MR findings of granulocytic sarcoma of the breasts

We report a case of isolated extramedullary relapse of acute myeloid leukaemia (AML) that presented as granulocytic sarcoma of both breasts, with no other signs of relapse even in the bone marrow. The T2 weighted coronal images on MR showed both multiple ill-defined heterogeneous hyperintense masses relative to breast parenchyma; these masses were seen also with a visual washout enhancement. Pathohistological study showed infiltration by myeloblasts, which were relatively uniform in appearance, featuring round or oval nuclei and a small cytoplasm. After chemotherapy and radiotherapy, both breast masses disappeared on MR images. Although the MR findings of granulocytic sarcoma were indistinguishable from those of multicentric carcinoma and malignant lymphoma, the MR images were useful for evaluating and monitoring responses to the treatments, as well as for detecting non-palpable relapsed tumours.