Follicular pancreatitis: A rare pancreatic inflammatory pseudotumor

Abstract

Inflammatory pseudotumors imitate neoplasms on imaging but actually represent focal inflammation. We report a case of follicular pancreatitis, which is a recently recognized distinct form of mass-forming focal chronic pancreatitis pathologically characterized by lymphoid infiltration with abundant reactive germinal centers. In our patient, follicular pancreatitis manifested as a pancreatic tail mass that was resected due to imaging findings, which were suggestive of pancreatic malignancy. We performed a literature review of this rare condition and present a summary of reported imaging findings. The most distinguishing feature from pancreatic adenocarcinoma is the enhancement pattern, as follicular pancreatitis enhances more than the surrounding pancreatic parenchyma on delayed post-contrast images which is unusual for pancreatic adenocarcinoma. If this benign diagnosis is suggested on imaging, unnecessary surgery and its potential complications may be avoided.

Keywords: Chronic pancreatitis; Follicular pancreatitis; Mass-forming pancreatitis.

Figure 1:

Contrast-enhanced abdominal CT in the portal venous phase demonstrated a 2.8 cm hypodense pancreatic tail mass (arrow).

Figure 2:

On 1.5 T MRI, the pancreatic tail mass (arrow) was (a) hypointense on axial non-contrast fat-suppressed T1-weighted images, (b) isointense on axial T2-weighted images, and (c) hyperintense on axial diffusion-weighted imaging (b=600 mm²/s). On axial post-contrast fat-suppressed T1-weighted imaging (gadobutrol), the pancreatic tail mass was (d) hypointense in the late hepatic arterial phase, (e) isointense in the portal venous phase, and (f) hyperintense in delayed phases.

Figure 3:

Endoscopic ultrasound demonstrated a well-defined, hypoechoic, solid-appearing pancreatic tail mass.

Figure 4:

On 18F-FDG PET/CT, the pancreatic tail mass had elevated FDG uptake (SUVmax 4.8).

Figure 5:

Hematoxylin and eosin stained slides of the pancreatic tail mass demonstrated scattered lymphoid follicles with reactive germinal centers and atrophic changes of the pancreatic acini and ducts at (a) 40x magnification and (b) 100x magnification.