Presacral extramedullary hematopoiesis: an alternative hypothesis.

Idiopathic extramedullary hematopoiesis (EMH) is the production of blood cells outside of the bone marrow without an underlying hematological pathology. This article examines the rare case of idiopathic EMH in the presacral area. A 65-year-old woman with a past medical history of a total abdominal hysterectomy and a negative hematological history presented with back and leg pain. MRI revealed a presacral mass. Fine needle aspiration revealed a diagnosis of EMH. The patient was managed conservatively with serial imaging. We present this patient with rare idiopathic, presacral EMH and review the literature on this topic. The current pathophysiology suggests that sacral fractures release hematopoietic stem cells, which in turn replicate to form an EMH mass. This review suggests a second mechanism in which surgical manipulation of the uterine tissue releases mesenchymal stem cells. These cells differentiate into stromal tissue that interacts with multipotent hematopoietic stem cells in order to form an EMH mass. Thus, idiopathic, presacral EMH may develop from either bone fractures or surgical manipulation of the uterus. Management of these patients should include watchful waiting unless intractable pain, new-onset weakness, or bowel/bladder dysfunction develops.