Abstracts

Rationale: Intraoperative functional mapping is a well-established technique in awake neurosurgery. Since its invention in the 1930s, electrical cortical stimulation (ECS) has been the gold standard for reversible cortical perturbation, allowing surgeons to safely delineate the extent of surgical resection 4. In ECS, a large electrical current is sometimes required to produce observable behavioral deficits, increasing the risk of seizures. >Here we assess cortical cooling (CC) as a novel method for intraoperative cortical mapping. CC was reported to be able to reversibly alter cortical function2 like ECS. Moreover, CC seems to alter behavior performance in a more graded fashion than ECS, which usually elicits complete functional arrest  3. This suggests that CC may offer different cortical mapping possibilities and complement ECS testing during neurosurgical procedures. Here we report the safety and efficacy of our CC series to examine this novel tool for intraoperative functional mapping. Methods:  This study was approved by the University of Iowa (UI) Institutional Review Board. The subjects were neurosurgical patients who required craniotomy for the treatment of either intractable epilepsy or intra-axial tumor between 2007 and 2019. There were 56 subjects enrolled in this study, and 40 subjects underwent CC. 27 subjects (67.5%) underwent anterior temporal lobectomy for epilepsy and remaining 13 subjects (32.5%) had tumor resection in the peri-Sylvian area. CC was performed to identify language-critical cortices and its network before initiating corticotomy. Surgical procedures were done awake or under general anesthesia based on preoperative evaluation. In the former cases, CC was performed during language tasks to identify speech related areas, preceded by ECS to determine the location of cooling. In the latter cases, CC was performed along with ECS in attempt to identify connectivity of speech related areas.   Two different types of cooling probes were used in this study (see details in Long et.al., 2016). One probe was a stainless-steel chamber with a 2 cm diameter circular footprint (Figure 1A) 1 which was actively cooled by infusing sterile chilled hypertonic saline through the chamber. The second probe was a titanium chamber with a 1 x 1 cm square Peltier element (Custom Thermoelectric, Bishopville, MD) attached to the bottom of chamber (Figure 1B), which used sterile chilled saline in the chamber to dissipate heat generated on the non-brain side of the Peltier element. For the safety assessment, examination was performed in an outpatient or pre-discharge setting. Medical records including the assessment by the study’s designated non-affiliated physician safety monitor and perioperative imaging studies were reviewed. Neurological deficits or appearance of imaging changes (e.g. diffusion restriction) which were otherwise unexplainable were evaluated for potential cooling-related complication. Results: Among the 40 CC subjects, 31 (77.5%) underwent awake surgery and 9 (22.5%) underwent general anesthesia. In total 77 cortical sites were cooled; the number of sites ranged from one to seven within subjects. No subjects experienced intraoperative seizures or post-operative neurological deficits attributed to CC. No subject had post-operative imaging changes related to CC. Six subjects (15%) had neurological deficits at follow up, although these were considered the results of surgical resection and not the result of CC. Conclusions: This study was not designed to compare the efficacy and safety of the two methods, but the results document the safety of CC as an intraoperative mapping method. Some disadvantages of CC are that it requires longer times and additional equipment in the OR compared to ECS and that it cannot yet target deep structures. Cortical cooling is a safe method, which has potential to be a low risk alternative of electrical cortical stimulation.

 

 Funding: This work was supported by the National Institutes of Health (grant numbers R01-DC004290-19, R01-DC015260-04).