12 Mar

Massive Hemothorax Due to Intrathoracic Extramedullary Hematopoiesis in a Patient With Thalassemia Intermedia: Discussion

Massive Hemothorax Due to Intrathoracic Extramedullary Hematopoiesis in a Patient With Thalassemia Intermedia: DiscussionIntrathoracic extramedullary hematopoiesis is a rare condition and is usually asymptomatic. Verani et al reviewed the literature in 1983 and collected 55 cases. With the exception of one patient who had dyspnea relieved with resection of an intrathoracic mass of erythropoietic tissue, the only previously reported complications have been due to spinal cord compression. Luyendijk et al in 1975 collected five cases of spinal cord compression from the literature and added one of their own. To our knowledge, our patient is the first reported case of hemothorax in this condition. Extramedullary hematopoiesis is seen in a variety of hematologic disorders. These include severe hemolytic anemias such as thalassemia and conditions such as myelofibrosis and myelophthistic anemia, where there is extensive replacement of normal marrow.

The most common sites of extramedullary hematopoiesis are the liver, spleen, and lymph nodes. Other sites are involved less frequently. The foci of heterotopic marrow are usually microscopic but they may be macroscopic and grow to a large size, as in this case. In the chest, tumor-like masses are formed which have a characteristic appearance. They are usually located in the lower paravertebral areas and are usually multiple and bilateral. They may have a lobulated appearance. Destruction of adjacent ribs and vertebrae is not seen. Pathologically, the masses are soft, deep red, and resemble splenic tissue on the cut surface. Histologically, they are formed of hematopoietic elements mixed with adiopose tissue.

The origin of the erythropoietic tissue in intrathoracic extramedullary hematopoiesis is unclear. It may arise by extrusion of hyperplastic marrow through the thinned cortex of ribs or vertebrae, with the periosteum forming the capsule of the mass. Alternatively, embryonic rests may transform into hematopoietic tissue under circumstances of bone marrow stress.
The diagnosis of intrathoracic extramedullary hematopoiesis can be established with reasonable certainty on the basis of the characteristic radiologic findings in a patient with a predisposing hematologic condition. Neurogenic tumors in the posterior mediastinum are the main considerations in differential diagnosis. Features that help to distinguish the two conditions are the frequent finding of lobulation and the absence of bone destruction in intrathoracic extramedullary hematopoiesis.

Categories: Thalassemia Intermedia
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