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Diagnosis of Carcinoid Tumors
Clinical Evaluation and Laboratory Studies
Various imaging modalities may be used either alone or in combination and may also be used in conjunction with fine needle biopsy. This involves inserting a thin needle into a tumor and extracting cells to be analyzed under a microscope in order to precisely characterize the type of cancer based on morphology. Computed Tomography (CT), Magnetic Resonance Imaging (MRI) or ultrasound may be used to guide the needle to the precise location of the tumor.
Somatostatin receptor scintigraphy (SRS), also called an octreotide scan, is a type of radionuclide scan used to detect carcinoid tumors. In a radionuclide scan, the patient is given an injection or swallows a small amount of radioactive material (a radionuclide). A scanner machine then measures the radioactivity in certain organs. This information is then used to produce an image of the internal organs.
In SRS, radioactive octreotide, a drug similar to somatostatin, is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to carcinoid tumor cells that have somatostatin receptors. A radiation-measuring device detects the radioactive material, showing where the carcinoid tumor cells are located in the body.
With the recent development of endoscopic ultrasonography (EUS), also called endoscopic ultrasound, as a sensitive imaging modality in the detection of primary neuroendocrine tumors of the duodenum and pancreas, the current recommendations are that patients undergo imaging with a combination of EUS, SRS, CT and MRI. By combining these imaging modalities, tumors can be detected in over 80% of cases.
Imaging alternatives for diagnosis of carcinoid tumors include:
Computerized Tomography (CT) with or without contrast dye. CT is reported to have a high sensitivity (up to 85%) for the identification of the spread of midgut tumors, however, the original tumor may not be visible if it is deep within the tissue. CT is effective for visualizing metastases to the liver and for determining lymph node involvement.
Magnetic Resonance Imaging (MRI) with or without contrast dye. MRI is helpful in confirming metastases of a carcinoid tumor to the liver. It is less sensitive than CT for identifying metastatic activity outside of the liver.
X-ray of the chest may be helpful in initially visualizing a lung carcinoid tumor.
Upper and lower GI series with contrast (barium) may be helpful in identifying abnormalities in lining of the gastrointestinal organs
Endoscopy (for foregut and upper midgut tumors), colonoscopy (for hindgut tumors) or bronchoscopy (for bronchial tumors) for identification of localized growths or polyps. Visualization is immediate and if certain abnormalities are found, the tissue can be excised during the test.
Ultrasound is helpful for visualizing liver metastases. It is also used for guiding fine needle biopsy for tumors in certain locations.
Radionuclide Imaging - Almost all carcinoid tumors have receptors for somatostatin which is a hormone-like substance secreted by the tumors. Somatostatin analogs, octreotide and lancreotide, have a strong affinity for the subtypes of somatostatin receptors expressed by carcinoid tumors. Radionuclide imaging scans include:
[111-In]-Octreotide Scintigraphy (Octreoscan) - When octreotide is attached to a radioactive isotope and injected into a patient, it bonds with the carcinoid cells thereby enabling the radioactive signal to be picked up and the area of the primary tumor to be identified (up to 95% sensitivity). Metastatic activity is also effectively identified with this technique. This is now considered to be the modality of choice for identifying and localizing carcinoid tumors. The effectiveness of [111-In]-octreotide scintigraphy is lower for hindgut tumors.
