Intra-Operative Ultrasound: Tips and Tricks for Making the Most in Neurosurgery

Purpose: Advances in intraoperative imaging and neuronavigation techniques have positively affected glioma surgery. The desire to reduce brain-shift-related problems while achieving the real-time identification of lesions and residual and anatomical relationships has strongly supported the introduction of intraoperative ultrasound (ioUS) in neuro-oncological surgery. This paper presents tips based on our experience with ioUS in neurosurgery. Methods: We retrospectively analyzed 264 patients who underwent high-grade glioma (HGG) resection at the University of Turin and 60 patients who were treated at the University of Rome. Results: The main issues are the correct choice of the probe and how to evaluate the anatomy to understand how the information from the three common US planes (axial, sagittal and coronal plane) can be used in each case. It is also important to correctly identify anatomical structures in ioUS imaging. In a normal brain, the sulci, sickle, tentorium, choroid plexus, ependyma and the walls of the vessels are all hyperechoic. In addition, some structures are hypoechoic with a homogeneous acoustic gradient: ventricles, cysts and everything that contains liquor. Tumors are usually hyperechoic in ioUS because of their higher cellularity. Conversely, acute edema that contains fluid is hypoechoic, while chronic edema is hyperechoic. Conclusions: IoUS is a real-time, accurate and inexpensive imaging method. The difficulties of interpretation can be overcome by experience in US imaging and a better understanding of the interaction between navigation and imaging fusion techniques. Training on a large number of cases is important for the correct assessment of ioUS information to obtain valuable, real-time information during HGG surgery.