MRI findings of pancreatic lymphoma and autoimmune pancreatitis: a comparative study

To clarify whether there are differences in MRI findings between pancreatic lymphomas and autoimmune pancreatitis (AIP).

MRI of 8 patients with pancreatic lymphomas and 21 patients with AIP were retrospectively reviewed. For multifocal pancreatic lymphomas (n=2) and AIP (n=4), the largest 2 lesions were evaluated. Ten pancreatic lymphomas and 25 AIP were compared on three bases: the signal intensity on T2-weighted images, internal homogeneity, and presence or absence of capsule-like rim. In 8 lymphomas and 19 AIP, the enhancement pattern on dynamic MRI was compared, as well.

On T2-weighted images, pancreatic lymphomas comprised 5, 5 and 4 lesions with low (iso), slightly high, and moderately high intensity, respectively, while the numbers for AIP were 14, 10, and 1 (P<0.01). Nine of 10 (90%) lymphomas appeared homogenous, and 11 of 25 (44%) AIP were homogenous (P<0.05). A capsule-like rim was present in 9 of 25 (36%) AIP, but was not seen in lymphomas (P<0.05). On dynamic MRI, 18 of 19 (94.7%) AIP showed persistent (n=5) or delayed enhancement (n=13), and 6 of 8 (75%) lymphomas showed low intensity without delayed enhancement (P<0.001).

MRI findings for pancreatic lymphomas and AIP were significantly different, which may be helpful for the differential diagnosis of these two diseases.