A computed tomography (CT) scan is a sophisticated imaging technique that uses X-rays and computer processing to create detailed, cross-sectional pictures of the body’s internal structures. For those concerned about stomach cancer (gastric cancer), the CT scan is a standard and important part of the diagnostic process. While its role is complex, it provides physicians with a non-invasive way to visualize the stomach, surrounding organs, and lymph nodes.
How CT Scans Visualize Stomach Cancer
Visualizing stomach cancer on a CT scan relies heavily on contrast agents to distinguish abnormal tissue. Patients typically receive both oral and intravenous contrast dyes for the best image quality. Oral contrast, often water, helps distend the stomach and clearly delineate the inner stomach lining from surrounding structures.
The primary tumor generally appears on the scan as localized thickening of the stomach wall or a distinct mass protruding into the stomach cavity. Intravenous contrast highlights the blood vessels and the tumor itself, since cancerous tissue often shows different enhancement patterns compared to the normal stomach wall. This enhancement helps the radiologist identify areas of concern, such as mucosal irregularity or focal infiltration. Modern multidetector CT (MDCT) scanners offer high-resolution images crucial for detecting these structural changes.
Defining the Extent of the Disease
The primary function of the CT scan in oncology is defining the full extent, or stage, of the disease, not just finding the primary tumor. This staging process, which uses the TNM system (Tumor, Node, Metastasis), guides all subsequent treatment decisions. The CT scan is the preoperative reference standard for checking cancer spread, especially to distant sites.
The scan checks for regional spread by examining the lymph nodes surrounding the stomach (N-staging). Enlarged lymph nodes suggest cancerous involvement, though the scan may struggle to detect microscopic metastases in normal-sized nodes. The CT scan is also highly effective at identifying distant spread (M-staging) to other organs.
Common sites checked for distant spread include the liver, lungs, and the peritoneum (the lining of the abdominal cavity). The overall accuracy of CT for determining distant metastasis is high, often reported around 85%. By mapping the disease, the CT scan helps physicians determine if the cancer is localized and potentially curable with surgery, or if it requires systemic treatment like chemotherapy.
Limitations in Early Detection
Despite its strength in staging advanced disease, the CT scan has limitations in detecting stomach cancer at its earliest stages. It is not used as a primary screening tool because it struggles to visualize very small or superficial tumors. Early-stage cancers are confined to the inner layers of the stomach wall and often do not cause the significant wall thickening a CT scanner is designed to pick up.
The detection rate for early gastric cancers using CT is low. Tumors under 30 millimeters in size may be missed in a large percentage of cases. Highly localized cancers cause only subtle changes or minimal wall thickening that can be easily overlooked or mistaken for a benign condition. This potential for false negative results means a clear CT scan does not definitively rule out a very early-stage stomach cancer.
Comprehensive Diagnostic Approach
Due to the CT scan’s limitations in early detection and the need for tissue confirmation, it is only one component of the diagnostic process. The gold standard for confirming stomach cancer is an upper gastrointestinal endoscopy. This procedure involves inserting a flexible tube with a camera down the throat to directly visualize the stomach lining.
During endoscopy, the physician takes biopsies from suspicious areas. These samples are examined under a microscope to definitively confirm cancer cells and determine the tumor type. Endoscopic ultrasound (EUS) is also often used to get a detailed picture of the tumor’s depth of invasion into the stomach wall layers. This local staging information from EUS complements the CT scan’s primary role of checking for distant spread.