Variations of hairy cell nuclei shapes with regard to ring-shaped nuclei simulating dysplastic neutrophilic granulocytes and review of the literature.

Introduction: Nuclei of hairy cells (HC) are typically oval, round or indented, but atypical shapes are occasionally described in HCL and may lead to a provisional wrong diagnosis.

Methods: The aim of this study was to quantify HC nuclei shapes classified into 11 categories on diagnostic bone marrow smears of 38 consecutive patients with HCL.

Results: HC in all 33 patients with evaluable smears at diagnosis exhibited a round/oval nucleus in 60.8-95.8%, an indented nucleus in 3.4-24.5% and a kidney-shaped nucleus in 0.4-7.0%. Other shapes of HC nuclei were found only in a proportion of patients: nuclei with two indentations in 0.4-6.5% HC (28 patients), overlapped nuclei in 0.5-3.5% HC (17) and lobulated nuclei in 0.4-4.5% HC (15). Two per cent or less of HC had the following nuclear shapes: that of an opposite indentation and impression (14 patients), dumb-bell (13), ring (10), horseshoe (5), two nuclei (8 patients).

Conclusion: Different shapes of HC nuclei similar to cells typical for other diagnoses are found usually in low frequencies. However, if their numbers are increased, they may cause diagnostic problems because cytology of blood and bone marrow smears is usually the first available diagnostic method.