[Intracranial granulocytic sarcoma extending from the posterior fossa to the carotid space via the jugular foramen: a case report].

Granulocytic sarcoma consists of neoplastic granulocytic precursors and myeloblasts. It is a focal lesion seen in 2-10.9% of acute myelogenous leukaemia (AML) patients. It usually develops either concurrently with the AML or after a remission. On rare occasions, it may be an initial manifestation of AML. Most common involvement sites are bone, periostium, soft tissue, lymph nodes and skin. Intracranial granulocytic sarcoma rarely occurs in meningeal or parenchymal form. We present an extremely rare case of intracranial granulocytic sarcoma extending from the posterior fossa to the carotid space via the jugular foramen in a 69 year old female. This form of involvement has not been previously reported. On MRI, the lesion appears isointense compared with normal grey matter in T1 and T2 weighted images and shows homogeneous contrast enhancement. With these findings, it is difficult to differentiate the lesion from other extraaxial tumours such as meningioma, paraganglioma, schwannoma, carcinoma, metastatic tumor, malignant lymphoma. However, granulocytic sarcoma, densely increased tumour cells restrict diffusion and reduce the extracellular volume fraction, tends to be markedly hyperintense on diffusion-weighted MR images and exhibits a marked decrease in ADC values. Therefore, DWI may be helpful in differentiating granulocytic sarcoma from other intracranial lesions.