Diagnosis and Evaluation of Stroke: Cerebral Hypoxia

Neurons are particularly vulnerable to oxygen deprivation. Cerebral hypoxia can be caused by arterial thrombosis, embolism, hypoperfusion, cervical artery dissection, or cryptogenic causes. About 1/3 of ischemic strokes are from cryptogenic causes. Embolic strokes are the next most common (20-30%), followed by extracranial atherosclerosis (15-20%) and intracranial atherosclerosis (10%). Hypoperfusion initially affects watershed areas of the brain and can be caused by several systemic etiologies: cardiac disorders such as cardiac arrest, myocardial infarction, or arrhythmias; pulmonary embolism from venous thrombus formation; or shock from sepsis, anaphylaxis, or hemorrhage. Cervical artery dissection occurs when the intimal and medial layers of an artery separate, leading to the formation of a false lumen between the layers. This is the most common cause of ischemic stroke in young adults. Thrombosis formation is most commonly caused by atherosclerosis, but arteritis or hypercoagulable states are also important risk factors to be considered. Important risk factors for the development of atherosclerosis include hypertension, diabetes mellitus, hyperlipidemia, cigarette smoking, obesity, chronic inflammation, blood vessel injury, and elevated homocysteine concentrations. Emboli can either be cardiac or non-cardiac. Cardiac emboli can be caused by arrhythmias, valvular disease, myocardial infarction, or structural heart disease, whereas non-cardiac emboli are usually from arterial atheroma, iatrogenic causes, or diffuse disseminated atheroemboli. The symptoms of stroke from cerebral hypoxia are dependent on the location of neuronal damage. The middle cerebral artery is the most common artery involved in stroke, and symptoms may include loss of sensation and/or movement in the upper extremity and face, aphasia and dysarthria, or horizontal gaze dysfunction. Symptoms of anterior cerebral artery involvement may include loss of sensation and/or movement in the lower extremities and loss of ability to organize and plan complex behaviors. Contralateral homonymous hemianopsia may be seen in cases of posterior cerebral artery involvement. In evaluating patients with suspected stroke, it is important to check their blood sugar to rule out hypoglycemia, use the Nation Institute of Health Stroke Scale to assess stroke severity, perform a thorough cardiorespiratory and neurological exam, and obtain imaging (non-contrast CT first to rule out hemorrhagic stroke, CT angiography, MRI). Patients with ischemic stroke should be evaluated with vascular imaging to evaluate for plaques or stenosis. Cardiac evaluation includes ECG, echocardiography, and Holter monitoring. Tissue plasminogen activator can be used to treat ischemic stroke within 4.5 hours of onset. Endovascular treatment can be used when the 4.5-hour window is passed and can be effective within 24 hours of symptoms. In cases of arterial stenosis, endarterectomy may be indicated to prevent recurrence. Antiplatelet therapy, antihypertensives, statins, anticoagulants, and lifestyle changes are also important in the medical management of stroke and the prevention of recurrence.