Real-time intraoperative ultrasound in brain surgery: neuronavigation and use of contrast-enhanced image fusion.

Abstract

Point-of-care devices for intraoperative imaging represent one of the greatest adjuvant to modern strategies for surgical planning and execution; this is particularly true in neurosurgery given the complexity of the central nervous system and the delicate surgical maneuvers needed to manipulate it without causing iatrogenic damage. Preoperative imaging revolving around the correct prescription of specific MRI sequences (including digital tensor imaging and subsequent tractography analysis; arterial spin labeling; dynamic susceptibility contrast perfusion-weighted imaging and blood oxygenation level dependent, better known as BOLD sequences for functional MRI) allowed surgeons to obtain important information regarding the location of brain lesions and their relationship with surrounding eloquent anatomical structures (1-7). Together with data obtained through highly-selective nuclear medicine investigations, meant to disclose the metabolic behavior of those lesions, preoperative imaging serves as the first step in the planning of any neurosurgical intervention (8-11). To forecast the complexity of brain surgery and tackle it appropriately, most of those information can nowadays be tested through virtual surgery platforms; the final surgical plan is then implemented into the surgical theatre by making good use of surgical aids such as neuronavigation systems (see Figures 1,2​1,2),), which can be easily integrated into operating microscopy (12-16). Nonetheless, all the efforts put into weighting the pros and cons of different approaches, and tailoring the treatment strategy around patient’s and lesion’s specific characteristics, cannot always prepare surgeons for unexpected intraoperative challenges, such as brain shift following cerebrospinal fluid (CSF) deliquoration, lack of well-defined microscopic boundaries, diffuse bleeding, etc. (17,18). Open in a separate window Figure 1 Awake craniotomy for a left-sided motor strip glioma. Upper row: Preoperative post-contrast T1WI MRI scan showing an irregular cortico-subcortical lesion in the left frontal operculum, characterised by ill-defined peripheral gadolinium uptake and central necrosis with a significant amount of surrounding vasogenic edema. Central Image: Screenshot of image fusion created for neuronavigation purposes by coupling IoUS and preoperative MRI scan. Real-time visualisation of the relation of the surgical cavity with subcortical association fibres, note the green fibres seen adjacent to the deep aspect of the surgical cavity indicating the Superior Longitudinal Fasciculus and Inferior Fronto-Occipital Fasciculus serving speech function, and the blues fibers indicating the cortico-spinal tract. The presence of these fibres was confirmed with subcortical stimulation during the procedure. Bottom row: Postoperative post-contrast T1WI MRI scan showing a complete surgical resection with a clear surgical cavity.