BACKGROUND: Hematopoiesis outside the bone marrow is known to occur in patients with severe anemia, leukemia, polycythemia, or myelofibrosis, and in patients affected by chronic poisoning by marrow-toxic substances. CASE DESCRIPTION: A 66-year-old right-handed man complained of 4 days of terrible right-sided, sharp, and shooting headache for which he saw his primary care provider. Routine laboratory examination showed a WBC count of 30800/microL. Neuroimaging showed a large, right frontotemporal, extra-axial, heterogeneously enhancing, dural based mass with associated recent intramural hemorrhage with evidence of midline shift and uncal herniation. The mass was resected using a right-sided extended craniotomy with anterior fossa and middle fossa approach. A hematoxylin-eosin-stained biopsy specimen showed whorls of tumor cells, diagnostic of a meningioma. Interspersed within the tumor bulk were nucleated RBCs, representing areas of extramedullary erythropoiesis within a meningioma. Flow cytometric evaluation confirmed the clinical suspicion of an underlying chronic lymphocytic leukemia. CONCLUSION: Occurrence of extramedullary hematopoiesis within a meningioma is extremely rare. Various theories may explain the occurrence of extramedullary hematopoiesis occurring within a meningioma in our patient, such as hematopoietic differentiation of multipotent mesenchymal tumor cells; direct extension of hematopoietic activity from the neighboring marrow cavity; displacement from bone marrow of stem cells that settle and develop in tissues where capillaries and blood vessels proliferate, such as a meningioma; or congenital heterotopia of totipotent connective tissue cells, which, under certain circumstances, may transform into hematopoietic tissue.
BACKGROUND: Hematopoiesis outside the bone marrow is known to occur in patients with severe anemia, leukemia, polycythemia, or myelofibrosis, and in patients affected by chronic poisoning by marrow-toxic substances. CASE DESCRIPTION: A 66-year-old right-handed man complained of 4 days of terrible right-sided, sharp, and shooting headache for which he saw his primary care provider. Routine laboratory examination showed a WBC count of 30800/microL. Neuroimaging showed a large, right frontotemporal, extra-axial, heterogeneously enhancing, dural based mass with associated recent intramural hemorrhage with evidence of midline shift and uncal herniation. The mass was resected using a right-sided extended craniotomy with anterior fossa and middle fossa approach. A hematoxylin-eosin-stained biopsy specimen showed whorls of tumor cells, diagnostic of a meningioma. Interspersed within the tumor bulk were nucleated RBCs, representing areas of extramedullary erythropoiesis within a meningioma. Flow cytometric evaluation confirmed the clinical suspicion of an underlying chronic lymphocytic leukemia. CONCLUSION: Occurrence of extramedullary hematopoiesis within a meningioma is extremely rare. Various theories may explain the occurrence of extramedullary hematopoiesis occurring within a meningioma in our patient, such as hematopoietic differentiation of multipotent mesenchymal tumor cells; direct extension of hematopoietic activity from the neighboring marrow cavity; displacement from bone marrow of stem cells that settle and develop in tissues where capillaries and blood vessels proliferate, such as a meningioma; or congenital heterotopia of totipotent connective tissue cells, which, under certain circumstances, may transform into hematopoietic tissue.