Current status of intraoperative real-time vibrography in neurosurgery

Intracranial lesions are often characterized by different elasticities. The aim of the present study was to test the application of vibrography during brain tumor surgery.

The real-time vibrography system consisted of a conventional ultrasound system (Siemens Sonoline Omnia) with a custom-designed RF interface and a 6.5-MHz endocavity curved array (Siemens 6.5EC10). The RF data were digitized using a 50-MHz, 12-bit PCI analog/digital (A/D) converter for real-time or offline processing. Static compression was replaced by low-frequency axial vibration of the probe. A special applicator equipped with a stepping motor moved the ultrasonic probe and produced a low frequency mechanical vibration of 5-10 Hz with a vibration amplitude of 0.3 mm and slight preliminary compression (total<1 mm). The maximum application time was 60 sec. A pneumatic holding device (Unitrac, Aesculap, Tuttlingen, Germany) was used.

Brain tissue is normally color coded between red and orange. In this study 41 out of 45 tumors could be detected via vibrography. Two tumors could not be detected with this imaging technique: a glioblastoma at a depth of 2 cm and a metastasis at a depth of 3 cm. Two additional tumors were not recognized because of technical problems. In 4 cases tumors with strain values identical to those in brain tissue (coded red or orange) but easily identified by a peripheral zone of high strain (yellow) were found. Tumors with strain values higher than those measured in brain tissue coded yellow and were softer than brain during surgical intervention. Higher strain was found in 23 tumors. Tumors with strain values lower than those in cerebral tissue were found to be harder during surgery and coded brown or black. Lower strain was found in 10 cases. Four tumors were inhomogeneous and could not be assigned to one of the above groups. Mortality was 0%, morbidity 2.3%. One patient displayed transient paresis of the lower extremity due to microsurgical difficulties during the approach. In one patient minimal bleeding of the cortical surface occurred in a frontobasal tumor; however, no postoperative deficits were noted.

Vibrography is a new low-risk technique for intraoperative imaging. In low-grade astrocytomas and oligodendrogliomas, this additional technique can be used to control resection. In other cortical and subcortical tumors (e. g. metastases), it can provide an impression of the intratumoral elasticities.