Pathologic findings:
Consists of several fragments of soft brownish tissues measuring 7.0
cm in aggregate dimension. These include a smooth capsule in some areas
and superficially resemble splenic parenchyma. Representative sections
submitted in three blocks.
| Fig 1: Low power capsule | Fig 2: Medium power capsule | Fig 3: High power megakaryocytes & erythroid cells |
| Fig 4: High power granulocytes | Fig 5: High power megakaryocytes & granulocytes | Fig 6: High power blasts |
Sections show diffuse cellular masses of heterogenous cells which include all three lineages of the haematopoietic marrow. Megakaryocytes are readily seen. Cells with small dark nuclei consistent with the erythroid series and many granulocytes of various maturation are also seen. Eosinophilic granulocytes are seen. In addition, several clusters of primitive looking precursor cells are also present. No significant adipose tissue is seen within the tumour.
Pathologic Diagnosis:
Left retroperitoneal mass - Extramedullary haematopoiesis, consistent with thalassaemia.
Pathologist Comments:
Extramedullary haematopoiesis (EMH) occurs normally in the developing fetus in the yolk sac and liver. Pathological EMH affects usually only the liver and spleen. Other than in these organs, EMH is rare. EMH is associated with haematological conditions most commonly thalassemia, spherocytosis and myelofibrosis (1). It may form nodules in the mediastinum, retroperitoneum or other soft tissues areas. These also had been reported in the lymph nodes, urinary bladder, prostate and thyroid (3). Remarkably, it had been reported in the endometrium not associated with haematologic disorders. Rarely, epidural EMH cause spinal cord compression which may be treated by radiotherapy(2).
When occuring outside the liver and spleen, EMH need to be distinguished from myelolipoma, in which a component of fatty tissues is admixed with the haematopoietic tissues. These are usually found within the adrenal gland and are accompanied by normal bone marrow.
Due to the relatively small mass of the lesion removed compared to the usually much larger spleen in thalassemia, it is unlikely that the excision would have any adverse effect on iron overload. Nonetheless, monitoring of serum iron and ferritin would be recommended in frequently transfused patients. Unlike the spleeen, such lesions are not involved in lymphoid B cell production and so their removal is not expected to affect B cell lymphoid function. If the lesion had not been removed, potential complications include rupture and haemoperitoneum. Lesions could be multiple and associated with enlargement of accessory spleens. Pre-operative diagnosis requires CT scan or MRI and a high index of suspicion.
Reference:
