Leptomeningeal melanomatosis with multiple cutaneous pigmented nevi: tumor cell proliferation and malignant transformation in an autopsy case.

We experienced a rare case of leptomeningeal melanomatosis. The proliferative activity and nuclear accumulation of p53 in this tumor were examined, since the relationship between this tumor type and growth has not yet been elucidated. A 33-year-old Japanese man was shown to have leptomeningeal melanomatosis with multiple cutaneous pigmented nevi. The autopsy findings showed the presence not only of benign diffuse melanosis of the leptomeninges but also of leptomeningeal melanomatosis in the subarachnoid space and brain parenchyma. In the brain parenchyma, the direct invasion of tumor cells from the subarachnoid space and Virchow-Robin spaces filled with melanoma cells were observed. Multiple hemorrhagic areas invaded by melanoma cells were also present. Immunohistochemical staining with a monoclonal antibody to melanoma cells showed positivity in the tumor cells. Proliferation analysis using the MIB-1 antibody demonstrated that the labeling index of tumor cells invading brain parenchyma (2.54%) was higher than that in other lesions of the inner (0.89%) and outer layer (0.76%) of the subarachnoid space. Nuclear accumulation of p53 protein was rarely seen in the tumor cells. We reported a case of leptomeningeal melanomatosis. Higher proliferative activity was found in invading cells of the brain parenchyma. Malignant transformation of the tumor did not appear to be associated with p53 gene mutation.