A filiform large cell lymphoma in the spleen: a case report with immunohistochemical and electron microscopic study

We describe histological, immunohistochemical, and ultrastructural findings in a filiform large cell lymphoma of the spleen in a 73-year-old man. The spleen weighed 300 g and contained a nodular mass of dimensions 4 x 2.8 x 3 cm that was lobular, raised, and well circumscribed. Light microscopically, the lesion was composed of compact cellular aggregates having large nuclei with evenly dispersed chromatin and a single large nucleolus or occasionally two to three small nucleoli. Immunohistochemically, the tumor cells were reactive to antibodies to leukocyte common antigen and MBI. Electron microscopically, most tumor cells were covered with tall, delicate, filiform cytoplasmic projections resembling microvilli in number and distribution. Filiform cytoplasmic projections varied from 50 to 200 nm in width and were at right or oblique angles to the surface. They appeared to be parallel but were frequently undulated, curved, or branching, forming in places small tufts. The pattern was more clearly noted on thick sections examined at an accelerating voltage of 200 kV.