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Published online before print July 14, 2005, 10.1148/radiol.2363041101
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(Radiology 2005;236:879-885.)
© RSNA, 2005

Gastrointestinal Imaging

Gastric Cancer Staging at Multi–Detector Row CT Gastrography: Comparison of Transverse and Volumetric CT Scanning1

Hye Jin Kim, MD, Ah Young Kim, MD, Seong Tae Oh, MD, Jung-Sun Kim, MD, Kyoung Won Kim, MD, Pyo Nyun Kim, MD, Moon-Gue Lee, MD and Hyun Kwon Ha, MD

1 From the Departments of Radiology (H.J.K., A.Y.K., K.W.K., P.N.K., M.G.L., H.K.H.), Surgery (S.T.O.), and Pathology (J.S.K.), Asan Medical Center, University of Ulsan College of Medicine, 388-1, Poongnap-dong, Songpa-ku, Seoul 138-736, Korea. From the 2003 RSNA Annual Meeting. Received June 22, 2004; revision requested September 1; revision received October 18; accepted January 21, 2005. Address correspondence to A.Y.K. (e-mail: aykim{at}amc.seoul.kr).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY
 References
 
PURPOSE: To prospectively evaluate the accuracy of multi–detector row computed tomography (CT) gastrography for preoperative staging of gastric cancer, with pathologic and surgical results as the reference standard.

MATERIALS AND METHODS: This study was approved by the institutional review board, and patients gave written informed consent. One hundred six patients (72 male, 34 female; mean age, 56 years) with endoscopically proved gastric cancer underwent unenhanced and contrast material–enhanced multi–detector row CT gastrography, with effervescent granules used as oral contrast material. Two experienced radiologists independently evaluated the depth of tumor invasion into the gastric wall (tumor staging), the involvement of regional lymph nodes (nodal staging), and the presence or absence of metastasis (metastatic staging) on transverse and volumetric CT images, which included images produced with multiplanar reformation and a virtual endoscopic technique. TNM staging of each tumor was compared with the pathologic and surgical results. Diagnostic accuracy in TNM staging was analyzed.

RESULTS: Gastric cancer was detected in 92 (87%) of 106 study patients with transverse CT imaging and in 104 (98%) with volumetric CT imaging. The overall accuracy of the tumor staging was 77% with transverse CT imaging and 84% with volumetric CT imaging (P < .001). The overall accuracy for lymph node staging was 62% with transverse CT imaging and 64% with volumetric CT imaging (P = .057). For staging of metastases, there was no difference between transverse and volumetric CT imaging (86% for both) (P > .99).

CONCLUSION: Multi–detector row CT gastrography with multiplanar reformation and virtual endoscopy, compared with transverse CT imaging, can improve the accuracy of preoperative staging of gastric cancer. This difference was significant for tumor staging but not for the staging of lymph nodes and metastases.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY
 References
 
Gastric cancer is one of the most frequent causes of cancer-related deaths in East Asia (1,2). With this circumstance, the early detection and accurate preoperative staging of gastric cancer is critical. Although clinically important advances in diagnosis, such as endoscopy and double-contrast barium swallow studies, allow the detection of small lesions early in the course of the disease, the depth of tumor invasion and the presence or absence of metastasis cannot be determined with these modalities. Therefore, the preoperative staging work-up of patients with gastric cancer is performed mainly with computed tomography (CT). Continued refinement of CT techniques has improved our ability to stage gastric cancer. Nevertheless, results with these techniques are not satisfactory, especially for evaluation of tumor depth and nodal involvement (3–20).

Currently, multi–detector row CT scanners allow thinner collimation and faster scanning, which markedly improve scanning resolution and enable rapid and easy handling of reconstruction of the obtained images. Virtual endoscopy is an emerging examination tool that is based on thin-section helical CT, and with it, cross-sectional transverse and multiplanar reformation (MPR) images are generated. These images include endoluminal perspective images of the gastrointestinal tract, including stomach or colon that resemble those obtained during conventional endoscopy. Therefore, it is natural to expect that multi–detector row CT gastrography performed with MPR and a virtual endoscopic technique (volumetric CT imaging) may improve accuracy of preoperative staging of gastric cancer (21–28). To our knowledge, there has been minimal focus on the diagnostic value of volumetric CT imaging in evaluation of patients with gastric cancer. Thus, the purpose of our study was to prospectively evaluate the accuracy of multi–detector row CT gastrography for the preoperative staging of gastric cancer, with pathologic and surgical results as the reference standard.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 SUMMARY
 References
 
Patient Populations
From July to December 2001, 124 consecutive patients with gastric cancer that was pathologically proved at endoscopic biopsy were enrolled in this study, which was approved by our institutional review board. Patients gave written informed consent and underwent unenhanced and contrast material–enhanced multi–detector row CT for preoperative staging 5–12 days (mean, 7 days) after endoscopic biopsy. Of these 124 patients, 14 were excluded because they did not undergo surgical resection because of disseminated peritoneal seeding (n = 2) or distant metastasis (n = 3) or because they underwent endoscopic mucosal resection for early gastric cancer (n = 9). Four patients were unavailable for follow-up. The final study population consisted of 106 patients who underwent surgery (early gastric cancer, 45 patients; advanced gastric cancer, 61 patients). They included 72 men and 34 women, with an age range of 28–76 years (mean, 56 years). At statistical analysis, a significant difference was not observed in age (P = .962) or sex (P = .836) between groups with early and advanced gastric cancer. The mean interval between CT examination and surgery was 18 days (range, 4–24 days). Ninety-nine of 106 patients underwent subtotal or total gastrectomy, and seven underwent palliative surgery because of extensive metastases or peritoneal seeding.

Pathologic TNM Stage
The pathologic staging was based on TNM staging according to the revised Japanese Classification of Gastric Carcinoma from the Japanese Gastric Cancer Association (29), as follows: pT1, tumor invasion of mucosa and/or muscularis mucosa or submucosa; pT2, tumor invasion of muscularis propria or subserosa; pT3, tumor penetration of serosa; and pT4, tumor invasion of adjacent structures. Lymph nodes were likewise categorized: N0, no evidence of lymph node metastasis; N1, metastasis to group 1 lymph nodes; N2, metastasis to group 2 lymph nodes but not to group 3 lymph nodes; and N3, metastasis to group 3 lymph nodes. Metastasis was classified as M0 when no other distant metastases were observed or M1 when distant metastases were found.

CT Examination
All 106 patients underwent CT after overnight fasting to empty the stomach. CT was performed with a four–detector row CT scanner (LightSpeed QX/I; GE Medical Systems, Milwaukee, Wis) with a high-speed mode. Before CT examination, 20 mg of scopolamine (Buscopan; Boehringer International, Ingelheim, Germany) was injected intramuscularly to relax the bowel wall and reduce peristaltic bowel movement. To achieve gastric distention, patients ingested effervescent granules (Top; Taejoon Pharmaceutical, Kyungkido, Republic of Korea), 8 g, with 10 mL of tap water just before CT.

Initially, unenhanced CT was performed from the diaphragmatic dome to the renal pedicle during a single breath hold with patients in the prone position, after a scout projection was obtained that showed the gaseous distended stomach. Scanning parameters for CT gastrography were as follows: beam collimation, four detector rows with a 1.25-mm section thickness produced (4 x 1.25 mm); section thickness, 2.5 mm; reconstruction interval, 2.5 mm; pitch, 6; gantry rotation time, 0.8 second; table feed, 7.5 mm per rotation; field of view, to fit; tube voltage, 120 kVp; and tube current–time product, 200 mAs. Patients were instructed to suspend respiration during scanning.

Contrast-enhanced CT then was performed after intravenous injection of 150 mL of iopromide (Ultravist 370; Schering, Berlin, Germany) through an 18-gauge angiographic catheter inserted into an antecubital vein by using a power injector (LF CT 9000; Liebel-Flarsheim, Cincinnati, Ohio) at a flow rate of 3 mL/sec. Contrast enhancement was performed to assess tumor staging, including that of distant metastases. Scanning was next performed with patients in the supine position, 72 seconds after initiation of contrast material injection, which corresponded to the venous phase. Lower abdominal scanning was performed continuously from the renal pedicle to the anus. The scanning parameters were as follows: beam collimation, 4 x 2.5 mm; section thickness, 5.0 mm; reconstruction interval, 2.5 mm; and table feed, 15.0 mm per rotation.

Raw data obtained from CT were reconstructed twice with a standard body reconstruction algorithm available on the scanner and routinely used for abdominal CT scanning. First, images for viewing at the workstation were reconstructed with 2.5-mm intervals. Second, images for the picture archiving and communication system were reconstructed with 5.0-mm intervals (transverse CT imaging). Volumetric CT imaging analysis was performed on a commercially available workstation by using a software package with volume-rendering capabilities (Advantage Workstation 3.1, GE Medical Systems). MPR and virtual endoscopy were the main techniques used for volumetric imaging analysis. A mean time of 10–15 minutes per patient was required to interpret volumetric images.

Image Analysis
Two experienced gastrointestinal radiologists (A.Y.K., H.J.K.) interpreted the CT images independently; they had 11 and 5 years, respectively, of experience in gastrointestinal radiology and experience with more than 50 cases of CT gastrography with correlation between findings at CT gastrography and results at gastroscopy. Both observers were partially blinded to the gastroscopic results (they knew that the patients had gastric cancer that had been proved with endoscopic results) and completely blinded to lesion location, size, macroscopic features, and stage of stomach cancers. Differences in assessment were resolved with consensus. First, transverse CT images were evaluated with picture archiving and communication system monitors in random order. Volumetric data analysis was then performed at the workstation, also in random order. To diminish learning effects, the interval between reading sessions was at least 2 weeks.

A lesion was determined to be cancerous when the gastric wall showed focal thickening of at least 6 mm or greater or when focal enhancement was seen in the gastric wall. The depth of tumor invasion was classified as follows: T1, gastric wall thickening with or without enhancement of the inner surface but with preservation of the low-attenuation stripe, corresponding submucosal layer, at the base of the lesion; T2, thickened gastric wall with loss or disruption of low-attenuation stripe but with a clear and smooth outer gastric surface around the lesion and a clear perigastric fat plane; T3, nodular or irregular outer border of the thickened gastric wall or perigastric fat infiltration; and T4, direct extension and invasion of tumor into a contiguous organ or structure. The location of the tumor was recorded.

Lymph nodes were considered metastatic if they were larger than 8 mm in the short-axis diameter and oval (30–32). The lymph node grouping was based on the revised Japanese Classification of Gastric Carcinoma (29), which is equivalent to the TNM classification. Metastases were recorded as present or absent, and the location of metastases also was recorded.

The diagnostic accuracy of the TNM stage of each gastric cancer at transverse CT imaging and at volumetric CT imaging was evaluated, with comparison with the pathologic and surgical results, which were used as the reference standard. The comparison was made after image interpretation had been accomplished.

Statistical Analysis
At staging of each tumor, lymph node, and metastasis, the difference in diagnostic accuracy of transverse CT imaging and of volumetric CT imaging was assessed by using the paired t test. For both imaging methods, a P value less than .05 was considered to indicate a statistically significant difference. Statistical analysis was conducted with statistical software (SPSS for Windows, version 10.0 for Windows; SPSS, Chicago, Ill).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 SUMMARY
 References
 
Tumor Staging of Gastric Cancer
In the present study, gastric cancer manifested as a thickened wall that showed contrast enhancement on the CT scan. The tumor detection rate was 87% (92 of 106) for transverse CT imaging and 98% (104 of 106) for volumetric CT imaging (P < .001). Among 45 patients with early gastric cancer (pT1 stage), 14 cases of gastric cancer were not detected with transverse CT imaging. In surgical and pathologic reports, these lesions were reported to have been located at the gastric angle (n = 4), the curvature of the gastric body (n = 7), or the prepyloric antrum (n = 3). Most of them, except those in two patients, however, were well demonstrated at volumetric CT imaging. These two missed cases proved to be flat-type stage IIb early gastric cancer, according to pathologic reports.

In comparison with transverse CT imaging, five early gastric cancer lesions were newly depicted with MPR, while seven were seen with virtual endoscopy. At volumetric CT imaging, these 12 newly detected early gastric cancers were pathologically classified as stage IIb + IIc early gastric cancer in seven patients, stage IIb early gastric cancer in three patients, and stage IIc early gastric cancer in two patients. At virtual endoscopy, three of the early gastric cancers were classified as stage IIb; two, as stage IIb + IIc; and two, as stage IIc (Fig 1).



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  		Figure 1a. Early gastric cancer in 33-year-old woman. (a, b) There is no identifiable gastric wall thickening on either the (a) transverse CT scan or the (b) coronal MPR image. (c) Virtual endoscopic image shows a shallow depressed lesion with surrounding mucosal nodularity (arrows) in the angle of the stomach, suggesting early gastric cancer (T1). (d) Photomicrograph of surgical specimen demonstrates a flat cancerous lesion (arrows) with a shallow depressed area (arrowheads). At histopathologic analysis, this lesion was diagnosed as type IIb + IIc early gastric cancer (pT1). (Hematoxylin-eosin stain; original magnification, x10.)

 


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  		Figure 1b. Early gastric cancer in 33-year-old woman. (a, b) There is no identifiable gastric wall thickening on either the (a) transverse CT scan or the (b) coronal MPR image. (c) Virtual endoscopic image shows a shallow depressed lesion with surrounding mucosal nodularity (arrows) in the angle of the stomach, suggesting early gastric cancer (T1). (d) Photomicrograph of surgical specimen demonstrates a flat cancerous lesion (arrows) with a shallow depressed area (arrowheads). At histopathologic analysis, this lesion was diagnosed as type IIb + IIc early gastric cancer (pT1). (Hematoxylin-eosin stain; original magnification, x10.)

 


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  		Figure 1c. Early gastric cancer in 33-year-old woman. (a, b) There is no identifiable gastric wall thickening on either the (a) transverse CT scan or the (b) coronal MPR image. (c) Virtual endoscopic image shows a shallow depressed lesion with surrounding mucosal nodularity (arrows) in the angle of the stomach, suggesting early gastric cancer (T1). (d) Photomicrograph of surgical specimen demonstrates a flat cancerous lesion (arrows) with a shallow depressed area (arrowheads). At histopathologic analysis, this lesion was diagnosed as type IIb + IIc early gastric cancer (pT1). (Hematoxylin-eosin stain; original magnification, x10.)

 


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  		Figure 1d. Early gastric cancer in 33-year-old woman. (a, b) There is no identifiable gastric wall thickening on either the (a) transverse CT scan or the (b) coronal MPR image. (c) Virtual endoscopic image shows a shallow depressed lesion with surrounding mucosal nodularity (arrows) in the angle of the stomach, suggesting early gastric cancer (T1). (d) Photomicrograph of surgical specimen demonstrates a flat cancerous lesion (arrows) with a shallow depressed area (arrowheads). At histopathologic analysis, this lesion was diagnosed as type IIb + IIc early gastric cancer (pT1). (Hematoxylin-eosin stain; original magnification, x10.)

 
The comparison between the pathologic and radiologic tumor staging is summarized in Table 1. The overall accuracy of tumor staging was 77% for transverse CT imaging and 84% for volumetric CT imaging (P < .001). As for the diagnostic accuracy of tumor staging, the superiority of volumetric CT imaging to transverse CT imaging was more evident in the pT1 (77% vs 84% in the tumors in stage pT1) (P < .001) (Figs 1–4). Differentiation between T1 or T2 and T3 or T4 cancers (extraserosal invasion) was correct in 80 (87%) of 92 lesions at transverse CT imaging and in 96 (92%) of 104 lesions at volumetric CT imaging (P > .05).


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  		TABLE 1. Accuracy of Contrast-enhanced Multi–Detector Row CT Gastrography for Tumor Staging

 


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  		Figure 2a. Early gastric cancer in 57-year-old man. (a) Transverse CT scan and (b) MPR image show slightly depressed lesion with focal irregular enhancing wall thickening (arrow) and intact low-attenuation stripe representing submucosal layer of the gastric wall (arrowhead) in the antrum of the stomach. This lesion was proved to be type IIc + IIb early gastric cancer (pT1).

 


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  		Figure 2b. Early gastric cancer in 57-year-old man. (a) Transverse CT scan and (b) MPR image show slightly depressed lesion with focal irregular enhancing wall thickening (arrow) and intact low-attenuation stripe representing submucosal layer of the gastric wall (arrowhead) in the antrum of the stomach. This lesion was proved to be type IIc + IIb early gastric cancer (pT1).

 


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  		Figure 3a. Early gastric cancer in 42-year-old woman. (a) Transverse CT scan and (b) coronal MPR image show focal gastric wall thickening with enhancement (arrow) at the antrum of the stomach. Perigastric fat surrounding the gastric lesion is relatively clear. This lesion was considered as stage T2 because the low-attenuation fat stripe is obliterated. This case was proved to be pathologic T1 cancer that mimicked T2 cancer because of extensive submucosal tumor infiltration.

 


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  		Figure 3b. Early gastric cancer in 42-year-old woman. (a) Transverse CT scan and (b) coronal MPR image show focal gastric wall thickening with enhancement (arrow) at the antrum of the stomach. Perigastric fat surrounding the gastric lesion is relatively clear. This lesion was considered as stage T2 because the low-attenuation fat stripe is obliterated. This case was proved to be pathologic T1 cancer that mimicked T2 cancer because of extensive submucosal tumor infiltration.

 


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  		Figure 4a. Advanced gastric cancer in 62-year-old man. (a) Transverse CT scan reveals irregular enhancing wall thickening (arrow) of the gastric antrum without perigastric fatty infiltration, which suggests stage T2. (b) Oblique sagittal MPR scan shows irregular enhancing wall thickening of the gastric antrum with perigastric soft-tissue stranding (arrow), which is suggestive of stage T3. (c) Photomicrograph of surgical specimen demonstrates tumor infiltration (arrow) into subserosal layer throughout the entire gastric wall. The pathologic stage of this lesion proved to be pT3. ss = Subserosal, T = tumor. (Hematoxylin-eosin stain; original magnification, x40.)

 


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  		Figure 4b. Advanced gastric cancer in 62-year-old man. (a) Transverse CT scan reveals irregular enhancing wall thickening (arrow) of the gastric antrum without perigastric fatty infiltration, which suggests stage T2. (b) Oblique sagittal MPR scan shows irregular enhancing wall thickening of the gastric antrum with perigastric soft-tissue stranding (arrow), which is suggestive of stage T3. (c) Photomicrograph of surgical specimen demonstrates tumor infiltration (arrow) into subserosal layer throughout the entire gastric wall. The pathologic stage of this lesion proved to be pT3. ss = Subserosal, T = tumor. (Hematoxylin-eosin stain; original magnification, x40.)

 


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  		Figure 4c. Advanced gastric cancer in 62-year-old man. (a) Transverse CT scan reveals irregular enhancing wall thickening (arrow) of the gastric antrum without perigastric fatty infiltration, which suggests stage T2. (b) Oblique sagittal MPR scan shows irregular enhancing wall thickening of the gastric antrum with perigastric soft-tissue stranding (arrow), which is suggestive of stage T3. (c) Photomicrograph of surgical specimen demonstrates tumor infiltration (arrow) into subserosal layer throughout the entire gastric wall. The pathologic stage of this lesion proved to be pT3. ss = Subserosal, T = tumor. (Hematoxylin-eosin stain; original magnification, x40.)

 
Lymph Node Staging of Gastric Cancer
The comparison between pathologic and radiologic staging of lymph nodes is summarized in Table 2. The overall accuracy for staging of lymph nodes was 62% (66 of 106 patients) with transverse CT imaging and 64% (68 of 106 patients) with volumetric CT imaging (Fig 5). There was no significant difference, however, between transverse CT imaging and volumetric CT imaging in the staging of lymph nodes (P = .057). Lesions were understaged in 15 (14%) of 106 patients with transverse CT imaging and in 12 (11%) of 106 with volumetric CT imaging. Lesions were overstaged in 25 (24%) patients with transverse CT imaging and in 26 (25%) with volumetric CT imaging.


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  		TABLE 2. Accuracy of Contrast-enhanced Multi–Detector Row CT Gastrography for Lymph Node Staging

 


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  		Figure 5a. Advanced gastric cancer in 44-year-old woman. (a) Transverse CT scan shows eccentric wall thickening (arrows) at prepyloric antrum of the stomach, but lymph node enlargement is not seen in the perigastric area, indicating N0 stage. (b) Sagittal MPR image reveals eccentric pyloric wall thickening (arrowhead) and an enlarged lymph node (arrow) in the subpyloric area, which suggests stage N1. This subpyloric lymph node was pathologically proved to be metastatic (N1).

 


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  		Figure 5b. Advanced gastric cancer in 44-year-old woman. (a) Transverse CT scan shows eccentric wall thickening (arrows) at prepyloric antrum of the stomach, but lymph node enlargement is not seen in the perigastric area, indicating N0 stage. (b) Sagittal MPR image reveals eccentric pyloric wall thickening (arrowhead) and an enlarged lymph node (arrow) in the subpyloric area, which suggests stage N1. This subpyloric lymph node was pathologically proved to be metastatic (N1).

 
Staging of Metastases of Gastric Cancer
The overall accuracy was 86% (six of seven patients) for both transverse CT imaging and volumetric CT imaging. In seven patients, M1 staging was pathologically confirmed at palliative surgery. The pathologic results in these patients included peritoneal seeding (n = 3) (Fig 6 ), colonic invasion (n = 1), and hepatic metastases (n = 3). In one patient, metastasis to the large intestine was missed at both transverse CT imaging and volumetric CT imaging. In this case, microscopic tumor invasion into the transverse colon through the mesocolon was discovered at histopathologic analysis but was missed at CT, even with MPR (Fig 7).



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  		Figure 6a. Advanced gastric cancer in 49-year-old man. (a) Transverse CT scan and (b) oblique sagittal MPR image show irregularly enhancing wall thickening of the antrum of the stomach (arrow) and diffuse haziness of the mesentery (*) with multiple lymphadenopathy (N), which is suggestive of pathologic stage M1. At excisional biopsy, this case was proved to be advanced gastric cancer, with peritoneal seeding observed histopathologically.

 


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  		Figure 6b. Advanced gastric cancer in 49-year-old man. (a) Transverse CT scan and (b) oblique sagittal MPR image show irregularly enhancing wall thickening of the antrum of the stomach (arrow) and diffuse haziness of the mesentery (*) with multiple lymphadenopathy (N), which is suggestive of pathologic stage M1. At excisional biopsy, this case was proved to be advanced gastric cancer, with peritoneal seeding observed histopathologically.

 


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  		Figure 7a. Advanced gastric cancer in 60-year-old woman. (a–c) Serial transverse CT scans show the encircling mass (T) in a at prepyloric antrum of the stomach. No perigastric fat infiltration, including the omentum and mesocolon, was observed on either CT scan or MPR image (not shown). In the surgical field, however, mesocolonic invasion of gastric cancer was discovered, and microinfiltration of tumor cells into transverse colon (TC) through mesocolon was confirmed pathologically.

 


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  		Figure 7b. Advanced gastric cancer in 60-year-old woman. (a–c) Serial transverse CT scans show the encircling mass (T) in a at prepyloric antrum of the stomach. No perigastric fat infiltration, including the omentum and mesocolon, was observed on either CT scan or MPR image (not shown). In the surgical field, however, mesocolonic invasion of gastric cancer was discovered, and microinfiltration of tumor cells into transverse colon (TC) through mesocolon was confirmed pathologically.

 


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  		Figure 7c. Advanced gastric cancer in 60-year-old woman. (a–c) Serial transverse CT scans show the encircling mass (T) in a at prepyloric antrum of the stomach. No perigastric fat infiltration, including the omentum and mesocolon, was observed on either CT scan or MPR image (not shown). In the surgical field, however, mesocolonic invasion of gastric cancer was discovered, and microinfiltration of tumor cells into transverse colon (TC) through mesocolon was confirmed pathologically.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
SUMMARY
 References
 
In the evaluation of gastric cancer, accurate lesion depiction at CT is a prerequisite for precise diagnosis and tumor staging. Moreover, with the development of minimally invasive surgery for the treatment of early gastric cancer, such as endoscopic mucosal resection or laparoscopic resection (32,33), detection and accurate staging at an early stage has become more important than in the past. Previous studies, however, have shown low detection rates for early gastric cancers, with a range of 26%–53% (14,19). Even with the circumstance that no abnormal finding at imaging is considered as stage T1, the accuracy of CT in tumor staging of gastric cancer was not satisfactory and ranged from 69% to 83% (14,16,17). Although recent dynamic CT studies with MPR images were expected to improve the tumor staging of gastric cancer, they showed an overall accuracy of 66% in tumor staging (20).

In this study, volumetric CT imaging with MPR and virtual endoscopy had an excellent detection rate (98%) for gastric cancer. In particular, the depiction of early gastric cancer (pathologic stage T1) was markedly improved (43 [96%] of 45 early gastric cancers) for volumetric CT imaging compared with the results with transverse CT imaging alone (31 [69%] of 45 early gastric cancers). We observed that 12 of 14 early gastric cancers that were not detected at transverse CT imaging were detected with volumetric CT imaging with MPR or virtual endoscopy. At volumetric imaging, these 12 newly detected early gastric cancers included 10 early gastric cancer lesions that were classified as stage IIb. On the basis of our data, the limitation of helical CT in the detection of flat or depressed cancers, as well as in the depiction of early gastric cancers, seems to be overcome with application of volumetric CT imaging. This improved detection and localization of T1 gastric cancers with volumetric CT imaging can help clinicians to make decisions about treatment planning. Because small T1 cancers have a very low rate of nodal involvement, patients with T1 cancer detected at helical CT would be candidates for endoscopic or laparoscopic resection.

As might be expected, the accuracy of tumor staging with volumetric CT imaging was superior to that with transverse CT imaging (overall accuracy, 84% vs 77%; P < .001), and the superiority of volumetric CT imaging was more evident in pathologic staging of T1 and T3 cancers. Both transverse CT imaging and volumetric CT imaging, however, showed a tendency toward overstaging of pathologically proved T1 or T2 cancers and toward understaging of pathologically proved T3 or T4 cancers. Seven of 45 early gastric cancer lesions were overstaged at both transverse CT imaging and volumetric CT imaging because of massive submucosal invasion of the cancer cells. Because these lesions would show little normal-appearing submucosal layer, it seems impossible to differentiate these T1 lesions from T2 cancers on the CT scan obtained with either transverse CT imaging or volumetric CT imaging.

It is also difficult to evaluate the extraserosal invasion of the tumor or the relationship of it with adjacent organs on the CT scan, especially when the interface is oblique or nearly parallel to the scanning direction. Although MPR images are expected to help overcome this problem, our results with T3 or T4 staging were not satisfactory and showed a tendency toward underestimation of the tumor stage. MPR images helped to correct understaging in only three patients. The accuracy of T3 staging with volumetric CT imaging (82%) was similar to that with conventional CT (80%–83%) obtained previously (14,17). In our experience, differentiation between T1 or T2 and T3 or T4 cancers (extraserosal invasion) was more accurate with volumetric CT imaging than with transverse CT imaging (92% vs 87%), but this difference was not statistically significant (P > .05). Although volumetric CT imaging offered more improved results in the evaluation of tumor depth than did transverse CT imaging, the diagnosis of microscopic infiltration of cancer cells beyond gastric serosa or into adjacent organs is difficult on a CT scan.

Clinically, staging of lymph nodes is as important as tumor staging in determining the type of surgery to be performed and in predicting the patient's prognosis (33). The reported accuracy of CT diagnosis, however, ranges from 51% to 70%, because size is the only criterion for assessment of lymph nodes and is a poor predictor of involvement (11,16,17). Although the improved staging of lymph nodes with MPR images was expected in our study, the detection rate was low for both transverse CT imaging and volumetric CT imaging (61% vs 63%), and these results did not differ from those in previous reports. Despite the identification of lymph nodes as small as 2–3 mm on high-spatial-resolution images, reliable detection of nodal metastases does not seem to be possible if the radiologic assessment of nodal involvement relies on morphologic criteria, such as the size or shape of the node.

Because of the lack of reliable CT criteria for metastatic nodes, wide ranges of sensitivity (48%–91%) have been reported for nodal staging with CT (6,7,10–13). With an 8-mm size criterion (30,32), we achieved a relatively high sensitivity of 62% but a low specificity of 87%, which suggests overstaging of nodes in 24% of cases and understaging in 14%. Contrary to our findings, those in previous studies with 10 mm as a size criterion for metastatic lymph nodes showed low sensitivity (24%–48%) and high specificity (99%–100%) (11–13), with more understaged nodes (36%) and fewer overstaged nodes (15%) than were indicated according to our results. Actually, nodal size criteria are in inverse proportion to the sensitivity of nodal involvement. In our opinion, higher sensitivity is more important than specificity, since understaging of lymph node involvement is dangerous to patients with gastric cancer because it can lead to undertreatment.

There are only a few reports in regard to staging of metastases of gastric cancer, because patients with distant metastases do not generally undergo surgery. Similarly, our study included a small population of M1 stage metastases. The aim of our study was to evaluate the accuracy of CT for preoperative staging, with pathologic and surgical results as the reference standard so that we enrolled only patients who underwent surgery. Hence, we could not sufficiently address the role of volumetric CT imaging in the staging of metastases. We think this was an inevitable limitation of our study.

Another major limitation of our study was a bias in the patient population. We included only patients whose lesions were diagnosed at endoscopic biopsy and who were scheduled to undergo a surgical procedure. Thus, our results for the detection of gastric cancer with volumetric CT imaging may be biased and cannot provide the value of CT in the screening of patients with gastric cancer. The value of CT in the screening of such patients will require further study in the future.

In this study, reconstruction processing of the obtained CT images was rapid and easy with a commercial workstation. With volumetric CT imaging, MPR and virtual endoscopic images were obtained in near real time, and their image quality was excellent, without blurring. Although some experience is demanded to handle reconstruction, the time required for reconstruction was tolerable, with a mean time of 10–15 minutes per patient. Postprocessing of CT images is no more time-consuming work.

Despite the limitations of staging with CT, which include an inability to identify metastatic lymph nodes definitely or determine the exact depth of tumors, multi–detector row CT gastrography is valuable in the treatment of gastric cancer. Preoperative CT is the modality of choice for planning curative or palliative surgery and provides baseline findings for comparison during chemotherapy in patients with inoperable cancer. Although CT has not been a routine examination for detection of gastric cancer until now, multi–detector row CT, concomitant with continued advancements in scanner and computer technology, may play a future role in the detection of early-stage gastric cancer in high-risk patients and in exact preoperative cancer staging.

In conclusion, in the preoperative staging of gastric cancer, multi–detector row CT gastrography with MPR and virtual endoscopy showed better results than did transverse CT imaging alone. In particular, the accuracy of tumor staging was significantly improved with the application of volumetric CT imaging (84% for volumetric CT imaging vs 77% for transverse CT imaging, P < .001). The differences in staging of lymph nodes and metastases between transverse CT imaging and volumetric CT imaging, however, were not significant.


   SUMMARY
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY
References
 
In the preoperative staging of gastric cancer, multi–detector row CT gastrography with multiplanar reconstruction and virtual endoscopy showed better results than did transverse CT imaging alone.


   FOOTNOTES
 

Abbreviations: MPR = multiplanar reformation

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, A.Y.K., H.K.H.; study concepts and design, A.Y.K.; literature research, H.J.K., K.W.K.; clinical studies, S.T.O., J.S.K.; data acquisition, H.J.K.; data analysis/interpretation, H.J.K., A.Y.K.; statistical analysis, H.J.K.; manuscript preparation, H.J.K.; manuscript definition of intellectual content, A.Y.K., H.K.H.; manuscript editing, P.N.K., M.G.L., H.K.H.; manuscript revision/review and final version approval, A.Y.K.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY
 References
 

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