mass in the antrum with adjacent gastric wall thickening (arrows). (c) Image from virtual gastroscopy shows the mass with a central ulcer. (d) Transparency-rendered image shows the well-defined mass (arrows) with a central ulcer in the antrum. (e) Endoscopic US image shows thickening of the entire gastric wall (arrows) with serosal interruption.

 

Figure 5
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  		Figure 5e.  Advanced gastric cancer (Borrmann type 2). (a) Image from conventional gastroscopy shows a mass with a central ulcer in the gastric antrum. (b) Oblique coronal 2D MPR image shows the enhanced mass in the antrum with adjacent gastric wall thickening (arrows). (c) Image from virtual gastroscopy shows the mass with a central ulcer. (d) Transparency-rendered image shows the well-defined mass (arrows) with a central ulcer in the antrum. (e) Endoscopic US image shows thickening of the entire gastric wall (arrows) with serosal interruption.

 

Figure 6
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  		Figure 6a.  Advanced gastric cancer (Borrmann type 3). (a) Image from conventional gastroscopy shows an ulcerated and infiltrative lesion at the gastric angle. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (b) Oblique coronal 2D MPR image shows an area of enhanced wall thickening (arrows) at the gastric angle. (c) Image from virtual gastroscopy shows the irregularly marginated mass (arrows) with a central ulcer. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (d) Transparency-rendered image shows the mass (arrows) with luminal narrowing of the gastric angle. Transparency rendering provides excellent anatomic information for the surgeon. (e) Endoscopic US image shows the gastric wall thickening (arrows) without serosal interruption.

 

Figure 6
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  		Figure 6b.  Advanced gastric cancer (Borrmann type 3). (a) Image from conventional gastroscopy shows an ulcerated and infiltrative lesion at the gastric angle. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (b) Oblique coronal 2D MPR image shows an area of enhanced wall thickening (arrows) at the gastric angle. (c) Image from virtual gastroscopy shows the irregularly marginated mass (arrows) with a central ulcer. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (d) Transparency-rendered image shows the mass (arrows) with luminal narrowing of the gastric angle. Transparency rendering provides excellent anatomic information for the surgeon. (e) Endoscopic US image shows the gastric wall thickening (arrows) without serosal interruption.

 

Figure 6
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  		Figure 6c.  Advanced gastric cancer (Borrmann type 3). (a) Image from conventional gastroscopy shows an ulcerated and infiltrative lesion at the gastric angle. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (b) Oblique coronal 2D MPR image shows an area of enhanced wall thickening (arrows) at the gastric angle. (c) Image from virtual gastroscopy shows the irregularly marginated mass (arrows) with a central ulcer. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (d) Transparency-rendered image shows the mass (arrows) with luminal narrowing of the gastric angle. Transparency rendering provides excellent anatomic information for the surgeon. (e) Endoscopic US image shows the gastric wall thickening (arrows) without serosal interruption.

 

Figure 6
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  		Figure 6d.  Advanced gastric cancer (Borrmann type 3). (a) Image from conventional gastroscopy shows an ulcerated and infiltrative lesion at the gastric angle. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (b) Oblique coronal 2D MPR image shows an area of enhanced wall thickening (arrows) at the gastric angle. (c) Image from virtual gastroscopy shows the irregularly marginated mass (arrows) with a central ulcer. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (d) Transparency-rendered image shows the mass (arrows) with luminal narrowing of the gastric angle. Transparency rendering provides excellent anatomic information for the surgeon. (e) Endoscopic US image shows the gastric wall thickening (arrows) without serosal interruption.

 

Figure 6
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  		Figure 6e.  Advanced gastric cancer (Borrmann type 3). (a) Image from conventional gastroscopy shows an ulcerated and infiltrative lesion at the gastric angle. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (b) Oblique coronal 2D MPR image shows an area of enhanced wall thickening (arrows) at the gastric angle. (c) Image from virtual gastroscopy shows the irregularly marginated mass (arrows) with a central ulcer. Clubbing and fusion of the converging folds are seen at the margin of the ulcer. (d) Transparency-rendered image shows the mass (arrows) with luminal narrowing of the gastric angle. Transparency rendering provides excellent anatomic information for the surgeon. (e) Endoscopic US image shows the gastric wall thickening (arrows) without serosal interruption.

 
Endoscopic US is now established as the diagnostic modality of choice for the preoperative staging of gastric cancer. Endoscopic US helps to determine resectability and prognosis. Patients with advanced gastric cancer are evaluated with a radial scanner (GF-UMQ 200; Olympus) with variable frequencies of 7.5 and 20 MHz. The assessment of tumor infiltration depth is based on the generally accepted five-layered structure of the gastric wall. With infiltration by the tumor, the normal layers of the gastric wall are distorted (17,18). However, endoscopic US has not been able to replace CT in preoperative staging of gastric cancer due to its limitation for demonstrating distant lymphadenopathy and metastasis.

Submucosal Lesions
Submucosal lesions that arise from mesenchymal cells are located in the wall of the gastrointestinal tract. CT gastrography allows differentiation of mucosal frrom submucosal lesions, as do gastroscopy and UGIS. Submucosal lesions can have a well-defined mass with overlying normal mucosa or can have mucosal ulceration (28–30). Endoscopic US allows reliable distinction between an intramural lesion and extrinsic compression. Cystic, solid, and vascular lesions can be differentiated. The layer of origin can be determined (15,16). However, endoscopic US has not been able to replace CT due to its limitation for the evaluation of distant lymphadenopathy and other abdominal organs.

Gastrointestinal Stromal Tumor.— GIST is an uncommon neoplasm that arises from mesenchymal cells in the wall of the gastrointestinal tract. GISTs are most frequently found in the stomach (60%–70%); they account for 2%–3% of all gastric tumors. Recently, the interstitial cell of Cajal, expressing the tyrosine kinase receptor KIT, has been proposed as the progenitor cell of GIST. The immunoreactivity for KIT (CD117) has differentiated GISTs from true leiomyomas, leiomyosarcomas, neurofibromas, and schwannomas. Eighty percent of stromal cell tumors are benign, and 20% are malignant. The lesion can be enucleated, locally excised, or removed by partial gastrectomy, depending on its size. Anatomic site, size, and mitotic rate were recently suggested as criteria for the prediction of GIST malignancy (28,29).

CT is useful in the detection of GIST. Small tumors appear as intramural masses. As the tumors grow, they stretch the overlying mucosa and can ulcerate. CT findings of GISTs that are suggestive of malignancy include large tumor size, an exophytic mass, and a mass containing areas of central necrosis or calcification. When tumors are large and exophytic, it may be difficult to determine their site of origin. Associated lymphadenopathy is uncommon (29,30).

CT gastrography performed with multi–detector row CT can be helpful in better characterizing the mass and determining its origin. Two-dimensional MPR is particularly useful for the evaluation of exophytic growth patterns, lymphadenopathy, and distant organ metastasis. Most GISTs appear as smooth well-defined submucosal masses. Virtual gastroscopy allows clear visualization of smooth well-defined masses with a central ulcer, right angles or slightly obtuse angles with the adjacent wall, and the bridging folds at the margin of the mass. Transparency rendering is useful for preoperative mapping and provides global orientation of the submucosal mass in the stomach, thereby providing useful anatomic information for a surgeon (Fig 7).


Figure 7
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  		Figure 7a.  Gastric GIST. (a) Image from conventional gastroscopy shows a smooth well-defined mass in the lower body of the stomach. There is a normal overlying mucosal fold. (b) Oblique coronal 2D MPR image shows the well-defined mass (arrows). (c) Image from virtual gastroscopy shows the smooth well-defined mass (arrows) and the normal overlying mucosal fold. (d) Transparency-rendered image shows the smooth well-defined submucosal mass and the bridging fold (arrows). (e) Endoscopic US image shows the well-defined hypoechoic mass in the submucosa.

 

Figure 7
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  		Figure 7b.  Gastric GIST. (a) Image from conventional gastroscopy shows a smooth well-defined mass in the lower body of the stomach. There is a normal overlying mucosal fold. (b) Oblique coronal 2D MPR image shows the well-defined mass (arrows). (c) Image from virtual gastroscopy shows the smooth well-defined mass (arrows) and the normal overlying mucosal fold. (d) Transparency-rendered image shows the smooth well-defined submucosal mass and the bridging fold (arrows). (e) Endoscopic US image shows the well-defined hypoechoic mass in the submucosa.

 

Figure 7
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  		Figure 7c.  Gastric GIST. (a) Image from conventional gastroscopy shows a smooth well-defined mass in the lower body of the stomach. There is a normal overlying mucosal fold. (b) Oblique coronal 2D MPR image shows the well-defined mass (arrows). (c) Image from virtual gastroscopy shows the smooth well-defined mass (arrows) and the normal overlying mucosal fold. (d) Transparency-rendered image shows the smooth well-defined submucosal mass and the bridging fold (arrows). (e) Endoscopic US image shows the well-defined hypoechoic mass in the submucosa.

 

Figure 7
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  		Figure 7d.  Gastric GIST. (a) Image from conventional gastroscopy shows a smooth well-defined mass in the lower body of the stomach. There is a normal overlying mucosal fold. (b) Oblique coronal 2D MPR image shows the well-defined mass (arrows). (c) Image from virtual gastroscopy shows the smooth well-defined mass (arrows) and the normal overlying mucosal fold. (d) Transparency-rendered image shows the smooth well-defined submucosal mass and the bridging fold (arrows). (e) Endoscopic US image shows the well-defined hypoechoic mass in the submucosa.

 

Figure 7
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  		Figure 7e.  Gastric GIST. (a) Image from conventional gastroscopy shows a smooth well-defined mass in the lower body of the stomach. There is a normal overlying mucosal fold. (b) Oblique coronal 2D MPR image shows the well-defined mass (arrows). (c) Image from virtual gastroscopy shows the smooth well-defined mass (arrows) and the normal overlying mucosal fold. (d) Transparency-rendered image shows the smooth well-defined submucosal mass and the bridging fold (arrows). (e) Endoscopic US image shows the well-defined hypoechoic mass in the submucosa.

 
Endoscopic US can demonstrate the layer of origin of a submucosal tumor. The submucosal tumor can be enucleated, locally excised, or removed by partial gastrectomy, depending on its size and origin. Endoscopic US findings of GIST that are suggestive of malignancy include large tumor size, irregular border, echogenic foci, and cystic spaces (15,16).

Gastric Lymphoma.— The stomach is the most frequent site of gastrointestinal tract involvement by non-Hodgkin lymphoma. Gastric lymphomas may appear as infiltrating, polypoid, nodular, or ulcerative lesions (31). If the lesion is confined to the stomach, gastric resection is the treatment of choice. Mucosa-associated lymphoid tissue (MALT) lymphoma is a low-grade lymphoma. It is thought to be associated with Helicobacter pylori (32,33).

CT is the primary imaging modality for pre-treatment evaluation of abdominal lymphoma. At CT, gastric lymphoma typically appears as segmental or diffuse wall thickening. The lesions are often indistinguishable from adenocarcinomas. Severe gastric wall thickening, more than one lesion, infrequent gastric outlet obstruction, and lymphadenopathy that extends below the renal hilum favor gastric lymphoma over adenocarcinoma as a diagnosis (34). However, CT is of limited value in diagnosing a low-grade MALT lesion if only a shallow lesion with minimal gastric wall thickening is present.

In patients with suspected gastric lymphoma, 2D MPR and CT gastrography may allow both depiction of a stomach lesion and staging of generalized lymphoma in the abdomen. 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. We have found CT gastrography to be helpful, especially in subtle lesions or complicated cases. Two-dimensional MPR and CT gastrography provide clear visualization of the gross morphology of a gastric lymphoma, including change in the gastric lumen, the gastric wall, and perigastric lymphadenopathy. Virtual gastroscopy allows better evaluation of the mucosal changes. Virtual gastroscopy demonstrates mucosal nodularity, a shallow or deep ulcer, single or multiple masses, rugal thickening, and enlarged areae gastricae (Fig 8). Furthermore, 2D MPR and CT gastrography may aid in early diagnosis of disease progression in patients undergoing therapy and follow-up for low-grade MALT lymphoma.


Figure 8
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  		Figure 8a.  Gastric lymphoma. (a) Image from conventional gastroscopy shows severe fold thickening from the fundus to the body of the stomach. (b) Oblique axial 2D MPR image shows the gastric wall thickening (arrows). There are multiple enlarged lymph nodes in the perigastric area. (c) Image from virtual gastroscopy shows the fold thickening. (d) Transparency-rendered image shows the severe fold thickening without luminal narrowing from the gastric fundus to the body. (e) Endoscopic US image shows a polypoid mass in the submucosa without interruption of the hypoechoic muscularis propria (arrowheads).

 

Figure 8
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  		Figure 8b.  Gastric lymphoma. (a) Image from conventional gastroscopy shows severe fold thickening from the fundus to the body of the stomach. (b) Oblique axial 2D MPR image shows the gastric wall thickening (arrows). There are multiple enlarged lymph nodes in the perigastric area. (c) Image from virtual gastroscopy shows the fold thickening. (d) Transparency-rendered image shows the severe fold thickening without luminal narrowing from the gastric fundus to the body. (e) Endoscopic US image shows a polypoid mass in the submucosa without interruption of the hypoechoic muscularis propria (arrowheads).

 

Figure 8
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  		Figure 8c.  Gastric lymphoma. (a) Image from conventional gastroscopy shows severe fold thickening from the fundus to the body of the stomach. (b) Oblique axial 2D MPR image shows the gastric wall thickening (arrows). There are multiple enlarged lymph nodes in the perigastric area. (c) Image from virtual gastroscopy shows the fold thickening. (d) Transparency-rendered image shows the severe fold thickening without luminal narrowing from the gastric fundus to the body. (e) Endoscopic US image shows a polypoid mass in the submucosa without interruption of the hypoechoic muscularis propria (arrowheads).

 

Figure 8
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  		Figure 8d.  Gastric lymphoma. (a) Image from conventional gastroscopy shows severe fold thickening from the fundus to the body of the stomach. (b) Oblique axial 2D MPR image shows the gastric wall thickening (arrows). There are multiple enlarged lymph nodes in the perigastric area. (c) Image from virtual gastroscopy shows the fold thickening. (d) Transparency-rendered image shows the severe fold thickening without luminal narrowing from the gastric fundus to the body. (e) Endoscopic US image shows a polypoid mass in the submucosa without interruption of the hypoechoic muscularis propria (arrowheads).

 

Figure 8
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  		Figure 8e.  Gastric lymphoma. (a) Image from conventional gastroscopy shows severe fold thickening from the fundus to the body of the stomach. (b) Oblique axial 2D MPR image shows the gastric wall thickening (arrows). There are multiple enlarged lymph nodes in the perigastric area. (c) Image from virtual gastroscopy shows the fold thickening. (d) Transparency-rendered image shows the severe fold thickening without luminal narrowing from the gastric fundus to the body. (e) Endoscopic US image shows a polypoid mass in the submucosa without interruption of the hypoechoic muscularis propria (arrowheads).

 
The role of endoscopic US in gastric lymphoma is for more accurate local tumor staging. Endoscopic US also has a role in evaluating MALT lymphoma. It helps determine the horizontal extension of the tumor, the depth of mural invasion, and the invasion of perigastric lymph nodes (Fig 9). After successful eradication of H pylori, about 60%–75% of these low-grade lymphomas regress. Regression is recognized as normalization of wall thickness at endoscopic US (17,18).


Figure 9
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  		Figure 9a.  Gastric MALT lymphoma. (a) Image from conventional gastroscopy shows multiple small nodular lesions along the greater curvature of the gastric body. (b) Image from virtual gastroscopy shows the multiple small nodular lesions. (c) Endoscopic US image shows gastric mucosal thickening (arrows) with superficial infiltration of the submucosa.

 

Figure 9
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  		Figure 9b.  Gastric MALT lymphoma. (a) Image from conventional gastroscopy shows multiple small nodular lesions along the greater curvature of the gastric body. (b) Image from virtual gastroscopy shows the multiple small nodular lesions. (c) Endoscopic US image shows gastric mucosal thickening (arrows) with superficial infiltration of the submucosa.

 

Figure 9
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  		Figure 9c.  Gastric MALT lymphoma. (a) Image from conventional gastroscopy shows multiple small nodular lesions along the greater curvature of the gastric body. (b) Image from virtual gastroscopy shows the multiple small nodular lesions. (c) Endoscopic US image shows gastric mucosal thickening (arrows) with superficial infiltration of the submucosa.

 
Gastric Varices.— The identification of gastric wall varices is important because the varices should not be mistaken for something else such as a polyp and thickened folds. In addition, the varices are present because of some other important pathologic state including portal hypertension and splenic vein occlusion. Gastric varices show thickened, tortuous folds or lobulated filling defects in the gastric fundus, resembling grapes (35,36). CT is valuable for the detection of gastric varices and identification of the underlying cause. Gastric varices appear as enhancing tubular vessels, located primarily along the body and fundus of the stomach. Because they are veins, they will enhance during the portal venous phase. Gastric varices can be mistaken for gastric wall thickening, gastric cancer, or perigastric lymphadenopathy if intravenous contrast material is not administered.

Two-dimensional MPR and CT gastrography allow clear visualization of the gastric varices. Two-dimensional MPR with contrast enhancement provides confirmation of the origin of the varices by demonstrating such conditions as hepatic cirrhosis, pancreatitis, and pancreatic carcinoma. It provides information about both gastric varices and their relationship to the portal venous system; this is important information for treatment (Fig 10). Virtual gastroscopy shows thickened, tortuous folds or a smooth well-defined nodule in the gastric fundus. Gastric varices can mimic thickened gastric folds at endoscopy. Endoscopic US demonstrates these vascular structures well and helps avoid iatrogenic variceal bleeding induced by endoscopic biopsy. Gastric varices are usually visualized in the submucosal layer as anechoic structures.


Figure 10
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  		Figure 10a.  Gastric varices due to portal hypertension. (a) Image from conventional gastroscopy shows tortuous folds and multiple grapelike nodules in the gastric fundus. (b) Oblique coronal 2D MPR image shows tortuous well-enhanced vascular structures (arrows) in the perigastric area along the fundus. (c) Image from virtual gastroscopy shows the tortuous folds.

 

Figure 10
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  		Figure 10b.  Gastric varices due to portal hypertension. (a) Image from conventional gastroscopy shows tortuous folds and multiple grapelike nodules in the gastric fundus. (b) Oblique coronal 2D MPR image shows tortuous well-enhanced vascular structures (arrows) in the perigastric area along the fundus. (c) Image from virtual gastroscopy shows the tortuous folds.

 

Figure 10
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  		Figure 10c.  Gastric varices due to portal hypertension. (a) Image from conventional gastroscopy shows tortuous folds and multiple grapelike nodules in the gastric fundus. (b) Oblique coronal 2D MPR image shows tortuous well-enhanced vascular structures (arrows) in the perigastric area along the fundus. (c) Image from virtual gastroscopy shows the tortuous folds.

 
Heterotopic Pancreas.— Heterotopic pancreas is defined as pancreatic tissue that lacks anatomic and vascular continuity with the main body of the pancreas. However, the heterotopic pancreatic tissue may have all of the elements of the normal pancreas, which include pancreatic acini, pancreatic ducts, and islets of Langerhans at histologic examination. It is found in 1%–2% of autopsies. The gross appearance of heterotopic pancreas in the stomach is usually a firm, yellow, finely lobulated nodule, which is usually located in the sub-mucosa but sometimes extends into the muscularis or serosa (37,38).

Most of the lesions are identified at CT as oval or round masses in the gastric wall that are similar to other submucosal lesions. Two-dimensional MPR and CT gastrography allow clear visualization of the heterotopic pancreas. Virtual gastroscopy shows a small, broad-based, usually round or oval, submucosal mass in the antrum, with a central umbilication that represents a rudimentary pancreatic duct (Fig 11). The mass is usually 1–3 cm in diameter and located along the greater curvature of the stomach, often in the gastric antrum within 6 cm of the pyloric canal (37).


Figure 11
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  		Figure 11a.  Heterotopic pancreas. (a) Image from conventional gastroscopy shows a smooth, broad-based submucosal mass with a central umbilication (arrow) in the gastric antrum. (b) Image from virtual gastroscopy shows the mass with its central umbilication (arrow). (c) Endoscopic US image shows submucosal thickening with a central duct (arrow).

 

Figure 11
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  		Figure 11b.  Heterotopic pancreas. (a) Image from conventional gastroscopy shows a smooth, broad-based submucosal mass with a central umbilication (arrow) in the gastric antrum. (b) Image from virtual gastroscopy shows the mass with its central umbilication (arrow). (c) Endoscopic US image shows submucosal thickening with a central duct (arrow).

 

Figure 11
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  		Figure 11c.  Heterotopic pancreas. (a) Image from conventional gastroscopy shows a smooth, broad-based submucosal mass with a central umbilication (arrow) in the gastric antrum. (b) Image from virtual gastroscopy shows the mass with its central umbilication (arrow). (c) Endoscopic US image shows submucosal thickening with a central duct (arrow).

 
Endoscopic US provides the most useful information regarding lesion location within the gastric wall and helps distinguish it from other submucosal lesions. The characteristic endoscopic US features of heterotopic pancreas are indistinct margins, heterogeneous appearance, and location either in the submucosa and muscularis propria or only in the submucosa. The lesions are mostly accompanied by an anechoic area and muscularis propria thickening. These features correlate closely with the histologic findings and are potentially useful in the preoperative diagnosis of heterotopic pancreas (38).

Extrinsic Compression of the Stomach
Extrinsic compression of the stomach is occasionally found during endoscopic examination. It is found in 37 of 6604 gastroduodenoscopy examinations (39). It is caused by adjacent normal viscera such as the spleen, liver, gallbladder, kidney, and aorta or abnormal lesions such as lymphadenopathy, pancreatic pseudocyst, and malignant tumor in adjacent organs. Two-dimensional MPR and CT gastrography provide clear visualization of the stomach and extragastric lesions. Two-dimensional MPR with contrast enhancement allows confirmation of the cause of the extrinsic compression. It provides information about both extragastric lesions and their relationship to the gastric wall (Fig 12). Endoscopic US allows identification and characterization of extrinsic compression of the stomach.


Figure 12
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  		Figure 12a.  Pancreatic mucinous cystic adenocarcinoma with gastric invasion. (a) Image from conventional gastroscopy shows a smooth masslike lesion in the gastric body. The lesion has the appearance of a normal mucosal fold. (b) Oblique coronal 2D MPR image shows a large pancreatic cystic mass with invasion of the gastric body (arrows). Splenic infarction is also noted (arrowheads). (c) Image from virtual gastroscopy shows the smooth masslike lesion of the gastric body. (d) Transparency-rendered image shows indentation of the gastric body (arrows).

 

Figure 12
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  		Figure 12b.  Pancreatic mucinous cystic adenocarcinoma with gastric invasion. (a) Image from conventional gastroscopy shows a smooth masslike lesion in the gastric body. The lesion has the appearance of a normal mucosal fold. (b) Oblique coronal 2D MPR image shows a large pancreatic cystic mass with invasion of the gastric body (arrows). Splenic infarction is also noted (arrowheads). (c) Image from virtual gastroscopy shows the smooth masslike lesion of the gastric body. (d) Transparency-rendered image shows indentation of the gastric body (arrows).

 

Figure 12
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  		Figure 12c.  Pancreatic mucinous cystic adenocarcinoma with gastric invasion. (a) Image from conventional gastroscopy shows a smooth masslike lesion in the gastric body. The lesion has the appearance of a normal mucosal fold. (b) Oblique coronal 2D MPR image shows a large pancreatic cystic mass with invasion of the gastric body (arrows). Splenic infarction is also noted (arrowheads). (c) Image from virtual gastroscopy shows the smooth masslike lesion of the gastric body. (d) Transparency-rendered image shows indentation of the gastric body (arrows).

 

Figure 12
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  		Figure 12d.  Pancreatic mucinous cystic adenocarcinoma with gastric invasion. (a) Image from conventional gastroscopy shows a smooth masslike lesion in the gastric body. The lesion has the appearance of a normal mucosal fold. (b) Oblique coronal 2D MPR image shows a large pancreatic cystic mass with invasion of the gastric body (arrows). Splenic infarction is also noted (arrowheads). (c) Image from virtual gastroscopy shows the smooth masslike lesion of the gastric body. (d) Transparency-rendered image shows indentation of the gastric body (arrows).

 
Achalasia
Achalasia is a well-known esophageal motility disorder characterized by absent primary peristalsis and incomplete relaxation of the lower esophageal sphincter. Most patients have primary achalasia caused by loss of the ganglion cells in the esophageal myenteric plexuses. However, others have secondary achalasia caused by mediastinal tumors (malignant tumor at the gastroesophageal junction) (40). Two-dimensional MPR can be useful in better characterizing the cause of achalasia. It is possible to distinguish primary from secondary achalasia. Primary achalasia demonstrates little or no esophageal wall thickening, no evidence of a mass, and smoothly tapered narrowing of the distal esophagus (Fig 13). Secondary achalasia appears as asymmetric thickening of the distal esophageal wall, a soft-tissue mass at the cardia, or lymphadenopathy. Two-dimensional MPR may also be helpful for identifying the site of the primary tumor in patients with secondary achalasia caused by remote tumors. In some cases, however, it may reveal a pseudomass at the cardia in patients without tumor because of inadequate distention of this region.


Figure 13
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  		Figure 13.  Primary achalasia. Oblique coronal 2D MPR image shows smooth, tapered, beaklike luminal narrowing of the distal esophagus (arrows).

 
Hiatal Hernia
Hiatal hernias are classified as sliding hiatal hernia, paraesophageal hernia, and mixed paraesophageal hernia. Sliding hiatal hernia is the most common type. In sliding hiatal hernia, the gastroesophageal junction is displaced superior to the hiatus. It is commonly associated with gastroesophageal reflux disease. In paraesophageal hernia, the gastroesophageal junction is inferior to the diaphragm, but the fundus and sometimes the whole stomach have migrated alongside the esophagus into the mediastinum. In mixed para-esophageal hernia, the gastroesophageal junction and a large part of the stomach have migrated into the mediastinum. Paraesophageal hernia is considered to be a potentially life-threatening condition because of the risk of volvulus, incarceration, or strangulation of the hernia (41).

Two-dimensional MPR can allow accurate identification of hiatal hernia and its complications (Fig 14). It is possible to achieve accurate classification of hiatal hernias. In paraesophageal hernia, 2D MPR is useful for detection of complications such as volvulus, incarceration, or strangulation of the hernia.


Figure 14
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  		Figure 14.  Paraesophageal hernia. Oblique coronal 2D MPR image shows that the gastric fundus has herniated through the esophageal hiatus (arrows).

 

   Limitations of 2D MPR and CT Gastrography
Top
 Abstract
 Introduction
 Imaging Techniques
 Clinical Applications
 Limitations of 2D MPR...
Conclusions
 References
 
Two-dimensional MPR, CT gastrography, and endoscopic US have some limitations. There is a significant learning curve before one becomes proficient in the use of these tools. The main disadvantage of 2D MPR and CT gastrography is that they are time-consuming. Although greater computer processing power makes faster CT gastrography available, it requires approximately 20–30 minutes per patient. With increased data volume, the results require a longer time to interpret. A second limitation is the inability to obtain histologic results. If a lesion is detected at CT gastrography, gastroscopic biopsy is necessary to confirm it. A third limitation is the difficulty of detecting flat or small lesions. Conventional gastroscopy more easily demonstrates these lesions by means of color changes.

A fourth limitation is patient exposure to substantial doses of ionizing radiation. In our studies, we used 145 mAs. The effective doses from our studies currently range between 6.2 and 7 mSv. The mean effective dose from the standard UGIS examination is about 10.2 mSv (42). The effective dose in our studies is lower than the dose for a standard UGIS. If we use low-dose CT gastrography, the effective dose is further decreased.


   Conclusions
Top
 Abstract
 Introduction
 Imaging Techniques
 Clinical Applications
 Limitations of 2D MPR...
 Conclusions
References
 
Recent advances in CT technology, 3D imaging software, and cheaper data storage capacity have made faster, simpler, and more accurate gastric imaging available. Two-dimensional MPR and CT gastrography, including virtual gastroscopy and transparency rendering, provide multiplane cross-sectional imaging, gastroscopic viewing, and UGIS imaging in the same data acquisition. They are also helpful in the detection and evaluation of gastric malignancies and a variety of inflammatory conditions that affect the stomach.

Two-dimensional MPR provides accurate staging of gastric cancer and extraluminal information such as the presence of lymphadenopathy and distant metastasis. The ability to visualize an abnormality in multiple planes increases confidence and helps better characterize the lesion. In many cases, abdominal disease is better shown in multiple planes other than the axial plane. Endoscopic US plays an important role in evaluating depth of tumor invasion and perigastric lymphadenopathy. Endoscopic US also allows differentiation of mucosal from submucosal lesions and intramural lesion from extrinsic compression. The main disadvantage of endoscopic US is that it is operator dependent. In the evaluation of gastric cancer, multiple views must be obtained. Endoscopic US also has limitations for the evaluation of distant lymphadenopathy and metastasis.

Virtual gastroscopy allows detection of subtle mucosal changes and differentiation of mucosal lesions from submucosal lesions in the same way as gastroscopy. It provides additional information for evaluation of mucosal detail in the stomach. Virtual gastroscopy has several advantages over gastroscopy: It has a wider field of view than conventional gastroscopy, the angle of the virtual camera can be adjusted omnidirectionally, and it has no blind point because retrospective reformation is available. Transparency rendering provides global orientation of the focal findings in the stomach in the same way as UGIS imaging. The referring physicians especially appreciate this orientation because it provides useful information for preoperative mapping.

Thus, CT gastrography is a promising method for evaluating gastric lesions despite its limitations. We believe that 2D MPR and CT gastrography, including virtual gastroscopy and transparency rendering, can provide the comprehensive information from a single data acquisition for various gastric diseases, which otherwise would be obtained only by performing four different examinations including gastroscopy, UGIS, endoscopic US, and CT; however, further studies are required to prove the accuracy, efficacy, and cost-effectiveness of virtual gastroscopy.


   Footnotes
 

Abbreviations: GIST = gastrointestinal stromal tumor, MALT = mucosa-associated lymphoid tissue, MPR = multiplanar reformation, 3D = three-dimensional, 2D = two-dimensional, UGIS = upper gastrointestinal series

See the commentary by Bhalla following this article.


   References
Top
 Abstract
 Introduction
 Imaging Techniques
 Clinical Applications
 Limitations of 2D MPR...
 Conclusions
 References
 

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