Interhemispheric approach is a common route for aneurysmal surgery, such as anterior communicating (A-com) artery and distal anterior cerebral artery (ACA) . There have been some attempts to preserve the bridging vein by mobilization or special dissection technique. Until now, there has been no intraoperative system for monitoring the venous blood flow. In the present study, we used microvascular Doppler sonography for venous blood flow velocity monitoring. Eleven cases of A-com aneurysm or distal ACA aneurysm were investigated in this study. Measurement of the venous blood flow velocity was performed at the following three different steps during the operation: before using the brain retractor (A), during brain retraction with the retractor (B), and after the operation (C) . We used two different techniques to dissect the bridging vein according to the severity of adhesion between the dura and the bridging vein. In 6 cases, the bridging vein was dissected free along the whole length between the cortex and superior sagittal sinus (SSS group) . In 5 cases, the vein was not dissected from the dura intentionally for a length of about 10 to 15 mm at its superior sagittal sinus side (dura group) .
There was a strong tendency for decrease in the, venous blood flow velocity during brain retraction in the SSS group. The blood flow velocity was well preserved in the dura group. Two out of 6 cases in the SSS group showed venous occlusion on postoperative angiography and they developed transient or permanent neurological deficit.
Our study revealed the importance of monitoring the venous blood flow velocity to minimize postoperative complications due to venous circulation disturbance.

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To clarify the significance of findings obtained by transcranial Doppler sonography (TCD) on vasospasm following subarachnoid hemorrhage, TCD monitoring was evaluated in an experimental model of vasospasm. The model consisted of mechanically stenosed arteries created by placing clips on the aorta and the femoral ar-teries in anesthetized rabbits. Flow velocity (FV) and Fourier's transformed pulsatility index (FPI_1-10=each amplitude/mean FV) of 10 harmonics were assessed with two types of stenosis: (1) proximal stenosis by proximal clipping and (2) peripheral stenosis by distal clipping.
Result: (1) proximal stenosis: at the stenotic region, FV, FPI₁and some parts of FPI_2-10were increased in accordance with an increase in stenosis with decreased flow volume. At the poststenotic resion, lower FV and higher FPI_{1, 2-10}were observed in comparison with the stenotic region. (2) peripheral stenosis: FV and FPI₁decreased with partial increase of FPI_2-10were observed in accordance with an increase in stenosis and a decrease in flow volume.
Conclusion: Fourier waveform analysis is useful in assessing a significant decrease in flow volume, and ap-pearance of ischemia due to vasospasm after subarachnoid hemorrhage.

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We performed TCD examinations using Transpect (Medasonics) in 744 cases (cerebral infarct or TIA: 482, control: 112, other diseases: 150) . In order to establish the TCD diagnostic criteria of MCA stenosis (MCAS), the highest mean flow velocity (MFV) in the control group was evaluated. MFV was 110 cm/s in cases aged between 17-29 years, 104 cm/s in cases aged 30-49 years, 94 cm/s in cases aged 50-69 years, and 64 cm/s in cases older than 70 years. For the detection of milder stenosis, an interhemispheric asymmetry index was calculated using the following formula:
Al=MV1-MV2/ (MV1+MV2) /2×100
where MV1 and MV2 represent mean velocities of the middle cerebral arteries. The diagnostic criteria of MCAS were considered to be an MFV higher than the highest MFV of the control group, and an AT more than 30%. The criterion of MCA occlusion (MCAO) was undetectable MCA signals in the presence of PCA, ACA, ICA signals. TCD findings in angiographically diagnosed MCAS (25 cases) and MCAO (12 cases) were assessed for sensitivity and specificity. The sensitivity of TCD diagnosis in MCAS and MCAO was 100%, respectively. The specificity was 98% in MCAS and 95% in MCAO. In conclusion, TCD is a very accurate method of diagnosing MCAS and MCAO.

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