Pancreatic neuroendocrine neoplasms at magnetic resonance imaging: comparison between grade 3 and grade 1/2 tumors

Abstract

BackgroundThe grading of pancreatic neuroendocrine neoplasms (PanNENs) is associated with the choice of treatment strategy. The aim of this study is to identify the magnetic resonance imaging (MRI) features in differentiating pancreatic neuroendocrine tumors (PanNETs) grade 1/2 (G1/G2) and pancreatic neuroendocrine carcinoma grade 3 (PanNEC G3).Patients and methodsA total of 59 patients with histologically proven PanNENs and who underwent pretreatment MRI were retrospectively analyzed. Tumor location, size, boundary, cystic or solid appearance, enhancement degree, pancreatic duct dilatation, metastases and MRI signal were evaluated. Apparent diffusion coefficients (ADCs) were measured on ADC maps. Receiver operating characteristic curve was used to determine the cut off values and the sensitivity and specificity of prediction. Spearman correlation and logistic regression analysis were adopted to identify the association between MRI features and pathological parameters.ResultsA total of 47 lesions were PanNETs G1/G2 and 12 lesions were PanNEC G3. G1/G2 tumors were more common with well-circumscribed border compared with PanNEC G3. Ill- defined boundary, big size, necrosis, low-moderate enhancement, pancreatic duct dilatation, metastases and high diffusion-weighted imaging (DWI) intensity were more common in PanNEC G3 than in PanNETs G1/G2. The ADC values of PanNEC G3 were also significantly lower compared with the PanNETs G1/G2 and normal pancreatic parenchyma. The cut off value of ADC was 0.95×10−3 mm2/s for differentiating PanNEC G3 from PanNETs G1/G2 with 72.3% sensitivity and 91.6% specificity, respectively. Ki-67 index and mitosis count positively correlated with tumor size, pancreatic duct dilatation and metastases (P<0.05) and negatively correlated with ADC values (P<0.01), respectively. Regression analysis further showed that metastases and ADC value were associated with PanNENs grade.ConclusionMetastases and ADC value may have potential for differentiating PanNEC G3 from PanNETs G1/G2.

Correlation Between Apparent Diffusion Coefficient Value on MRI and Histopathologic WHO Grades of Neuroendocrine Tumors

“…Our results show a significant difference in both avgADC and minADC values between low grade (G1+G2) and high grade (G3) NETs. These findings are in line with other studies that compared G1+G2 vs G3 NET [9,11,13,14,17,18]. We chose to compare G1+G2 vs G3 because of the different treatment and prognosis of these groups as mentioned above.…”

“…[9] found a significant but weaker negative correlation of -0.33. Others reported a negative correlation between avgADC and Ki67-index (Guo et al [11]: -0.41, Wang et al [17]: -0.70). The avgADC and minADC values we found per WHO grade were similar to the values found by previous studies and are summarized in Table 3.…”

“…Treatment strategy for NET is related to the histological tumor grade and more specific the differentiation between low grade (WHO G1 and G2) and high grade (G3) tumors [11]. Low grade NET can be treated with surgical resection and/or targeted therapy for example somatostatin analogs, receptor targeted radionuclide agents, bevacizumab, sunitinib, and everolimus [3,6].…”

“…Alternative treatment strategies in inoperable patients include radiofrequency ablation, transarterial chemoembolization, and radioembolization. Both treatment strategy and prognosis are strongly dependent on histological grade with a poorer prognosis and higher metastatic rate for G3 tumors [9,11]. The possibility to predict tumor grade on a noninvasive basis and without ionizing radiation would certainly be advantageous.…”

Imaging in Pancreatic Neuroendocrine Tumors

“…10,12,26 Ill-defined margins, larger size, necrosis, predominant solid component, arterial hypoenhancement, pancreatic duct dilatation, presence of metastases, and diffusion restriction were more common in grade 3 than in grade 1 or 2 NETs. 27,28 In addition different DWI-based texture analysis parameters including correlation, contrast, inverse difference moment, maximum intensity, and entropy have been shown to differ between different grades of pancreatic NETs. 27…”