The World Society of Stereotactic and Functional Neurosurgery (WSSFN) had its 15th Quadrennial Meeting in Toronto, Canada May 24-27, 2009 (Detailed program). More than 500 functional neurosurgeons from around the world convened to discuss their latest findings. As a group, functional neurosurgeons have the highest percentage of interest in MRgFUS of any group of clinical physicians (virtually 100%).
There has been a surge in interest using deep brain stimulation (DBS) for neuromodulation in functional neurosurgery over the last decade. The main limitations of DBS for movement disorders, pain and behavioral disorders are cost in both money and time, and the necessity of a neurosurgical operation that entails some risk of hemorrhage, infection, mechanical failure, neurologic damage, etc. One tremendous advantage of MRgFUS is the non-invasive nature of the technique. Any form of lesioning, including MRgFUS, gains significant advantage through targeting techniques that assure a safe, effective lesion location. MRgFUS offers distinct advantages over other techniques through MR thermometry (visualization of the actual energy focus prior to lesioning) and neurophysiological assessment through transient neuromodulation effects. This counters the main advantage of DBS, which is its reversibility in the face of a misplaced lead (with adverse neurologic symptoms.)
In Toronto, many papers discussed the exciting prospects of treating movement disorders (Parkinson’s Disease, Essential Tremor, Dystonia), chronic pain, behavioral disorders (depression, obsessive-compulsive disorder, Tourette’s syndrome, anorexia nervosa), and systemic disorders (obesity, hypertension) through either stimulation or lesioning in the brain. Most of this patient population, a significant percentage of the world’s populace, may well benefit from MRgFUS as the optimal lesioning technique over the next decade. To accomplish this, MRgFUS must fulfill two promises: 1.) allow temporary alterations in function that will confirm the appropriate neurophysiologic and anatomic requirements for a safe and effective lesion (neuromodulation), and 2.) prove to be a precise and reliable mechanism for altering the brain’s circuitry long-term.
Helen Mayberg (Emory) reported neuronal hyperactivity in CG25 in the cingulate gyrus in patients suffering from depression. This was associated with diffuse hypoactivity in the prefrontal cortex. Andres Lozano reported placing DBS leads in CG25, setting the frequency to 130 Hz, and having 60% of the patients improve (Biol Psych 461-467, 2008). Such a high stimulation frequency mimics ablation, and thus MRgFUS may be used to treat depression in the future. CG25 is clearly not the final answer, given that 40% of patients do not respond. She postulated an overactive basal frontal cortex (VLPF47), and is also studying patients with Bipolar II disorder. She stressed that depression is an active process, not an absence of elevated mood. The effect of treatment is not one of “mood elevation,” but of inhibiting the active depressing process.
George Ojemann (U Washington) gave an eloquent lecture discussing speech problems after dominant temporal lobectomy, noting especially the verbal memory deficit that is a vexing problem in some of those patients. Stereotactic radiosurgery would offer a theoretical benefit in being a minimally invasive lesioning technique with less risk of verbal memory deficit. However, he mentioned the serious downside of having to wait one to two years for improvement in seizures after stereotactic radiosurgery, which would not be an issue after MRgFUS.
During a heated discussion about stimulation vs lesioning, Rees Cosgrove (Lahey Clinic, Burlington, MA) made a very critical point: the use of DBS is an important phase through which to pass in the development of the field, due to the safer reversibility in identifying the ideal targets. But, in the long run, when optimal targets for various indications have been proven, we will ideally have access to a technique to lesion precisely, with physiologic verification prior to actual permanent lesioning. MRgFUS may well be that modality.
The use of focused ultrasound surgery for neuromodulation, specifically for functional mapping and ideal target localization during the FUS procedure before making the permanent lesion, is an exciting prospect. There is much research to be done before this might become routine. If MRgFUS increases the assurance of a lesion being in exactly the right location for maximum effect and minimal complications, it may well enable the optimal treatment to become FUS lesioning. This may be true even in a challenging target, such as the subthalamic nucleus (STN, a current favorite for DBS placement), guided by FUS neuromodulation.
Dr. Michael Schulder, the past-president of the American Society of Stereotactic and Functional Neurosurgery (ASSFN), is very enthusiastic about a session on MRgFUS at the upcoming ASSFN meeting in New York City June 13-16, 2010 (http://www.assfn.org/ ).
Also of interest in 2010 will be the European Society of Stereotactic and Functional Neurosurgery (ESSFN), in Athens, Greece, September 22-25, 2010 (http://www.essfn2010.org/?pid=11 ).
Hopefully, by the World Society of Stereotactic and Functional Neurosurgery 16th Quadrennial Meeting in Japan, in May, 2013, there will be multiple MRgFUS presentations on a wide variety of indications.