This splenic section from a patient with hairy cell leukemia shows infiltration with a monotonous population of medium-sized cells with clear cytoplasm and interlocking cell borders, giving a halo or "fried egg" appearance.
From Warnke, RA, Weiss, LM, Chan, JK, Cleary, ML, Dorfman, RF. Tumors of the lymph nodes and spleen. Atlas of tumor pathology (electronic fascicle), Third series, fascicle 14,1995, Washington, DC. Armed Forces Institute of Pathology.