Primary Pancreatic Lymphoma: A Review of Imaging Features and Differentiation from Adenocarcinoma

Abstract

Primary pancreatic lymphoma (PPL) is defined as extranodal lymphoma with the bulk of disease confined to the pancreas. It is a rare diagnosis which accounts for less than 1% of pancreatic tumors and less than 2% of extranodal lymphomas. Despite its rarity, it is important to recognize features which may differentiate PPL from other pancreatic masses, particularly pancreatic adenocarcinoma. There are several imaging features that can help with this task. We present two cases of patients with primary pancreatic lymphoma which illustrate how it can mimic pancreatic adenocarcinoma and discuss imaging features which are specific to PPL. The first case is a 65 year old Hispanic male with low grade follicular lymphoma treated with cyclophosphamide, vincristine, prednisone and rituximab with complete response. A follow-up CT scan showed recurrent lymphoma confined to the pancreas (Figure 1). PPL typically manifests on CT as a hypoenhancing mass and this case shows how PPL can involve adjacent vasculature and mimic adenocarcinoma. Without the relevant history, this CT scan would be highly concerning for a pancreatic adenocarcinoma with perineural invasion encasing the celiac axis. Our second case shows features which can help differentiate PPL from adenocarcinoma. A 42 year old African American female with HIV presented with abdominal pain, anorexia, weight loss, chills, and non-drenching sweats. Initial CT showed a pancreatic mass (Figure 2) which was biopsied using EUS guidance. Pathology showed Burkitt's lymphoma. Staging scans showed disease confined to the pancreas. This case again shows the typical appearance of PPL, a homogenous, hypovascular pancreatic mass (typically in the head). Even though the mass is large, there is no dilation of the main pancreatic duct, a distinguishing feature of PPL. This patient's scan also showed lymphadenopathy (LAD) below the level of the left renal vein (Figure 3). LAD low in the retroperitoneum has been described as a specific feature of PPL which can differentiate it from adenocarcinoma. PPL also exhibits a more invasive growth pattern than adenocarcinoma, often without respect to normal anatomic boundaries. If PET/CT is utilized in these cases, both entities show hypermetabolism, but PPL shows much higher hypermetabolic activity than adenocarcinoma.Figure 1Figure 2Figure 3