SOLITARY RETICULOHISTIOCYTOMA IN PREGNANCY - IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY OF A CASE WITH UNUSUAL IMMUNOPHENOTYPE

A case of a solitary reticulohistiocytoma during pregnancy is reported . The tumor arose on the right thigh of a 31-year-old woman during the 2nd month of gestation. Physical examination 6 months later revealed a 9 x 6 mm yellowish white papule. A biopsy showed a dermal proliferat ion of spindle to polygonal cells embedded in fibrous tissue with admi red neutrophils, eosinophils, and lymphocytes. Immunohistochemistry wa s positive for S-100, factor XIIIa, HLA-DR, KP-1, vimentin, and neuron -specific enolase. Ultrastructurally, the cells showed abundant lipid, lysozomes, and endoplasmic reticulum. No Birbeck granules could be id entified. The results suggest an aberrant immunophenotype intermediate between indeterminate cells and dermal dendritic cells. The relations hip of these lineages to reticulohistiocytoma and other dermal prolife rative disorders is reviewed.