The role of CT and MRI in assessing the degree of malignancy of neuroendocrine tumors of the pancreas

Purpose: Assessment of the diagnostic value of CT and MRI in determining the malignancy grade of pancreatic neuroendocrine tumors (NETs).
Materials and methods: The study included 89 patients with pancreatic NETs. The diagnosis was established based on morphological examination after surgery or tumor biopsy. 54 patients underwent CT with contrast agent, 71 patients underwent MRI with MR contrast agent (MRCA). Based on CT and MRI data, the size, shape, structure, and signs of tumor necrosis were assessed, and quantitative indicators of density on CT and signal intensity on MRI in tumor tissue in different contrast phases were measured, and the absolute and relative percentages of contrast agent washout were calculated. Additionally, the presence of calcifications in NETs was determined using CT data, IS on T2-weighted images (WI), on diffusion-weighted images (DWI) with a b-factor of 50, 400 and 800 s/mm2 was determined using MRI data, and the value of the apparent diffusion coefficient (ADC) was measured on ADC-maps.
Results: The analysis of CT and MRI data revealed that the tumor size did not depend on the degree of malignancy and did not correlate with the Ki-67 index. The number of nodes statistically significantly differed: multiple lesions were more common in Grade 1, and solitary ones in Grade 2. The shape and contours of the tumors also depended on the degree of malignancy: oval or round tumors with clear contours prevailed in Grade 1, while irregularly shaped tumors with unclear contours prevailed in Grade 3, which was accompanied by a higher Ki-67 level. Contrast agent accumulation decreased with increasing malignancy degree, especially in the arterial and venous phases according to CT data, while an inverse relationship with the Ki-67 index was observed. Contrast agent washout according to CT was significantly lower in Grade 3. No significant differences in contrast agent washout and ADC values were found in MRI, with the exception of a moderate inverse relationship between MRCA accumulation on T1-WI FS and Ki-67. MRCA accumulation and washout were inversely correlated with Ki-67.
Conclusion: CT and MRI can be used to assess the grade of pancreatic NETs, improving preoperative risk stratification. The most reliable imaging markers of aggressiveness include poor margins, irregular shape, hypovascularity, severe necrosis, poor or negative washout, and decreased SI on T1-WI FS.

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