Diagnosing Colorectal Cancer
Your doctor has several tests and procedures that are useful in the evaluation of patients with colorectal cancer. Patients with colorectal cancer are seen at Virginia Mason's Seattle Main Clinic.
CT (Computed Tomography) Scan
Current guidelines or consensus recommendations include abdominal and pelvic CT scans in all patients with invasive colorectal cancers. The CT scan will provide information about the spread of the tumor to distant sites, such as the liver, and may provide information regarding the size and extent of the primary tumor.
All patients with the diagnosis of colorectal cancer should undergo colonoscopy, even if the diagnosis has already been established with another test such as a barium enema or sigmoidoscopy. Up to seven percent of patients will have another cancer, and a larger number will have precancerous polyps that should be addressed prior to the colon cancer operation.
PET (Positron emission tomography) Scan
PET scans show how tissues are metabolizing sugar. Malignant tumors use sugar at a higher rate than normal tissues or benign tumors. The patient is given an intravenous injection of a radioactive substance, called a radioisotope or tracer, which has been attached to a simple sugar. The scan can then show all sites in the body with tumors. This procedure, performed in the nuclear imaging department, is used in most patients who have metastatic colorectal cancers, or tumors that have spread to sites distant from the primary tumor. Most patients presenting with colorectal cancer do not require PET scans as part of their diagnostic workup.
Magnetic Resonance Imaging (MRI)
MRI provides excellent anatomic imaging of the entire body. However, MRI is not used in the routine diagnostic evaluation of patients with colorectal cancer. Occasionally, CT scans or PET scans will provide conflicting or unclear information with regard to abnormalities in sites such as the liver or pelvis. In these circumstances, our Gastrointestinal Cancer Conference may recommend the addition of an MRI in the evaluation of our patients.
Transrectal or Endoscopic Ultrasound (TRUS or EUS)
Patients with rectal cancers that involve the entire thickness of the rectum and/or have cancer that has spread to the lymph nodes receive radiation as part of their treatment. The best test to determine the extent of rectal cancer (or "stage" the tumor) is with newer ultrasound techniques. Tumors very close to the anus can be studied with a transrectal ultrasound (TRUS) performed by our radiologists. Tumors in the mid or upper rectum are best evaluated with an endoscopic ultrasound (EUS) performed by gastroenterologists with special training. Our team members at Virginia Mason are experts in this important diagnostic test.