Extramedullary hematopoiesis involving the central nervous system and surrounding structures.

Extramedullary hematopoiesis in central nervous system is a rare condition that can present in association with hematologic conditions. In this single-center retrospective study from 1988 to 2010, we identified 8 cases of extramedullary hematopoiesis involving the central nervous system or meninges. Most were incidental autopsy findings, usually microscopic collections of cells in the meninges or around blood vessels in the brain of infants (4 cases; age, 10 days to 5 months), in 1 young child (age, 6.5 years with anemia), and 1 elderly adult (age, 81 years with end-stage idiopathic myelofibrosis). Two individuals (both with polycythemia rubra vera) presented with symptomatic intracranial or spinal canal lesions (age, 67 and 68 years). Mixed populations of immature hematopoietic cells were identified by characteristic morphology and appropriate immunohistochemistry. The precise pathogenesis of extramedullary hematopoiesis in central nervous system is unknown. In infants, extramedullary hematopoiesis is unlikely to be pathologic and most likely represents a resolving fetal state. The older children and adults with incidental or symptomatic extramedullary hematopoiesis usually have some underlying hematologic condition, which should be sought if not already recognized.