We reviewed smears of 102 bone marrow aspirates and 3 spleen punctures of 30 patients with hairy cell leukaemia (HCL) to find the occurrence of hairy cells with ring-shaped nuclei. No such cells were found in 18 bone marrow aspirates designated as non-evaluable, because of the poor smears quality or low numbers of hairy cells (under 500). Hairy cells with ring-shaped nuclei were found in 4 bone marrow aspirates of two patients with a frequency of 1.5% and 1.0% of hairy cells in the first patient and 0.3% and 0.1% in the second one. It seems that if cells with ring-shaped nuclei occur more frequently than in 0.1%, it is possible to find them in all other aspirates of such a patient. Besides these 4 aspirates with hairy cells with ring-shaped nuclei we found one or two such hairy cells in 5 other bone marrow aspirates and in one puncture from the spleen of another patient but with a low frequency between 2/5000 and 1/16,000. We found hairy cells with ring-shaped nuclei in all aspirates from 2 of 30 patients (7%) while at least one such cell was found in 8 patients (27%) with HCL. Neutrophil bands with a bent nucleus and its overlapping ends, simulating ring-shaped nuclei but with easily recognizable edges of overlapping ends, were found with a frequency of about 1 per mille of all nucleated bone marrow cells in 18 aspirates of 11 patients with HCL.

Keywords: Bone Marrow /ultrastructure/; Cell Nucleus /ultrastructure/; Humans; Leukemia, Hairy Cell /pathology/; Spleen /pathology/