DIAGNOSIS: INTRACEREBRAL GRANULOCYTIC SARCOMA
Granulocytic sarcoma (GS) is a rare extramedullary tumor composed of leukemic myeloblasts and myeloid precursors, which most often manifests in patients with AML, myelodysplastic syndromes, and myeloproliferative disorders, especially in those with CD56-positive leukemic cells (1). GS was first described in 1811 by Burns et al.(2) and termed chloroma because of the greenish appearance, which is contributed to myeloperoxidase activity in the tumor cells. Any organ may be involved such as the lymph nodes, skin, stomach and colon. The tumor often appears as a solitary mass. However, it can also present with multifocal lesions. GS most often occurs after manifestation of leukemic disease, but it may also preceed onset of leukemia. The intraparenchymatous CNS manifestation of GS is a rare event with about 20 cases described to date (3-6). The process of brain invasion is not completely understood. It has been proposed that leukemic cells migrate from the bone marrow through Haversian canals to the subperiosteum and the dura. After penetrating superficial arachnoid veins tumor cells enter the subarachnoid space (7). Disruption of the pial-glial barrier may lead to further migration of leukemic cells into the brain parenchyma.
In imaging studies, GS presents as iso- or hyperdense mass on CT and hypo- to iso intense on both T1- and T2-weighted MRI. As the lesion can be attached to the dural surface it may simulate meningiomas. Intraparenchymal GS occasionally show similar signal intensity as metastases. Cerebello-pontine masses have also been described which have to be distinguished from neurinomas (8).
Histopathological differentiation between GS and of lymphoma can be difficult, especially if the granulocytic sarcoma expresses markers of the B-cell lineage and the tumor precedes a medullar manifestation of AML. In this case markers of the myeloid lineage like chloroacetate esterase, lysozyme, CD15 and 56 should lead to the right diagnosis.
Patients with malignant tumors receiving radio- and/or chemotherapy have an increased risk for secondary malignancies, such as secondary leukemias. Therefore one should be aware of the possibility that a focal brain lesion may not necessarily represent metastatic carcinoma but may in fact be due to a concomitant or secondary hematological malignancy as in our case.
Contributed by Miletic H, Scheid C, Stenzel W, Lee JY, Deckert M