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EDUCATION EXHIBIT |
1 Mallinckrodt Institute of Radiology, St Louis, Missouri
Throughout the 20th century, gastric cancer has been one of the two leading causes of cancer deaths worldwide (1). In the United States, gastric cancer ranks 14th in the number of cancer-related deaths, which reflects the fairly poor prognosis of this relatively rare neoplasm.
Early detection is hindered by the relative non-specificity of symptoms in patients with gastric neoplasms, which most commonly include weight loss, abdominal pain, and nausea (2). The latter two can easily be ameliorated by over-the-counter medications, resulting in further delay in diagnosis. Other symptoms, including early satiety, and hematemesis may prompt patients to seek medical attention earlier.
Surgery has been the key to treatment, but until recently, no clear standards for surgery have been used. This has contributed to the poor survival rates of 5%–15% in the United States, which are considerably lower than in Japan, where gastric cancer is endemic (1). Screening programs and awareness of the disease have led to improved identification of the disease at an early stage and resultant improved survival. Of late, large Western tertiary medical centers have shown a promising increase in the early detection of gastric cancer (2). This trend combined with increased awareness of the disease and more standardized treatment standards should result in improved outcomes for gastric neoplasms in the Western world.
Historically, diagnosis of gastric masses has been with barium studies, which have shown excellent results when double-contrast techniques are employed (3). Endoscopy has become the diagnostic method of choice given the ability to directly visualize abnormal areas and simultaneously biopsy any suspicious lesions.
Once the diagnosis is made, accurate staging has become crucial for proper treatment selection. Recent work has centered on the added value of 2-[fluorine-18]fluoro-2-deoxy-D-glucose positron emission tomography detection of gastric cancer metastases when combined with multidetector CT with intravenous contrast material (4). Depth of tumor invasion determines the T stage, which greatly influences survival (1). Endoscopic US has proved to be quite accurate in assessing this component; however, the extent of disease may be overestimated when a great degree of inflammation is present, and endoscopic US is limited in assessing nodal involvement (5). The highest accuracy in staging is achieved when endoscopic US is combined with high-quality multi-detector CT (1,5).
In the preceding article, Kim et al (6) highlight the potential future of multidetector CT in the evaluation of gastric masses and cancers. Using a dedicated protocol, they show how this relatively noninvasive technique can be used to evaluate the gastric wall and perigastric extension of disease. With expansion of the role of CT in evaluation of the T stage, CT may be more accurate in defining the appropriate method of treatment and predicting survival.
Their specialized protocol is employed whenever an upper gastrointestinal series reveals an abnormality or when a patient has symptoms that might be referable to a gastric pathologic condition (6). Images are obtained in both prone and supine positions without and with intravenous contrast material. The 3D techniques used are similar to those employed elsewhere in the gastrointestinal tract and increased confidence and lesion characterization (6).
Using their techniques, Kim et al (6) show beautiful correlation among optical gastroscopy, multidetector CT with postprocessing (virtual gastroscopy, transparency rendering), and endoscopic US for a variety of gastric pathologic conditions. Their examples nicely show the power of this emerging technique and hint at the potential of a single examination to depict mucosal detail, demonstrate the T stage of a lesion, and show extragastric disease. Their work also shows that we are not quite there, as endoscopic US is still superior at evaluating the layers of the gastric wall and optical gastroscopy allows biopsy, which is almost always warranted.
Their work also opens the door to issues that will warrant further consideration in the near future. As much of their work was done on a four-row CT scanner, does the improved spatial resolution of higher-numbered-row scanners improve mucosal detail? Initial work addressing the accuracy of T staging with four-row CT suggests that four-row CT may be sufficient but that 16-row CT may allow quicker examination times and lower radiation dose (7,8). The question of radiation dose in this era of dose awareness also becomes an important one. Is there a role for dose reduction in one or both positions without adverse effect on diagnostic outcome, as has been studied in virtual colonography (9,10)? This becomes particularly important as this technique becomes more widely accepted and indications for performing this protocol become less specific than those used by Kim et al (6). We have all seen this "indication creep" in CT protocols (most notably urinary colic CT and pulmonary embolism protocols) performed for fairly nonspecific symptoms (11).
The need for contrast material is another key element that needs to be studied, as there may be a role for virtual gastroscopy in screening for gastric cancer in endemic areas. Work by Inamoto et al (8) demonstrated fairly high sensitivity (92.7%) and specificity (91.9%) for malignant lesions compared with those of optical gastroscopy. Its major limitation is in the detection of flat lesions, which might improve with the quicker examination times of higher-numbered-row CT scanners and alternative positioning, such as lateral decubitus (8,12). As with virtual colonography, virtual gastroscopy is much better tolerated by patients than conventional endoscopy and may result in better compliance (13).
Kim et al (6) have wonderfully shown what is possible with meticulous attention to detail with current multidetector CT of the stomach. Future studies must show whether this technique is accurate and cost-effective and must help define which patients will benefit from this CT application.
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