[Warfarin-induced hemorrhagic pseudocyst in the pelvis of a woman with an inherited disorder of blood coagulation, complicated by pelvic bone pseudoxanthoma mimicking Erdheim-Chester disease].

A fifty-year-old woman with developmental dysplasia of the hip underwent total hip arhtroplasty, and subsequently developed recurrent venous thrombophilia of the lower extremities. Hematological examination revealed an inherited disorder of blood coagulation (homozygous mutation of the 5,10-methylenetetrahydrofolate reductase gene) and therefore longterm Warfarin anticoagulation therapy was started. A year later she was diagnosed with a large pelvic posthemorrhagic pseudocyst (hematoma) located below the musculus iliacus and adhering to bone in the region of posterior acetabulum. The condition was complicated by usuration and focal osteolysis of the adjacent pelvic bone. Histological examination of the hematoma showed characteristics of an unusual pseudoxanthoma mimicking Erdheim-Chester disease. The differential diagnosis of histological findings is discussed and recent relevant literature is reviewed.