Physiologic versus malignant uncinate process uptake on ⁶⁸Ga-DOTA-TATE PET/MRI

Introduction: Radiotracer uptake in the uncinate process is a frequent normal finding at somatostatin receptor PET imaging. In patients with neuroendocrine tumors, however, this physiologic activity can occasionally be difficult to distinguish from pancreatic masses, proximal small bowel tumors, or nodal metastases, and requires careful evaluation of CT or MR images to confirm the absence of an associated structural abnormality. PET and MRI data can be obtained concurrently with PET/MRI, which allows for optimal co-localization of abnormalities detected on either or both modalities. Materials and Methods: We evaluated for the presence or absence of uncinate process uptake on ⁶⁸Ga-DOTA-TATE PET/MRIs in 86 patients with known or suspected primary neuroendocrine tumors and characterized the uptake as either focal or diffuse. In cases where uncinate process uptake was present, T1 pre-contrast, T2, diffusion-weighted, and post-contrast MR images were reviewed to assess for underlying structural lesions as a cause for the uptake, and SUVmax was obtained from the PET images.

Results: Uncinate process activity was present in 39 of 86 cases (45%) and absent in the remaining 47 cases. In the 39 patients with uncinate process uptake, 28 had diffuse uptake and 11 had focal uptake. All cases (28) of diffuse uncinate uptake were without restricted diffusion or other MR abnormality and deemed physiologic. Nine out of 11 cases (82%) with focal uptake demonstrated an associated pathologic lesion with restricted diffusion or other MR abnormality, while the remaining 2 were physiologic. Radiotracer uptake in cases with physiologic uncinate activity had lower SUVmax (10.5+/-7.2) when compared to cases of malignant disease (SUVmax 63.2+/-52.0)(p < 0.001).

Conclusions: Physiologic uncinate process uptake is commonly found in patients undergoing somatostatin receptor PET imaging. More than one-third of our patients had physiologic uncinate activity at ⁶⁸Ga-DOTA-TATE PET/MRI. Although there is some overlap, SUVmax values appear to be valuable in determining whether uptake in the uncinate process is physiologic, and features such as a diffuse pattern of uptake and absence of a DWI abnormality can improve interpretive confidence.

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