Colonic histiocytic neoplasm mimicking malignant histiocytosis and presenting as intussusception.

It is now apparent that distinction between the so-called malignant histiocytosis and lymphoma can be made using panels of established immunohistochemical markers and/or genotypic analysis. Many, if not all, of the previously diagnosed cases of malignant histiocytosis have been shown to be of lymphoid, rather than histiocytic, lineage. We report a rare case of colonic histiocytic neoplasm accompanied by a lymphoreticular dissemination that mimicked that of malignant histiocytosis. In addition, barium studies and computed axial tomography confirmed an intussusception that subsequently developed. The histiocytic nature of the neoplastic cells was supported by immunohistochemical, ultrastructural, and cytochemical studies. To our knowledge our case may represent the fifth documented case of a histiocytic malignancy reported in the literature. The relationship among the various cases will be discussed as well as the significance of the focal S-100 immunoreactivity observed in the present case.