Carcinoid syndrome other imaging findings

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

Overview

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 Findings

Other imaging modalities for gastrointestinal carcinoids include the use of:

• 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)
• Angiography

Somatostatin Receptor Scintigraphy

• It is the gold-standard in confirming the location of functioning neuroendocrine tumour tissue.
• There are five different somatostatin receptor (SSTR) subtype, more than 70% of neuroendocrine tumors of both the gastrointestinal tract and pancreas express multiple subtypes, with a predominance of receptor subtype 2 [sst(2)] and receptor subtype 5 [sst(5)].
• 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, imaging is accomplished in one session, 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%. However, failed detection may result from various technical issues, small tumor size, or inadequate expression of SSTRs.

Bone Scintigraphy

• 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.
• However, 123I-MIBG appears to be about half as sensitive as 111In-octreotide scintigraphy in detecting tumors.

Endoscopic Ultrasonography (EUS)

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. In one study, the EUS was reported to have an accuracy of 90% for the localization and staging of colorectal carcinoids.

Positron Emission Tomography (PET)

A promising approach for positron emission tomography (PET) as an imaging modality to visualize gastrointestinal carcinoids appears to be the use of the radioactive-labeled serotonin precursor 11C-5-hydroxytryptophan (11C-5-HTP). With 11C-5-HTP, tumor detection rates have been reported to be as high as 100%, and some investigators have concluded that 11C-5-HTP PET should be used as a universal detection method for detecting neuroendocrine tumors.

Angiography

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

• Demonstrate the degree of tumor vascularity
• Identify the sources of vascular supply
• Delineate the relationship of the tumor to adjacent major vascular structures
• Provide information regarding vascular invasion