後頭蓋窩から頚静脈孔を通り頚動脈周囲に進展するgranulocytic sarcomaの1例

Intracranial Granulocytic Sarcoma Extending from the Posterior Fossa to the Carotid Space Via the Jugular Foramen: A Case Report

Ⅰ．はじめに

　Granulocytic sarcomaは，骨髄球系前駆細胞よりなる骨髄以外に発生する腫瘍である．稀な腫瘍であり通常，急性骨髄性白血病（AML：acute myelogenous leukemia）の診断時や経過中にみられるが，AMLの診断に先行してみられることもある．好発部位は骨，骨膜，軟部組織，リンパ節および皮膚であり，頭蓋内での発生は稀である．今回われわれは，後頭蓋窩から頚静脈孔を通り頚動脈周囲に進展した極めて稀な症例を経験し，またMRI拡散強調画像（DWI：diffusion weighted image）が術前診断に有用であったため，文献的考察を加えて報告する．

　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.