CNS Blood Supply, Stroke, & Head Trauma

Question 1

Which two systems supply the brain?

Answer 1

• the internal carotid (anterior system) (80%) and the vertebrobasilar (posterior system) (20%) systems

Question 2

Which meninges are pierced by the major arteries supplying the CNS?

Answer 2

• the dura mater and arachnoid mater; they lie in the subarachnoid space, floating in CSF

Question 3

Follow the path of the vertebrobasilar system.

Answer 3

• vertebral arteries ascend through the transverse foramina of the cervical vertebrae and then enter the cranial cavity through the foramen magnum
• each vertebral artery gives off branches to form the anterior spinal artery, the two posterior inferior cerebellar arteries, and the two anterior inferior cerebellar arteries
• the two vertebral arteries then converge at the ponto-medullary junction to form the basilar artery
• the basilar artery gives off many small pontine branches, and then the two superior cerebellar arteries, before terminating into the two posterior cerebral arteries at the level of the midbrain
• (basilar artery also gives of labyrinthine arterial branches)

Question 4

Explain the blood supply to the spinal cord.

Answer 4

• the spinal cord has 3 major arteries: 1 anterior spinal artery and 2 posterior spinal arteries
• the anterior spinal artery is formed by branches arising from the vertebral arteries before they merge into the basilar artery
• the 2 posterior spinal arteries arise from either the vertebral arteries themselves or from their posterior inferior cerebellar arterial branches
• throughout the length of the spinal cord, these 3 vessels receive blood supply reinforcements via numerous segmental/radicular arteries (a major segmental/radicular artery is the artery of Adamkiewicz - which arises directly from the aorta)

Question 5

What portions of the spinal cord does each spinal artery supply? Are there any major watershed areas of the spinal cord?

Answer 5

• the anterior spinal artery supplies the anterior 2/3’s of the cord
• the posterior spinal arteries supply the posterior 1/3
• major watershed areas are those areas right before the next major segmental reinforcement: T4 and L1 (for anterior spinal cord), and T1-T3 (for posterior)

Question 6

What portions of the brain are supplied by each branch of the vertebrobasilar system?

Answer 6

• posterior inferior cerebellar arteries supply the inferior cerebellum and the lateral medulla
• anterior inferior cerebellar arteries supply the inferior cerebellum and the lateral pons
• labyrinthine arteries supply the labyrinths
• pontine arteries supply the medial pons
• posterior cerebral arteries supply the midbrain, inferior temporal lobes, and occipital lobe

Question 7

Follow the path of the internal carotid system.

Answer 7

• internal carotids enter the skull via the carotid canal and emerge into the middle cranial fossa via the foramen lacerum before ascending on each side of the pituitary gland
• each internal carotid gives off an opthalamic arterial branch, which enters the optic canal
• posteriorly, the internal carotids give off branches to form the posterior communicating arteries (these connect with the posterior cerebral arteries) and the anterior choroidal arteries
• they then terminate into two branches: the middle cerebral arteries (running laterally) and the anterior cerebral arteries (running anteriorly)
• an anterior communicating artery connects the two anterior cerebral arteries

Question 8

What portions of the brain are supplied by each branch of the carotid system?

Answer 8

• opthalamic arteries supply the retinas
• middle cerebral arteries supply the deep structures (basal ganglia, thalamus, etc.), superior temporal lobes, and the inferior lateral regions of the frontal and parietal lobes
• anterior cerebral arteries supply the medial and superior lateral regions of the frontal and parietal lobes

Question 9

Which branches of the middle cerebral artery supply the deep structures (basal ganglia, internal capsule, thalamus, etc)?

Answer 9

• the lenticulostriatal branches

Question 10

Both the anterior and middle cerebral arteries supply parts of the frontal and parietal lobes - how does this affect the supply to the homunculus?

Answer 10

• the ACA supplies the genitals, feet, and lower limbs
• the MCA supplies the head, neck, hands, and upper limbs
• note that the MCA supplies the internal capsule, where fibers projecting to every part of the body are condensed

Question 11

What is a berry aneurysm? What is the most common site? What are some others? Which artery is most commonly occluded via embolism?

Answer 11

• these are aneurysms that occur at arterial branch points; these areas lack a media (due to the turning/branching) and are therefore at risk (also increases risk of rupture)
• most common: at the branch points of the anterior communicating artery and anterior cerebral artery (40% of brain aneurysms occur here)
• other common areas: junction of the internal carotid and posterior communicating artery, bifurcation of the middle cerebral artery
• the middle cerebral artery is the most common site of embolic occlusion (the embolus is usually from the left heart due to atrial fibrillation)

Question 12

Circle of Willis

Answer 12

• connections between the 2 anterior carotid systems as well as connections between the carotid systems with the posterior vertebrobasilar system
• (anterior communicating artery –> anterior cerebral artery + middle cerebral artery –> posterior communicating artery –> posterior cerebral arteries –> posterior communicating artery –> middle cerebral artery + anterior cerebral artery –> back to anterior communicating artery)
• provides a high degree of collateral flow

Question 13

Give a generalized explanation of which parts of the cerebral hemispheres are supplied by each cerebral artery.

Answer 13

• anterior cerebral artery: supplies the medial hemisphere
• middle cerebral artery: supplies the lateral hemisphere
• posterior cerebral artery: supplies the occipital lobe

Question 14

The thoracic region of the spinal cord is most vulnerable to receiving insufficient blood supply, especially anteriorly - occlusion of the anterior spinal artery will result in what signs and symptoms?

Answer 14

• (this leads to acute thoracic cord syndrome)
• paraplegia and incontinence
• the spinothalamic tracts are mainly lost, with preservation of the dorsal columns

Question 15

Explain the venous drainage of the spinal cord.

Answer 15

• there are 6 longitdunal interconnecting venous channels (an anterior spinal vein, a posterior spinal vein, 2 anterolateral veins, and 2 posterolateral veins)
• these drain via the anterior and posterior radicular veins into the internal vertebral venous plexus (between dura mater and vertebral periosteum), which eventually drains into the main venous system

Question 16

Which cerebral artery is the largest?

Answer 16

• the middle cerebral artery

Question 17

What is a stroke? What are the two main types?

Answer 17

• blockage (ischemia) or rupture (hemorrhage) of vessels in the cerebral circulation, resulting in a focal neurological syndrome
• 85% are ischemic, 15% are hemorrhagic
• if it involves the anterior/carotid system: focal epilepsy, contralateral sensory/motor deficit, psychological deficit (ex: aphasia)
• if it involves the posterior/vertebrobasilar system: vision loss, focal brainstem lesion

Question 18

Explain the venous drainage of the brain.

Answer 18

• (note that these veins are valve-less)
• deep veins, superficial veins, and dural venous sinuses are involved
• the deep veins drain the internal structures of the forebrain; they merge within each hemisphere to form the 2 internal cerebral veins, which then merge in the midline to form the great cerebral vein
• venous blood then flows into the internal jugular vein

Question 19

Explain the difference between a transient ischemic attack (TIA) and an ischemic stroke.

Answer 19

• TIA: a transient, fully reversible neurological event that lasts less than 24 hours (typically they last less than 1 hour)
• ischemic stroke: the sudden onset of neurological deficits as a result of an ischemic event (deficit lasts more than 24 hours); more commonly due to embolism than to thrombosis

Question 20

What percentage of patients with a stroke will suffer a second one within twelve months? What percentage with a TIA will suffer a stroke within one WEEK?

Answer 20

• about 10% of patients with a stroke will suffer a 2nd one within a year
• 5-7% of patients with a TIA will suffer a stroke within the next week!

Question 21

What are the major risk factors for TIAs and ischemic strokes?

Answer 21

• diabetes, hypertension, and dyslipidemia
• since embolism is the most common mechanism for ischemic stroke (vs. thrombosis), myocardial dysfunctions are also major risk factors (cardiac mural emboli are the most common source of cerebral embolism)

Question 22

What clinical signs indicate a patient has suffered a hemorrhagic stroke?

Answer 22

• rapid onset of neurological deficits
• neck stiffness, coma, seizures, vomiting, headache, diastolic BP greater than 110 mmHg
• the only way to be sure, however, is with neuroimaging

Question 23

Which neuroimaging is recommended for detecting strokes?

Answer 23

• non-contrast CT imaging is used MAINLY for detecting hemorrhagic strokes (ischemic strokes are hard to detect with imaging)
• the sensitivity of the imaging for hemorrhagic stroke is 95-100% during the first 12 hours, but severely decreases as the blood is cleared - after 1 week, it is 50% sensitive; by week 2 or 3, it will no longer be detectable

Question 24

Other than the neuroimaging, what other investigations should be performed in a patient with a stroke?

Answer 24

• CT angiography and Duplex Doppler scan of the carotid arteries should be done ASAP - to check for stenosis of these major vessels
• blood tests and ECG should be done to rule out coronary artery disease (CAD)

Question 25

How do we treat ischemic strokes? What do we give to prevent ischemic strokes?

Answer 25

• treatment: IV tissue plasminogen activator (tPA) to dissolve the clots (thrombolysis) causing the ischemia (must be given within the 1st 4 and a half hours to be effective)
• prevention with antiplatelets: aspirin (the mainstay), dipyridamole (side effects decrease compliance), clopidogrel (PPIs interfere with clopidogrel!), warfarin
• in patients who received thrombolysis, wait 24 hours before giving prophylactic aspirin

Question 26

Patients suffering a stroke recover via two mechanisms - what are they?

Answer 26

• 1st recovery: due to resolution of the harmful local features (edema, loss of circulation, toxins, etc.)
• 2nd recovery: due to neural plasticity (new connections are made)

Question 27

What is a subarachnoid hemorrhage? How do patients commonly present? What are the most common causes?

Answer 27

• SAH is bleeding into the subarachnoid space, resulting in raised ICP (blood is also toxic to the brain parenchyma; the CSF and brain ECF are in full communication) - it is a medical emergency
• patients present with “the worst headache of my life,” nausea, vomiting, and photophobia; 50% also have a loss of consciousness
• most common causes: ruptured intracranial aneurysm (ruptured berry aneurysm, usually of the anterior communicating artery branch points) and trauma

Question 28

What investigations do we use when a subarachnoid hemorrhage is suspected? How do we treat them?

Answer 28

• investigations: CT followed by a LP if unrevealing; if ruptured aneurysm is the cause, we can confirm with a cerebral angiography; FBC, clotting profile, electrolytes (hyponatremia may result), troponin I; ECG (50% have abnormal ECGs)
• the LP will have increased RBC count and a yellow-ish tinge (called xanthochromia) due to the presence of bilirubin
• treatment: stabilize (cardio-pulmonary support) + surgical clipping or endovascular coil embolization
• give these patients Ca2+ channel blockers, stool softeners, and antitussives (cough suppressant) to prevent future vasospasms/re-bleeding during the recovery period; also give anticonvulsants to decrease risk of seizure (which would most likely cause re-bleeding)

Question 29

What are the major risk factors for subarachnoid hemorrhage?

Answer 29

• older age (greater than 50), female, black
• smoking, HTN, ADPKD (adult polycystic kidney disease), Marfan’s syndrome, Ehlers-Danlos syndrome
• family history of SAH

Question 30

A patient presents with “the worst headache of his life” and one eye is unresponsive to light and points down and out - what should you suspect?

Answer 30

• a ruptured aneurysm at the junction of the internal carotid and posterior communicating arteries (compression of the 3rd CN), resulting in SAH

Question 31

Subdural and Epidural Hematomas

Answer 31

• subdural (SDH): between the dura and arachnoid; can be due to whiplash forces, tearing the veins (much more common) separating the dura and arachnoid does not require much pressure - venous pressure is enough to do so; slow
• epidural (EDH): between the skull and dura; nearly always due to skull fracture with laceration of meningeal arteries (less than 1% of head injuries) to separate the dura mater and the skull, you need arterial pressure, which requires a skull fracture to rupture an artery; rapid (can result in herniation, CN III compression)
• patients present with loss of consciousness/drowsiness, unilateral headache, and unilaterally slightly enlarged pupil
• in acutely deteriorating patients, emergency drainage holes (burr holes) or craniotomy is needed

Question 32

What is a concussion? How are these diagnosed? What is a contusion?

Answer 32

• a concussion is a function (not structural) brain injury resulting in rapid onset of symptoms (headache, nausea, confusion, memory disturbances, loss of consciousness) and eventual spontaneous resolution (10-14 days later)
• it is clinical diagnosis without any reliable tests/markers
• a contusion is a surface bruise of the brain resulting from the brain hitting the skull

Question 33

What are some complications of a concussion?

Answer 33

• impaired performance
• cerebral edema (called “2nd impact syndrome”)
• prolonged symptoms
• depression
• CTE (chronic traumatic encephalopathy: cumulative cognitive deficits due to repeated concussions)

Question 34

What is the most prevalent cause of neurological morbidity?

Answer 34

• cerebrovascular disease! (via embolism, thrombosis, or rupture)

Question 35

What percentage of the cardiac output does the brain receive? What percentage of the body’s oxygen consumption is due to the brain?

Answer 35

• brain receives 15% of cardiac output and is responsible for 20% of the body’s O2 consumption

Question 36

What is the leading cause of death in patients younger than 45 years of age?

Answer 36

• trauma

- 50% of these cases involve the head

Question 37

When does cerebral vasodilation occur? What about vasoconstriction?

Answer 37

• cerebral vasodilation (along with systemic constriction) results in increased blood flow to the brain and occurs in: acidosis, hypotension, and hypoxia
• cerebral vasoconstriction occurs in: alkalosis and hypertension

Question 38

What drives the autoregulation of cerebral blood flow? Between what range of cerebral perfusion pressure (CPP) does autoregulation occur?

Answer 38

• autoregulation is primarily driven by the pressure of CO2 (pO2 drives it in cases of severe hypoxia) this is why therapeutic hyperventilation helps lower ICP! the decrease in pCO2 decreases cerebral perfusion by vasoconstriction
• CPP will increase as pCO2 increases until pCO2 exceeds 90 mmHg (normal is 40 mmHg) and then CPP plateaus off at this point
• when CPP is between 50-150 mmHg, autoregulation occurs; outside of this range, this regulation is lost
• (CPP = MAP - ICP) normal ICP = 0-10 mmHg

Question 39

Which clinical signs suggest a skull fracture has occurred?

Answer 39

• subconjunctival bleeding, hemotympanum, CSF rhinorrhea, CSF otorrhea, Battle’s sign (bruising around the post-auricular surface), and raccoon eyes

Question 40

The Glasgow-Coma Scale scores range from 3 to 15 - which score classifies as a severe traumatic brain injury?

Answer 40

• any score less than 9 suggests the trauma was very severe (these make up 10% of head injuries presenting to the ED)
• a score between 9 and 13 suggests a moderate injury
• a score of 14-15 suggests a mild injury (these make up 70-80% of head injuries presenting to the ED)

Question 41

Even if a patient has a GCS of 15, under what conditions should you still perform a CT scan?

Answer 41

• if you suspect a skull fracture, if the patient is on anticoagulation therapy, if the patient is drunk, if the patient is elderly, and/or if the patient has any of the following: abnormal neurology, any L.O.C., vomiting twice or more, seizure, ongoing headaches, amnesia

Question 42

How can you tell the difference between an epidural hematoma, subdural hematoma, subarachnoid hemorrhage, and intracerebral hemorrhage?

Answer 42

• EDH: the blood will NOT cross suture lines (b/c dura mater and bone are very tightly attached here); classic lens shaped lesion
• SDH: the blood WILL cross suture lines, but will NOT enter the sulci (b/c arachnoid is blocking); classic crescent-shaped lesion
• SAH: the blood WILL enter the sulci
• intracerebral hemorrhage: blood will be past the meninges

Question 43

What is global central ischemia? What can cause this condition? How do patients present based on severity?

Answer 43

• global central ischemia is a global version of ischemic stroke
• it can be due to: global decreased perfusion (diffuse atherosclerosis), acute decrease in blood flow (shock), chronic hypoxia (anemia), or repeated episodes of hypoglycemia (as occurs with insulinomas)
• mild: transient confusion; complete recovery
• moderate: infarction of watershed areas and cortical necrosis
• severe: diffuse necrosis; survival unlikely/vegetative stae

Question 44

Ischemic stroke can be due to thrombosis or embolism - what is a third potential cause? How can we tell all these apart (on autopsy)?

Answer 44

• (embolism is most common cause)
• lacunar stroke via hyaline arteriosclerosis (secondary to HTN, diabetes, etc.) of the small branches (most commonly affected are the lenticulostriate vessels); these result in small circular infarcts
• a thrombotic stroke (usually at branch points) will result in pale infarcts
• an embolic stroke (usually in MCA via thrombi from left heart) will result in hemorrhagic infarcts (because the embolus will get lysed and reperfusion injury will occur)

Question 45

What is an intracerebral hemorrhage? What do they result from? What is the most common site of an intracerebral hemorrhage?

Answer 45

• bleeding into the brain parenchyma (AKA intraparenchymal hemorrhage or hypertensive hemorrhage)
• results from ruptured Charcot-Bouchard microaneurysms (these form from unmanaged HTN)
• most common site is in the basal ganglia (due to ruptured aneurysms in the lenticulostriate vessels)

Question 46

What is a major potential complication of hematomas and hemorrhages? What are the areas where this most commonly occurs?

Answer 46

• herniation! (displacement of brain tissue due to a mass effect or raised ICP)
• most common: subfalcine hernation (frontal lobe’s cingulate gyrus herniates into the falx cerebri and compresses the anterior cerebral artery)
• tonsillar herniation (cerebellar tonsils herniate through the foramen magnum and compress the brainstem)
• uncal herniation (uncus of temporal lobe herniates into the tentorium and compresses CN III, posterior cerebral artery, and brainstem’s vascular supply)

Question 47

How will a patient suffering from a stroke involving the middle cerebral artery present?

Answer 47

• motor and sensory cortexes affected involve upper limb and face: contralateral paralysis of upper limb and face; contralateral loss of sensation in face, upper AND lower limbs
• temporal lobe and frontal lobe affected: aphasia if in left (dominant) hemisphere

Question 48

How will a patient suffering from a stroke involving the anterior cerebral artery present?

Answer 48

• motor and sensory cortexes affected involve lower limb: contralateral paralysis and contralateral loss of sensation of lower limb

Question 49

How will a patient suffering from a stroke involving the lenticulostriate artery?

Answer 49

• striatum and internal capsule affected: contralateral hemiparesis/hemiplegia
• (due to lacunar strokes, secondary to unmanaged HTN)

Question 50

How will a patient suffering from a stroke involving the anterior spinal artery present?

Answer 50

• lateral corticospinal tract affected: contralateral hemiparesis
• medial lemnisucs affected: contralateral loss of proprioception
• (note that these strokes are usually bilateral)

Question 51

How will a patient suffering from a stroke involving the posterior inferior cerebellar artery present?

Answer 51

• lateral medulla affected (nucleus ambiggus, vestibular nuclei, sympathetic fibers, etc.): dysphagia and hoarseness, vomiting, vertigo, nystagmus, decreased gag reflex, ipsilateral Horner’s syndrome
• inferior cerebellar peduncle affected: ataxia
• lateral spinothalamic tract affected: ipsilateral loss of pain and temperature of face

Question 52

How will a patient suffering from a stroke involving the anterior inferior cerebellar artery present?

Answer 52

• lateral pons affected (facial nucleus, CN nuclei, vestibular nuclei, cochlear nuclei, sympathetic fibers, etc.): facial paralysis, vomiting, vertigo, nystagmus, loss of lacrimation and salivation and taste, ipsialteral Horner’s syndrome, ipsilateral loss of hearing, loss of pain and temp in face
• middle and inferior cerebellar peduncles affected: ataxia

Question 53

How will a patient suffering from a stroke involving the posterior cerebral artery present?

Answer 53

• occipital cortex/visual cortex affected: contralateral hemianopia w/ macular sparing

Question 54

How will a patient suffering from a stroke involving the basilar artery present?

Answer 54

• pons, medulla, lower midbrain, corticospinal and corticobulbar tracts, etc. affected: “locked-in syndrome” (conscious and able to blink/some eye movement w/ quadriplegia and loss of facial, mouth, and tongue movements)

Question 55

How will a patient suffering from a stroke involving the anterior communicating artery present?

Answer 55

• most common lesion here is an aneurysm, not a stroke

- cranial nerves impinged by aneurysm: visual field defects

Question 56

How will a patient suffering from a stroke involving the posterior communicating artery present?

Answer 56

• most common lesion here is an aneurysm, not a stroke

- cranial nerve III palsy: pupil is dilated, eye is “down and out”, ptosis