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    Gastrointestinal Carcinoid Tumors Treatment (PDQ®): Treatment - Health Professional Information [NCI] - General Information About Gastrointestinal Carcinoid Tumors

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    Imaging

    Imaging modalities for GI carcinoids include the use of somatostatin scintigraphy with 111Indium-octreotide; bone scintigraphy with 99mTc-methylene diphosphonate (99mTcMDP); 123 I-metaiodobenzylguanidine (MIBG) scintigraphy; computed tomography (CT); capsule endoscopy (CE); enteroscopy; and angiography.[26]

    Somatostatin receptor scintigraphy

    There are five different somatostatin receptor (SSTR) subtypes; more than 70% of NETs of both the GI tract and pancreas express multiple subtypes, with a predominance of receptor subtype 2 [sst(2)] and receptor subtype 5 [sst(5)].[50,51] 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.[26,52,53] 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.[26,54]

    Bone scintigraphy

    Bone scintigraphy with 99mTcMDP is the primary imaging modality for identifying bone involvement in NETs and detection rates are reported to be 90% or higher.[26] 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.[26,55]

    CT/MRI

    CT and magnetic resonance imaging (MRI) are important modalities used in the initial localization of carcinoid primaries and/or metastases. The median detection rate and sensitivity of CT and/or MRI have been estimated at 80%; detection rates by CT alone vary between 76% and 100%, while MRI detection rates vary between 67% and 100%.[26] CT and MRI may be used for initial localization of the tumor only because both imaging techniques may miss lesions otherwise detected by 111In-octreotide scintigraphy; one study has shown that lesions in 50% of patients were missed, especially in lymph nodes and extrahepatic locations.[26,56]

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