Diagnosis of spinal extramedullary hemopoiesis by magnetic resonance imaging

Abstract

Extramedullary hemopoiesis is an uncommon complication in patients with thalassemia. When it occurs in the extradural space, paraparesis due to spinal cord compression will result. In the past, the diagnosis of such a complication often rested upon myelography, computed tomography, and biopsy [l]. We report a case accurately diagnosed by magnetic resonance imaging (MRI). The patient was a 2%year-old woman who had a known history of thalassemia intermedia complicated by secondary hemochromatosis. She required regular transfusion of about 4 units of blood each year for the past 3 years. The pretransfusion hemoglobin level was around 8 g/dL. In March 1992, she presented with progressive weakness and paresthesias of both lower limbs. Examination showed hypotonia and a pyramidal pattern of weakness involving both lower limbs. The knee and ankle jerks were diminished, and there were bilateral extensor plantar reflexes. A sensory level up to T-5 developed over a few days’ time and there was no sacral sparing. Urinary and bowel functions remained normal. A clinical diagnosis of cord compression was made. Plain radiographs of the thoracic and lumbar spine showed rib expansion, accentuation of the vertical trabeculae of the vertebral bodies, and thinning of the cortical bone. No paravertebral mass nor narrowing of the disc space was noted. Computed tomography demonstrated a soft tissue mass at the TS-9 level that, after contrast injection, was shown to cause significant cord compression. However, this did not correlate well with the clinical findings, which suggested a lesion at a higher level. Thus, MRI of the thoracic spine was performed and showed an elongated extradural soft tissue mass posterior to the spinal cord extending from the T3-4 to mid-T-8 level (Figure 1). The spinal cord was compressed and displaced anteriorly. Marrow hyperplasia was evident by the enlargement of the medial ends of the ribs and the laminae as well as the transverse processes of the vertebral bodies. The signal intensity of the mass was similar to that of bone marrow, and no contrast enhancement with gadolinium was noted. Therefore, a radiologic diagnosis of extradural cord compression by extramedullary hemopoietic tissue was made. Laminectomy Figure 1. Sagittal Tl-weighted image showing an extradural mass of medium intensity that extends from the T3-4 to mid-T-8 level, occupying the posterior portion of the spinal canal and displacing the cord anteriorly.