Imaging Acute Neurologic Disease : A Symptom - Based Approach

Introduction The assessment of the patient with acute impairment of consciousness requires an organized, systematic approach, beginning with the history (the diagnosis is suspected on the history alone in over 85% of cases), the physical examination, and basic laboratory testing. It is only after these steps that well-chosen neuroimaging is performed, always with a specific question in mind. This review synthesizes clinical, laboratory, and radiological approaches with a strategy that will provide useful diagnostic and prognostic information.We also provide a special focus on the potential future role of novel neurodiagnostics in the acute care setting. Consciousness is composed of two principal components: alertness and awareness. Alertness is a function of the ascending reticular activating system (ARAS) in the rostral brainstem tegmentum (from the midpons through the midbrain) and then the thalamus and its projections through the cerebral white matter to the cerebral cortex. This allows for an eyes-open vigilant state, including arousability and spontaneous wake and sleep cycles. (This system and its various neurotransmitters will be discussed later.) Awareness depends on the integrity of integrated cerebral gray-matter structures and their interconnecting fibers running through the white matter. Awareness has multiple inter-related functions, including sensation, perception, memory, attention (with selectivity), emotions, judgment, motivation, and planned action, with various interconnected anatomical loci. Thus, consciousness is not a unitary phenomenon, but has multiple components. It is best to describe impairment of consciousness in terms of the type of impairment and its degree. Note also that a patient can be fully awake and aware, but may not be responsive due to central (including psychogenic) or peripheral nervous system causes. Thus, the absence of response is not necessarily proof of a disorder of consciousness (DOC).