Carcinoid syndrome other imaging findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Parminder Dhingra, M.D. [2]

Other imaging studies for carcinoid tumor include somatostatin scintigraphy with 111Indium–octreotide, bone scintigraphy with 99mTc-methylene diphosphonate (99mTcMDP), 123 I-metaiodobenzylguanidine (MIBG) scintigraphy, capsule endoscopy (CE), enteroscopy, and angiography.

Other imaging modalities for gastrointestinal carcinoids include the use of:^[1]

• Somatostatin scintigraphy with 111Indium-octreotide
• Bone scintigraphy with 99mTc-methylene diphosphonate (99mTcMDP)
• 123 I-metaiodobenzylguanidine (MIBG) scintigraphy
• Capsule endoscopy (CE)
• Enteroscopy
• Positron emission tomography (PET)/CT scan
• Angiography

• It is the gold standard in confirming the location of functioning neuroendocrine tumour tissue.^[2]
• There are five different somatostatin receptor (SSTR) subtype, more than 70% of neuroendocrine tumors of both the gastrointestinal tract and pancreas express multiple subtypes predominantly 2 and 5.
• Midgut carcinoids predominantly express somatostatin receptors from sub-group 2 (sst2).^[3]
• The synthetic radiolabeled SSTR analog 111In-DTP-d-Phe10-{octreotide} affords an important method, somatostatin receptor scintigraphy (SRS), to localize carcinoid tumors, especially sst(2)-positive and sst(5)-positive tumors,and small primary tumors and metastases are diagnosed more readily than with conventional imaging or imaging techniques requiring multiple sessions.
• Overall sensitivity of the octreotide scan is reported to be as high as 90%.

• Bone scintigraphy with 99mTcMDP is the primary imaging modality for identifying bone involvement in neuroendocrine tumors and detection rates are reported to be 90% or higher.
• 123I-MIBG is concentrated by carcinoid tumors in as many as 70% of cases using the same mechanism as norepinephrine and is used successfully to visualize carcinoids.^[4]
• However, 123I-MIBG appears to be about half as sensitive as 111In-octreotide scintigraphy in detecting tumors.

• Endoscopic ultrasonography (EUS) may be a sensitive method for the detection of gastric and duodenal carcinoids and may be superior to conventional ultrasound, particularly in the detection of small tumors (2 mm–3 mm) that are localized in the bowel lumen.

• PET-CT scan is now playing an ever-increasing role in both localizing disseminated cancer and monitoring the disease response to systemic therapies.^[5]
• Carcinoid-specific agents includes: 5-hydroxy-l-tryptophan (5-HTP),64Cu-1,4,8,11-tetra-azacyclo-tetradecane-N,N′,N″, N‴-tera-acetic acid (TETA-OC) and 18F-dopa have been used.

MRI angiography has replaced angiography to a large extent. However, selective angiography may be useful to:

• Demonstrate the degree of tumor vascularity
• Angiography of the superior and inferior mesenteric artery has a reasonable sensitivity for the localization of the primary tumor, lymph node and liver metastases.
• Delineate the relationship of the tumor to adjacent major vascular structures
• Provide information regarding vascular invasion.

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