Atypical malignant histiocytosis. Its appearance as a single meningeal tumor or as multiple skin tumors.

We studied two unusual cases of malignant histiocytosis (MH). In one case, a solitary intracranial tumor developed in a 20-year-old man eight months before the characteristic symptoms of MH appeared. In the other, a 73-year-old man had multiple nodular skin lesions four months before malignant histiocytes appeared in his blood. In both, the tumor cells were identified as malignant histiocytes by light and electron microscopic, cytochemical, and cytoimmunological criteria.