Retroperitoneal Erdheim-Chester disease without skeletal bone involvement mimicking uterine sarcoma with multiple organ involvement.

Erdheim-Chester disease (ECD) is a rare type of non-Langerhans cell histiocytosis and is characterized by the diffuse histiocytic infiltration of multiple organs. Retroperitoneal ECD, especially with uterine involvement, is extremely rare. We report about a 73-year-old woman who presented with vaginal spotting for a month and experienced abdominal pain along with pus-like urine. Computed tomography revealed an irregular mass-like lesion in the uterus, possibly a uterine sarcoma, invading the ureter, rectosigmoid, and bladder. A tissue biopsy of the retroperitoneal mass revealed typical morphological and immunohistochemical features of ECD. However, clinical features, especially long bone involvement, did not coincide with ECD, and BRAF V600E gene mutation was not detected. We made a diagnosis of atypical retroperitoneal ECD mimicking uterine sarcoma with multiple organ involvement.