Erdheim-Chester Disease Involving the Left Uterine Adnexa: Mimicking an Ovarian Carcinoma Clinically.

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis (LCH) that results in multiorgan disease involving the skin, bones, lungs, and kidneys. Female reproductive system manifestation of ECD was rare. Herein, we report a case of ECD involving the left ovary and fallopian tube. A 69-year-old woman presented with abdominal pain for 20 days. Magnetic resonance imaging revealed a solid and cystic mass on the left pelvic cavity. Histological examination revealed ovarian and fallopian tube infiltration by abundant histiocytes, with single small nuclei and foamy cytoplasm, reactive small lymphocytes, and plasma cells. Based on histopathological and immunohistochemical findings of positivity for CD68, CD163, and BRAF V600E and negativity for CD1α and S100, the molecular finding of BRAF V600E mutation, the patient was diagnosed with ECD. Positron emission tomography examination did not reveal any other lesions. The patient recovered well 12 months after surgery without any treatment. ECD involving the left fallopian tube and ovary was rare and needed to be differentiated from LCH, Rosai-Dorfman disease (RDD), juvenile xanthogranuloma (JXG), IgG4+ -related disease (IgG4+ RD), and metastatic signet ring cell carcinoma.