Langerhans cell histiocytosis mimicking a residual cyst.

Langerhans cell histiocytosis (LCH) is an uncommon myeloid neoplasm characterized by clonal neoplastic proliferation of Langerhans-type dendritic cells associated with a reactive inflammatory infiltrate composed predominantly of lymphocytes and eosinophils. Only three cases of LCH mimicking periapical lesions have been reported in the English-language literature to date. Herein, we report a rare case of LCH involving the mandible of a 45-years-old woman mimicking microscopically and radiographically a residual cyst. The patient underwent enucleation and curettage of the lesion. Microscopically, the lesion showed fibrous tissue with an intense inflammatory infiltrate and histiocytes with irregular to elongated nuclei with prominent nuclear grooves. The tumor cells were positive for S-100 protein, CD1a, and CD207. After careful evaluation through imaging tests to rule out lesions in other anatomical locations, the diagnosis was solitary LCH of the mandible. After four years of follow-up, the patient remained with no evidence of recurrence. This case emphasizes the importance of a carefully clinical, radiographic, and microscopical evaluation of bone lesions, including periapical or residual cysts, since some neoplasms can mimic common benign lesions of the jaws. Although conservative approaches to treating solitary mandibular bone lesions of LCH can be employed, long-term follow-up is strongly recommended.