Imaging Tests
with Francesco Grasso, MD
What are the differences between the imaging systems?
Colorectal cancer is one of the most treatable forms of cancer when it’s detected in its earliest stages. Symptoms of colorectal cancer include a change in bowel habits such as diarrhea, constipation or narrow stools; rectal bleeding or blood in the stool; abdominal pain or cramping; and unexplained weakness and fatigue. However, cancer in its early stages does not present any symptoms and is usually detected by screening tests.
Although many people are uncomfortable discussing symptoms, physicians at GBMC emphasize the importance of having these signs evaluated. According to Francesco Grasso, MD, Colorectal Surgeon at GBMC, colorectal cancer may be diagnosed through physical exams, blood tests or colonoscopy. If abnormalities such as polyps are detected during colonoscopy, they are removed and immediately submitted for an exam under the microscope (biopsy).
If cancer is present in the colon or rectum, physicians may use imaging tests to determine if the cancer has spread. “Before recommending treatment, we want to get a complete picture of the cancer,” says Dr. Grasso. That picture is often obtained through computerized imaging tests such as endorectal ultrasound, computed tomography (CT) scan, positron emission tomography (PET) scan or a combination of these techniques.
Endorectal ultrasound uses the same technology as abdominal ultrasound (used to view a fetus in the womb), but the technique is different. Unlike abdominal ultrasound, which obtains images from the outside of the body, endorectal ultrasound is performed by inserting a special instrument into the rectum. “Endorectal ultrasound is used to determine how deeply the cancer has invaded the rectal wall,” says Dr. Grasso. "The test also allows physicians to determine if the cancer has spread to the liver, pelvic lymph nodes or other organs and tissues.”
CT scan obtains x-ray images of a specific cross-section of the body. The CT scanner takes multiple pictures of internal organs while it rotates around the patient. In most cases, patients receive a contrast agent or dye that helps outline structures of the body, making it easier to pinpoint the cancer. CT scan technology is also useful for precisely guiding a biopsy needle into a tumor that appears to have metastasized or spread to other organs.
PET scan is used to scan the patient’s whole body and look for cancer that may have spread from the colon or rectum. During a PET scan, a small amount of radioactive sugar is injected into the patient. If cancer is present, the cancerous cells will absorb the sugar faster, making the tumor easy for the PET machine to detect. In recent years, PET scans have become more accurate because newer devices combine the PET technology with a CT scan in a procedure known as a PET/CT scan.
Information from imaging tests is used to help stage the cancer and determine the best treatment for each patient. Staging is a diagnostic process that shows whether the cancer has spread and how far. Stage I cancer has not yet spread outside the colon or rectal wall. Stage II has grown through the wall of the colon or rectum but hasn’t spread to nearby lymph nodes. Stage III has invaded the lymph nodes but has not spread to other parts of the body. Stage IV has spread to distant sites such as the liver, lungs, abdomen or
ovaries.
“Staging is essential in deciding the therapeutic approach. We need to decide which treatments will be used and in what order to provide the best outcome for our patients,” says Dr. Grasso. "The goal of treatment is to remove the cancer while allowing patients to maintain bowel function that is as close to normal as possible".
Depending on the stage of the disease, colorectal cancer may be treated through surgery, chemotherapy, radiation therapy or a combination. “CT and PET scans are done to make sure there is no distant disease before we take a patient to surgery,” says Dr. Grasso. “If imaging tests show the cancer has metastasized to the lungs or liver, we may elect not to perform major surgery.” If the cancer has grown through the colon or rectal wall, a combination of radiation therapy and chemotherapy may be used to help shrink the tumor prior to surgery.
At GBMC, treatment decisions are made by a team of multidisciplinary oncology experts. “We work together to attack cancer on multiple fronts,” says Dr. Grasso. “The entire team discusses cases, determines the best treatment and then coordinates care for each individual patient.”
