Week 5: Blood Supply

What protects the brain?

Scalp and meninges

SCALP stands for

Skin

subcutaneous Connective tissue

galea Aponeurotica

Loose areolar connective tissue

Pericranium

Meninges the PAD the brain

Pia, Arachnoid, Dura

Two portions of dura mater:

Periosteal (outer), meningeal (inner)

The two layers of dura mater form what in cranial cavity?

Falx cerebri and tentorium cerebelli

Falx cerebri:

Sickle shaped ("falx") between the left and right hemispheres

Tentorium cerebelli:

"tent" over cerebellum; has the tentorial notch which allows for midbrain to pass through

Describe the arachnoid mater:

Wispy, "spidery" layer; adheres to meningeal dura and CSF is below the arachnoid layer (subarachnoid space)

Describe the pia mater:

Innermost layer; very thin that adheres closely to the brain

What does it mean by saying the meninges form 3 potential spaces?

These spaces don't exist unless injury occurs and causes blood or CSF to flow into it

3 potential spaces:

Subdural, epidural, subarachnoid

Where is epidural space?

Above dura; between skull and periosteal dura

Where is subdural space?

Below meningeal dura and above arachnoid

Where is subarachnoid space?

Between arachnoid and pia; contains CSF (space is always there)

What are the arachnoid trabeculae?

Fine filaments loosely connecting arachnoid to pia

The __________ ___________ artery branches off the external carotid artery; if it breaks it could bleed into the epidural space and push dura away from the skull

Middle meningeal

The 4 ventricles that house CSF

2 lateral ventricles, third ventricle, fourth ventricle

What is CSF formed by?

Choroid plexus located in ventricles

Flow of CSF

Lateral ventricles

Interventricular foramen of Monro

Third ventricle

Cerebral Aqueduct

Fourth ventricle

Foramen of Magendie (and Lushka)

What does a blockage anywhere in the flow of CSF cause?

Hydrocephalus; increased intracranial pressure

Where is an epidural hematoma?

In potential space between dura and skull; causes concave shape on imaging

Etiology of epidural hematoma:

- Usually from rupture of middle meningeal artery due to temporal bone fracture

- Pt. may have no s/s initially (lucid interval) but within a few hours lead to elevated ICP and herniation and death w/o surgery

Where is a subdural hematoma?

In potential space between dura and arachnoid; two types chronic and acute

Causes of subdural hematoma?

- Rupture of bridging veins which are susceptible to shear injury as they cross arachnoid into dura

- Venous blood spreads out over a large area to form crescent shaped hematoma

Which hematoma is common in elderly patients? Why?

Chronic subdural hematoma; because brain moved more freely due to atrophy and bridging veins become susceptible to shear injury

What is a chronic subdural hematoma?

Can be from minimal trauma; venous blood slowly collects over a period of weeks to months leading to vague s/s (ex: headache, cognitive impairment, unsteady gait)

What is an acute subdural hematoma?

Impact velocity must be quite high for significant subdural hematoma to occur right after injury (serious, worse prognosis(=)

Which hemorrhage will blood be seen in contours of brain sulci on CT?

Subarachnoid hemorrhage

Two types of subarachnoid hemorrhage:

Non-traumatic (spontaneous) and traumatic

Cause of traumatic subarachnoid hemorrhage:

Bleeding into CSF from damaged vessels due to contusions and other traumatic injuries, more common than spontaneous

Signs of traumatic subarachnoid hemorrhage:

Headache usually severe due to meningeal irritation from blood in CSF; deficits typically related to presence of other cerebral injuries (ex: fracture)

Signs/symptoms of spontaneous subarachnoid hemorrhage:

Sudden catastrophic headache (ex: hit in head w/ bat); local neuro deficits, coma, impaired LOC, death

Spontaneous subarachnoid hemorrhage post-incident fatality rate:

25% post-incident; overall mortality is 50%

Spontaneous subarachnoid hemorrhage etiology:

Rupture of arterial aneurysms (75-80% most occurring in anterior circulation)

4-5% due to arteriovenous malformation

Spontaneous subarachnoid hemorrhage and CT:

CT within 3 days after rupture can detect hemorrhage in >95% of cases; angiogram used next to determine location/size

In which hemorrhage does delayed vasospasm occur 3-4 days after injury (peaking at 10 days) in ~50% of patients and can lead to ischemia or infarction?

Spontaneous subarachnoid hemorrhage

What is hydrocephalus?

Excess CSF fluid in intracranial cavity

What does hydrocephalus result from?

Excess CSF production (rare); obstruction of CSF flow (common); decreased reabsorption of CSF

Main signs and symptoms of hydrocephalus:

Shuffling, magnetic gait

Incontinence

Mental decline (wet, wacky, and weird)

Treatment of hydrocephalus:

Drain CSF from ventricles via drains, shunts, or endoscopic neurosurgery

What is a coup/contrecoup injury?

Hits their head on that side "coup" (initial injury), then bouncing back since brain is mobile is "contrecoup"

What is a traumatic intracerebral hemorrhage?

Contusion in brain tissue itself of cerebral hemispheres where cerebral gyri lie immediately adjacent to ridges of bony skull (common in temporal and frontal poles)

Signs and symptoms of elevated intracranial pressure:

Headache, altered mental status (depressed/decreased altertness), nausea/vomiting, papilledema, visual loss, diplopia, cushing's triad (HTN, bradycardia, irregular respirations)

How does increased intracranial pressure happen?

Suddenly or slowly, leading to irreversible brain damage and death

How can increased intracranial pressure be treated?

meds, ventricular drainage, induced coma, hemicraniectomy

Etiology of Headaches:

Mechanical traction, inflammation, irritation other structures w/ innervation (BV, meninges, scalp, skull)

Classifications of headaches

Vascular, tension type, or secondary

T/F: Brain parenchyma has no pain receptors

True

Cause of vascular headaches

Likely from inflammatory, autonomic, serotonergic, neuroendocrine, and other influences on blood vessel diameter

Types of vascular headaches:

Migraine, cluster

_____% of patients have family history of migraines

75

Migraine symptoms can be triggered by what?

Foods, stress, eye strain, menstrual cycle, and sleep pattern changes

Aura and migraines:

Aura typically precedes migraines; blurry vision, and/or shimmering distortions

Symptoms of migraines:

Throbbing pain, worsens with light, noise, and sudden head movement, possibly with nausea/vomiting, tender scalp

Signs of tension-type of headaches:

Steady dull ache, "band-like sensation," mild-moderate pain which happen time to time

Chronic tension type of headaches:

Can happen daily for years and is often associated with psychological stress or post-trauma

Treatment for tension-type headaches:

Muscle-relaxation techniques, NSAIDS, other analgesics

What is a secondary headache?

Multiple other causes such as: head trauma, intracranial hemorrhage, cerebral vasoconstriction syndrome, low CSF pressure, epidural abscess, meningitis

What is the dominant hemisphere?

Left hemisphere for 90% of people; Broca's and Wernicke's are in here

Origination of anterior circulation:

Aorta/Brachiocephalic arteries -> Common carotids -> Internal/external carotids -> bilateral internal carotid's

Origination of posterior circulation:

Subclavian arteries -> Bilateral vertebral arteries -> basilar arteries

Anterior circulation of Circle of Willis

ICA, ACA, AComm, MCA

Posterior circulation of Circle of Willis

PComm, PCA

Vascular territories of ACA:

Antero-medial surface; anterior part of parietal, anterior limb of internal capsule, basal ganglia, caudate nuscleus, putamen

Vascular territories of MCA:

Lateral portion of brain; sylvian fissue, superior and inferior portion

Vascular territories of PCA:

Inferior.medial of temporal and occipital lobe, some penetrating vessels of posterior limb of internal capsule and most of thalamus

Ischemic stroke

Infarction to brain tissue, isn't getting blood

5th leading cause of death in the US and major cause of permanent disability

Stroke

Embolus cause of ischemic stroke

Very sudden, cardioembolic in nature, breaks off clot and lodges in vessel to brain

Thrombosis cause of ischemic stroke

Stuttering course, clot formed locally on blood vessel due to atherosclerotic plaque

Mechanisms of ischemic stroke:

Embolus, thrombosis, large vessel infarcts, small vessel infarcts, cortical lesions, subcortical lesions

Stroke risk factors:

Hypertension, diabetes, hypercholesterolemia, cigarette smoking, positive family history, cardiac disease, prior history of stroke or vascular disease

4 areas of MCA infarct occlusion:

Stem, superior division, inferior division, deep territory

_____ is most common site of infarct

MCA

Left MCA superior division infarct

Right face and arm weakness of UMN type

Nonfluent or Broca's aphasia

May have right face and arm cortical type sensory loss

Left MCA inferior division infarct

Fluent, Wernicke's aphasia

Right visual field deficit

Right arm and face cortical sensory loss

Motor findings are usually absent

Patient may be initially confused or crazy but otherwise intact

Mild right side weakness may be present especially at onset of symptoms

Left MCA deep territory infarct

Right pure motor hemiparesis of UMN-type

Larger infarcts may produce "cortical" deficits, such as aphasia as well

Left MCA stem infarct

Combination of above

Right hemiplegia, right hemianesthesia

Right homonymous hemianopia

Global aphasia (Broca and Wernike)

Left gaze preference

Right MCA superior division infarct

Left face and arm weakness of UMN type

Left hemineglect is present to a variable extent

May also be some left face and arm cortical-type sensory loss

Right MCA inferior division infarct

Profound left hemineglect

Left visual field and somatosensory deficits are often present; however, these may be difficult to test convincingly because of the neglect

Motor neglect with decreased voluntary or spontaneous initiation of movements on the left side can also occur (However, even patients with left motor neglect usually have

normal strength on the left side, as evidenced by occasional spontaneous movements or purposeful withdrawal from pain) Some mild, left-sided weakness may be present

Often a right gaze preference, especially at onset

Right MCA deep territory infarct

Left pure motor hemiparesis of UMN

Left hemineglect w/ larger infarcts

Right MCA stem infarct

Combination of the above

Left hemiplegia and left hemianesthesia

Left homonymous hemianopia

Profound left hemineglect

There is usually a right gaze preference

ACA Infarct generalized:

Contralateral UMN weakness and sensory loss (LE>UE)

Dominant ACA stroke = transcortical motor aphasia

Non-dominant ACA stroke = contralateral neglect

Variable frontal lobe dysfunction

Left ACA infarct

Right leg weakness of UMN type

Right cortical type sensory loss

Grasp reflex and frontal lobe behavioral abnormalities

Transcortical aphasia

Right hemiplegia (larger infarcts)

What is transcortical motor aphasia:

Presents like Broca's, repetition is spared but cannot voluntarily speak a response

PCA infarcts generalized:

Contralateral homonymous hemianopsia

If extending into thalamus/internal capsule = contralateral sensory loss and hemiparesis

Left PCA Infarct

Right homonymous hemianopia

Extension to the splenium of the corpus callosum can cause alexia without agraphia

Larger infarcts, including the thalamus and internal capsule, may cause aphasia

Right hemisensory loss, and right hemiparesis.

Right PCA Infarct

L homonymous hemianopia

L hemisensory loss (larger infarcts)

L hemiparesis

What is alexia without agraphia?

Cannot read but can write

What type of infarct do you see alexia without agraphia?

Left PCA infarct

What is a watershed infarct?

Type of stroke that affects the border zones between 2 different blood supply regions (most common ACA-MCA, MCA-PCA)

What is seen in ACA-MCA watershed infarcts?

In the dominant hemisphere, transcortical aphasia syndromes

What is seen in MCA-PCA watershed infarcts?

Disturbances of higher order visual processing (see things not there or not see things)

What is a transient ischemic attack (TIA)?

Neuro deficit lasting ~10 minutes, caused by temporary brain ischemia; considered a neuro emergency

Causes of TIA?

Embolus temporarily occludes blood vessel, thrombus formation on blood vessel wall

Why are TIA's neuro emergencies?

15% of patients with TIA will have a full CVA (50% occur within 48 hours)

All venous drainage of cerebrum reaches _____________ veins

internal jugular

What are the deep veins?

Great vein of Galen and Inferior sagittal sinus

How do the deep veins drain?

Great vein of Galen and inferior sagittal sinus form the straight sinus into the confluence of sinuses into the sigmoid sinus and into the internal jugular vein

What is a superior sagittal thrombosis associated with?

Hypercoagulable states (ex: post-partum), obstruction of venous drainage results in increased intracranial pressure