Partial epilepsy: A pictorial review of 3 TESLA magnetic resonance imaging features

Epilepsy is a disease with serious consequences for patients and society. In many cases seizures are sufficiently disabling to justify surgical evaluation. In this context, Magnetic Resonance Imaging (MRI) is one of the most valuable tools for the preoperative localization of epileptogenic foci. Because these lesions show a large variety of presentations (including subtle imaging characteristics), their analysis requires careful and systematic interpretation of MRI data. Several studies have shown that 3 Tesla (T) MRI provides a better image quality than 1.5 T MRI regarding the detection and characterization of structural lesions, indicating that high-field-strength imaging should be considered for patients with intractable epilepsy who might benefit from surgery. Likewise, advanced MRI postprocessing and quantitative analysis techniques such as thickness and volume measurements of cortical gray matter have emerged and in the near future, these techniques will routinely enable more precise evaluations of such patients. Finally, the familiarity with radiologic findings of the potential epileptogenic substrates in association with combined use of higher field strengths (3 T, 7 T, and greater) and new quantitative analytical post-processing techniques will lead to improvements regarding the clinical imaging of these patients. We present a pictorial review of the major pathologies related to partial epilepsy, highlighting the key findings of 3 T MRI

Narrative review of epilepsy: getting the most out of your neuroimaging

Neuroimaging represents an important step in the evaluation of pediatric epilepsy. The crucial role of brain imaging in the diagnosis, follow-up and presurgical assessment of patients with epilepsy is noted and has to be familiar to all neuroradiologists and trainees approaching pediatric brain imaging. Morphological qualitative imaging shows the majority of cerebral lesions/alterations underlying focal epilepsy and can highlight some features which are useful in the differential diagnosis of the different types of epilepsy. Recent advances in MRI acquisitions including diffusion-weighted imaging (DWI), post-acquisition image processing techniques, and quantification of imaging data are increasing the accuracy of lesion detection during the last decades. Functional MRI (fMRI) can be really useful and helps to identify cortical eloquent areas that are essential for language, motor function, and memory, and diffusion tensor imaging (DTI) can reveal white matter tracts that are vital for these functions, thus reducing the risk of epilepsy surgery causing new morbidities. Also positron emission tomography (PET), single photon emission computed tomography (SPECT), simultaneous electroencephalogram (EEG) and fMRI, and electrical and magnetic source imaging can be used to assess the exact localization of epileptic foci and help in the design of intracranial EEG recording strategies. The main role of these “hybrid” techniques is to obtain quantitative and qualitative informations, a necessary step to evaluate and demonstrate the complex relationship between abnormal structural and functional data and to manage a “patient-tailored” surgical approach in epileptic patients

FAM222B Is Not a Likely Novel Candidate Gene for Cerebral Cavernous Malformations

Cerebral cavernous malformations (CCMs) are prevalent slow-flow vascular lesions which harbour the risk to develop intracranial haemorrhages, focal neurological deficits, and epileptic seizures. Autosomal dominantly inherited CCMs were found to be associated with heterozygous inactivating mutations in 3 genes, CCM1(KRIT1), CCM2(MGC4607), and CCM3(PDCD10) in 1999, 2003 and 2005, respectively. Despite the availability of high-throughput sequencing techniques, no further CCM gene has been published since. Here, we report on the identification of an autosomal dominantly inherited frameshift mutation in a gene of thus far unknown function, FAM222B(C17orf63), through exome sequencing of CCM patients mutation-negative for CCM1-3. A yeast 2-hybrid screen revealed interactions of FAM222B with the tubulin cytoskeleton and STAMBP which is known to be associated with microcephaly-capillary malformation syndrome. However, a phenotype similar to existing models was not found, neither in fam222bb/fam222ba double mutant zebrafish generated by transcription activator-like effector nucleases nor in an in vitro sprouting assay using human umbilical vein endothelial cells transfected with siRNA against FAM222B. These observations led to the assumption that aberrant FAM222B is not involved in the formation of CCMs

Doctor of Philosophy

dissertationDestabilization of the endothelial monolayer lining blood vessels has profound consequences on organismal homeostasis. Vascular instability plays a well-known role in the pathophysiology of diseases from sepsis to stroke. A variety of factors are known to influence endothelial function, including the extracellular milieu, biomechanical factors, various molecular pathways, as well as genetic elements. Many factors promoting vascular instability have been described; however, far fewer studies have identified factors promoting stability. No overarching theory of vascular stability has yet been proposed that takes into account extracellular, biomechanical, molecular, and genetic variables. In this dissertation, I detail studies of extracellular matrix cues, molecular pathways, and genetic factors in an attempt to identify commonalities associated with regulation of vascular stability. I first show that the extracellular matrix protein elastin normalizes endothelial cell function. Next, I demonstrate a critical role of the small GTPase ARF6 in mediating cytokine-induced endothelial instability. I also identify a crucial role of ARF6 in mediating transduction of mechanical signals in the endothelium. Finally, I describe a central role of various genes associated with a human disease, Cerebral Cavernous Malformation (CCM), in endothelial stability. During the course of these studies, I developed and utilized a variety of tools not often found in molecular biology labs. I built new apparatuses and wrote software programs to answer the questions I had, rather than relying on what had already been built by others. Perhaps my largest contribution to the Li laboratory has been to propagate the use of these new systems to molecular biologists who may have a better capability to ask important questions, and who now have the ability to answer their own questions more quickly, more efficiently, and without the inherent bias associated with the standard protocols used in the majority of molecular biology labs. Finally, during my last two years in the laboratory, I further refined and integrated the tools I developed with new tools available from the Broad Institute to quantitatively evaluate endothelial stability through measurement of both structural and functional phenotypes. Using quantification of structural and functional phenotypes, I identified multiple drugs that ameliorate in vitro CCM models, and found two drugs that significantly reduce the formation of lesions in murine models of CCM disease. Further, I found that one of these compounds was protective against diverse destabilizing cues in the endothelium. These discoveries are important for the study of CCM disease, for patients with CCM disease, and have implications for many other diseases in the future. Overall, my studies resulted in specific new mechanistic insights into a wide-variety of factors that promote endothelial stability. More important is the development of a multilayered strategy and platform that can be applied to study effects of extracellular, biomechanical, molecular, and genetic cues on the endothelium either alone or in any combination. In the immediate future, this platform will serve as a vehicle for creating an over-arching model of vascular stability. Beyond this application, this same platform can be rapidly scaled to answer broad questions about factors crucial in health and disease across a wide variety of other cell and organ types. I intend to use the approach I developed and describe in my dissertation to try to untangle how all genes, all proteins, all diseases, and all drugs interact - a lofty goal to be sure

Identification of Intracranial Lesions with Dual-Energy Computed Tomography and Magnetic Resonance Phase Imaging

On conventional Single-energy Computed Tomography (SECT), lesions with an attenuation greater than 100 Hounsfield Units (HU) can be definitively diagnosed as calcification. However, low-density calcifications and hemorrhage may have overlapping attenuation ranges between 40 and 100 HU and, therefore, cannot be differentiated with SECT alone. On T2*-weighted Gradient Recalled Echo (GRE) MRI, these lesions appear as “foci of susceptibility” in which their signal is hypointense due to the magnetic susceptibility of the lesions differing from that of the background tissue. Dual-energy Computed Tomography (DECT) and Phase-Sensitive Magnetic Resonance Imaging (PS-MRI) represent two new imaging paradigms which both have the potential to more accurately identify intracranial calcification and hemorrhage. In DECT, x-ray tomography is acquired at two tube voltages; because x-ray attenuation is energy- and material-dependent, the data can be used to differentiate between materials that may have the same signal level on SECT. PS-MRI utilizes the phase data from T2*-weighted MRI acquisitions to determine how the local magnetic field varies across the image. By applying post-processing algorithms such as Quantitative Susceptibility Mapping (QSM), the phase can be used to calculate the magnetic susceptibility of a lesion. Since calcifications are diamagnetic and hemorrhage paramagnetic, we can make inferences about a lesion’s composition from these algorithms. The objective of this dissertation work was to characterize brain lesions, discovered with traditional imaging methods, as either hemorrhagic or calcific by using Dual-Energy Computed Tomography (DECT) and Phase-Sensitive Magnetic Resonance Imaging (PS-MRI). To this end, MRI-compatible phantoms featuring models of both calcific and hemorrhagic lesions were developed and validated. This resulted in two phantoms with biologically similar lesion models that were then used to test the feasibility of differentiating calcific and hemorrhagic lesions with PS-MRI post-processing methods, in which QSM was able to accurately differentiate calcific and hemorrhagic lesion models. Finally, we undertook a patient trial testing the feasibility of identifying calcification and chronic hemorrhage in humans using both DECT and QSM in which the two modalities had accuracies of 99.7% (327/328) and 99.4% (326/328), respectively. The two modalities were concordant for 99.3% (148/149) lesions with SECT attenuation under 100 HU

Doctor of Philosophy

dissertationEndothelial cells exist in a state of dynamic stability allowing for a balance between quiescence and response. These cells create the barrier system of the vasculature as well as drive the growth of new vessels. The disease Cerebral Cavernous Malformation (CCM) disrupts both processes and is characterized by leaky, cavernous vascular lesions in the CNS, resulting in headache, seizure, and stroke. CCM occurs in both a sporadic and familial form thought to follow the Knudsen two-hit model of retinoblastoma. Studies have been primarily focused on late stage disease, leaving little understanding of the earliest stages and the precise role of the second hit. We sought to study early developmental onset to identify morphological characteristics that could provide mechanistic insight to the key initiating factors. We generated an inducible endothelial knockout mouse model of CCM and found that when the second hit occurs at birth, mice develop cavernous malformations in the brain and the retina. We determined that lesions arise in a spatially and temporally predictable pattern in a limited developmental window. We further showed vessel defects are preceded by endothelial hypersprouting and an impaired cellular response to flow. In the context of CCM, this suggests that an inability of cells to react to their environment could result in lesion development. Our findings that loss of the second hit in adulthood was insufficient to cause disease, combined with the predictable nature of development, iv suggested that environmental factors may be necessary contributors to disease onset. While loss of the genetic hits in adulthood was not enough to cause disease we found that, when combined with localized vascular endothelial growth factor (VEGF), lesions can arise. Changes in the surrounding tissue environment can be caused by disrupted barrier functions, promoting a disease state like that seen in CCM. In our pursuit to further understand barrier function in the face of environmental challenges, we defined the novel process of endothelial extrusion. Extrusion is the removal of an apoptotic cell from a monolayer, prior to its structural collapse, via contraction of an actin ring. Together these studies offer insights into endothelial barrier function, stability, and disease

The Molecular Pathogenesis Of Cerebral Cavernous Malformations

Cerebral cavernous malformation (CCM) is a human genetic, cerebrovascular disease that is caused by loss of function mutations in three non-homologous protein coding genes: KRIT1, CCM2, and PDCD10. These proteins form a heterotrimeric CCM adaptor complex that is required in endothelial cells to prevent disease. How loss of this complex causes disease remains unknown. Here, utilizing a neonatal mouse model of disease, we demonstrate that the CCM complex negatively regulates Mitogen-Activated Protein Kinase Kinase Kinase 3 (MAP3K3 aka MEKK3) signaling in endothelial cells. During disease, loss of the CCM complex results in gain of MEKK3 signaling and pathologic overexpression of downstream target transcription factors Kruppel-like Factor 2 and Kruppel-like factor 4 (KLF2 and KLF4). This endothelial MEKK3-KLF2/4 signaling pathway represents the proximal signaling events that are required for lesion formation. If the CCM complex negatively regulates MEKK3 signaling, what are the upstream activators of MEKK3 in the context of disease? We demonstrate that gram-negative bacterial infection and lipopolysaccharide (LPS) activation of endothelial Toll-like receptor 4 (TLR4) drives MEKK3 signaling to stimulate lesion formation. Commensal bacteria in the gut microbiome produce the vast majority of endogenous LPS. We further show through germ-free and broad-spectrum antibiotic experiments, along with 16S fecal analysis of mice spontaneously resistant to lesion formation, that the gram-negative, bacterial microbiome is a primary driver of lesion formation. These studies reveal that endothelial TLR4—MEKK3—KLF2/4 signaling is required for lesion formation and that inhibition of this pathway may be of therapeutic value for CCM patients. They further demonstrate an unexpected role for the gut microbiome in this cerebrovascular disease and suggest that manipulation of host-microbiome interactions may be a viable therapeutic strategy for this lifelong, progressive disease

Assessment of the potentials and limitations of cortical-based analysis for the integration of structure and function in normal and pathological brains using MRI

The software package Brainvisa (www.brainvisa.tnfo) offers a wide range of possibilities for cortical analysis using its automatic sulci recognition feature. Automated sulci identification is an attractive feature as the manual labelling of the cortical sulci is often challenging even for the experienced neuro-radiologists. This can also be of interest in fMRI studies of individual subjects where activated regions of the cortex can simply be identified using sulcal labels without the need for normalization to an atlas. As it will be explained later in this thesis, normalization to atlas can especially be problematic for pathologic brains. In addition, Brainvisa allows for sulcal morphometry from structural MR images by estimating a wide range of sulcal properties such as size, coordinates, direction, and pattern. Morphometry of abnormal brains has gained huge interest and has been widely used in finding the biomarkers of several neurological diseases or psychiatric disorders. However mainly because of its complexity, only a limited use of sulcal morphometry has been reported so far. With a wide range of possibilities for sulcal morphometry offered by Brainvisa, it is possible to thoroughly investigate the sulcal changes due to the abnormality. However, as any other automated method, Brainvisa can be susceptible to limitations associated with image quality. Factors such as noise, spatial resolution, and so on, can have an impact on the detection of the cortical folds and estimation of their attributes. Hence the robustness of Brainvisa needs to be assessed. This can be done by estimating the reliability and reproducibility of results as well as exploring the changes in results caused by other factors. This thesis is an attempt to investigate the possible benefits of sulci identification and sulcal morphometry for functional and structural MRI studies as well as the limitations of Brainvisa. In addition, the possibility of improvement of activation localization with functional MRI studies is further investigated. This investigation was motivated by a review of other cortical-based analysis methods, namely the cortical surface-based methods, which are discussed in the literature review chapter of this thesis. The application of these approaches in functional MRI data analysis and their potential benefits is used in this investigation