Extranodal Rosai-Dorfman Disease Presenting as a Pancreatic Mass Associated With Superior Mesenteric Artery Thrombosis.

Rosai-Dorfman disease (RDD) is a rare, nonmalignant histiocytic disease that classically presents as bulky lymphadenopathy. Although RDD can be seen in various organ systems, gastrointestinal involvement is uncommon. We present a case of RDD involving the pancreatic head causing biliary obstruction, arterial thrombus, abdominal pain, and concern for malignancy. Endoscopic ultrasound and pancreas biopsy demonstrated a mass without malignant features and pathological features including benign pancreatic parenchyma, noncaseating granulomas, and mixed acute and chronic inflammation including histiocytes with emperipolesis and a staining pattern that confirmed a diagnosis of RDD. She experienced symptom relief and reduced mass size and metabolic activity after treatment with cobimetinib. When there is uncertainty surrounding the etiology of a slow-growing pancreatic mass with atypical features, the differential diagnosis should include uncommon causes such as RDD and may warrant evaluation in a tertiary referral center to avoid extensive and unnecessary surgery.