Hairy cell leukemia presenting as a peripancreatic mass: cytomorphology and radiographic correlates.

Hairy cell leukemia (HCL) usually presents with peripheral cytopenias, diffuse marrow infiltration, and splenomegaly. This chronic lymphoproliferative disorder is not typically associated with lymphadenopathy or mass lesions. We report a case of HCL first treated by splenectomy, followed by several years of interferon therapy. Twenty-five years later, the patient presented with weight loss, fatigue, and a large PET-avid mass surrounding the head of the pancreas. Fine-needle aspiration was pursued to investigate the unusual and infiltrative appearance of the lesion, which was suggestive of another primary malignancy. Cytology smears showed discohesive lymphoid cells with round nuclei and delicate cytoplasmic projections. Flow cytometry confirmed the presence of a clonal B-cell population with bright expression of CD20 as well as CD25 and CD103, diagnostic of HCL. This is the first report of HCL presenting as a peripancreatic mass. The importance of correlation with radiology and clinical history is emphasized when evaluating such lesions.