Download MBBS Neuroanaesthesia PPT 8 CNS Anatomy and Anaesthesia Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Neuroanaesthesia PPT 8 CNS Anatomy and Anaesthesia Lecture Notes

CNS ANATOMY

AND

ANAESTHESIA

BRAIN ANATOMY

? The brain is a highly organized organ weighing about

1.4 kg (2% of total body weight) and contains about
100 billion neurons.

? It is protected by a bony covering called the skull.

? It is covered by three layers of connective tissue

known as meninges:

Duramater
Arachnoid mater
Piamater
Parts of Brain

?Cerebrum

?Diencephalon

?Brainstem :

midbrain, pons

and medulla

?Cerebellum
Cerebrum

?Two cerebral hemispheres

?Each hemisphere is divided into four lobes ?

frontal, parietal, temporal and occipital

?The cerebrum is responsible for all conscious

(voluntary) activities, thought, memory,
intelligence, learning, personality development,
judgement, vision.
Frontal lobe:

? The frontal lobes are the cerebral hemispheres anterior to

the Rolandic fissure (central sulcus)

? Important areas within the frontal lobes are the motor

area, Broca's speech area (in the dominant hemisphere)
and the frontal eye fields

? Patients with bilateral frontal lobe dysfunction present

typically with personality disorders, dementia, apathy and
disinhibition

? The anterior 7 cm of one frontal lobe can be resected

without significant neurological sequelae, provided
the contralateral hemisphere is normal

? Resections more posterior than this in the dominant

hemisphere are likely to damage the anterior speech
area
Temporal lobe:

? The temporal lobe lies anteriorly below the Sylvian fissure and

becomes the parietal lobe posteriorly at the angular gyrus

? Its medial border is the uncus and is of particular clinical

importance because it overhangs the tentorial hiatus adjacent to the
midbrain

? When intracranial pressure rises in the supratentorial compartment,

uncus transgresses the tentorial hiatus, compressing the third nerve,
midbrain and posterior cerebral artery described as `uncal
herniation

? The temporal lobe has many roles including memory, the cortical

representation of olfactory, auditory and vestibular information,
some aspects of emotion and behaviour, Wernicke's speech area
(in the dominant hemisphere) and parts of the visual field
pathway

? Seizures are common because structures in this lobe are

particularly epileptogenic

? Amygdalohippocampectomy with or without temporal lobectomy

may be required for intractable forms of epilepsy with proven
mesial temporal sclerosis on imaging
? The anterior portion of one temporal lobe (approximately

at the junction of the Rolandic and Sylvian fissures) may
be resected with low risk of neurodisability

? Generally, this amounts to 4 cm of the dominant lobe or

6 cm of the non-dominant lobe

? The upper part of the superior temporal gyrus is

generally preserved to protect the branches of the middle
cerebral artery (MCA) lying in the Sylvian fissure

? More posterior resection may also damage the speech

area in the dominant hemisphere

? Care is needed if resecting the medial aspect of the uncus

because of its proximity to the optic tract
Parietal lobe:

? These extend from the Rolandic fissure to the

parietooccipital sulcus posteriorly and to the temporal
lobe inferiorly

? The dominant hemisphere shares speech function with the

adjacent temporal lobe, while both sides contain the
sensory cortex and visual association areas

? Parietal lobe dysfunction may produce cortical sensory

loss or sensory inattention

? In the dominant hemisphere, the result is dysphasia

? Dysfunction in the non-dominant hemisphere produces

dyspraxia (e.g.difficulty dressing, using a knife and fork)
or difficulty with spatial orientation

? Impairment of the visual association areas may give rise

to visual agnosia (inability to recognize objects) or to
alexia (inability to read)
Occipital lobe:

? Lesions within the occipital lobe typically present with a

homonymous field defect without macular sparing, Visual
hallucinations may also be a feature

? Resection of the occipital lobe will result in a contralateral

homonymous hemianopia

? The extent of resection is restricted to 3.5 cm from the occipital

pole in the dominant hemisphere because of the angular gyrus,
where lesions can produce dyslexia, dysgraphia and acalculia

? In the non-dominant hemisphere, up to 7 cm may be resected
Diencephalon

?Thalamus

?Epithalamus

?Hypothalamus

? The thalamus is involved in a number of functions

including relaying sensory and motor signals to the
cerebral cortex and regulating consciousness, sleep

and alertness

? The epithalamus functions as a connection between the

limbic system to other parts of the brain.

? Other functions of epithalamus include the secretion of

melatonin by the pineal gland (involved in circadian
rhythms) and regulation of motor pathways and emotions
? The hypothalamus links the nervous system to the endocrine

system via the pituitary gland

? It is the link between mind and body, it controls and

integrates activities of autonomic NS

? It manufactures and transports releasing hormones that

control the Master Gland

? It is also an important area for regulating homeostatic

activities, such as hunger, thirst, sex drive, temprature and
even addictions

BRAINSTEM

? Located between the cerebrum and

the spinal cord

-Provides a pathway for tracts running

between higher and lower neural centers.

? Consists of the midbrain, pons, and

medulla oblongata.

? Each region is about an inch in length

? Microscopically, it consists of deep gray

matter surrounded by white matter fiber

tracts.
? Shortest brain stem, not more than 2cm in length, lies in

the posterior cranial Fossa

? For descriptive purpose, divided into dorsal tectum and

right and left cerebral Peduncles

? Each cerebral peduncles divide further into ventral crus

cerebri and a dorsal tegmentum by a pigmented lamina

" Substantia nigra"

? Tegmentum contains Reticular formation

? Functions as Reticular Activating System :

? Filters background stimuli

? Regulates sleep wake cycle

? Regulates conciousness

? Maintain muscle tone

Superior colliculus
Receives afferent from
? Retina (vision)
? Spinal cord (tactile)
? Inferior colliculus (auditory)
? Occipital cortex (modulating path)
Efferent goes to
? Retina, spinal cord, brain stem nuclei, tegmentum
? Reflex movement of eyes, head and neck in response to visual

stimuli

Inferior colliculus
? Receives afferent from lateral leminiscus
? Gives efferent to medial geniculate body
? Controls auditory reflex helps in localizing the source of sound
? Seperated from medula in front by a furrow in which

VI, VII, VIII nerve appears

? The pons shows a convex anterior surface with

prominent transversely running fibres i.e the middle
cerebellar peduncles

? The anterior surface of pons is marked in the midline

by a shallow groove basilar sulcus which lodges the
basilar artery
? Trigeminal nerve emerges from the anterior surface, at

the junction between pons and middle cerebellar
peduncle

? Superior surface is related to superior cerebellar artery

and Inferior surface related to anterior inferior cerebellar
artery

? Posterior surface is hidden by cerebellum and bounded

laterally by superior cerebellar paduncle

? On transverse section pons is subdivided into ventral and dorsal

part

? Ventral part of the pons contains
Pontine nuclei:

? Recieves AFFERENT corticopontine fibres from frontal,

temporal,parietal and occipital lobes of cerebrum of the same side.

? The EFFERENT fibres form the transverse fibres of pons (

pontocerebellar fibers) that cross the mid line and enter cerebellum

? It has been estimated that there are about twenty million neurons in

pontine nuclei.

? Most of them are glutaminergic.


? The dorsal part of the pons may be regarded as

continuation of the part of the medulla behind the
pyramids

? Superiorly continous with the tegmentum of the midbrain

? Posterior surface help to form floor of fourth ventricle

? The dorsal part is bounded laterally by inferior cerebellar

peduncle in the lower part of the pons and superior
cerebellar peduncle in upper part.

Cerebellopontine angle
Irregularly shaped potential space in the posterior fossa of

brain

Anteriorly : posterior surface of temporal bone
Posteriorly : anterior surface of cerebellum
Medially : cisterns of pons and medulla and olive
Superiorly : inferior border of pons and cerebellar peduncle

CP angle contains :
? Facial nerve (VII)
? Vestibulocochlear nerve (VIII)
? Glossopharyngeal nerve (IX)
? Nervous intermedius
? Labyrinthine artery

Medulla Oblongata:

? Medulla is broad above and joins with pons
it is narrow below and continous as spinal cord

? Length is about 3cm, width is about 2cm at its upper end

? Surfaces shows series of fissures
?

Anterior median fissure

?

Posterior median fissure
? Bulbopontine sulcus :
seperates medulla and pons ventrally
VI, VII and VIII cranial nerves arises from it.
? Two median fissures ( ant and post) divide medulla into 2

symmetrical halves.

Each half of medulla is marked by 2 longitudinal sulci
( anterolateral and posterolateral).
These 2 sulci divide each half of medulla into anterior, posterior and

lateral region.

? Anterolateral sulci : between pyramids and olive
? Posterolateral sulci : between olive and inferior cerebellar

peduncle


Cerebellum:

? The cerebellum consists of a group of midline structures,

the lingula, vermis and flocculonodular lobe, and two
laterally placed hemispheres

? Lesions affecting midline structures typically produce

truncal ataxia, which may make it difficult for the patient
to stand or even to sit

? Obstructive hydrocephalus is common

? Invasion of the floor of the fourth ventricle by tumour

may give rise to vomiting or cranial nerve dysfunction

LOBES OF CEREBELLUM

Inferior surface

Divisions of lobes

Anterior lobe

Anatomical

Posterior lobe

Flocculonodular lobe

Anterior lobe

Flocculonodular lobe

Posterior lobe

Superior surface

Anterior lobe

Posterior lobe
Functional(Evolutionary)

Paleocerebellum

Neocerebellum

Archicerebellum

Archi-cerebellum
posterior lobe
(Vestibular part)
?It is formed of the flocculo-nodular
lobe + associated fastigial nuclei,
lying on inf. Surface in front of postero
-lateral fissure.
? ?Embryologically, it is the oldest part
of cerebellum.
? It receives afferent Fibres. From
vestibular apparatus of internal ear Via
vestibulo-cerebellar tracts.
?It is concerned with equlibrium

Neocerebellum

Archicerebellum

Paleocerebellum
Paleo-cerebellum
(spinal part) :
?it is formed of midline
vermis + surrounding
paravermis + globose &
emboliform nuclei.
?It receives afferent proprio-
ceptive impulses from Ms.&
tendons Via spino-cerebellar
tracts (dorsal & ventral)
mainly.
?it sends efferents to red
nucleus of midbrain.
?it is concerned with muscle

Paleocerebellum

tone

Neo-cerebellum
(cerebral part)
?It is the remaining largest part of
cerebellum.
?It includes the most 2-cerebellar
hemispheres + dendate nuclei.
?It receives afferent impulses
from the cerebral cortex+pons
Via cerebro-ponto- cerebellar
pathway.
?it sends efferents to Ventro
lateral nucleus of thalamus.
?it controls voluntary

Neocerebellum

movements (muscle
coordination).
Deep nucleuses of cerebellum

Cerebellar Cortex

? Molecular Layer
? Purkinje Cell Layer
? Granular Layer

Corpus Medullare
(Medullary Center)
Deep Cerebellar Nuclei

? Fastigial Nuclei
? Nucleus Interpositus
? Emboliform Nucleus
? Globose Nucleus
? Dentate Nucleus

Dentate nucleus

Emboliform nucleus

Globose nucleus

Fastigial nucleus

Nucleus interpositus
? Lesions within the hemispheres usually cause ipsilateral

limb ataxia

? Vertigo may result from damage to the vestibular reflex

pathways

? Nystagmus is typically the result of involvement of the

flocculonodular lobe

? Other features associated with disorders of the cerebellum

include hypotonia, dysarthria and pendular reflexes
Arterial supply:

?The cerebral circulation is made up of two

components

?The anterior circulation is fed by the internal
carotid arteries and the posterior part is from the
vertebral arteries (the vertebrobasilar circulation)

?The arterial anastomosis in the suprasellar cistern

is named the ` circle of Willis' after Thomas
Willis


?The segment of the anterior cerebral artery

proximal to the AComA is known as the A1
segment

?The distal ACA has four segments named

according to their location in relation to the
corpus callosum, the

A2 (infracallosal)
A3 (pre-callosal)
A4 (supracallosal)
A5 (post-callosal) segments

?The ACA supplies the orbital surface and the

medial surface of the frontal lobe and the medial
surface of the hemisphere above the corpus
callosum back to the parieto-occipital sulcus

?The motor and sensory cortex to the lower limb are

within the territory of supply of the ACA
? The MCA is divided into four segments,
the M1 (sphenoidal)
M2 (insular)
M3 (opercular)
M4 (cortical) segments

? MCA supplies most of the lateral aspect of the

hemisphere except the superior frontal (supplied by the
ACA) and the inferior temporal gyrus and the occipital
cortex (supplied by PCA)

? PCA is divided into four segments,
P1 (precommunicating)
P2 (post-communicating)
P3 (quadrigeminal)
P4 (cortical)

? The PCA gives off three kinds of branches:
(i) central perforating branches to the diencephalon and midbrain
(ii) ventricular branches to the choroid plexus and walls of the
lateral and third ventricles
(iii) cerebral branches to the cerebral cortex and splenium of the
corpus callosum
? PCA supplies the inferior and infero lateral surface of

the temporal lobe and the inferior and most of the
lateral surface of the occipital lobe

? The contralateral visual field lies entirely within its
territory

? Hypoplasia or absence of one or more of the

communicating arteries can be particularly important at
times when one of the major feeding arteries is temporarily
occluded

? This is important for neurovascular procedures like carotid

endarterectomy or when gaining proximal control of a
ruptured intracranial aneurysm

? If both the AComA and PComA are hypoplastic, then the

middle cerebral territory is supplied only by the ipsilateral
internal carotid artery (the so-called isolated MCA)
? Cerebral vessels are different from their systemic vessels as they

possess only a rudimentary tunica adventitia

? This is particularly relevant to subarachnoid haemorrhage, which

causes vasospasm

? A second difference is that the tunica media of both large and

small cerebral arteries has its muscle fibres orientated

circumferentially

? This results in a point of potential weakness at the apex of vessel

branches and may lead to aneurysm formation


? Approximately 85% of berry aneurysms develop in the anterior

circulation

Venous supply:

? The general pattern for venous drainage of the hemi spheres is into

the nearest venous sinus

? The superior sagittal sinus occupies the convex margin of the falx

and is triangular in cross-section

? Because of its semi-rigid walls, the sinus is noncollapsable resulting

in a high risk of air embolism during surgery if the sinus is opened
with the head elevated

? Venous lakes are occasionally present within the diploic of the skull

adjacent to the sinus, and can result in excessive bleeding or air
embolus when a craniotomy flap is being turned
? The lateral margin of the superior sagittal sinus at the level of the

internal occipital protuberance turns to one side, usually the right
as the transverse sinus

? The straight sinus turns to form the opposite transverse sinus at this

point

? The basal ganglia and adjacent structures drain via the internal

cerebral veins, which lie in the roof of the third ventricle

? The internal cerebral and basal veins join to form the great

cerebral vein of Galen beneath the splenium of the corpus
callosum

? This short vein joins the inferior sagittal sinus (which runs in the

free edge of the falx) to form the straight sinus
? The superior cerebral veins (usually 8?12 in number) lie

beneath the arachnoid on the surface of the cerebral cortex
and drain the superior and medial surface of the
hemisphere into the superior sagittal sinus

? To do this, they must bridge the subdural space (hence the

alternative name of `bridging veins')

? If the hemisphere is atrophic and therefore relatively

mobile within the cranium, these veins are likely to be
torn by even minor head injury, giving rise to chronic
subdural haematoma

? Although venous anastomoses exist on the lateral surface of the

hemisphere, largely between the superior anastomotic vein
(draining upwards in the central sulcus to the superior sagittal
sinus ? the vein of Trolard), the Sylvian vein (draining downwards
in the Sylvian fissure to the sphenoparietal sinus) and the angular
or inferior anastomotic vein (draining via the vein of Labbe into
the transverse sinus), sudden occlusion of large veins or a patent
venous sinus may result in brain swelling or even venous
infarction

? As a general rule, the anterior one-third of the superior sagittal

sinus may be ligated, but only one bridging vein should be divided
distal to this if complications are to be avoided
? If the sinus has been occluded gradually, for example

by a parasagittal meningioma, then there is time for
venous collaterals to develop

? Venous-phase angiography is particularly useful in

tumours adjacent to the major venous sinuses or to the
vein of Galen to determine if the sinus is completely
occluded and can be resected en bloc with the tumour
or whether the sinus is patent and requires
reconstruction
Structural Development of The Brain

?Embryonic vesicle: Forebrain (Prosencephalon)
a. Anterior portion (Telencephalon) produces Lateral
Ventricles, cerebrum and basal ganglia.
b. Posterior portion (Diencephalon) produces Third
Ventricle, Thalamus, Hypothalamus, post. Pituitary
gland, and pineal gland

?Embryonic vesicle: Midbrain (Mesencephalon)

produces cerebral aqueduct, and midbrain.

? Embryonic vesicle: Hindbrain (Rhombencephalon)

a. Anterior portion (Metencephalon): produces fourth

ventricle, cerebellum, and pons

b. Posterior portion (Myelencephalon): produces fourth
ventricle, and medulla oblongata
Spinal cord

? A long nerve cord that begins at the foramen magnum

and ends at the first or second lumbar vertebra

? Divided into 31segments, each segment gives rise to a

pair of spinal nerves (part of the PNS)

? In general, the location of the spinal nerve corresponds

with the location of the effector organ

The concept of the `three-column' spine, as proposed by

Holdsworth in 1970

? Anterior column of the spine is formed by the anterior

longitudinal ligament, the anterior annulus fibrosus and

anterior part of the vertebral body

? Middle column is formed by the posterior longitudinal

ligament, the posterior annulus fibrosus and the posterior

wall of the vertebral body

? The posterior column is formed by the posterior arch and

supraspinous and interspinous ligaments, as well as the

ligamentum flavum
?Most spinal nerves form net -works called plexuses

?C1to C4from cervical plexus which serves the head,

face, and neck

?C5toT1 from brachial plexus which serves the

shoulder, arm, and hands

?T 2 toT11do not from any plexus

?T12 to S5form lumbosacral plexus which serves the

lower body and lower limbs


?Coccygeal nerves do not form any plexus
? Cross sectional anatomy of the spinal cord:
Two grooves divide spinal cord into right left halves
1. Ant. median fissure or groove (deep)
2. post median sulcus(shallow groove)

? The spinal cord consist of white matter surrounded by

gray matter.

? Gray matter resembles a butterfly. The upper and lower

wings of gray matter are called posterior horn and
anterior horn respectively
?Lat. horn is located between post. and ant. horns

on either side

?Central canal contains CSF

?The gray matter further divides the white matter

into 3regains on each side.

a) The anterior column
b) The lateral column
c) The posterior column

Tracts of The Spinal Cord

Tracts: The nerve tracts of the spinal cord provide a

two-way communication system between the brain

and the body

a) Ascending tract: conduct sensory impulses to the

brain

b) Descending tract: conduct motor impulses from

the brain to motor neurons reaching muscles,

glands, etc
Ascending Tracts

?Fasciculus gracilis (transmits sensory impulses

from lower limbs) and Fasciculus Cuneatus

(transmits sensory impulses from upper limbs)

?Located in posterior funiculi and conduct sensory

impulses associated with senses of touch, pressure
and body movement from skin, muscles, tendons,
and joints to the brain.
?Spinocerebellar tract: conduct impulses

(sensory) required for coordination of muscle
movements from lower limb and trunk muscles
to cerebellum

?Spinothalamic tract: conduct sensory impulses

for pain and temperature to brain.
Descending Tracts

?Corticospinal tract: conducts motor impulses

associated with voluntary movement from the

brain to skeletal muscles

?Reticulospinal tract: conducts motor impulses

associated with maintenance of muscle tone and

the activity of sweat glands from the brain

?Rubrospinal tract: conducts motor impulses

associated with muscular coordination and the

maintenance of posture from the brain
? The adult spinal cord terminates at about the

lower border of L1 as the conus medullaris

? Below this, the spinal canal contains

peripheral nerves known as the caudaequina

? Lesions above this level produce upper motor

neuron signs and those below it a lower
motor neuron pattern

? Lesions of the conus itself may produce a

mixed picture

Extrinsic spinal cord compression

? This produces symmetrical corticospinal (`pyramidal') involvement,

with upper motor neuron weakness below the level of the
compression (increased tone, clonus, little or no muscle wasting, no
fasciculation, exaggerated tendon reflexes and extensor plantar
responses), together with a sensory loss

? However if the mass is laterally placed, then the pattern may

initially be of hemisection of the cord ? the Brown?Sequard
syndrome

? This produces ipsilateral pyramidal weakness, loss of fine touch and

impaired proprioception but contralateral impairment of pain and
temperature sensation
Central cord syndromes

? Syringomyelia or intramedullary tumours affecting the

cervicothoracic region will first involve the pain and
temperature fibre

? The result of central cord involvement is therefore a

`suspended' sensory loss, with a cape-type distribution of
loss of sensitivity to pain in the upper limbs and trunk but
with sparing of the lower limbs

Cauda equina compression

? This may result from a lumbar disc prolapse

? Usually accompanied by sciatica, which may be bilateral

or unilateral and there may be weakness or sensory loss
in a radicular distribution

? In addition, there is perineal sensory loss in a saddle

distribution, painless retention of urine with dribbling
overflow incontinence and loss of anal tone
Blood supply:

? The anterior and posterior spinal arteries form a

longitudinal anastomotic channel that is fed by spinal
branches of the vertebral, deep cervical, intercostals and
lumbar arteries

? In the cervical region, it accompanies one of the nerve

roots and is known as the artery of Adamkiewicz

? Its position is variable but is generally on the left side

(two-thirds of cases) and arises between T10 and T12 in
75% of patients

? The artery of Adamkiewicz is vulnerable to damage

during operations on the thoracic spine, particularly
during excision of neurofibromas or meningiomas, or if
an intercostal vessel is divided during excision of a
thoracic disc

? Atherosclerotic disease of the radicular artery or

prolonged hypotension may induce infarction of the
anterior half of the cord up to mid-dorsal level, producing
paraplegia, incontinence and spinothalamic sensory loss