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Extra-medullary hematopoiesis is a rare condition that corresponds to the ectopic development of hematopoietic tissue outside the bone marrow, in response to bone marrow hyperstimulation. This phenomenon occurs mainly in embryonic hematopoiesis sites (spleen, liver, and lymph nodes), and sometimes in other organs such as the kidneys and lungs. Mediastinal localization is rarer. We present the case of a patient in whom the diagnosis of beta-thalassemia was raised in view of paravertebral tissue masses related to extra-medullary hematopoiesis.ObservationA 36-year-old patient hospitalized in our department for the stage II dyspnea, according to the New York Heart Association Classification with progression over three weeks. A thoracic CT scan was performed showing the presence, on each side of the dorsal spine, of two spontaneously dense masses, which were enhanced after contrast. Biologically, the blood smear showed erythroblastemia at 78%, made up of acidophilic erythroblasts with Howell-Jolly bodies, and anisopoikilocytosis of the red blood cells, made up of target red blood cells and sickle cell disease. Hemoglobin electrophoresis showed a hemoglobin F level at 90%. We supplemented this with molecular biology. The result was indicative of β0 thalassemia (β0/β0 allele).ConclusionThis case report describes an exceptional case of spinal extra-medullary hematopoiesis in which the diagnosis of B-thallasemia was based on molecular biology.