Solitary congenital histiocytoma: two cases.

Background. Solitary histiocytoma is an uncommon form of Hashimoto-Pritzker syndrome and an exceptional type of histiocytosis with cells of undetermined origin. A solitary often ulcerated congenital nodule is generally observed. We report two cases, one of each form. Case reports. Both cases presented an ulcerative budding congenital tumefaction of the plantar aspect of the right foot for the first child and the parieto-axillary region in the second. Histology disclosed a granulomatous infiltrate of histiocytes positive for specific immunolabels (protein S100 and CD1a). In the first case, electron microscopy revealed histiocytes devoid of Birbeck granules and myelinoid bodies leading to the diagnosis of Langerhans histiocytosis with cells of unknown origin. In the second case, 18 p. 100 of the cells contained Birbeck granules. There has been no recurrence after a 5-year follow-up in a case. Discussion. These cases recall the congenital nature of some types of solitary histiocytomas. Indeed, congenital Langerhans histiocytoma can occur as a unique nodule. The tumefaction may lie in any localization. Histological diagnosis is required. The benign nature of these lesions is confirmed by the absence of distant lesions and the lack of recurrence after complete excision. About a dozen cases have been reported. Most have been Hashimoto-Pritzker syndromes. Only one case has been reported with cells of undetermined origin. The diagnosis of histiocytosis with cells of undetermined undetermined origin is made when the ultrastructure study demonstrates the vacuity of the histiocyte cytoplasm. This condition is similar to Hashimoto-Pritzker syndrome by the absence of recurrence and systemic diffusion. It can however be observed in adults. The undetermined cell types would correspond different phases of Langerhans cell maturation or involution.