Sacral extramedullary haematopoiesis, radiologically mimicking malignancy

Extramedullary haematopoiesis (EMH) refers to ectopic haematopoietic elements outside the bone marrow. Although it frequently occurs in the liver, spleen and lymph nodes, EMH presenting as a destructive lytic lesion of the sacrum with associated presacral soft tissue mass masquerading as malignancy has been scarcely reported. Imaging workup on a pregnant woman suspected of having haemolytic anaemia revealed a lytic destructive lesion involving the sacrum with homogeneously enhancing presacral soft tissue density mass. A preliminary diagnosis of primary sacral malignancy with liver and splenic metastasis was made; however, additional MRI workup revealed the presacral soft tissue component had similar signal intensity to the adjacent bone marrow, suggesting a haematological disorder like EMH. Whenever a sacral lytic lesion with associated soft tissue presacral mass is encountered, the diagnosis of EMH should be considered in addition to common malignancies involving the sacrococcygeal region. Moreover, MRI and biopsy efficiently diagnose atypical EMH and exclude malignancies.