被殻部海綿状血管腫によるヘミバリスム—MRIによる診断とヘミバリスムの機序

CASE REPORT: HEMIBALLISM DUE TO A PUTAMINAL CAVERNOUS HEMANGIOM

　抄録　被殻の海綿状血管腫と思われる病巣により発症し，CTガイド下定位生検術後の出血により消失，更に術後，血腫吸収に伴い再発をみたヘミバリスムの1例を報告する。51歳女性，徐々に増強してきた左上下肢のヘミバリスムおよび軽度左片痲痺を主訴に来院した。CTスキャンで右被殻に，圧排像を伴う淡い高吸収域があり，delayed enhancementで増強された。血管撮影で異常所見は認めず，MRIではT1WIで周囲灰白質と等信号，T2WIで高信号，および周囲にring状低信号を呈した。海綿状血管腫を疑いCTガイド下定位生検術を施行したが，確定診断は得られなかった。術後，右被殻から尾状核にかけて小出血がおこり，ヘミバリスムは全く消失したが，血腫吸収とともに徐々に再発をみた。本症例の神経放射線学的所見はCT，血管撮影，MRIともに，海綿状血管腫に典型的な像であった。本症例の発生機序は，被殻部病変により，被殻から淡蒼球に至る抑制系ニューロンの活動低下がおきたためと推測された。停止の機序は，生検後に生じた線条体小血腫の圧迫により，視床や大脳皮質から線条体に至る興奮性ニューロンの遮断が生じ，淡蒼球の活動が低下したためと考えられた。

A rare case of reversible hemiballism due to putaminal pathological process in a 51-year-old woman is described. She was hospitalized for evaluation of hemiballism and muscle weakness on the left side. A cranial computed tomography scan demonstrated a high density lesion in the right putamen with enhancement on delayed scan. Angiographic examination revealed no apparent abnormalities. Magnetic resonance imaging with T 1 weighted showed a isodense lesion in the right putamen, while T 2 weighted image revealed a ring like low signal area around a high signal lesion. These findings were compatible with the diagnosis of cavernous hemangioma. In order to establish the final diagnosis, CT-guided stereotaxic biopsy was carried out. But histological specimen showed only gliosis and calsification. Immediately after the biopsy, a small hemorrhage took place in the right putamen extending to the head of caudate nucleus head. Following this episode, hemiballism ceased, however, it gradually returned along with absorption of hemorrhage. The specu-lated pathophysiology of this on-and-off hemibal-lism was as follows ; it initially developed as the result of suppression of inhibitory fibers from the striatum to the pallidum by a minor hemorrhage of putaminal cavernous hemangioma, and ceased by declining the activities of the pallidum due to interruption of excitatory fibers from the thalamus and the cortex to the striatum.