What is the role of radionuclide imaging in the workup of carcinoid tumors?

Updated: Feb 12, 2019
  • Author: Cameron K Tebbi, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Answer

Radionuclide imaging with somatostatin analogs attached to radioactive tracer can be used to advantage for diagnosis of carcinoid tumors.

  • Radiotracers currently used include indium-111 diethylenetriamine pentaacetic acid (111 In-DTPA) and yttrium. Most neuroendocrine tumors have receptors for somatostatins. Five somatostatin receptor subtypes, designated SSTR-1 to SSTR-5, are identified. Binding affinity of somatostatin analogs to these subtypes may vary, with highest affinity for SSTR-2, medium affinity for SSTR-2 and SSTR-5, and lowest affinity for SSTR-1 and SSTR-4. Carcinoid tumors often express SSTR-1 to SSTR-3 and, infrequently, SSTR-2. Nevertheless, for tumors that measure less than 1 cm in diameter, the sensitivity of111 In-DTPA octreotide imaging reaches 80-90%.

  • This technique can be used to identify primary and metastatic disease and is approved for radionuclide scanning of carcinoid tumors. An advantage is that, if the result is positive, this technique can be used as a treatment modality.

  • In a study of 40 patients, somatostatin-receptor scintigraphy (SRS) helped in detecting localized tumors in 78% of patients versus 82% with CT scanning. However, SRS helped in identifying primary tumors in 2 patients missed on CT scanning. In 16% of patients, SRS depicted lesions not found with other modalities. No false-positive results were observed.

  • Overall, SRS appears to be the imaging method of choice for localizing and evaluating the extent of carcinoid tumor.

  • Bone metastasis is not uncommon in carcinoid tumors. In a study of 12 patients, 11 of whom had liver metastasis, 8 had bone involvement, as detected on SRS.

  • 6-Fluoro-[18F]L-dihydroxyphenylalanine positron emission/computed tomography for imaging carcinoid tumor has been reported. [81]

  • Technetium-99m bone scanning can aid in the detection of metastases.


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