[Transcranial Doppler sonography in neurosurgery].

Using a 2 MHz transcranial Doppler sonographic system, it has become possible to measure flow velocities in the large basal vessels of the circle of Willis through thin areas of the cranial bone. After having used the method for one year on patients with neurovascular diseases, we now know that it can be employed as a matter of routine, after one has become familiar with it, and that it is of great diagnostic value. Knowing the measuring depth, achived by range gating, and with the aid of compression tests and standardised recording angles, it is possible to reliably identify the investigated vessel sections. In patients with subarachnoid haemorrhage it is possible to non-invasively detect and grade vasospasm and follow its individual course. Angiography and surgery can be reliably timed during a spasm-free interval. Preventive postoperative therapy following subarachnoid haemorrhage with hypervolaemia and hypertonia is simplified, as is the differential diagnosis as to whether secondary deteriorations are due to spasm or raised intracranial pressure. After extracranial/intracranial bypass operations, shunt patency and the effect of intracranial haemodynamics can be investigated without requiring angiography. Other fields of application concern the investigation of the evolution of haemodynamics after surgery on intracerebral arteriovenous malformations and for monitoring the cranial circulation in raised intracranial pressure.