Cns path congenital, edema

Congenital Malformations

• Development of CNS proceeds according to a precise schedule

a) each morphological event is cornerstone for those that

followi) myelination initiated late in embryonic developmentii) only after cellular

differentiation and migrationiii) congenital anomalies reflect

interruptions in the completion of critical developmental processes

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• Neural tube defects (dysraphic states) reflect impaired closure of the dorsal aspect of vertebral column

a) Spina Bifidai) most common in lumbosacral

region. Further classified according to extent of defect

- Spina bifida acculta: restricted to vertebral arches, usually

asymptomatic small tuft of hair or dimple


- Meningocele: more extensive bony and soft tissue

defects. Protrusions of meninges as fluid filled sac. Lateral aspects covered by skin, apex is ulcerated

- Meningomyelocele: More extensive defect with spinal cord flattened

-Rachischisis: extreme defect, spinal column converted into gaping canal

ii) Pathogenesis- induced at 8-9th gestational

day in experimental animals (rats and chicks) by chemicals (trypan blue, vitamins)


- maternal folic acid deficiency- other potential associated

malformationsinclude:

1.Arnold-Chiari Syndrome2.Hydrocephalus3. hydromyelia4. polymicrogyria

b) Anencephalyi) congenital absence of part or all brainii) is second in incidence to spina

bifidaiii) concurrent with spina bifidawww.freelivedoctor.com

iv) highly vascularized, poorly differentiated

-“cerebrovasculosa”, lies on flattened base of the skull

Spinal Cord MalformationsSpinal Cord Malformations• Uncommon congenital disorders include:

a) duplications (rare)i) complete (dimyelia)ii) partial duplications into 2

separate structures (diastematamyelia)

b) hydromyeliai) dilation of central canal of spinal cord


c) Syringomyeliai) tubular cavitation (syrinx) which extends for variable distances

along entire length of spinal cord- may or may not

communicate with central canal

ii) usually encountered in adults- many cases thought to represent congenital malformation

iii) causes relate to trauma, ischemia,tumors

iv) motor and sensory deficits anatomical location in spinal cord


d) syringobulbiai) variant of syringomyeliaii) slit like cavities located in

medulla

Arnold-Chiari MalformationArnold-Chiari Malformation• Involves medulla and cerebellum

a) brainstem and cerebellum compacted into bowl-shaped posterior fossa

b) often associated with syringomyelia or

c) lumbar meningomyeloceled) symptoms depends on severity of defecte) Pathogenesis:


i) may occur when meningomyelocele anchors lower end of spinal cord

- causes downward growth of spinal cord and- creates traction on medulla

ii) curvature of medullaiii) breaking of quadringeminal

plateiv) intracranial pressure

associated with hydrocephalusf) Pathology:

i) caudal aspect of cerebellar vermis is herniated through an enlarged foramen magnumwww.freelivedoctor.com

Dandy-Walker MalformationDandy-Walker Malformation

• Enlarged posterior fossa•Cerebellar vermis is absent or only in rudimentary form

a) in its place is a large midline cyst• Dysplasias of brain stem nuclei are common

HydrocephalusHydrocephalus• Congenital hydrocephalus

a) excessive amount of CSFb) enlarged ventriclesc) congenital atresia of the aquaduct of Sylvius is most common cause


i) 1 in 1000 live birthsd) other causes

i) aqueduct narrowing by gliossis- may be caused by transplacental

transmission of viruses that induce ependymitis• Noncommunicating hydrocephalus

a) portion of ventricular system is enlarged

i) e.g., mass in 3rd ventricle• Communicating hydrocephalus

a) enlargement of entire ventricular system www.freelivedoctor.com

• Communicating hydrocephalusa) impairment of reabsorption

• Hydrocephalusa) hemispheres are enlargedb) ventricular system is dilated


• Hydrocephalus ex vacuoa) dilation of ventricular system with

CSF volume secondary to loss of brain parenchyma

Disorders of Cerebral GyriDisorders of Cerebral Gyri• Frequently associated with mental retardation

a) polymicrogyriai) presence of small and excessive

gyrib) pachygyria

i) gyri in # and usually broad


c) lissencephalyi) cortical surfaces are smooth or imperfectly formed gyri

d) heterotopiasi) focal defects that lead to

modules of ectopic neuronsii) mental retardationiii) may be caused by maternal

alcoholism


Chromosome AbnormalitiesChromosome Abnormalities

• Associated with congenital defectsa) derrangements in autosomes 1-12

i) incompatible with lifeii) spontaneously aborted

b) Down Syndromei) trisomy 21

- mental retardation- distinct facial features, etc.

ii) mild cerebral atrophyiii) patients often develop

Alzheimer disease pathology by 4th decade


c) Trisomy 13-15i) Holoprosencephaly

- microcephalic brain- absence of corpus collusum- absence of interhemispheric fissure- rarely compatible with life beyond a few weeks

ii) arhinencepahaly- absence of olfactory tracts and bulbs (rhinencephalon)- associated with holoprosencephaly or as

solitary lesionwww.freelivedoctor.com

Cerebral edema, raised ICP and Cerebral edema, raised ICP and herniationherniation

• Brain and spinal cord exist in rigid compartment• Cerebral edema

a) brain parenchymal edema may occur in a variety of conditions

i) vasogenic edema- BBB disruption, resulting in increases in permeability- may be focal or generalized

ii) cytotoxic edema- increase intracellular

volume(hypoxia/ischemia inhibiting

active pumps)


b) Interstitial edema (i.e., hydrocephalus)

i) occurs around lateral ventricles• ICP

a) mean CSF pressure greater than 200 mm H2O with patient recumbent

i) most occur with mass effectb) if severe enough will cause brain to displace where herniation may occur

i) subfalcine (cingulate) herniation- asymmetric expansion of

cerebral hemisphere displaces cingulate gyrus under the Falx cerebri www.freelivedoctor.com

- may be associated with compression of branches of

the anterior cerebral arteryii) transtentorial (uncinate)

herniation- medial aspects of temporal lobe is compressed against

tentorium cerebelli- 3rd cranial nerve is compressed- pupillary dilation and ocular movement impairment on

side of lesion


- progression of this type of herniation hemorrhages in pons and midbrain (Duret hemorrhages)- may result from the tearing of

penetrating veins and arteries supplying upper brainstem

iii) tonsilar herniation- displacement of cerebellum (tonsils) through foramen

magnum- this type of herniation is life threatening ( compression of brainstem - - CV and resp centers) www.freelivedoctor.com

CNS TRAUMACNS TRAUMA

• Epidural hematomaa) accumulation of blood between

calvaria and the durai) usually results from a blow to

the head - if not quickly treated, is generally fatal

• Pathogenesis:a) dura securely bound to inner aspect

of Calvaria (analogons to periosteum)


b) middle meningeal arteries occupy space between dura and calvaria

i) grooved into inner table of boneii) branches across temporal-

parietal area (mainly as 3 major vessels)

c) temporal bone one of thinnest bones of skull

i) vulnerable to fractures- minor trauma may cause

fracture- and transect branches of

middle meningeal artery life threatening epidural

hemorrhage


• Pathology:a) blood escapes into epidural space

i) thereby separating dura from calvaria- progressive enlargement of hematoma

b) asymptomatic for first 4-8 hoursc) when hematoma volume 30 to 50

mli) symptoms resemble space

occupying lesionii) downward displacement of CSFiii) if hematoma continues, ICP

eventually exceeds cerebral venous pressure!


- venous sinuses are compressed cerebral ischemia (hypoxia)

- diffuse cortical impairment confusion and disorientation

d) ”Cushing Reflex” is protective response to CBF and oxygenation

i) HR (increases filling)ii) myocardial contractility iii) systolic BP

e) hematoma can to ~60 mli) after compensation is

exhausted ii) brain shifted laterally away

from side of hematomawww.freelivedoctor.com

iii) medial temporal lobe compressed against midbrain displaces it through in tentorium fatal event known as “transtentorial herniation”

iv) 3rd nerve compressionv) pupil fixed and dilated (same

side)vi) further compression further hypoxia and impairs neuronal

functionvii) damage to reticular formation

expressed clinically as decline in level of consciousnesswww.freelivedoctor.com

viii) shortly thereafter hemorrhage and necrosis of

brainstem irreversible damage death or irreversible coma

f) epidural hematomas are progressive and if not treated, are fatal in ~4-48

hrsg) concussion

i) transient loss of consciousness due to trauma

ii) mainly to brainstems reticular formation- e.g., boxing “knock-out” - deflects head up and

posteriorly


- these motions import quick torque on brainstem and cause

functional paralysis of neurons of reticular formation

iii) a blow to temporal-parietal area may cause skull fracture but does NOT

generally cause a concussion- lateral movement of

cerebral hemispheres is prevented by the Falx


Subdural HematomaSubdural Hematoma

• Reflects torn bridging veins in subdural space

a) major cause of deathi) fallsii) assaultsiii) vehicular accidentsiv) sporting mishaps

• Pathogenesis:a) cerebral hemispheres tethered

loosely by blood vessels and cranial nerves and float in CSF


b) when brain impacts skulli) stationary head struck ii) moving head strikes object

c) cause shearing effect in subdural space

i) tears veins d) unlike epidural space, subdural

space can expandi) since bleeding usually is from

veinsii) usually stops spontaneously

(i.e., bleeding)- with only ~ 25-50 ml- from local tamponade effect

e) can compress veins thrombosisf) usually bilateral


• Pathology:a) even if small can cause irritation

i) between hematoma and dura - leads to granulation tissue

(several weeks)- creates membrane above

hematoma (i.e., outer membrane)

- fibroblasts form fibrous membrane

b) static subdural hematoma has 3 routes of evolution


i) may be reabsorbed only small amounts of residual

hemosiderinii) remain static with potential for

calcificationiii) hemorrhage may enlarge

(rebleeding, usually within 6 months)

iv) granulation tissue is vulnerable to re-bleed (shaking of head)

c) during genesis of subdural hematoma

i) bridging vein severance is precisely located to the subdural space

- compartmentalizes blood away from CSF


- absence of blood in CSF does NOT negate presence of

subdural hematomad) clinical S & S:

i) stretching meninges headache

ii) pressure on motor cortex contralateral weaknessiii) focal cortical irritation seizuresiv) bilateral subdural hematoma cognitive dysfunction

- misdiagnose as dementiav) rebleeding may cause transtentorial herniation


Subarachnoid HemorrhageSubarachnoid Hemorrhage

• Any bleeding into subarachnoid space• Seen with traumatic head injuries

a) 2/3 of cases reflect rupture of pre-existing arterial aneurysm (discussed later)

b) 10% occur as AVMc) remainder from variety of conditions

i) infectionsii) blood dyscrasiasiii) tumorsiv) vasculitis


Cerebral ContusionCerebral Contusion• Traumatic bruise of the brain surface

a) usually result from anteroposterior displacement

i) similar to subdural hematomaii) severity corresponds to

acceleration of headb) lesion at point impact referred to as

i) coup injury (i.e., contusion)- same side as impact

c) lesion (i.e., contusion) on opposite side as impact referred to as

i) counter coup contusionwww.freelivedoctor.com

d) contusions are permanent (necrotic tissue)

i) phagocytized rapidly

Penetrating WoundsPenetrating Wounds• In absence of injury to vital brain structures immediate threat to life is hemorrhage

a) lethal transtentorial herniationb) herniation of cerebellar tonsils into foramen magnum

i) compression of medulla- disabling CV and Resp.

centers• Velocity contributes a blast effect to projectile


a) high velocityi) disrupts tissue by its own massii) centrifugal blast

- enlarges diameter of cylinder causing disruption

iii) can cause immediate death- explosive in ICP, which - herniates cerebellar tonsils into foramen magnum

d) seizures are a threat in healed penetrating wounds

i) 6-12 months after the trauma


Spinal Cord InjuriesSpinal Cord Injuries

• Often lead to paraplegia or quadriplegiaa) direct injury via

i) penetrating injuries- stab- bullets

b) indirecti) fracturesii) displacement of vertebrae

c) trauma may complicate injury via blood supply necrosis


• Hyperextension vs. hyperflexiona) vertebral bodies aligned by 2

longitudinal ligamentsi) anterior spinal ligamentii) posterior spinal ligament

b) hyperextension injuryi) forehead struck from front and driven posteriorly

- diving head first into shallow water- posterior displacement tears anterior spinal ligament- cord damaged by posterior bony processes www.freelivedoctor.com

c) hyperflexion injuryi) head or shoulders hit from

behind- head driven forward - sharp forward angulation of spinal cord

d) consequences of spinal cord injury vary

i) concussion- mildest injury- transient and reversible of spinal cord function

ii) contusion- more severe trauma ranging from (minor transient

bruise hemorrhage)


- spinal cord necrosis and edema caused by contusion

myelomalacia hematoma

within cord hematomyelia

iii) lacerations and transactions- usually produced by penetrating wounds- are irreversible- cause paralysis of lower

limbs (paraplegia)- or quadriplegia (all 4

extemitites www.freelivedoctor.com

Circulatory DisordersCirculatory Disorders

Vascular Malformations may lead to Vascular Malformations may lead to hemorrhagehemorrhage

• AVM (ArterioVenous Malformations)a) most common congenital vascular malformation

i) has greatest clinical significance

- seizures- intracranial hemorrhages

(subarachnoid)- 2nd – 3rd decades


b) typically seen in cerebral cortexc) abnormal blood vessels replace

cortical grey matter and extend deeply into white matter

d) defect enlarges with time involves larger area • Cavernous angioma

a) less common than AVMb) similar to cavernous angioma

elsewherei) liver

c) formed by large, irregular, thin-walled vascular channels


d) most are asymptomatici) may cause intracranial bleedingii) epilepsy oriii) focal neurological disturbances

• Telaigiectasiaa) focal aggregate of small vesselsb) may initiate seizures, but rarely

rupture• Venous angioma

a) focus of few enlarged veinsb) distributed randomly in spinal cord

and brainc) usually asymtomatic and overlaps in pastwith cavernous angioma www.freelivedoctor.com

Cerebral aneurysmsCerebral aneurysms• Rupture and lead to fatal hemorrhage

a) result from vascular pressure and weakened arterial wall• Causes:

a) developmental defects:i) berry (saccular, medial defect)

b) atherosclerotici) produce mass effect

c) hypertensioni) associated with arteriolar

lipohyalinosis andii) induces Charcot-Bouchard aneurysmwww.freelivedoctor.com

d) bacterial infectionsi) leads to mycotic aneurysms

e) traumai) rarely caused dissecting

aneurysms1. Berry aneurysm

a) consequence of arterial defectsb) arise during embryogenesis

i) when arteries bifurcatec) greater than 90% of sacular

aneurysms occur at branch points in carotid system

d) rupture results in life-threatening SAH

i) ~35% mortality during initial hemorrhage


2.Atherosclerotic aneurysma) localized mainly in major cerebral arteries

i) vertebralii) basilariii) internal carotid

b) fibrous replacement of media and c) destruction of internal elastic

membranei) weakens arterial wall

aneurysmd) they are fusiform and elongatee) rarely rupture

i) major complication is thrombosis www.freelivedoctor.com

3.Mycotic aneurysma) infections of arterial wall

i) septic emboli (inflammation)- usually from cardiac valve

b) may also cause cerebal abscess or meningitis

Cerebral HemorrhageCerebral Hemorrhage• Causes stroke (apoplexy)

a) hemorrhage without trauma are “spontaneous”b) most are caused by vascular

anomalies (aneurysms)c) long standing hypertension www.freelivedoctor.com

i) occurs in preferential sites (order of frequency)

- basal ganglia-thalamus (65%)

- pons (15%)- cerebellum (8%)- Other causes of cerebral

hemorrhage, independent of hypertension: AVM leakage, erosion of blood vessel by neoplasm, bleeding diathesis – (e.g., thrombocytopenic purpura), endothelial injury via microorganisms (e.g., ricketisiae), embolic infarction (hemorrhage into area of necrosis)


d) compromises integrity of arterial wall by depositing

i) lipidii) hyaline material (i.e., protein)iii) i and ii known as

“lipohyalinosis”iv) weakening wall leads to

Charcot- Bouchard aneurysm- located mainly along trunk

of a blood vessel rather than at its bifurcation

e) onset of symptoms is abrupti) weakness usually dominates


ii) when hemorrhage is progressive

- death within hours to days- as hematoma enlarges, may cause death via transtentorial herniation- may rupture into ventricle

withmassive hemorrhage distension of 4th ventricle and compression of vital centers

- Routine hemorrhage catastrophic loss of consciousness damage to

reticular formation – death prior to arriving at hospital


- cerebellar hemorrhage ataxia and severe occipital

headache and vomiting

Cerebral Ischemia and InfarctionCerebral Ischemia and Infarction• Major causes of stroke

a) global ischemiai) cardiac arrestii) external hemorrhageiii) thrombosis

- regional ischemiaiv) hypoxia

- near drowning, CO poisoning, suffocationwww.freelivedoctor.com

1.Global Ischemiaa) pattern of injury reflects anatomy of cerebral vasculature

i) Watershed infarcts:anterior, middle and posterior cerebral arteries perfuse

overlapping territories- no anastamoses between

their terminal branches- areas of overlap are

therefore not perfused as well and infarcts (via global ischemia) occur in these “watershed areas”www.freelivedoctor.com

ii) Laminar necrosis: also reflects topography of cerebral

vasculature- intraparenchymal pial

vessels- penetrate at right angles

and are deep penetrators into grey matter- more focal areas of ischemia

iii) Selective neuronal sensitivity- Purkinje cells of cerebellum- pyramidal neurons of

Sommer sector I hippocampuswww.freelivedoctor.com

- these are very sensitive areas to ischemial hypoxia

these neurons are more vulnerable and develop

localized necrosis 2.Regionsl Ischemia and Cerebral Infarction

a) atherosclerosisi) occlusive disease

- major causes of M & Mii) infarcts caused by

embolyization are hemorrhagiciii) infarcts initiated via

thrombosis are ischemic (“bland”)www.freelivedoctor.com

b) infarcts via emboli (see ii) occlude flow abruptly distal segment becomes necrotic and leak blood into region

c) thrombosis progresses slowly and gradually causing ischemia guards against secondary hemorrhaged) infarct transforms affected tissue into friable debris

i) eliminated by macrophagesii) initially infracted surrounded

by blood capillariesiii) when infarcted area in phagocytized, remnant cystic

cavityiv) Liquefactive necrosis


e) clinical outcome dependent on structures involved

i) proximal and MCA occluded by atherosclerosis and

thrombosis- resultant infarct transects internal capsule

hemiparesis or hemiplegiaf) localized ischemia associated with 3 distinct clinical syndromes

i) TIA (transient ischemic attack)- focal cerebral dysfunction

last less than 24 hrs (usually only a few minutes in duration)

- signifies risk for infarctwww.freelivedoctor.com

ii) stroke in evolution- progression of neurological symptoms while patient is

under observation- uncommon and usually

reflects propagation of a thrombus in carotid or basilar artery

iii) complete stroke- stable neurologic defects

resulting from cerebral infarct


3.Regional Occlusive CVD• Classified into 5 categories (caliber and nature of vessel)

a) large extracranial and intracranial arteries

i) frequently involved in atherosclerosis

- common carotid (at bifurcation of ECA and ICA) - occlusion of ICA ipsilateral hemisphere


- occlusion of carotid artery produce infarcts (most often)

to portions of distribution of the MCA

b) Circle of Willisi) deficits depend on collateral circulationii) MCA often occluded by thrombosis complicating atherosclerosis in circle of Willis


c) Parenchymal arteries and arteriolesi) rarely become atheroscleroticii) damaged by hypertensioniii) small lacunar infarctsiv) when occur in numbers

- multiple infarct dementiav) fibronoid necrosis

(hypertensive encephalopathy) via malignant hypertension

- minute hemorrhages (petechiae)


d) capillary bedi) small emboli (fat or air) occlude capillary bed

- petechiae most common in white matter

e) cerebral veinsi) venous sinus thrombosis is potentially lethal for the following:

- systemic dehydration (e.g., infants with g.i. fluid loss)- phlebitis (mastoiditis or bacteremia)- obstruction by neoplasm- sickle cell diseasewww.freelivedoctor.com

CSFCSF

• Constitutes accessory circulatory systema) produced mainly by choroids plexus

i) ~500 ml/dayii) reabsorbed by arachnoid villi

• Obstruction to flow of CSF is within the ventricles, hydrocephalus is noncommunicating

a) congenital malformationb) neoplasmsc) inflammationd) hemorrhage


• Aqueduct of Sylvius is most common location of obstruction (congenital malformation)• Viral ependymitis during embryogenesis may result in congenital aqueduct stenosis


Cns path congenital, edema

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