Features of primary pancreatic lymphoma: A bi-institutional review with an emphasis on typical and atypical imaging features

ARTICLE HIGHLIGHTS

Research background

Primary pancreatic lymphoma (PPL) is a rare neoplasm. The ability to differentiate PPL from other pancreatic malignancies including pancreatic ductal adenocarcinoma (PDAC) is important for appropriate management. However, the nonspecific characteristics currently associated with PPL and a lack of information regarding PPL’s distinctive imaging features makes diagnosis difficult.

Research motivation

Identifying typical and atypical features of PPL on computed tomography (CT), as well as other diagnostic features that may differentiate PPL from its mimics, may enable definitive diagnosis. The discovery of features which distinguish PPL from PDAC early-on is critical to avoid unnecessary surgery.

Research objectives

This study aims to evaluate the typical and atypical CT imaging appearances of PPL. In addition, it distinguishes various clinical and laboratory markers which may be useful to identify PPL. An emphasis was placed on differentiating PPL from PDAC, which can be difficult to do using the current characteristics associated with PPL.

Research methods

Radiology, clinical, and pathology databases from two institutions were searched for reports between January 2000 and December 2020 containing the strings “pancreas lymphoma” or “pancreatic lymphoma”. The exclusion criteria were: (1) Lymphoma with mediastinal or pelvic adenopathy, bone marrow or hepatosplenic involvement which were considered to be systemic lymphoma and not PPL; (2) Pancreatic tumors suspected to be lymphoma on CT and later biopsy-proven to be another diagnosis on histological examination; (3) Subjects without a pretreatment multiphasic CT examination; and (4) Subjects whose medical records were not available of review. Multislice CT scans of the abdomen were viewed in the pre-contrast, arterial, venous, and delayed phases. The clinical presentation, management, laboratory findings, and imaging features of all included patients (n = 29) were evaluated.

Research results

All twenty-nine subjects were symptomatic, but only 14% demonstrated B symptoms and 24% demonstrated obstructive jaundice. Lactate dehydrogenase (LDH) levels were elevated in 17 of the 21 cases for which LDH levels were recorded (81%), however cancer antigen 19-9 (CA 19-9) levels were within normal limits for 18 out of the 20 cases for which values were recorded (90%). Pancreatic ductal dilation was absent in 83% of cases and no patients presented pancreatic atrophy. Atypical features of PPL included pancreatic bile duct dilation (17%), common bile duct (CBD) dilation (41%), necrosis (10%), and infiltration of the mesenteric root (14%). Size did not impact the prevalence of pancreatic and CBD dilation, necrosis, or mesenteric root infiltration (P = 0.525, P = 0.294, P = 0.543, and P = 0.097, respectively).

Research conclusions

The decreased prevalence of obstructive jaundice, elevated CA 19-9 levels, pancreatic ductal dilation, and pancreatic atrophy, as well as the increased elevation of LDH levels, encasement of the small mesenteric artery and/or vein without invasion or stenosis, and lymphadenopathy limited to the peripancreatic region, may be useful for distinguish PPL from its mimics, such as PDAC. However, in addition to the occasional appearance of pancreatic ductal dilation, this study identified multiple atypical features of PPL including the presence of CBD dilation, necrosis, and infiltration of the mesenteric root.

Research perspectives

Prospective studies with larger cohorts must be conducted to support the findings of this paper and the potential use of its highlighted imaging and clinical features for definitive diagnosis of PPL. In addition, there is a need for direct comparison of the frequency of these features in PPL vs PDAC, to determine how useful they are in differentiating the two entities.