Not all GI neuroendocrine tumors/cancers can cause the carcinoid syndrome. For example, rectal carcinoids usually do not make the hormone-like substances that cause these symptoms.

Most cases of carcinoid syndrome are seen when the cancer has already spread to other parts of the body. Normally, blood coming from the GI tract first flows through the liver, where substances made by GI carcinoid tumors are broken down before they can reach the rest of the body. This prevents carcinoid symptoms. But if the neuroendocrine cancer spreads elsewhere (including to the liver itself), the substances it makes can enter the main bloodstream and reach other parts of the body, where it can cause symptoms.

Exams and Tests Used to Diagnose GI Carcinoid Tumors

If there is a reason to suspect you may have a GI neuroendocrine tumor/cancer, the doctor will use one or more methods to find out if the disease is present.

Medical History and Physical Exam

A medical history is an interview in which the doctor asks questions about symptoms and risk factors you may have. The doctor will likely ask about symptoms of the carcinoid syndrome, as well as symptoms that might be caused by a mass in the stomach, intestines, or rectum.

Some patients with neuroendocrine tumors/cancers also have cancers or benign tumors of other organs, so doctors may ask about symptoms that might suggest other tumors are present. A thorough physical exam will provide information about signs of neuroendocrine tumors/cancers and other health problems. The doctor may pay special attention to the abdomen, looking for a tumor mass or enlarged liver.

These studies use a barium-containing solution that coats the lining of the esophagus, stomach, and intestines. The coating of barium helps find abnormalities of the lining of these organs. These are often useful for the diagnosis of some GI carcinoid tumors. They are least effective in finding small intestine carcinoids. Barium studies can be used to examine the upper or lower parts of the digestive system. You will probably have to fast and may need to take laxatives and/or enemas to cleanse the bowel the night before or the morning of these exams.

A barium swallow (also known as an upper GI series) is used to examine the lining of the esophagus, stomach, and the first part of the small intestine. Patients getting this test drink a barium solution before the x-ray pictures are taken. A small bowel follow through is a continuation of this test that is sometimes used to look for problems in the small intestine. For this test, x-rays are taken at regular intervals over the course of a few hours as the barium passes through the intestines.

Another option for looking at the small intestine is enteroclysis. In this test, a thin tube is passed from the mouth down through the stomach to the start of the small intestine. Barium contrast is sent through the tube, along with a substance that creates more air in the intestines, causing them to expand. X-rays of the intestines are then taken. This test may be quicker and give more complete results than a small bowel follow through, although placement of the tube can be uncomfortable, even when using medicine to numb the throat.

A barium enema with air contrast (also known as double-contrast barium enema or a lower GI series) is used to look at the inner surface of the large intestine. For this test, the barium solution is given through the anus while the patient is lying on the x-ray table. When the colon is about half full of barium, the patient rolls over so the barium spreads throughout the colon. In addition to barium, air can be blown into the large intestine to help push the barium towards the wall of this organ and better coat its inner surface. X-rays are then taken.

Barium x-rays are used less these days than in the past. In many cases they are being replaced by endoscopy -- where the doctor actually looks into the colon or stomach with a narrow fiber optic scope.

Computed Tomography (CT)

The CT scan is an x-ray procedure that produces detailed cross-sectional images of your body. Instead of taking one picture, like a standard x-ray, a CT scanner takes many pictures as it rotates around you. A computer then combines these into an images of slices of the part of your body that is being studied. Often after the first set of pictures is taken you will get an intravenous (IV) injection of a contrast agent, or dye, which helps better outline structures in your body. A second set of pictures is then taken.

CT scans can help tell if your neuroendocrine tumor/cancer has spread into lymph nodes or other organs such as your liver. They can also be used to guide a biopsy needle precisely into a suspected area of cancer spread. For a CT-guided needle biopsy, the patient remains on the CT scanning table, while a doctor moves a biopsy needle in the body toward the location of the mass. CT scans are repeated until the doctor is confident that the needle is within the mass. A fine-needle biopsy sample (tiny fragment of tissue) or a core-needle biopsy sample (a thin cylinder of tissue about ½-inch long and less than 1/8-inch in diameter) is then removed and looked at under a microscope.

CT scans take longer than regular x-rays. You need to lie still on a table for 15 to 30 minutes while they are being done. But they are getting faster, and your stay might be shorter. You might feel a bit confined by the ring you lay within when the pictures are being taken.

You may need an IV line through which the contrast dye is injected. The injection can sometimes cause flushing. Some people are allergic and get hives. Rarely, more serious reactions like trouble breathing and low blood pressure can occur. Be sure to tell the doctor if you have ever had a reaction to any contrast material used for x-rays. 

Magnetic Resonance Imaging (MRI)

MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed by the body and then released in a pattern formed by the type of tissue and by certain diseases. A computer translates the pattern into a detailed image of parts of the body. Like a CT scanner, this produces cross-sectional slices of the body. An MRI can produce slices that are parallel with the length of your body. As with a CT scan, a contrast material might be used, but it is not needed as often.

MRI scans are a little more uncomfortable than CT scans. They take longer -- often up to an hour. You have to be placed inside tube-like equipment, which is confining and can upset people with a fear of enclosed spaces. Newer, "open" MRI machines can help with this if needed. The MRI machine makes a buzzing noise that some people may find disturbing. Some places will provide headphones with music to block this sound.

Radionuclide Scans

Scans using small amounts of radioactivity and special cameras may be helpful in looking for carcinoid tumors. They can help determine the extent of the tumor, as well as help locate it if doctors aren't sure where it is in the body.

The most commonly used scan is somatostatin receptor scintigraphy (SRS), also known as the OctreoScan. It uses radioactive indium-111-lableled octreotide, a hormone-like substance that attaches to carcinoid cells, which is bound to radioactive indium-111. A small amount of this substance is injected into a vein. It travels through the blood and is attracted to carcinoid tumors. About 4 hours after the injection, a special camera can be used to show where the radioactivity has collected in the body. Additional scans may be done on the following few days as well.

Another test, known as an I-131 MIBG scan, is used less often. This test uses a chemical called MIBG to which radioactive iodine (I-131) is attached. This is injected into a vein, and the body is scanned several hours or days later with a special camera to look for areas that picked up the radioactivity. These would most likely be carcinoid tumors, although other kinds of neuroendocrine tumors will also pick up this chemical.

Positron Emission Tomography (PET)

A PET scan is another imaging test that uses low levels of radioactivity to look for tumors. PET scanning for neuroendocrine tumors/cancers uses a radioactive form of 5-hydroxytryptophan, a chemical that is taken up and used by carcinoid cells. A special camera can detect the radioactivity. Some doctors have found PET scans to be more accurate than CT scans for detecting spread of disease. However, this technique is not available in every hospital.

Endoscopy

These tests use a flexible lighted tube (endoscope) with a video camera on the end. The camera is connected to a monitor, which allows the doctor to clearly see any masses in the lining of the digestive organs. If abnormal areas are found, small pieces of tissue can be removed through the endoscope (biopsy). The tissue can be looked at under the microscope to find out if cancer is present and what kind of cancer it is.

For upper endoscopy (also known as an EGD), patients are sedated (made sleepy) and a tube is passed down through the mouth to show the esophagus, stomach, and first part of the small bowel.

In a colonoscopy (also known as a lower endoscopy), a long-flexible tube known as a colonoscope is inserted through the anus up into the colon. The colonoscope allows the doctor to see the lining of the entire rectum and colon. This test usually requires that you take laxatives or have an enema beforehand to make sure the bowels are empty. You will be given intravenous medicine to make you feel relaxed and sleepy during the procedure. A colonoscopy may be done in a hospital outpatient department, in a clinic, or in a doctor's office. It usually takes 15 to 30 minutes, although it may take longer if a tumor is seen and/or a biopsy taken.

For a suspected rectal tumor, a proctoscopy may be done. This involves using a shorter, hollow tube (a proctoscope), which is about 10 inches long and about 1 inch in diameter and may have a light on the end of it. The doctor coats the proctoscope with a lubricant and then gently pushes it into the anus and rectum. By shining a light into this tube, the doctor has a clear view of the lining of the rectum and anus. This test usually requires that you take laxatives or have an enema beforehand to make sure the bowels are empty.

Unfortunately, neither upper nor lower endoscopy can reach all areas of the small intestine, where many carcinoid tumors begin. This can delay finding these tumors. A newer technique, known as capsule endoscopy, may help in some cases. For this test, a person swallows a capsule (about the size of a large vitamin pill) that contains a light source and a very small camera. Like any other pill, the capsule goes through the stomach and into the small intestine. As it travels (usually over the course of about 8 hours), it takes thousands of pictures. These images are transmitted electronically to a device worn around the person's waist, while he or she goes on with normal daily activities. The pictures can then be downloaded onto a computer, where the doctor can watch them as a video. The capsule passes out of the body during a normal bowel movement and is discarded. This is still a fairly new technique, and its use is still being studied.

Endoscopic Ultrasound

This is a fairly new technique used in some patients having endoscopy. For this test, the endoscope has a small ultrasound probe on the end. This probe releases sound waves and then detects the echoes that bounce off tissues of the digestive tract wall. A computer then translates the pattern of echoes into an image of the wall of the esophagus, stomach, intestine, or rectum. Endoscopic ultrasound is sometimes useful in determining how far a tumor has spread through the wall of the esophagus, stomach, intestine, or rectum. The test can also help predict whether the tumor has spread beyond the wall of these organs to nearby tissues or lymph nodes.

Biopsy

Even if an imaging test finds a mass, it cannot tell if the mass is a carcinoid tumor, some other type of tumor (benign or cancerous), or a localized infection. The only way to know for sure is to remove cells from the abnormal area and look at them under a microscope. This procedure is called a biopsy.

There are several ways to take a sample from a gastrointestinal tumor. One way is through the endoscope. When a tumor is found, the doctor can use a biopsy forceps (pincers or tongs) through the tube to take a small sample of it. Another way to sample a tumor is with a CT-guided needle biopsy, as was described in the section on CT scans.

Bleeding after a biopsy from a neuroendocrine tumor/cancer is a rare but potentially serious problem. If bleeding becomes a problem, doctors can sometimes inject drugs into the tumor that constrict blood vessels to stop the bleeding.

In rare cases, neither an endoscopic biopsy nor a CT-guided needle biopsy will be able to get enough tissue to identify the type of tumor. This is sometimes the case with tumors in the small intestine. In such cases, a laparotomy (a surgical operation that involves opening the abdomen) to remove a tissue sample may be needed.

Blood and Urine Tests

Tests of the blood and urine can be very helpful in diagnosing carcinoid syndrome in patients who have symptoms that may be caused by it.

Serotonin is a substance made by some carcinoid tumors, especially those in the small intestine, and is likely the cause of some of the symptoms. It is broken down by the body into 5-hydroxyindoleactic acid (5-HIAA), which is released into the urine. A commonly used test to look for carcinoid syndrome measures the levels of 5-HIAA in a urine sample collected over 24 hours. Measuring the serotonin levels in the blood or urine may also give useful information. These tests can help diagnose some carcinoid tumors, but they are not always 100% accurate. Some foods and medicines can affect the results, and some small GI carcinoid tumors may not release enough of these substances to result in a positive test.

Other commonly used tests to look for carcinoids can include blood tests for chromogranin A (CgA), neuron-specific enolase (NSE), and substance P. Depending on the where the tumor might be located and on the patient's symptoms, doctors may do other blood tests as well.

Some of these tests can also be used to show how well treatment is working, as the levels of these substances tend to go down as tumors shrink.