Brain differs from other organs in regard to blood supply and reactions to inadequate blood supply: (1) Neurons can withstand an interruption of oxygen for only 5 10 minutes and neurons do not regenerate. (2) Many small as well as large areas of brain are vital for specific and important functions, such as the speech area and cardiorespiratory centers, and irreversible damage to such regions can be disabling or fatal. (3) Increased fluid such as edema or blood can enlarge the brain but not the skull, producing devastating secondary damage to the brain from internal pressure effects.
Emboli entering the internal carotid artery are aimed at the large middle cerebral artery and they usually bypass the smaller and acutely branching anterior cerebral and posterior communicating arteries. For this reason, most cerebral infarcts include part or all of the territory supplied by one of the middle cerebral arteries.
In subarachnoid hemorrhage (SAH), blood outside the blood vessels in the subarachnoid space is very irritating to those vessels, and they tend to contract (vasospasm), depriving their target areas of blood. Thus, "minor" SAH might cause cerebral infarcts, and the pressure of the combined blood in the subarachnoid space and cerebral edema from various causes (including vasospasm or the primary injury) might overcome the pressure of arterial blood flow, causing cessation of brain blood flow and brain death. Such pressure can also push brain tissue into adjacent anatomic compartments (herniation) with disasterous consequences.
Stroke syndromes: Transient ischemic attack (TIA); clinical event from temporary cerebral ischemia, totally resolved in 24 hours.
Lacunar stroke; clinical term for a small (< 1 cm) infarct tending to be in internal capsule, pons or pyramid and causing motor symptoms. Different authorities vary widely on this definition and on the "nature" of "lacunes."
Large artery atherosclerosis; 70% or more stenosis of the internal carotid artery at the bifurcation in the neck ipsilateral to a stroke or TIA should be treated with carotid endarterectomy, if the patient is a surgical candidate.
Small artery disease; associated with systemic hypertension.
Collagen vascular disease; SLE, Wegener's granulomatosis, periarteritis nodosa.
Primary angiitis of the CNS; giant cell arteritis affecting mainly or solely the CNS.
Infectious; AIDS, Lyme disease, varicella zoster virus, neurosyphilis, endocarditis, malaria, tuberculosis.
Hematologic conditions; venous thrombosis, clotting factor deficiencies, sickle cell disease, myeloproliferative syndromes.
Cardiac disease; mitral stenosis, prosthetic valve, marantic endocarditis, atrial myxoma, atrial fibrillation, ASD, VSD, post myocardial infarction.
Drug abuse; cocaine, amphetamines.
Pregnancy; cerebral venous thrombosis, toxemia, peripartum thrombosis, pituitary apoplexy, amniotic fluid embolism.
Anoxic encephalopathy Lack or very low flow of blood to brain with low arterial O2 tension, causing neuronal necrosis/apoptosis. Only 5 10 minutes required.
a. Perinatal Placental insufficiency/infarction, placenta previa with hemorrhage, maternal cardiac arrhythmia.
b. Adult Cardiac arrhythmia, choking (no e acceptor for respiratory chain), poisoning (affects respiratory enzymes), hypoglycemia (500 Unit bolus of insulin drives blood sugar into somatic cells; no fuel for respiratory enzymes), carbon monoxide (displaces O2 from hemoglobin).
2. Clinical course
a. Perinatal "Cerebral palsy" varies with each patient. Mental and musculoskeletal problems.
b. Adult May have faulty memory, babbling speech, bizarre behavior, stupor, confusion, coma, partial paralysis. Tremors can be seen since neocortex normally suppresses tremors. Global ischemia affects many or all neocortical areas and functions.
Cerebral infarct: Death of neurons & often glial cells and blood vessels; loss of function, often in territory supplied by a middle cerebral artery, with upper extremity flexion & lower extremity extension (typical "CVA").
1. Embolic Loosened carotid or other atherosclerotic plaque, cardiac valve thrombus breaking off, iatrogenic manipulation.
2. Thrombotic Local arterial blockage; blood dyscrasia (polycythemia, neoplasia, etc.).
3. Ischemic Arterial blockage with little or no blood leaking from blood vessels in area where neuronal damage occurs. Also termed "pale" infarct.
4. Hemorrhagic Arterial or venous blockage with sizable oozing of blood from damaged blood vessels in the infarcted region. Although blood is spread within the infarcted tissue, the damage is from neuronal death, not from the blood.
Intracerebral hemorrhage: Blood, usually under systolic pressure, dissects through cerebral tissue, forming a mass, or hematoma. Functional loss minimal to life threatening.
1. Hypertension Long standing blood pressure elevation; mostly basal ganglia "blowout," next common pons/cerebellum. Can be seen with less hypertension if blood coagulation is compromised. Headache, nausea, vomiting, seizures, confusion, stupor, coma.
2. Aneurysm Usually only subarachnoid hemorrhage, but some aneurysms "blow out" in a thin stream that shoots into cerebral tissue, becoming intracerebral as well. Usually aneurysm at junction of internal carotid artery or proximal middle cerebral artery branch.
3. Blood dyscrasia Including neoplasia (leukemia, etc.) and anticoagulant therapy.
Subarachnoid hemorrhage (SAH): Trauma is most common cause, then ruptured saccular (congenital, berry) aneurysm. Classical non traumatic clinical picture with a ruptured aneurysm: Patient complains of "the most excruciating headache of my life;" loss of consciousness may (or may not) ensue relatively rapidly. Note: Migraine headache usually involves a life crisis, not a "ruptured berry," but it may be difficult to tell the difference without neuroimaging. Any vascular problem in the subarachnoid space can have associated hemorrhage; e.g., ruptured vascular malformation, infected blood vessels. Overflow from the ventricular system after an intracerebral and subsequent intraventricular hemorrhage also causes SAH.
"Stroke" is a clinical term referring to cerebral infarct or hemorrhage wherein there is a sudden and dramatic development of neurologic deficit. Loss of motor and/or sensory function. Prognosis is better if the non dominant hemisphere is affected.