Octreoscan is used to visualize hormone-producing tumors of the nervous and endocrine systems, or neuroendocrine tumors. Most tumors of this nature contain cells with a receptor for the hormone somatostatin. In octreoscan, octreotide, an analogue of somatostatin, is labeled with a radioactive tracer and injected intravenously; the radioactive octreotide attaches to somatostatin receptors on the tumor cells and can then be observed with a special scanning camera. A variation of nuclear scanning, called single-photon emission computed tomography, or SPECT, enhances the sensitivity of the test.
Purpose of the Octreoscan
- To identify and pinpoint the location of benign or malignant (cancerous) neuroendocrine tumors (such as carcinoid tumors, small cell lung cancer, pituitary adenoma, neuroblastoma, medullary thyroid carcinoma and islet cell tumor of pancreas) prior to their surgical removal; this test can identify both primary cancer and cancer that has metastasized (spread) from other locations
- To monitor the effectiveness of therapy for neuroendocrine tumors and to detect recurrences or progression of disease
Who Performs It
- A technician trained in nuclear medicine
- This test should not be performed in women who are pregnant or breastfeeding because of possible risks to the fetus or infant.
- Patients with an allergy to shellfish or iodine could experience a severe allergic reaction to radioactive iodine; another type of radiotracer should be used.
- The presence of residual barium due to recent contrast x-rays of the gastrointestinal tract can cause defects in the scan that may be misinterpreted as growths. In addition, various abnormalities other than neuroendocrine tumors can also pick up octreotide, including certain infections, rheumatoid arthritis, and nonhormonal cancers. These factors may lead to false-positive results.
Before the Octreoscan
- Inform your doctor if you have an allergy to shellfish or iodine so that a noniodinated radiotracer can be used.
- If an iodinated dye is being used, you will receive iodine for 3 days prior to the test to preclude uptake of the radiotracer by the thyroid gland.
- If you have been receiving octreotide as a form of anticancer therapy, the agent will be discontinued for 2 weeks prior to the scan.
What You Experience
- The examiner injects radioactive octreotide into a vein in your arm or hand. Other than this injection, the procedure is painless.
- One hour after the injection, you will lie on a table under a large camera that records the gamma rays emitted by the radioactive material. You may be asked to assume various positions—on your back, side, and stomach—as the camera scans the length of your body.
- A computer translates signals from the scanner into images that are recorded on film. (More detailed images may also be obtained using SPECT.)
- About 2 hours after the octreotide injection, you will usually be given a fatty meal to help clear the radioactive material from your gallbladder.
- After 4 hours, you will be given a strong laxative to clear the octreotide from your bowel.
- Nuclear scanning is repeated at periodic intervals—for example, 2, 4, 24, and 48 hours after the octreotide is administered.
- You are free to go home in between scanning sessions.
Risks and Complications
- The trace amount of radioactive material used in this test is not associated with any significant risks or complications.
After the Octreoscan
- Drink plenty of fluids to help your kidneys excrete the radioactive octreotide.
- You may leave the testing facility and resume your normal activities.
- Blood may collect and clot under the skin (hematoma) at the injection site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
- A physician trained in nuclear medicine interprets the results of the scans.
- If no abnormality is found, no further testing may be necessary.
- If surgery is to be performed to remove neuroendocrine tumors, the scans will be used to help plan the procedure.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media