To the Editors:
We read with interest the article by Kügler et al. 1 on paravertebral intrathoracic extramedullary haematopoiesis (EMH). Intrathoracic EMH was first noted by Guizetti as early as 1912 during an autopsy, and is typically located in the lower retropleural paravertebral region 2. In addition to the congenital haemolytic anaemias, myeloproliferative syndromes and bone marrow insufficiencies described, EMH can also occur as a reactive process to chronic anaemic conditions such as pernicious anaemia, B12 folate deficiency and Gaucher's disease.
The diagnosis of intrathoracic EMH can be difficult, and clinicians should have a high index of suspicion if the patient has a history of chronic anaemia. Neurogenic tumours (particularly neurolemmoma) remain the most common cause of a posterior mediastinal mass 3. Other possibilities include hydatid cysts, liposarcoma, lateral meningocele, cartilaginous tumours, lymphoma and azygous lobes. On computed tomography scanning, intrathoracic EMH is well circumscribed and has smooth borders, it is homogeneous in character, generally noncalcified and may have adipose tissue within the mass. Magnetic resonance imaging may be useful in some cases to demonstrate adipose components in the mass and adjacent bone cortex integrity 3. When the target site is situated away from the reticulo-endothelial organs, radioactive 99MTc sulphur colloid or iron-52 marrow scans can be used to demonstrate areas of haematopoietic activity, and thereby “light up” the EMH regions 4. Nevertheless, we agree that a definitive diagnosis can only come from biopsy of the mass.
In our experience, fine-needle aspiration often provides insufficient material for confirmatory cytological examination and may even be misleading 2, 5. A percutaneous biopsy approach can be technically difficult due to the specific location of the mass. Also, there is a significant risk of severe bleeding if the lesion is highly vascular 2. Recently, we have advocated video-assisted thoracic surgery biopsy with intra-operative frozen section for the diagnosis of this condition (fig. 1⇓). Video-assisted thoracic surgery carries the advantages of an open biopsy by direct visualisation of the mass. In addition, any haemorrhage that results from the biopsy can be better controlled compared with the percutaneous approach. Furthermore, the lesion can be resected in the same operation with minimal trauma.
Intra-operative photo of a video-assisted thoracic surgery biopsy of intrathoracic paravertebral extramedullary haematopoeisis.
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