Localized lymphoid hyperplasia can manifest as a focal mass-like lesion that is well-defined from the surrounding tissue (2
). Localized lymphoid hyperplasia has been described as a hypoechoic mass on ultrasonograms and as a well demarcated mass on CT images (2
). In our case, the localized lymphoid hyperplasia was visualized in the form of a discernible mass with delayed enhancement on the imaging studies. Given that the border between the localized lymphoid hyperplasia and the surrounding pancreas parenchyma was sharply demarcated on the pathologic specimen, it seems to be natural that the localized lymphoid hyperplasia was seen as a circumscribed round mass on all imaging studies. In the previous reports (4
) on lymphoid hyperplasia of the liver, the lesions appeared to be hypo- and hyperintense nodules on the T1- and T2-weighted images, respectively, which is similar to our case. In regard to contrast enhancement, reactive lymphoid hyperplasia of the liver showed a variety of dynamic enhancement patterns from arterial hypervascularity followed by washout to arterial hypovascularity with slight enhancement. In our case, the localized lymphoid hyperplasia of the pancreas showed arterial hypovascularity with delayed enhancement. We think that the enhancement pattern in our case was attributed to the presence of a rich fibrous matrix in the lesions.
The dilatation of the pancreatic duct is one of valuable additional findings for characterizing any pancreatic tumor. The presence of dilatation of the pancreatic duct that is induced by a pancreatic mass usually increases the possibility of malignant tumor. According to the previous reports (2
), pancreatic localized lymphoid hyperplasia was accompanied with the dilatation of the pancreatic duct or common bile duct, and this was interpreted to be the result of the mass effect of localized lymphoid hyperplasia on the pancreatic duct or the common bile duct. In our case, the diameter of the pancreatic duct showed a normal caliber. This may reflect that pancreatic localized lymphoid hyperplasia is unrelated to the pancreatic duct for its origin and the tumor has a benign histology. In addition, the one mass that was located in the uncinate process seemed to have no mass effect or a minimal mass effect on the main pancreatic duct.
Localized lymphoid hyperplasia is not considered to have any malignant potential (4
). Given that pseudolymphoma may denote a low-grade mucosa-associated lymphoid tissue (MALT) lymphoma, and malignant transformation of pseudolymphoma has been sporadically reported in the literature (5
), the term "localized lymphoid hyperplasia" seems to more accurately reflect the pathologic findings of our case than the term "pseudolymphoma".
The differential diagnosis of localized lymphoid hyperplasia of the pancreas includes neuroendocrine tumor, autoimmune pancreatitis, lymphoma and solid pseudopapillary tumor. Although neuroendocrine tumors are usually thought to be seen as hypervascular masses on the arterial phase images, the degree, uniformity and temporal change of the enhancement on the dynamic contrast-enhanced images can be highly variable (8
). Especially, more attention needs to be paid to distinguish between a delayed-enhancing, nonfunctioning neuroendocrine tumor and localized lymphoid hyperplasia. Given the imaging findings of localized lymphoid hyperplasia of the pancreas in this case, the presence of cystic or necrotic change in the mass may favor a diagnosis of neuroendocrine tumor. The localized form of autoimmune pancreatitis may present with a focal mass-like lesion and it share several imaging features with our case, such as delayed enhancement, a nondilated pancreatic duct and tumor multiplicity (9
). However, the localized form of autoimmune pancreatitis was reported to be often accompanied by wall thickening and enhancement of the common bile duct and upstream dilatation, and particularly in the cases whose pancreatic head was involved (9
), which may be diagnostic points to differentiate it from localized lymphoid hyperplasia. Pancreatic lymphoma sometimes manifests as a localized, well circumscribed mass in the pancreas, and this is not accompanied by dilatation of the pancreatic duct (10
). In contrast with pancreatic localized lymphoid hyperplasia, pancreatic lymphoma appears as a heterogeneous mass with low to intermediate signal intensity on the T2-weighted images and as a hypovascular mass on the contrast-enhanced images. Finally, solid pseudopapillary tumor (SPT) needs to be included in the list of the differential diagnoses because small (less than 3 cm) SPTs can appear as well-defined solid lesions with delayed enhancement (11
In summary, we present here an interesting case of double pancreatic localized lymphoid hyperplasia with the US, CT and MR imaging findings. Although it is rare, localized lymphoid hyperplasia of the pancreas should be included in the differential diagnosis of pancreatic tumor, and especially when the imaging studies show a localized, delayed enhancing mass of the pancreas without any dilatation of the pancreatic duct.