Primary Pancreatic Follicular Lymphoma: An Elusive Diagnosis Behind a Pancreatic Mass
Introduction/Background/Significance: Primary pancreatic follicular lymphoma (PPFL) is an extremely rare subtype of extranodal follicular lymphoma, accounting for 0.1%-0.5% of malignant lymphomas and 0.2% of primary pancreatic tumors with only 31 cases reported in the last three decades. The diagnosis of PPFL can be challenging due to its rarity and overlap of clinical and radiologic features with other more common pancreatic masses, such as pancreatic ductal adenocarcinoma (PDAC). We report a case of asymptomatic PPFL incidentally detected on imaging, highlighting the importance of maintaining a broad differential and the critical role of histopathology in identifying such rare presentations.
Materials and Methods/Case Presentation/Objective: A 76-year-old male with significant smoking history underwent low-dose computed tomography (CT) screening, revealing suspicious lung nodules. Subsequent positron emission tomography (PET)-CT imaging incidentally demonstrated increased uptake (SUV 14.02) in the pancreatic head and second portion of the duodenum. Contrast-enhanced CT abdomen showed an exophytic pancreatic head mass measuring 2.1 × 1.4 cm, abutting and compressing the duodenum, raising concern for pancreatic malignancy. Magnetic Resonance Imaging (MRI) confirmed the lesion, absent on imaging two years prior. Endoscopic ultrasound (EUS) identified a 2.3 × 2.1 cm heterogenous pancreatic head mass with small cystic spaces and smooth margins, abutting the duodenal wall and superior border of the pancreas. The common bile duct ran through the mass with thickened walls and slight narrowing, but no strictures or lesions. EUS-guided core needle biopsy revealed small B-cell lymphoma consistent with classic follicular lymphoma.
At the time of diagnosis, the patient denied decreased appetite, early satiety, fever, night sweats or unintentional weight loss. He had a significant smoking history but no history of alcohol abuse or family history of pancreatic cancer. Physical examination was unremarkable, with benign abdominal examination, no lymphadenopathy, or palpable organomegaly.
Bone marrow biopsy showed no morphologic evidence of lymphoma; however, flow cytometry detected a small CD10-positive B-cell clone consistent with follicular lymphoma, confirming low-level marrow involvement consistent with stage IV disease. While observation is generally recommended for low-burden follicular lymphoma, the pancreatic head location raised concern for obstructive symptoms with disease progression, leading to the decision for a short course of palliative radiation.
Results/Description/Main Outcome Measures: This case underscores the diagnostic challenge posed by PPFL which can closely resemble PDAC both clinically and radiologically. Unlike PDAC, which often presents with symptoms such as jaundice, weight loss, and ductal obstruction, PPFL may remain asymptomatic and lack invasive features. Accurate identification relies on histopathologic evaluation and immunophenotyping from EUS-guided biopsies, which reveal a monoclonal B-cell population in lymphoma rather than malignant epithelial cells typical of PDAC. Recognizing PPFL is essential to avoid unnecessary surgical intervention and to guide appropriate evaluation and treatment planning.
Conclusions: Primary pancreatic follicular lymphoma is a rare but important diagnostic consideration for pancreatic masses, given its potential to resemble more common malignancies like PDAC. Awareness of PPFL as a potential mimic of pancreatic neoplasms can prevent overtreatment and guide clinicians toward minimally invasive diagnostic approaches and management tailored to the indolent nature of the disease.
