Diagnosis of Carcinoids
Diagnosis of carcinoid tumors involves urine and blood tests, imaging tests (e.g., x-ray, CT scan, MRI scan), and may involve exploratory surgery. In some cases, physicians administer a drug (e.g., calcium gluconate, pentagastrin, alcohol) to provoke flushing and help in the diagnosis. These drugs are administered under careful observation in a hospital because they may cause serious side effects.
When a carcinoid is suspected, the levels of serotonin or its by-products (usually 5-hydroxyindoleacetic acid [5-HIAA]) in the patient's urine are measured over a 24-hour period. High levels of other peptides (e.g., neuropeptide, neurotensin, secretin) may indicate a carcinoid tumor as well. Blood tests also may be used to measure the plasma level of these substances.
Serotonin-rich foods (e.g., bananas, avocados, pineapple, eggplant, walnuts) can interfere with the results of this test. Three days prior to undergoing the test, the patient should eliminate these foods from the diet. Drugs such as guaifenesin (present in cough medicines), acetaminophen (e.g., Tylenol), methocarbamol (muscle relaxant), and phenothiazines (tranquilizers) also can interfere with test results and should be discontinued prior to testing.
Imaging tests used to diagnose carcinoid tumors depend on the location of the tumor and whether or not the tumor has spread (metastasized). Tests include x-rays, computed tomography (CT scan), magnetic resonance imaging (MRI scan), and positron-emission tomography (PET scan).
CT scan uses x-rays to produce detailed images of abdominal organs and lymph nodes. In some cases, a contrast agent (dye) is used to detect metastasis. MRI scan uses magnetic fields to produce a cross-sectional image and detect tumors. PET scan is used to detect cell growth by producing detailed images of physical and chemical changes in the body.
Colonoscopy and upper and lower (barium enema) GI series may be used to detect carcinoid tumors of the GI tract. In colonoscopy, the physician inserts a very thin tube containing a light and a lens (called a colonoscope) into the rectum and colon to check for tumors. Small instruments can be inserted through the colonoscope to remove tissue for testing (called biopsy).
In an upper GI series (also called a barium swallow), the patient swallows a solution containing the mineral barium and x-rays of the upper tract (e.g., esophagus, stomach) are taken. In a lower GI series (also called a barium enema), the patient receives an enema with a solution containing barium and x-rays of the lower tract (e.g., intestines) are taken.
Because most carcinoids have receptors for the hormone somatostatin, angiography and radionuclide scan can be used to detect approximately 90% of tumors. These tests involve injecting a radioactive form of somatostatin into the bloodstream and using nuclear scanning to locate the tumor and determine its growth.
Exploratory surgery of the abdomen may be performed to locate a carcinoid tumor and determine its size.