Characteristics of ill-demarcated small pancreatic ductal adenocarcinoma on MRI: a multi-institutional retrospective cohort study.

PURPOSE: To investigate the frequency of visually ill-demarcated small pancreatic ductal adenocarcinomas (PDACs) and compare their clinicopathologic and MRI characteristics with those of well-demarcated tumors.

MATERIALS AND

METHODS

This multicenter retrospective study enrolled 210 patients with surgically confirmed small PDACs (≤ 20 mm) who underwent preoperative unenhanced MRI. Clinical and pathological data were collected. Two radiologists independently evaluated the following MRI features: (a) tumor delineation (well-demarcated or ill-demarcated), (b) tumor signal intensity, and (c) secondary signs, including distal parenchymal signal intensity, parenchymal atrophy, main pancreatic duct (MPD) stenosis and dilatation, and small retention cyst. Clinicopathologic features and MRI findings were compared between well-demarcated and ill-demarcated PDACs using the Mann-Whitney and Fisher's exact tests. Multivariate logistic regression analysis was performed to identify independent factors associated with ill-demarcated PDAC.

RESULTS

Visually ill-demarcated tumors accounted for 46.7% of small PDACs. Compared with well-demarcated tumors, ill-demarcated tumors were associated with less frequent elevation of tumor marker levels (P = 0.001) and smaller tumor size (P < 0.001). Abnormal distal parenchymal signal intensity was observed more frequently on T1-weighted imaging than on diffusion-weighted imaging (P = 0.012) or T2-weighted imaging (P < 0.001), and was significantly more frequent in ill-demarcated tumors across all MRI sequences (all P < 0.05). MPD stenosis and dilatation on T2-weighted imaging were more frequent in ill-demarcated tumors (both P < 0.001). Ill-demarcated tumors were also more frequently associated with at least one secondary sign (P = 0.002). On multivariable analysis, smaller tumor size (P = 0.002) and the presence of MPD dilatation (P = 0.002) were independently associated with ill-demarcated PDAC.

CONCLUSION

Nearly half of the small PDACs were visually ill-demarcated on MRI. Therefore, when a focal tumor is not clearly visible, careful assessment of secondary MRI findings, particularly distal parenchymal signal abnormalities on T1-weighted imaging and MPD dilatation on T2-weighted imaging, may aid in the diagnosis.