Extradural Extramedulllary Hematopoiesis: a rare MRI Diagnosis with atypical Features M. N. Ahmad, N. Uddin*, S. Muzaffar**, S. N. Adil**, Z. Tasneem* Departments of Radiology, Pathology**, Intern*, Aga Khan University Hospital, Karachi. Introduction Extra-medullary hematopoiesis occurring in spinal epidural space with resulting cord compression is rare. We report a case of extra-medullary hematopoiesis causing thoracic spinal cord compression in a patient of myelofibrosis. Because of atypical MRI findings, it posed a significant diagnostic challenge. Therefore, we have discussed MRI features of this rare complication in correlation with relevant literature. Pathophysiology and management of this entity are also presented. Case Report A forty year old male, ex-smoker, presented with pain in lower back for six months and weakness in both legs for four months. These symptoms were progressive in nature making him unable to walk without support. He was complaining of sensory loss up to thoracic level. He had no history of fever, weight loss, jaundice, blood transfusion or trauma. Past history was significant for gouty arthritis. On examination, he was conscious. Speech and other higher mental functions were normal. He was unable to walk without support. There was decreased bulk and strength of both legs with 2/5 power proximally and distally. Reflexes were exaggerated and Babinski's sign was positive. He also had decrease sensation up to T4 dermatome. Upper limbs were normal and rest of the examination was unremarkable. Laboratory investigations revealed hemoglobin of 129 g/l ( 130-180 g/l ), Red blood cell count was 4.9x10 12 /l ( 4.5-6.5 x 10 12 /l ) , Hematocrit 0.40 ( 0.40-0.54 ), MCV 90.7 fl ( 76-100 fl ), MCH 26.1 pg ( 27-32 pg ) and WBC count 10.9x10 9 /l ( 4.0-11.0 x 10 9 /l ) with 8.06x10 9 /l (74 %) polymorphs ( 2.0-7.9 x 10 9 /l ). Peripheral blood smear was notable for leucoerythroblastic picture showing nucleated RBCs, occasional polychromatic cells, myelocytes and metamyelocytes. X-ray chest was normal. X-ray spine showed loss of normal lumbar curve, lumbar osteophytes and spurs. There was no fracture, lysthesis or bony contusion. Para-vertebral soft tissues were normal. Pedicels of L5 shows hazy appearance and margins were not clearly defined. The MRI examination demonstrated an extra-dural linear mass on the posterior aspect of spinal cord, causing significant compression of the dorsal spinal cord especially at the level of C5-C6. It was extending approximately from the disk of C7/T1 down to D12/L1 level. The mass was isointense to the spinal cord on the T1 weighted pulse sequences without contrast, but on T2 weighted sequences it was hyperintense (Figure 1). After contrast injection, the mass appeared to be diffusely intense and enhancing, indicating this to be cellular in nature and not in favor of blood or abscess (Figure 2). The vertebral body bone marrow signals were reduced, generally, indicating possible bone marrow infiltration or significant red marrow conversion. There was no evidence of pre-or para-vertebral mass. Based on clinical and radiological findings the diagnosis of spinal cord compression by a mass possibly lymphoma or extra-dural hematopoiesis was suggested. However, absence of a pre- or para- vertebral mass made the diagnosis of extradural extramedullary hematopoiesis, questionable. He received high dose steroids and spinal laminectomy was done at T1-T2 level; it revealed a bleeding & reddish colored mass. On histopathological examination it turned out to be an extramedullary hematopoietic tissue, because it exhibited both erythroid and myeloid cell lines. Megkaryocytes were also identified. There was no evidence malignancy or granuloma formation (Figure 3). J Pak Med Assoc 221