Andrew Steven

Functional Neuroimaging: Fundamental Principles and Clinical Applications

SUMMARY Functional imaging modalities, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), are rapidly changing the scope and practice of neuroradiology. While these modalities have long been used in research, they are increasingly being used in clinical practice to enable reliable identification of eloquent cortex and white matter tracts in order to guide treatment planning and to serve as a diagnostic supplement when traditional imaging fails. An understanding of the scientific principles underlying fMRI and DTI is necessary in current radiological practice. fMRI relies on a compensatory hemodynamic response seen in cortical activation and the intrinsic discrepant magnetic properties of deoxy- and oxyhemoglobin. Neuronal activity can be indirectly visualized based on a hemodynamic response, termed neurovascular coupling. fMRI demonstrates utility in identifying areas of cortical activation (i.e., task-based activation) and in discerning areas of neuronal connectivity when used during the resting state, termed resting state fMRI. While fMRI is limited to visualization of gray matter, DTI permits visualization of white matter tracts through diffusion restriction along different axes. We will discuss the physical, statistical and physiological principles underlying these functional imaging modalities and explore new promising clinical applications.

Use of Magnetic Resonance in the Evaluation of Cranial Trauma

MR imaging is an extremely useful tool in the evaluation of traumatic brain injury in the emergency department. Although CT still plays the dominant role in urgent patient triage, MR imagings impact on traumatic brain injury imaging continues to expand. MR imaging has shown superiority to CT for certain traumatic processes, such as diffuse axonal injury, cerebral contusion, and infarction. Magnetic resonance angiography and magnetic resonance venography allow emergent vascular imaging for patients that should avoid ionizing radiation or intravenous contrast.

Potential of glyburide to reduce intracerebral edema in brain metastases

Metastatic disease to the brain results in significant morbidity because of edema in the central nervous system. Current anti-edema therapies are either expensive or result in unwanted long-term side effects. Sulfonylurea receptor 1 (Sur1) is a transmembrane protein that, when activated in the central nervous system, allows for unregulated sodium influx into cells, a process that has been linked to cytotoxic edema formation in ischemic stroke, subarachnoid hemorrhage, spinal cord injury, traumatic brain injury, and, most recently, brain metastases. In this focused review, we explore preclinical data linking Sur1 channel formation to development of edema and reference evidence suggesting that the antidiabetic sulfonylurea drug glyburide (a Sur1 inhibitor) is an inexpensive and well-tolerated agent that can be clinically tested to reduce or prevent malignancy and/or treatment-associated edema.

Neurologic and Head and Neck Manifestations of Sickle Cell Disease

Sickle cell disease is a common, inherited disordered characterized by chronic hemolytic anemia with repetitive episodes of vasoocclusion resulting from deformed red blood cells. This article reviews the most significant neurologic and head and neck manifestations of this disease.

Venous Thrombosis: Causes and Imaging Appearance.

Cerebral venous sinus thrombosis is an elusive diagnosis with profound potential neurologic consequences. Although there are numerous reported predisposing conditions, by far the most common is a prothrombotic hypercoagulable state. Recent advances in MRI and computed tomography have improved diagnostic accuracy for this increasingly recognized disorder. Familiarity with imaging techniques and potential pitfalls is essential for accurate diagnosis and management of these patients.

Varicella-Zoster Virus Vasculopathy: A Case Report Demonstrating Vasculitis using Black-Blood MRI.

Infections are rare but important causes of stroke. Among these, varicella zoster virus has been known to cause ischemic stroke. During an attack of herpes zoster ophthalmicus, it has been hypothesized that the virus replicates in the trigeminal ganglion and travels via the trigeminal nerve centrally to cause cerebral vasculopathy. Here we present a case of a 69 year-old Caucasian immunocompromised woman who suffered recurrent ischemic infarcts within the same vascular distribution following an episode of zoster ophthalmicus three months prior. An imaging technique termed black-blood magnetic resonance imaging was utilized to aid in the diagnosis of cerebral vasculitis. The case is used to provide a literature review of the pathogenesis, diagnosis, and treatment of cerebral varicella zoster vasculopathy. In situations where an isolated unilateral cerebral vasculopathy is identified, neurologists are urged to consider varicella zoster as a treatable etiologic agent, as untreated vasculopathy can lead to further strokes.

T2*-based MR imaging of hyperglycemia-induced hemichorea-hemiballism

INTRODUCTION Hyperglycemia can induce hemichorea-hemiballism, especially in elderly type II diabetics. CT and MRI findings include hyperdensity and T1-shortening in the contralateral lentiform nucleus, respectively. This study explores the associated imaging findings on T2*-based sequences. METHODS Six patients with clinically documented hyperglycemia-induced hemichorea-hemiballism who had undergone MR imaging with a T2*-based sequence (T2* gradient echo or susceptibility-weighted imaging) were included in this retrospective case series. RESULTS All six patients demonstrated T1-shortening contralateral to their hemichorea-hemiballism. T2*-based sequences demonstrated unilateral hypointense signal within the striatum in four patients. One patient had mild bilateral striatal hyperintensities, while another did not show significant signal changes. CONCLUSION It is important for the radiologist to be aware of the signal changes that can be seen on T2*-based sequences in hyperglycemia-induced hemochorea-hemiballism.

Advanced Neuroimaging of Tinnitus

Although tinnitus may originate in damage to the peripheral auditory apparatus, its perception and distressing symptomatology are consequences of alterations to auditory, sensory, and limbic neural networks. This has been described in several studies, some using advanced structural MR imaging techniques such as diffusion tensor imaging. An understanding of these complex changes could enable development of targeted treatment. New MR imaging techniques enabling detailed depiction of the labyrinth may be useful when diagnosis of Meniere disease is equivocal. Advances in computed tomography and MR imaging have enabled noninvasive diagnosis of dural arteriovenous fistulae.