The diagnosis of gastric cancer can be divided into qualitative diagnosis and stage diagnosis: qualitative diagnosis is used to determine whether a patient’s gastric lesion is cancerous; stage diagnosis is used to assess the extent of gastric cancer progression, including local progression of the lesion and the presence of metastases.
Gastroscopy and histologic biopsy are the gold standard and preferred method for qualitative diagnosis of gastric cancer, while imaging is an important tool for stage diagnosis of gastric cancer. Patients with gastric cancer often need to undergo a series of imaging tests to assess the extent of disease progression so that physicians can develop a treatment plan. The following imaging tests are commonly used for gastric cancer.
CT
CT is one of the most important tools for assessing the progression of gastric cancer. A CT exam allows the doctor to know:
- the extent of the tumor occupying the stomach;
- How deeply the tumor has invaded the stomach wall;
- whether the tumor has penetrated the stomach wall and grown into other organs surrounding the stomach;
- Whether there is metastasis in the lymph nodes around the stomach;
- Whether the tumor has distant metastases (e.g. liver metastases, peritoneal metastases, etc.).
CT examination is divided into enhancement CT and plain CT according to whether contrast is injected or not. Patients with gastric cancer who do not have contraindications to the use of contrast should undergo enhancement CT scan. Three-dimensional reconstruction using a computer based on enhanced CT can provide more diagnostic information about the stage of the disease.
Barium meal angiography of the upper gastrointestinal tract
Barium meal angiography of the upper gastrointestinal tract can be used for screening and diagnosis of gastric cancer, but it is less detectable and less accurate than gastroscopy, and histologic biopsy samples are not available, so it is mostly used clinically in patients who cannot tolerate gastroscopy.
For patients with upper gastric or cardia cancer, upper gastrointestinal barium meal imaging can assist in determining whether there is esophageal involvement.
Magnetic resonance imaging (MRI)
In imaging of gastric cancer, MRI is less commonly used than CT. Although some small sample studies have found that MRI imaging has better contrast resolution than CT, MRI currently has a very limited role in the diagnosis of gastric cancer at the disease stage. Usually, MRI is recommended when the intrahepatic lesions in patients with gastric cancer cannot be clearly identified as metastases by CT, or when the patient is allergic to CT contrast agents.
Ultrasound
Transabdominal ultrasonography has a low detection rate and little diagnostic value for the stage of gastric cancer, so transabdominal ultrasonography is rarely performed on patients with gastric cancer in clinical practice. The use of ultrasound is only considered by physicians when there is clinical suspicion of metastasis to body surface lymph nodes such as supraclavicular lymph nodes in patients with gastric cancer.
PET-CT
In recent years, positron emission computed tomography (PET-CT) examinations of malignant tumors have gradually emerged. For patients with a confirmed diagnosis of gastric cancer, PET-CT is valuable for the diagnosis of the disease stage and is mainly used to screen for the presence of metastases throughout the body.
However, PET-CT is not a “one-size-fits-all” test and has its limitations:
- Indolent cell carcinoma and/or poorly differentiated adenocarcinoma (two histologic types of gastric cancer) do not show up on PET-CT, so these two types of gastric cancer are very easy to miss on PET-CT;
- Gastric cancers with early stage disease are prone to false positive diagnosis of lymph node metastasis on PET-CT.
Overall, for patients diagnosed with gastric cancer, physicians will prefer enhanced CT for stage diagnosis; PET-CT can be added if distant metastases are suspected and the patient is financially well off; MRI can be added when there are lesions in the liver and CT cannot determine whether they are metastases; and barium meal imaging of the upper gastrointestinal tract can be added before surgery for upper gastric or cardia cancer to help determine whether the esophagus is involved. In addition, for patients who are clinically suspected of having gastric lesions but refuse to undergo gastroscopy, doctors will consider upper gastrointestinal imaging for preliminary diagnosis. (Written by Jingyu Huang, Department of Gastrointestinal Oncology, The First Affiliated Hospital of China Medical University, and Weilan Zhang, Department of Radiology, The First Affiliated Hospital of China Medical University)