Cytology and immunocytology of infectious mononucleosis in fine needle aspirates of lymph nodes.

Two cases of infectious mononucleosis with atypical clinical presentations were initially diagnosed by fine needle aspiration (FNA) of lymph nodes and subsequently confirmed by serologic studies. The cytologic features that allowed recognition included a high percentage of cells with relatively abundant cytoplasm that stained pale to deep blue using a Giemsa-type stain. Many of the cells had plasmacytoid features. The cells ranged in size from small lymphocytes to large immunoblastic forms. Other features included mitotic figures and occasional binucleated forms. Immunologic studies showed a mixture of B and T cells, with many of the cells having a cytotoxic/suppressor phenotype. The features seem to be relatively characteristic and distinct from those of malignant processes that could be aspirated in lymph nodes. Recognition of infectious mononucleosis by FNA in these cases allowed for confirmation by serologic studies, thereby avoiding the need for an excisional biopsy. These cases show that FNA of lymph nodes may shed light on the nature of the process underlying the lymphadenopathy in selected cases of clinically atypical infectious mononucleosis.