内頸動脈閉塞性疾患に対する超音波ドプラ血流検査法による診断とその限界

ULTRASONIC DOPPLER SONOGRAPHY FOR INTERNAL CAROTID OBSTRUCTIVE DISEASE AND ITS LIMITATION

　内頸動脈閉塞性疾患は，多彩な神経症状を呈するため臨床症状よりの診断は困難であり，しかも，血管吻合術や血栓除去術などの外科的治療を考慮されなければならない疾患である。そして，その確定診断に必要な脳血管撮影は，侵襲的でありまれに重篤な副作用を惹起するため，むやみに施行できない。このような意味において，超音波血流検査法は本疾患に対する非侵襲的検査法として，脳血管障害の診療には必須の検査となりつつある。

　今日まで，多くの著者^{1,4,6,15,17,21）}が，眼動脈血流の逆流を超音波ドプラ法で検出することにより，内頸動脈閉塞性疾患の診断が可能であることを報告している。しかし，内頸動脈閉塞症の16％〜41％の症例においては，眼動脈血流は逆流しておらず^11,22），眼動脈の逆流にのみ注目した場合の診断率もまた良くないことも明らかである。したがつて，眼動脈のみならず，総頸動脈血流や内頸動脈血流を直接検出することにより，診断率を上昇させようとする努力が少数の研究者によつてなされている^8,15,26）が，その診断率や診断法にいまだ多くの問題点や意見の不一致がのこされている。そこで著者らは，内頸動脈完全閉塞症，内頸動脈高度狭窄症，軽度狭窄症，中大脳動脈基幹部閉塞症の疾患群における，眼動脈や滑車上動脈血流のみならず，内頸動脈血流の超音波所見を詳細に分析することにより，各疾患に対する，超音波ドプラ血流検査法の診断率を検討しその限界を考察した。

A lot of reports suggested that obstructive lesions in the internal carotid artery (ICA) could be di-agnosed noninvasively using ultrasonic Doppler technique. However, diagnostic reliability for these diseases as well as the technical procedure in using ultrasonic Doppler flowmeter did vary among the authors. In the present study, diagnostic reliability of Doppler ultrasound was examined on the diseases of complete occlusion, high grade stenosis, low grade stenosis of the ICA and stem occlusion of the middle cerebral artery.

Blood flows in the supratrochlear, ophthalmic and internal carotid arteries were measured by the directional ultrasonic Doppler flowmeter of dual filter type. Signals of the blood flow were analysed by a sound spectrograph to produce a sonogram.

Clinical subjects consisted of 50 occlusions, 18 stenoses more than 50%, 32 stenoses less than 50% of the ICA, 26 stem occlusions of the middle cere-bral artery and 80 ICAs without obstructive lesions. All of them were diagnosed angiographically.

Ultrasonic Doppler findings of blood flows in the supratrochlear and ophthalmic arteries were classified into five groups; 1) normal flow type with normal response, 2) no flow signal type, 3) mixed flow type, 4) reversed flow type, 5) physio-logical flow type with abnormal response.

Blood flows in the ICA was divided into two groups; continuous flow type and discontinuous flow type according to a critical live of S= 3.625d-2.5 (S and d; maximum blood flow velocity at systolic and diastolic).

Finally, blood flow findings of both internal carotid and ophthalmic arterial territory in a patient were combinedly analysed and classified into normal, probably abnormal or abnormal Doppler finding.

The diagnostic reliability of the Doppler ultra-sound was good for the occlusions and high grade stenoses of the ICA. Ultrasonic Doppler finding was abnormal in 92% and probably abnormal inthe other 8% of the 50 complete occlusions. It was abnormal in 39%, probably abnormal in 17% and normal in 44% of the 18 high grade stenoses, but all of 6 cases with more than 75% stenosis had abnormal Doppler findings.

Diagnostic reliability was not satisfactory for the low grade stenoses of the ICA and the stem occlusion of the middle cerebral artery. The Doppler finding was abnormal only in 3%, probably abnormal in 19% and normal in 78% of the low grade stenoses. It was probably abnormal in 35% of the stem occlusion of the middle cerebral artery.

These diagnostic levels might be a limitation of the conventional ultrasonic flowmeters of directional continuous wave Doppler ultrasound. Newly developing ultrasonic instruments, such as B-mode or Doppler imaging of arteries, shall improve di-agnostic reliability for stenotic lesions of the ICA.