Extramedullary hand mirror cells in pathologic conditions of lymphoid tissue

The hand mirror (HM) cell phenomenon, which usually affects pathologic cells of lymphoid tissue in bone marrow, especially in acute lymphoblastic leukemia (ALL), was seen in B-cell lymphoma cells in cerebrospinal fluid (CSF). It was subsequently detected not only in the bone marrow, but also in extramedullary sites of the lymphoma. Subsequent phase-contrast microscopic study of 45 consecutive specimens of CSF revealed lymphoid cells with HM features in a case of ALL (in which HM cells were subsequently found in the bone marrow) and in a case of acute viral meningoencephalitis. These observations demonstrate that the HM cell phenomenon, which is considered to be a cellular alteration resulting from incorporation in the cell of antigen-antibody complexes, is not unique to bone marrow. It can be present in extramedullary sites and can be seen in exfoliated cells in CSF, where its detection is facilitated by the use of phase-contrast microscopy.