What is the recommended imaging modality for the initial evaluation of a patient with a suspected gastroenteropancreatic (GEP) neuroendocrine tumor (NET)?

From the Guidelines

For the initial evaluation of a patient with suspected gastroenteropancreatic neuroendocrine tumor (GEP-NET), CT is the recommended imaging modality, but it is crucial to consider the complementary role of other imaging techniques such as MRI and PET-CT for comprehensive assessment and staging. The choice of imaging modality depends on various factors including the suspected location of the tumor, the presence of specific symptoms, and the need for detailed anatomical information. CT provides excellent anatomical detail and can detect primary tumors as well as metastatic disease, offering a comprehensive assessment of tumor location, size, and spread 1. This modality allows for evaluation of the entire abdomen and pelvis, which is crucial since GEP-NETs can arise from various locations in the gastrointestinal tract and pancreas.

Key Considerations for Imaging Modalities

• CT with contrast enhancement is particularly valuable as NETs are typically hypervascular and show characteristic enhancement patterns.
• MRI is advantageous for examination of the liver and the pancreas and is usually preferred in the initial staging and for the preoperative imaging work-up, especially with the use of diffusion-weighted imaging (DWI) 1.
• PET-CT with 68Ga-DOTA-somatostatin analogue (SSA) provides high sensitivity for imaging of most types of NET lesions and should be part of the tumour staging, preoperative imaging, and restaging 1.
• The sensitivity to detect NET disease by 68Ga-DOTA-SSA-PET-CT is 92% (range 64%-100%) and specificity 95% (range 83%-100%), making it a valuable tool for detecting lymph node, bone, and peritoneal lesions as well as unknown primary tumours 1.

Clinical Application and Recommendations

Given the strengths and limitations of each imaging modality, the initial evaluation of a patient with suspected GEP-NET should start with CT, but consideration should be given to promptly proceeding with more specialized imaging like MRI or PET-CT based on initial findings and clinical context. This approach ensures that patients receive comprehensive and accurate staging, which is critical for guiding treatment decisions and improving outcomes. The use of PET with [18F]fluoro-deoxy-glucose (FDG) is optional in NENs but is the tracer of choice for G3 and high G2 NETs, which generally have higher glucose metabolism and less SSTR expression than the low-grade NETs 1.

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From the Research

Recommended Imaging Modality for GEP-NET

The recommended imaging modality for the initial evaluation of a patient with a suspected gastroenteropancreatic (GEP) neuroendocrine tumor (NET) is:

• 68Ga-DOTATATE PET/CT, as it is the most sensitive imaging tool for these tumors 2, 3, 4
• This imaging modality is superior to traditional imaging in identifying primary or metastatic lesions and is clinically most useful for initial staging and in surveillance and monitoring response to therapy in the metastatic setting 2, 5

Key Findings

• 68Ga-DOTATATE PET/CT is indicated for localization of the primary tumor in select cases, staging patients with known NET, and selecting patients for PRRT 4
• SSTR-PET identifies extrahepatic metastatic disease in >1/3 of patients with presumed liver-only metastases on CI 3
• Stage migration following SSTR-PET may result in frequent moderate or significant management change 3

Comparison with Other Imaging Modalities

• SSTR PET/CT is superior to SRS and should be used whenever available 5
• (18)F-DOPA and (18)F-FDG PET/CT is inferior to SSTR PET/CT at least in patients with well-differentiated GEP-NETs 5
• CT and MRI are useful for morphological imaging, but molecular imaging techniques such as SSTR-PET are more beneficial for patient management 5, 6