MS 4 - Neuroimaging and mental health disorders
1. To understand the concept of mental illness as illustrated by obsessive compulsive disorder (OCD) and Tourette-Syndrome (TS).
2. To show how neuroimaging is furthering our understanding of OCD and TS.
3. To understand the central role of neuroimaging in functional neurosurgery of OCD and TS.
Over the last decade, neuroimaging has been central to research in mental illness elucidating disorders of the underlying rather complex network. However, neuroimaging has not only been relevant to research but also to clinical management of patient. This can be illustrated in two diseases: Obsessive compulsive disorder (OCD) and Tourette syndrome (TS). Neuroimaging was central to the process of identifying anatomic targets for surgical intervention. In this intervention - functional stereotactic neurosurgery - electrodes are placed in these targets, an intervention known as "deep brain stimulation". This intervention in turn is also reliant on imaging. This session will, therefore, clarify the important role of imaging in the understanding and treatment of mental health disorders.
1. To understand the concept of severe mental illness exemplified by OCD.
2. To demonstrate the impact of neuroimaging - structural and functional MRI and PET - to our understanding of OCD as a neural network disorder.
3. To show the central role of neuroimaging in enabling us to pinpoint the critical neural target for successful treatment with deep brain stimulation.
Obsessive compulsive disorder (OCD) has a life time prevalence world wide of 1-2% and is the 11th leading cause of non-fatal burden (WHO). OCD is characterised by anxiety provoking thoughts, images and impulses which trigger mental or motor rituals designed to neutralise the anxiety. This leads to temporary relief only and patients become trapped in a vicious circle of disabling thoughts and actions. Effective treatments are available but 10-20% remain resistant. Deep brain stimulation (DBS) has been shown to be effective in 50-60% of such cases who have extremely severe OCD. Understanding the neural basis of OCD is important in order to develop new treatments and better targets for DBS. This talk will review how our understanding of OCD has developed over the past 20 years following advances in neuroimaging. Early PET findings showed that patients with OCD have increased metabolism in fronto-striatal circuitry which is decreased following successful pharmacological treatment. This concept of OCD as a network disorder has been elaborated since then but has also been found to be more complex. For example, tractography studies have shown altered topography and connectivity between the orbitofrontal cortex and striatum; structural MRI has shown reduced volumes of not only prefrontal and cingulate cortex but also hippocampus and increased volumes of pallidum and thalamus. MRI spectroscopy has contributed to our understanding of the neurochemical basis of OCD with abnormalities of GABA and glutamate being implicated. In the light of these neuroimaging findings the psychological understanding of the behavioural characteristics of OCD has been modified which might pave the way for better interventions.
1. To understand the importance on neuroimaging in understanding Tourette-Syndrome as a neural network disorder.
2. To introduce the concept of DBS as a treatment for severe medication refractory Tourette-Syndrome and the role of neuroimaging of the DBS electrical field.
3. To show how the clinical efficacy of DBS for Tourette-Syndrome can be related to simulated electrical field on a voxel by voxel basis.
In this lecture I will describe the potential of deep brain stimulation as a treatment for severe, medication refractory Tourette syndrome. I will introduce the concept of patient-specific simulations of the DBS electrical field using neuroimaging. I will show how the clinical efficacy of DBS for Tourette syndrome can be related to simulated electrical field on a voxel by voxel basis.
Precision neurosurgical targeting in Tourette's and obsessive compulsive disorder (OCD): critical role of neuroimaging
1. To understand the essential differences between diagnostic and stereotactic MR imaging.
2. To introduce the concept of image-guided and image-verified DBS surgery.
3. To provide an overview of the different anatomical targets used for DBS in Tourette syndrome and OCD surgery and describe their radiological correlates.
Functional neurosurgery involves precise surgical targeting of anatomic structures to modulate neurologic function. Preoperative stereotactic localization places several demands on image acquisition that go beyond those required for diagnostic imaging. MRI coils must accommodate the relevant stereotactic frame. Target structures are often small placing demands on image resolution. Specific MR sequences that provide high tissue contrast between the target structure and the surrounding tissues must be used while ensuring clinically practical acquisition times. Geometric distortion represents a significant obstacle to accurate spatial representation and can render MR images useless for the purpose of accurate anatomic targeting. Numerous anatomical targets have been proposed in the management of Tourette syndrome (e.g. globus pallidus, centromedian/parafascicular nucleus) and obsessive compulsive disorder (ventral capsule / ventral striatum, anterior cingulate gyrus, anteromedial subthalamic nucleus). A vital step to assessing the efficacy of each anatomical target is confirming the anatomical location of the intervention, whether after placement of a stereotactic lesion or a deep brain stimulation lead. Many commercially available DBS leads are MR conditional and the gold standard in verification is obtaining a stereotactic MRI as part of the surgical procedure. It is imperative that appropriate safety precautions be followed when obtaining such images. Likewise, it is inappropriate that a radiology department places a blanket ban on MR imaging of DBS patients. MR physicists and neuroradiologists are an essential part of the multidisciplinary team that offers neurosurgical interventions in patients with mental health disorders, including Tourette syndrome and obsessive compulsive disorder.