CNS Chapter 23 slide 1-30.pptx

Central Nervous System CHAPTER 23cns SEEMI USMANI Cerebral Edema     Cerebral edema is the accumulation of excess fluid within the brain parenchyma Can cause an increase in intracranial pressure Vasogenic: extracellular fluid  Integrity of BBB disrupted, fluid escapes into interstitium  Caused...

Central Nervous System CHAPTER 23cns SEEMI USMANI Cerebral Edema     Cerebral edema is the accumulation of excess fluid within the brain parenchyma Can cause an increase in intracranial pressure Vasogenic: extracellular fluid  Integrity of BBB disrupted, fluid escapes into interstitium  Caused by tumors, ischemia, hemorrhage, injury, infections  Results in disturbances in consciousness Cytotoxic: intracellular fluid  Secondary to neuronal membrane injury  Hypoxia-Ischemia- impaired Na/K pump function-cell swelling  Hypo-osmolar states like hyponatremia- fluid shifts into cells by osmosis adu.edu Cerebral Edema In generalized edema the gyri are flattened, and the sulci are narrowed, and the ventricular cavities are compressed adu.edu Hydrocephalus Hydrocephalus is defined as abnormal increase in CSF within the ventricular system  This disorder most often is a consequence of impaired flow, resorption or rarely overproduction of CSF  Noncommunicating hydrocephalusenlargement of part of the ventricular system  Caused by: obstruction- tumor, hemorrhage, inflammation, congenital malformations  Communicating hydrocephalusenlargement of entire ventricular system  Caused by decreased reabsorption by arachnoid villi- block in CSF pathway to the adu.edu villi, e.g. blood debris, post meningitis scars  Hydrocephalus      Hydrocephalus ex vacuo : A compensatory increase in CSF volume can follow the loss of brain parenchyma as after infarcts or brain atrophy with degenerative diseases Manifestations: If it develops in infancy before closure of sutures- enlargement of the head If develops later- increase in I/C pressureheadache, vomiting, papilledema, may cause herniations adu.edu Intracranial Pressure (ICP)       The brain tissue, blood & CSF in the rigid confines of skull contribute to intracranial pressure ( normal 0-15mmHg) Rise in I/C pressure mainly buffered by changes in volume of CSF Causes of raised I/C pressure- mass effect Brain tumor, abscess, hemorrhage, edema Increased CSF- obstruction to outflow Increased venous pressure- e.g. venous sinus thrombosis adu.edu ICP is pressure exerted by tissue & fluid volumes of the three compartments within the rigid skull Porths pathophysiology 10% 10% adu.edu 80%  Effects of raised ICP: Decrease in Cerebral Perfusion Pressure or CPP (CPP= MAP-ICP)- CPP is 70 to 100mmHg  Decrease in cerebral perfusion- neuronal death may occur  Decrease in level of consciousness is an early sign of raised ICP – confusion to stupor to coma  Herniations  Cushing triad- late sign, triggered by ischemia of VMC in an attempt to increase CPP  Progressively increasing systolic BP, progressively decreasing diastolic BP ( widening of pulse pressure), bradycardia  Important indicator of raised ICP & cerebral adu.edu ischemia  Herniation When the volume of tissue, CSF, or blood increases- intracranial pressure rises  Rise in intracranial pressure leads to herniation of brain tissue  There are three main types of herniation:  Cingulate (subfalcine) herniation:  Herniation of cingulate gyrus under the edge of falx cerebri, caused by an asymmetric expansion of a cerebral hemisphere  May be associated with compression of the anterior cerebral artery  Will eventually compromise vital centers adu.edu in the medulla  Herniation         Transtentorial herniation: Medial aspect of the temporal lobe herniating into tentorial notch  Pressure on midbrain: III cranial nerve is compromised -ipsilateral pupil dilation The posterior cerebral artery may be compressed, resulting in ischemic injury to visual cortex Pressure on opposite side cerebral peduncle of midbrain- hemiparesis ipsilateral to herniation Later coma, FDPs & respiratory arrest Tonsillar herniation: Displacement of the cerebellar tonsils through the foramen magnum Is life-threatening- causes brain stem compression and damage to the cardio-respiratory centers in the medulla- respiratory & cardiac arrest adu.edu CEREBROVASCULAR DISEASES      Are brain disorders caused by pathologic processes involving blood vessels Three main pathogenic mechanisms are (1) thrombotic occlusion, (2) embolic occlusion, and (3) vascular rupture Stroke is the clinical term for acute-onset neurologic deficits resulting from hemorrhagic or obstructive vascular lesions Thrombosis and embolism result in infarction of regions supplied by the affected vessel Hemorrhage due to rupture of vessels- leads to direct tissue damage as well as secondary ischemic injury adu.edu Global Cerebral Ischemia  Ischemia, due to tissue hypoperfusion can be caused by hypotension, vascular obstruction, or both  Widespread ischemic-hypoxic injury can occur in the setting of severe systemic hypotension (usually when systolic pressures fall below 50 mm Hg), as in cardiac arrest, shock With mild injury- a transient confusional state with complete recovery In severe global cerebral ischemia, widespread neuronal death In those who survive- persistent vegetative state or brain death    adu.edu Focal Cerebral Ischemia Cerebral arterial occlusion leading to focal ischemia and infarction in the distribution of the blocked vessel  Ischemic Stroke :  Embolic occlusions:  Are more common than infarctions due to thrombosis  Causes:  Cardiac mural thrombi (recent MI, ventricular aneurysm)  Atrial fibrillation, valvular disease (bacterial endocarditis)  Emboli from atheromatous plaques within the carotid arteries  Emboli from DVT may cross over to the arterial circulation through cardiac defects and lodge in the adu.edu  Ischemic Stroke       Thrombotic occlusions: Usually are superimposed on atherosclerotic plaques Common sites: carotid bifurcation, the origin of middle cerebral artery, and at either end of the basilar artery There may be thrombus fragmentation and distal embolization Focal symptoms depend on vessel involved These nonhemorrhagic infarcts resulting from acute vascular occlusions can be treated with thrombolytic therapy- saves ischemic but viable tissue around necrotic tissue adu.edu      Transient ischemic attacks ( TIAs): Are focal ischemic neurological deficits (without infarction) that last for less than 24h( mostly 1-2h) “brain angina” – temporary ischemia, reverses before infarction occurs Caused by emboli, atherosclerotic disease TIAs provide a warning of impending stroketimely intervention may prevent a stroke adu.edu Hemorrhagic stroke        Is caused by rupture of a blood vessel & hemorrhage into the brain tissue Causes: Hypertension: causes accelerated atherosclerosis, and small vessel disease- hyaline arteriolosclerosis of deep penetrating arteries & arterioles Rupture of an aneurysm, AVMs Sudden event, associated with a high morbidity & mortality Focal symptoms depend on vessel involved Hemorrhage & resultant cerebral edema- raise intracranial pressure- severe headache, coma & death adu.edu Stroke         Manifestations of Acute Stroke: The acute manifestations depend on blood vessel involved Symptoms are sudden in onset, focal & unilateral There may be weakness of face, arm, or leg, numbness, monocular vision loss, speech disturbances (dysarthria), language disturbance (aphasia) In case of TIAs symptoms resolve spontaneously Diagnosis: CT scan, MRI, Arteriography Treatment: I/V thrombolytic treatment ( tPA) in selected patients adu.edu Intracranial Hemorrhage       Hemorrhages within the brain are associated with: (1) hypertension and other diseases leading to vascular wall injury (2) structural lesions such as arteriovenous malformations (3) tumors Subarachnoid hemorrhages most commonly are caused by ruptured aneurysms Subdural or epidural hemorrhages usually are associated with trauma adu.edu Primary Brain Parenchymal Hemorrhage      Spontaneous (nontraumatic) intraparenchymal hemorrhages are most common in mid- late adult life Most are due to the rupture of a small intraparenchymal vessel Hypertension is the leading underlying cause Can be devastating when it affects large parts of the brain, or extends into the ventricles- or it can affect small regions and be clinically silent hypertensive Typically occur in the basal ganglia, Massive hemorrhage rupturing thalamus, pons, and cerebellum into a lateral ventricle. adu.edu Subarachnoid Hemorrhage- Saccular (berry) aneurysms     The most frequent cause of nontraumatic subarachnoid hemorrhage is rupture of a saccular (berry) aneurysm Subarachnoid hemorrhage may also result from: vascular malformations, rupture of intracerebral hemorrhage into ventricles, hematologic disturbances, tumors Berry aneurysm develop over time due to underlying defects in the vessel media There is an increased risk of aneurysms in patients with ADPKD & in those with genetic disorders of ECM adu.edu About 90% of saccular aneurysms occur in the anterior circulation near major arterial branch points Saccular (berry) aneurysms      Probability of rupture increases with sizeaneurysms larger than 1 cm in diameter have a roughly 50% risk of bleeding/ year Rupture is associated with acute increase in intracranial pressure- patient develops sudden, excruciating headache & rapidly loses consciousness Risk of ischemic injury from vasospasm of other vessels Healing and meningeal scarring may obstruct CSF flow leading to hydrocephalus Other types of cranial aneurysms; mycotic, traumatic, dissecting, atherosclerotic adu.edu Vascular Malformations     Arteriovenous malformations (AVMs) are the most common vascular malformations AVMs, can rupture & are dangerous- affect males more frequently- manifest between10 and 30 years with seizures, an intracerebral hemorrhage (causing hemorrhagic stroke) or a subarachnoid hemorrhage Shunting of blood from arterial to low pressure venous system- rupture a AVMs; tangled network of arteries & veins adu.edu CNS Trauma     A blow to the head may be penetrating or blunt; it may cause an open or a closed injury Head injury can be injury to skull, brain, both When the brain is damaged, the injuries may involve the parenchyma, the vasculature, or both Repetitive trauma (in athletes in contact sports) can lead to later development of neurodegenerative processes Contusions seen in temporal lobes adu.edu Traumatic Parenchymal Injuries   Concussion: momentary interruption of brain function with or without loss of consciousness  Caused by mild head injury- brain imaging negative  Recovery within 24 h- post concussion syndrome  Repetitive mild injury- chronic traumatic encephalopathy Diffuse axonal injury:  The movement of one region of brain relative to another- angular acceleration  Stretching, tearing of axons in white matter of cerebral hemispheres, corpus collosum, brain stem  May lead to coma, death  Most common cause for vegetative state adu.edu Traumatic Parenchymal Injuries        Contusions: A contusion is caused by rapid tissue displacement, disruption of vascular channels, with subsequent hemorrhage, tissue injury, and edema Coup- contrecoup injuries- contusions at the point of impact & on the opposite side of brain due to rebound Contusions mainly seen in frontal & temporal lobesmay involve apices of gyri only , or deeper tissues Can cause mass effects from edema- increased ICP Lacerations: penetration of the brain by a bullet or displaced fracture of skull- tissue tearing, vascular disruption, and hemorrhage adu.edu Traumatic Vascular Injury    CNS trauma disrupts vessel walls, leading to hemorrhage Depending on the affected vessel, the hemorrhage may be epidural, subdural, subarachnoid, or intraparenchym al Raise I/C pressure- leading to herniations Intracerebral Hematoma: Within the brain parenchyma caused by acceleration forces or contusions may coalesce  More common in frontal & adu.edu temporal lobes  Epidural Hematoma Almost always caused by skull fracturesespecially causing rupture of the middle meningeal artery  In infants, traumatic displacement of easily deformable skull may tear a vessel, even in the absence of a skull fracture  Blood accumulating under arterial pressure from the torn vessel dissects the dura away from the inner skull surface, producing a hematoma that causes rapid compression of brain  Typically, unconsciousness followed by a lucid interval for several hours then unconsciousness  Constitutes a neurosurgical emergency necessitating prompt drainage and repair to adu.edu  Subdural hematoma       Rapid movement of the brain during trauma can tear the bridging veins passing through the subarachnoid and subdural space to the dural sinuses Produces subdural hematomas- most commonly over the lateral aspects of the cerebral hemispheres In patients with brain atrophy, the bridging veins are stretched out, accounting for the higher rate of subdural hematomas in elderly persons Acute presentation: manifest acutely within the first 48 hours after injury- raised ICP Subdural hematomas organize by lysis of the clot, & growth of granulation tissue Chronic subdural hematomas: subdural hematomas commonly rebleed from the thin-walled vessels of the granulation tissue- may manifest clinically later adu.edu Infections          Meningitis: is an inflammatory process involving the leptomeninges within the subarachnoid space If the infection spreads into the underlying brain it is termed meningoencephalitis Bacterial ( acute pyogenic) meningitis: Causative organisms: Strep. Pneumoniae, N. Meningitides In neonates E.coli, & group B streptococci Risk factors: sepsis, basilar skull fractures, mastoiditis, neurosurgery Purulent exudate in CSF, meninges thickenadhesions- may impair CSF flow- hydrocephalus Clinically- due to meningeal irritation and neurologic impairment - headache, neck stiffness, photophobia, vomiting, seizures, cranial nerve palsies Systemic signs of infection- fever adu.edu Infections Dx:  Lumbar puncture for CSF examination – high neutrophil count with elevated protein, and reduced glucose  CSF- culture  Treatment: Antibiotics, corticosteroids  Brain Abscesses:  Bacterial meningitis may be associated with abscesses in the brain  Abscesses are destructive lesions, and patients present with focal deficits as well as general signs related to increased intracranial adu.edu pressure- and progressive herniation  Pyogenic meningitis- a thick layer of suppurative exudate covers the brain stem and cerebellum