頸部頸動脈石灰化プラークの破綻によるartery-to-artery embolismの1例

Artery-to-artery Embolism Due to Ruptured Calcified Carotid Plaque

Ⅰ．はじめに

　脳塞栓を起こす栓子は“hyper-dense MCA sign”¹⁰⁾のようにCT上高吸収値としてみられることがある．しかし脳動脈末梢に石灰化の高吸収値をみた場合，動脈自体の石灰化と考えるであろう．また頸動脈のcalcified plaqueは，soft plaqueに比べ塞栓源とはなりにくいとされている⁷⁾．今回，発症時のCTで左中大脳動脈末梢が多発性の高吸収値を呈し，頸動脈超音波検査と頸動脈内膜剥離術（CEA）の術中所見でcalcified plaqueが塞栓源と判明したartery-to-artery embolismの1例を報告する．

　Calcified carotid plaques are thought to be less likely to be symptomatic than non-calcified plaques. We present a patient with an unusual cerebral embolism that appeared as very high density on CT and was ascertained to derive from a calcified plaque. This 46-year-old male was admitted within 1 hr of sudden aphasia onset. The admission CT scan showed multiple high-intensity lesions that appeared like calcification. They were high intensity on MRI FLAIR images. MRA showed occlusion of the posterior trunk of the middle cerebral artery. As we considered cerebral embolism, the patient received heparin followed by warfarin. Routine MRA and DSA detected no abnormality, however, a carotid echogram showed a hyperechoic plaque at the left carotid bifurcation. As the NASCET method indicated 6.5% stenosis, carotid endarterectomy was not indicated. However, the thrombus at the bifurcation gradually enlarged despite adequate medical treatment (PT-INR 2.2 - 2.7) and we decided to surgically remove the calcified plaque, thought to be the embolus source. We removed the plaque content through a defect in the plaque membrane. Intraoperatively we found that the rapidly enlarging lesion was the plaque content rather than a thrombus. Pathologically, calcification was more dominant than atherosclerosis. His postoperative course was good and he required only aspirin. This case was peculiar in that the calcification mimicked a hyperdensity embolus and that the lesion derived from a calcified plaque which is usually stable. Repeat carotid ultrasonography is easy and useful when routine investigation fails to reveal the embolic source.