INTRAOPERATIVE USE OF DOPPLER ULTRASOUND AND ENDOSCOPIC MONITORING IN THE STEREOTAXIC BIOPSY OF MALIGNANT BRAIN-TUMORS

An intraoperative monitoring tool is described that prevents mechanical injury to intracerebral vessels during stereotactic surgery. The method, which combines pulse Doppler ultrasonography and fiberendoscopy, allowed stereotactic biopsy to be performed without serious intracerebral bleeding in 25 patients with hypervascular malignant brain tumors, 13 with glioblastoma multiforme, five with anaplastic astrocytoma, five with metastatic tumor, and two with malignant lymphoma. The ultrasound apparatus has a built-in fast-Fourier transformation system analyzer and an improved filtering system that provide real-time measurement of blood flow velocity. The source of flow (arterial or venous) could be identified by both real-time sonography and acoustic signal frequencies. It was possible to measure the size and distance of a vessel by adjusting the Doppler signal gain dial from initially waxing to waning sounds, because the acoustic signal was adjusted to the axial now of each vessel in 0.1-mm steps. Each of three Doppler probes (1 mm, 2 mm, and 3 mm in diameter) fit through the outer cannula of the biopsy needle. Vessels located within 7 mm from the tip of these probes could be detected easily and rapidly, so the biopsy needle could be advanced safely to the desired target in 7-mm steps. If sonograms revealed blood flow, indicating the presence of larger vessels in the intended stereotactic trajectory, the angle of the needle was changed slightly to avoid vascular injury. Because the fiberendoscope was connected to a video processor, the vessel could be visualized at a higher magnification on the video display, unless there was active bleeding. This technically simple and reliable system enhances operative safety while maintaining accuracy.