Narrow Neuroanatomy Flashcards
(116 cards)
1
Q
Anterior Cerebral Artery Segments
A
A1 (horizontal): origin from the ICA to the ACOM
A2 (vertical): from ACOM to the origin of the bifurcation into pericallosal and callosomarginal arteries
A3 (callosal): runs in the pericallosal sulcus (distal to the pericallosal artery/bifurcation)
2
Q
ACA branches
A
A1: medial lenticulostriate artery recurrent artery of Heubner anterior communicating artery A2: orbitofrontal artery frontopolar artery A3: pericallosal artery callosomarginal artery
3
Q
Arterial Supply of the Cerebellum - Description
A
Cerebellum is essentially supplied by three paired arteries
posterior inferior cerebellar arteries
anterior inferior cerebellar arteries
superior cerebellar arteries
Very variable is arterial supply and arterial branches
4
Q
Arterial Supply of the Cerebellum - origin
A
PICA - vertebral arteries
AICA - lower third of the basilar artery
SCA - upper third of the basilar artery
5
Q
Arterial Supply of the Cerebellum - course/relations
A
PICA
- anterior medullary segment - from its origin around the inferior aspect of the medullary olive
- lateral medullary segment - forms ‘caudal loop’ which is located anteroinferior to the tip of the cerebellar tonsil
- posterior medullary segment - ascends posterior to the medulla behind CN IX and CN X and along the posterior medullary velum
- supratonsillar segment - junction between the posterior medullary segment and the supratonsillar segment is upwardly convex and is the site of origin of small choroidal branches (known as the “choroid point”)
AICA
- passing backward to be distributed to the anterior part of the undersurface of the cerebellum
- anastomoses with the PICA and the SCA
SCA
passes laterally, immediately below the oculomotor nerve, which separates it from the posterior cerebral artery
winds around the cerebral peduncle, and arrives at the upper surface of the cerebellum
anastomoses with AICA and PICA
segments - prepontine segment, ambient segment, quadrigeminal segment
6
Q
Arterial Supply of the Cerebellum - branches
A
PICA
anterior and lateral medullary segments - small perforating medullary branches
supratonsillar segment - tonsillohemispheric branch, inferior vermian branch
AICA
labyrinthine passes into the IAM
lateral branch passes around the flocculus and into the hemispheric fissure (supplying both superior and inferior semilunar lobules)
medial branch supplies the biventral lobule
SCA
perforating branches to pons, midbrain, inferior colliculus
lateral branch - largest branch of the SCA and gives off hemispheric branches
hemispheric branches - arise from the lateral branch, and course superiorly over the superior cerebellar hemisphere (supplies dentate nucleus, superior vermis, medial quadrigeminal lobule, superior semilunar lobule)
superior vermian branch - terminal branch(es) of the SCA and anastomose with inferior vermian branches of the PICA
7
Q
Arterial Supply of the Cerebellum - Supply
A
• PICA o posteriorinferior cerebellar vermis (includes cerebellar tonsils, nucleus gracilis, biventral lobule, superior semilunar lobule) o inferior portion of the vermis o lower part of the medulla • AICA o middle cerebellar peduncle o infrolateral portion of the pons o flocculus o anteroinferior surface of the cerebellum • SCA o whole superior surface of the cerebellar hemispheres down to the great horizontal fissure o the superior vermis o dentate nucleus o most of the cerebellar white matter o parts of the midbrain, pons
8
Q
Arterial Supply of the Cerebellum - Variants
A
PICA
absence
small or large depending on PICA-AICA dominance
variable origin (basilar, extracranial vertebral)
AICA
absence
small or large depending on PICA-AICA dominance
origin from middle third, or vertebrobasilar junction
SCA
unilateral duplication: 28%
bilateral duplication: 8%
triplication: 2%
when multiple, upper branch may arise from the PCA and usually supplies the vermis, whereas the lower branch supplies the hemisphere
9
Q
Basilar Artery - Description
A
Part of the posterior cerebral circulation
10
Q
Basilar artery - origin
A
Arises from the confluence of the left and right vertebral arteries at the base of the pons as they rise towards the base of the brain
11
Q
Basilar artery - Course/relations
A
Ascends in the sulcus basilaris (groove in the pons) within the pontine cistern
Terminates by dividing into PCAs (P1) just inferior to the pituitary stalk (at the upper pontine border)
12
Q
Basilar artery - Branches
A
Anterior inferior cerebellar artery (AICA)
Labyrinthine artery (~15% - more commonly a branch of AICA)
Pontine arteries
Superior cerebellar artery (SCA)
13
Q
Basilar artery - Supply
A
Labyrinthine artery courses to internal auditory meatus to supply internal ear
AICA supplies anterior inferior quarter of cerebellum
Pontine branches supply pons and adjacent parts of midbrain
SCA runs around the cerebral peduncles laterally to supply the superior half of cerebellum and parts of the midbrain
PCA supplies posterior aspect of the brain (occipital lobe)
14
Q
Basilar artery - Variants
A
Persistent carotid-vertebrobasilar anastomoses (mnemonic: TOHP)
Basilar artery fenestration / Island formation
Basilar artery forms in caudal position
Basilar artery is continuation of only one vertebral artery
Two basilar arteries with otherwise normal branches
Anastomosing network instead of a basilar artery
15
Q
Circle of Willis - Description
A
This is the central arterial anastomotic ring of the brain between the internal carotid and vertebrobasilar systems
Complete circle of Willis (in which no component is absent or hypoplastic) is only seen in 20-25% of individuals
Posterior circle anomalies are seen in nearly 50% of anatomical specimens
16
Q
Circle of Willis - Origin
A
The Circle of Willis has 10 components:
2 internal carotid arteries (ICA)
2 proximal anterior cerebral artery (ACA) segments
1 anterior communicating artery (ACOM)
2 posterior communicating arteries (PCOM)
Basilar artery
2 posterior cerebral artery (PCA) segments
17
Q
Circle of Willis - course/relations
A
Lies within suprasellar cistern
Inferior: sella turcica, pituitary
Superior: hypothalamus, optic chiasm and pituitary stalk
18
Q
Circle of Willis - embryology
A
ICAs develop from 3rd aortic arches, dorsal aortae, and the vascular plexus around the forebrain
Embryonic ICAs divide into cranial and caudal divisions
cranial gives rise to ACAs and ACOMs
caudal gives rise to PCOMS and proximal segments of the PCAs
Paired dorsal longitudinal neural arteries fuse to form the basilar artery
19
Q
Circle of Willis - Supply
A
The Circle of Willis supplies the entire central base of the brain (including hypothalamus, internal capsule, optic tracts, thalamus, midbrain)
20
Q
Circle of Willis - Variants
A
Variants are the rule, not exception. The textbook version is only present in 20-25% of cases
Hypoplasia of one or both PCOM ~30% (configuration D,E,F,G)
Hypoplastic/absent A1 segment of ACA ~15% (configuration C)
Absent or fenestrated ACOM ~12.5% (configuration B)
Origin of PCA from the ICA with absent/hypoplastic P1 segment (foetal PCOM) ~20% (not shown)
Infundibular dilatations of the PCOM origin
Single (Azygous) ACA trunk can be present
Persistent Primitive Carotid-Vertebrobasilar anastomoses
21
Q
Circle of willis Common variants
A
Hypoplasia of one or both PCOM ~30%
Hypoplastic/absent A1 segment of ACA ~15%
Absent or fenestrated ACOM ~12.5%
Origin of PCA from the ICA with absent/hypoplastic P1 segment (foetal PCOM) ~20%
Duplicated ACOM
Absence of ICA, MCA is derived from the contralateral ICA
22
Q
Middle Cerebral Artery - Description
A
MCA is one of the three major paired arteries that supply blood to the brain
The MCA is divided into three segments:
M1 (horizontal segment): from the origin to bifurcation/trifurcation (the limen insulae)
M2 (sylvian segment): runs posteriorly within the sylvian fissure, makes a hairpin turn, then to the cortical surface
M3 (cortical segment): branches emerging from the Sylvian fissure onto the convex surface of the hemisphere
23
Q
Middle Cerebral Artery - Origin
A
Arises from the ICA as the larger of the two main terminal branches (lateral to the optic chiasm)
24
Q
Middle Cerebral Artery - Course/relations
A
Continues into the lateral sulcus where it branches and provides many branches that supply the cerebral cortex
Medial: optic chiasm, pituitary fossa
25
Middle Cerebral Artery - branches
```
M1 (FOUR)
- (Some medial lenticulostriate)
lateral lenticulostriate penetrating arteries: supplies -
- basal ganglia
- anterior temporal artery
- polar temporal artery
- uncal artery (with branches also from the anterior choroidal artery)
M2 (TWO trunks)
- most commonly, it divides into two trunks-superior and inferior (may trifurcate into a third inferior division):
- superior terminal branch
lateral frontobasal artery
prefrontal sulcal artery
precentral sulcal (pre-Rolandic) artery
central sulcal (Rolandic) arteries
inferior terminal branch
three temporal branches (middle, posterior)
branch to the angular gyrus
two parietal branches (anterior, posterior)
M3
cortical branches
```
26
Middle Cerebral Artery - Supply
Supplies the majority of the lateral surface of the hemisphere, except the superior portion of the parietal lobe (via ACA) and the inferior portion of the temporal and occipital lobes (via PCA)
Also supplies part of the internal capsule and basal ganglia
27
Middle Cerebral Artery - Variants
MCA duplication: parallels the main MCA
Accessory MCA
MCA fenestration
Early branching of the M1 segment within 1 cm of origin
MCA originates from the contralateral ICA
28
Pituitary arterial supply - Description
The pituitary has rich blood supply, with both a portal circulation (to the anterior pituitary) and arterial supply (to the posterior pituitary)
Anterior pituitary receives blood which descends from the hypothalamus along the infundibulum as a portal system (venous channels connecting two capillary beds)
29
Pituitary arterial supply - Portal system
Superior hypophyseal arteries give superior branches which supply the superior most infundibulum which receives axons from a number of hypothalamic nuclei
These axons release various releasing and inhibiting factors which are then taken down the infundibulum in the hypophyseal portal venous plexus, and thus delivered to the anterior pituitary where they control the release of its numerous hormones
30
Pituitary arterial supply - arterial system
Inferior hypophyseal artery forms rich network of arterial supply
circuminfundibular anastomosis: surrounds the pituitary stalk (ascending and descending infundibular branches)
inferior hypophyseal arterial circle (inferior capsular arterial rete): surrounds the base of the pituitary
31
Pituitary arterial supply - branches
```
From above
superior hypophyseal artery (ICA C6)
infundibular artery
prechiasmal artery
From below/side
inferior hypophyseal artery (from the meningohypophyseal trunk ICA C4)
capsular artery
artery of the inferior cavernous sinus
```
32
Posterior Cerebral artery - segments
P1: origin to the PCOM, located within the interpeduncular cistern
P2: from PCOM around the mid-brain, divided into P2A (anterior) and P2P (posterior) sub-segments
P3: quadrigeminal segment (within the quadrigeminal cistern)
P4: cortical segment
33
Posterior Cerebral artery - branches/supply
Supplies thalamus (thalamogeniculate branches)
posteromedial ganglionic branches
posterolateral ganglionic branches
Fornix, thalamus, caudate nucleus, and choroid plexus
posterior choroidal branches (medial and lateral)
Cortical branches
anterior temporal
posterior temporal
lateral occipital
medial occipital
posterior pericallosal (supplies corpus callosum)
34
Cavernous Sinus - Description
Cavernous sinus is one of the paired dural venous sinuses
Located on either side of the pituitary fossa, between two layers of the dura
Anteriorly it is bounded by the superior orbital fissure and posteriorly by the petrous apex
35
Cavernous Sinus - tributaries
Superior ophthalmic vein
Inferior ophthalmic vein
Sphenoparietal sinus
Superficial middle cerebral vein
36
Cavernous Sinus - drainage
Superior petrosal sinus to the transverse sinus (ultimately into the IJV)
Inferior petrosal sinus directly to the jugular bulb (ultimately into the IJV)
Emissary viens passing through the foramen ovale to the pterygoid plexus
emissary veins connect the extracranial venous system with the intracranial venous sinuses
Cavernous sinuses connect to each other via the intercavernous sinuses
37
Cavernous Sinus - relations
Medial: pituitary fossa
Lateral: temporal lobe
Anterior: superior and inferior orbital fissures, globe
Posterior: Meckel’s cave
Superior: clinoid processes, optic chiasm/nerves/tracts, ICA, AComA
Inferior: (ROS) Foramen rotundum connecting to the pterygopalatine fossa (anteriorly), foramen ovale and spinosum connecting to the infratemporal fossa (posteriorly)
38
Cavernous Sinus - Contents
Cavernous sinus transmits multiple cranial nerves to the superior orbital fissure and foramen ovale: OTOMCA
O: oculomotor nerve
T: trochlear nerve
O: opthalmic branch of trigeminal nerve
M: maxillary branch of trigeminal nerve
C: internal carotid artery + sympathetics
A: abducent nerve
Note
OTOM runs within the lateral wall of the cavernous sinus, CA runs within cavernous sinus
mandibular branch of trigeminal nerve is not associated with the cavernous sinus since it has descended vertically through the foramen ovale underneath the trigeminal ganglion (Gasser ganglion)
ICA has two cavernous sinus branches: meningohypophyseal trunk and inferolateral trunk
39
Cerebral Dural Venous Sinus - Unpaired dural sinuses
```
Superior saggittal sinus
Inferior saggittal sinus
Straight Sinus
Occipital sinus
Intercavernous sinus
```
40
Superior saggittal sinus
runs from the anterior aspect of the falx cerebri to its termination at the confluence of sinuses at the occipital protuberance
receives venous blood from the cortical veins through the cerebral hemispheres
41
Inferior saggittal sinus
runs along the inferior edge of the falx cerebri and drains into the straight sinus
receives tributaries from the falx and some small veins from the medial surface of the cerebral hemispheres
42
Straight Sinus
found at the junction between the falx cerebri and the tentorium cerebelli
receives the inferior sagittal sinus, the vein of Galen, some superior cerebellar veins
runs posteroinferiorly towards the confluence of sinuses, although the exact drainage is variable: confluence of sinuses (56%), left transverse sinus (21%), right transverse sinus (13%)
occasionally duplicated, hypoplastic or absent
when absent a persistent falcine sinus drains directly into the superior sagittal sinus
43
Occipital sinus
located on the inner surface of the occipital bone and drains postero-superiorly to the confluence of the sinuses
receives tributaries from the margins of the foramen magnum
44
Intercavernous sinus
connect the left and right cavernous sinuses (along with the basilar sinus)
has anterior and posterior parts
lies in the anterior and posterior borders of the diaphragma sellae
45
Intercavernous sinus
connect the left and right cavernous sinuses (along with the basilar sinus)
has anterior and posterior parts
lies in the anterior and posterior borders of the diaphragma sellae
46
Paired cerebral dural sinuses
```
Transverse sinus
Sigmoid sinus
Inferior petrosal sinus
Superior petrosal sinus
Cavernous sinus
Sphenoparietal sinus
Basilar venous sinus
```
47
Transverse sinus
drains the superior sagittal sinus, the occipital sinus, superior petrosal sinus and the straight sinus
empties into the sigmoid sinus which in turn reaches the jugular bulb
highly variable anatomy: aplasia/hypoplasia of the left more common than right
48
Sigmoid sinus
continuation of the transverse sinus (and is similarly variable in size)
passes inferiorly in an S shaped groove posteromedial to the mastoid air-cells to the jugular foramen and ends in the jugular bulb
49
Inferior petrosal sinus
drains blood from the cavernous sinus to the jugular foramen
runs in a shallow groove between the petrous temporal bone and basilar occipital bone (on either side of the clivus)
connected across the midline by the basilar plexus
receives tributaries from the medulla oblongata, pons, inferior surface of the cerebellum and labyrinthine veins
50
Superior petrosal sinus
drains the cavernous sinus to the transverse sinus
runs along superior aspect of the petrous temporal bone
receives cerebellar veins, inferior cerebral veins, labyrinthine vein
51
Cavernous sinus
located on either side of the pituitary fossa and body of the sphenoid bone
receives venous blood from the superior opthalmic vein, inferior ophthalmic vein and the sphenoparietal sinus
contains the OTOMCA structures
drains into inferior petrosal sinus, superior petrosal sinus and the pterygoid plexus via emissary veins
52
Sphenoparietal sinus
located along the posteroinferior ridge of the lesser wing of the sphenoid bone
drains into the cavernous sinus
receives tributaries from the superficial middle cerebral vein, middle meningeal vein, anterior temporal diploic vein
53
Basilar venous sinus
connects the: inferior petrosal sinuses, cavernous sinuses, intercavernous sinus, superior petrosal sinuses, internal vertebral venous plexus, marginal sinus (around the margins of foramen magnum)
54
Cerebral veins - descriptions
Cerebral veins drain the brain parenchyma and are located in the subarachnoid space
Pierce the meninges and drain further into the dural venous sinuses
Cerebral venous system can be divided into: superficial (cortical) cerebral veins and deep (subependymal) cerebral veins
55
Cerebral veins (superficial) - course/relations
superficial venous system comprises the sagittal sinuses and cortical veins
cortical veins course along the cortical sulci, drain the cortex and some of the adjacent white matter
numerous cortical veins and most of them are unnamed; large cortical veins can be named according to their location
cortical venous system can be subdivided into superior, middle and inferior groups
three important veins of the superficial system (SIS):
Superior Anastomotic Vein (of Trolard): runs superoposteriorly from the posterior border of the lateral sulcus to the superior sagittal sinus in the parietal region
Inferior Anastomotic Vein (of Labbe): runs inferoposteriorly from the posterior end of the lateral sulcus to the transverse sinus
Superficial Middle Cerebral Vein: runs anteriorly along the lateral sulcus to drain via the sphenoid sinus to the cavernous sinus
56
Cerebral veins (deep) - course/relations
three important veins of the deep system (BIG):
Internal Cerebral Vein: formed posterior to the interventricular foramen (of Munro) at the venous angle
major tributaries are the choroid vein, septal vein and thalamostriate vein
internal cerebral veins then run posteriorly in the roof of the third ventricle and unite beneath the splenium of the corpus callosoum to form the Great Cerebral Vein
Great Cerebral Vein (of Galen): runs posterosuperiorly behind the splenium of the corpus callosum
it receives the basal veins and posterior fossa veins and unites with the inferior sagittal sinus to form the straight sinus
Basal Vein (of Rosenthal): formed at the anterior perforator substance by the union of the anterior cerebral vein, deep middle cerebral vein (from the insula), and striate veins (from the inferior surface of the basal ganglia)
the basal vein passes around the midbrain to join the Great Cerebral Vein
Medullary veins are numerous and originate 1-2 cm below cortical gray matter and pass through deep medullary white matter and drain into subependymal veins
Subependymal veins receive medullary veins and aggregate into greater tributaries, mainly into septal veins, thalamostriate veins, internal cerebral veins, basal vein of Rosenthal and vein of Galen
57
Cerebral Ventricles - Description/features
The ventricles are fluid filled spaces within the brain
Composed of two lateral ventricles, a third and fourth ventricle
Interconnections between the ventricles occurs through the following:
interventricular foramen (of Monro): lateral to third
cerebral aqueduct (of Sylvius): third to fourth
median aperture (of Magendie): fourth to cisterna magna
two lateral apertures (of Luschka): fourth to cerebellopontine cistern
58
Cerebral Ventricles - lateral ventricles
```
One in each cerebral hemisphere
Each has a frontal horn, body, temporal horn and an occipital horn
Each communicates with the third ventricle by means of an interventricular foramen (of Munro) at the junction of the anterior horn and body
Contains the choroid plexus which produces CSF
Frontal horn relations
roof: corpus callosum (rostrum / genu)
lateral: caudate nucleus
medial: septum pellucidum
Body relations
roof: corpus callosum body
medial: septum pellucidum
floor: thalamus
Temporal horn relations
lateral: tapetum of the corpus callosum
roof: tail of caudate nucleus, amygdaloid nucleus
floor: hippocampus
Occipital horn relations
lateral: tapetum of corpus callosum
floor: collateral sulcus
```
59
Cerebral Ventricles - third ventricles
The third ventricle is a slit-like cavity between the thalami
Sometimes the thalami are connected to each other, forming the interthalamic adhesion
Relations
lateral: thalamus
floor: hypothalamus
roof: anterior commissure, body of fornix
anterior: lamina terminalis
Has several recesses:
supra-optic recess (above the optic chiasm)
infundibular recess (above the pituitary stalk)
posteriorly there is a pineal and suprapineal recesses
Choroid plexuses of the third ventricle invaginates the roof of the ventricle
Cerebral aqueduct is the narrow channel in the midbrain that connects the third and fourth ventricles
60
Cerebral Ventricles - fourth ventricle
Extends from the cerebral aqueduct (of Sylvius) to the obex and is filled with CSF
Relations:
roof: cerebellum
floor (ventrally): rhomboid fossa (formed by the back of the pons and medulla oblongata)
lateral walls: cerebellar peduncles
CSF enters the ventricle via the cerebral aqueduct and leaves via one of four routes:
via the obex and into the central spinal canal
via the median aperture (of Magendie) into the cisterna magna
via ones of the two lateral apertures (of Luschka) into the cerebellopontine cistern
61
Cerebral Ventricles - arterial supply
Anterior choroidal arteries (branch of ICA)
Posterior choroidal arteries (branch of PCA)
PICA
AICA
62
Cerebral Ventricles - venous drainage
Internal cerebral vein
Inferior petrosal sinus
Occipital sinus
63
Intracranial cisterns - description/contents
Subarachnoid cisterns are areas within the subarachnoid space where the pia mater and arachnoid membrane are not in close approximation
- cerebrospinal fluid (CSF) gathers to form pools
Contains CSF and the cerebral vessels
Subarachnoid space communicates with the fourth ventricle by means of apertures
- one median aperture (Magendie) drains CSF into the cisterna magna
- two lateral apertures (Luschka) drains CSF into the cerebellopontine angle cistern
64
Major cisterns
```
Cisterna magna/cerebellomedullary cistern
Supracellar cistern
pontine cistern
cerebellopontine angle cistern
inderpeduncular cistern
quadrigeminal cistern
ambient cistern
```
65
Cisterna magna / cerebellomedullary cistern
largest subarachnoid cistern
located between the cerebellum and the dorsal surface of the medulla oblongata
CSF produced in the ventricular system drains into the cisterna magna from the fourth ventricle via the median aperture (of Magendie)
contents: vertebral arteries, CN 9-12
66
Supracellar cistern
located above the sella turcica, under the hypothalamus
shape of a pentagon at the level of the optic chiasm
shape of a six-point star at the level of cerebral peduncles
contents: optic chiasm, infundibular stalk, anterior part of the circle of Willis
67
Pontine cistern
occupies a large space on the ventral aspect of the pons (between pons and clivus)
continuous with the cerebellopontine angle cistern laterally, cisterna magna behind, and the interpeduncular cistern anteriorly
contents: basilar artery, SCA, AICA, CN 6
68
Cerebellopontine angle cistern
receives CSF via the lateral apertures (of Luschka) of the fourth ventricle
contents: AICA, CN 5, 7, 8
69
Interpeduncular cistern
lies between cerebral peduncles and the dorsum sellae
encloses the cerebral peduncles and structures contained within the interpedunclar fossa
continuous with the pontine cistern, ambient cisterns and the suprasellar cistern
contains: the posterior part of the circle of Willis
70
Quadrigeminal cistern
located between the splenium of the corpus callosum and the superior surface of the cerebellum
continuous with ambient cistern
contents: great cerebral vein, SCA
71
Ambient cistern
thin, sheet-like extension of the quadrigeminal cistern that extends laterally around the midbrain
acts as the connection between the quadrigeminal cistern and the interpeduncular cistern
contents: PCA
72
Cerebral Meninges - description and features
Cerebral meninges surround the brain
- Made up of three layers (from outermost to innermost):
- Dura mater
- dense fibrocollagenous sheet
tightly adherent to the skull at sutural attachments
2 layers
outer periosteal layer that forms over the periosteum of inner calvarium
inner meningeal layer that folds inward to form the falx cerebri, tentorium cerebelli, falx cerebelli
two layers are adherent except were separated by the dural venous sinuses
Arachnoid mater
thin, nearly transparent layer
outer surface is loosely adherent to dura and is easily separated
follows the dura and does not does not invaginate into sulci
outpouchings that pierce the dura in the venous dural sinuses are known as arachnoid granulations (involved in CSF reabsorption)
Pia mater
covers the brain and invaginates into sulci
Dura mater also known as pachymeninx
Arachnoid mater and pia mater are collectively known as the leptomeninges
Meninges provide a framework for blood vessels, nerves, lymphatics and CSF
Two potential spaces:
epidural (extradural) space - between the bone and the dura mater
subdural space - between the dura mater and the arachnoid mater
Subarachnoid space is a CSF containing space between the arachnoid and pia mater
Subpial space also known as Virchow-Robin space
73
Cerebral Meninges Arterial supply:
MMA
Accessory meningeal artery
Meningeal branches of the opthalmic artery
Branches directly from the ICA
Meningeal branches of the vertebral artery
Ascending pharyngeal artery
74
Cerebral meninges: innervation
Anterior fossa: V1
Middle fossa: V1-3
Posterior fossa: C1-3, hypoglossal, vagus
75
Basal Ganglia
The basal ganglia includes: caudate nucleus, putamen, globus pallidus, subthalamic nucleus, substantia nigra
Has important role in speech, vision, movement, posture, motivation
Lentiform nucleus = putamen + globus pallidus
Corpus striatum = caudate nucleus + lentiform nucleus
76
Lentiform Nucleus
Putamen forms the outermost portion of the lentiform nucleus
Separated from the more medial globus pallidus by a thin lateral medullary lamina
Putamen is related laterally to the external capsule, claustrum, extreme capsule and then the insula
Globus pallidus is divided into medial and lateral portions by the medial medullary lamina
77
Caudate nucleus
Caudate nucleus is in the wall of the lateral ventricle
Has a head, body and tail
Head of the caudate lies anteriorly just posterior to the genu of the corpus callosum, bound laterally by the anterior limb of the internal capsule
Body extends supe
roposteriorly and lateral to the thalamus
Tail of the nucleus curves inferiorly then anteriorly into the temporal lobe to reach the amygdaloid body
78
Subthalamic nucleus
Functionally part of the basal ganglia
| Located inferior to the thalamus, superior to the substantia nigra and medial to the internal capsule
79
Substiantia Nigra
Lies in the midbrain, superior to the cerebral peduncles
Divided into two parts: the pars reticulata (medial) and pars compacta (lateral)
Separated from the globus pallidus by the internal capsule
80
Basal Ganglia: arterial supply
Medial and lateral lenticulostriate Branches (ACA and MCA)
Recurrent artery of Heubner (ACA)
Anterior choroidal artery (ICA)
81
Basal ganglia: venous drainage
Internal cerebral veins to great cerebral vein (of Galen)
82
Cerebellum
The cerebellum lies in the posterior cranial fossa
Involved in the processing of sensory information for motor control
Separated from the occipital lobe by the tentorium
Falx cerebelli runs between hemispheres
Separated from the brainstem by the 4th ventricle
3 pairs of cerebellar peduncles connect the cerebellum to the brainstem:
- superior - connects to midbrain
- middle - connects to pons
- inferior - connects to medulla
The cerebellum can be divided into two hemispheres with a midline vermis
- vermis is divided into 9 lobules
Fissures: primary, horizontal, prepyramidal, postpyramidal, posterolateral, retrotonsillar
Based on surface appearance, three lobes can be distinguished in the cerebellum, called the flocculonodular lobe, the anterior lobe (above the primary fissure), and posterior lobe (below the primary fissure)
Has two cerebellar tonsils
83
Cerebellum: arterial supply
PICA: inferior surface of the hemispheres and vermis
AICA: anterolateral surface of undersurface of the hemisphere
SCA: superior aspect of the hemispheres
84
Cerebellum: venous drainage
Superior and posterior surface: to the straight and transverse sinuses
Inferior surface: to the inferior petrosal, sigmoid and occipital sinuses
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Cerebellum: relations
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• Posterior: occipital bone
• Anterior: mastoid, brainstem, 4th ventricle
• Surrounded by the dural sinuses: sigmoid, straight, transverse, occipital
• CSF cisterns:
o cisterna magna
o quadrigeminal cistern
o ambient cistern
o cerebellopontine cistern
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Cerebellum: variant anatomy
Variant anatomy:
• Cerebellar agenesis
• Mega cisterna magna
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Corpus Callosum
• Corpus callosum links the cerebral cortex of the left and right cerebral hemispheres
• Largest fibre pathway in the brain
• ~10cm in length and is C-shaped
• Divided into four parts (anterior to posterior):
o rostrum (continuous with the lamina terminalis)
o genu
o body
o splenium
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Corpus Callosum: relations
• Superior: interhemispheric fissure in which runs the falx cerebri and the anterior cerebral vessels, inferior saggital sinus, corpus callosum
• Inferior: septum pellucidum anteriorly, and the fornix and its commissure posteriorly
• Lateral
o genu: forceps minor which connects medial and lateral surfaces of the frontal lobes
o trunk and splenium: tapetum which extend laterally along the lateral surface of the occipital and temporal horns of the lateral ventricle
o splenium: forceps major which connect the occipital lobes
• Separated from cingulate gyrus by the callosal sulcus
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Corpus Callosum: arterial supply
* Rich blood supply
* Pericallosal arteries (branches of the ACA) - provides majority of blood
* Posterior pericallosal arteries (branches of the PCA)
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Corpus Callosum: venous drainage
• Anterior Cerebral Vein (to Great Cerebral Vein)
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Corpus Callosum: variant anatomy
• Additional blood supply from:
o subcallosal artery (50% of patients) - branch of AComA
o median callosal artery (30% of patients) - branch of AComA
• Dysgenesis of the corpus callosum (an in utero developmental anomaly)
o types
complete
partial
o and also can be divided into:
primary agenesis: the corpus callosum never forms
secondary dysgenesis: the corpus callosum forms normally and is subsequently destroyed
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DCML
Dorsal column = in spinal cord
Medial lemniscal = in the brain stem
Sensory pathway of fine touch, vibration, two-point discrimination, and proprioception (position sense) from the skin and joints.
It transmits information from the body to the postcentral gyrus of the cerebral cortex.
The first-order neurons reside in dorsal root ganglia and send their axons through the gracile fasciculus and cuneate fasciculus.
The first-order axons make contact with second order neurons at the gracile and cuneate nuclei in the lower medulla.
The second-order neurons send their axons to the thalamus (VPL)
The third order neurons arise from thalamus to the postcentral gyrus.
The gracile fasciculus carries input from the lower half of the body
The cuneate fasciculus carries input from the upper half of the body.
The gracile fasciculus arise from the fibers more medial than the cuneate fasciculus
When the axons of second-order neurons of the dorsal column system decussate in the medulla, they are called internal arcuate fibers. The crossings of the internal arcuate fibers form the medial lemniscus.
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Internal capsule
• The internal capsule is a deep subcortical structure that contains a concentration of white matter projection fibres
• These fibres form the corona radiata
• Made up of 5 parts
o anterior limb: between head of the caudate and lentiform nucleus
o genu: medial to the apex of the lentiform nucleus (the bend in the V-shape)
o posterior limb: between the thalamus and lentiform nucleus
o retrolentiform part: posterior to the lentiform nucleus
o sublentiform part: inferior to the lentiform nucleus
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Internal capsule: vasculature
Arterial supply:
• Medial lenticulostriate artery (ACA branch) - anterior limb
• Lateral lenticulostriate artery (MCA branch) - anterior limb
• Recurrent artery of Heubner (ACA branch) - anterior limb
• Anterior choroidal artery (ICA branch) - posterior limb
• Multiple other small perforating branches from the MCA - genu
Venous drainage:
• Internal cerebral veins to the great cerebral vein (of Galen)
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Medulla oblongata
• Medulla oblongata is the most caudal part of the brainstem and is between the pons inferiorly and spinal cord superiorly
• Contains the vital autonomic cardiovascular and respiratory centers controlling heart rate, blood pressure, and breathing
• Medulla is separated into two main parts:
o ventral medulla which contains the olive, pyramidal tracts, and CN 9-12 rootlets
o tegmentum (dorsal) medulla which contain the CN nuclei and white matter tracts
• Ventral medulla
o pyramids are paired structures located at the medial aspect of ventral medulla and flank the anterior median fissure
contains the the corticospinal tracts
corticospinal tracts decussate
o olivary bodies are paired structures located at lateral aspect of ventral medulla
separated from the pyramids by an anterolateral sulcus
also a post-olivary sulcus lateral to the olivary bodies
olivary bodies contain the superior and inferior olivary nuclei
o anteriorly there is an anterior median fissure
• Dorsal medulla
o posterior median sulcus and more lateral posterolateral sulcus
between these sulci are the fasciculus gracilis and nuclei forming gracilis tubercle at the midline
fasciculus cuneatus and nuclei forming cuneate tubercle more laterally
o superior dorsal aspect of medulla forms the floor of the inferior 4th ventricle
o inferior cerebellar peduncle
o inferiorly surrounded by the cisterna magna
• Embryology: myelencephalon aspect of the rhombencephalon (or hindbrain) becomes the medulla
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Medulla oblongata: Relations
* Anterior: basilar part of the occipital bone
* Posterior: 4th ventricle, cerebellum, cisterna magna
* Hypoglossal nerve rootlets arise anterior to the olive
* Glossopharyngeal, vagus and accessory nerve fibres emerge posterior to the olives
* CN 6-8 arise between pons and medulla
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Medulla oblongata: vasculature
```
Arterial supply:
• Anterior: vertebral arteries, anterior spinal artery
• Posterior: PICA
Venous drainage:
• Anterior: inferior petrosal sinus
• Posterior: occipital sinus
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Midbrain
• Three portions:
o tectum (posterior)
o tegmentum
o cerebral peduncles (anterior)
Tectum:
• Composed of the tectal (quadrigeminal) plate, superior and inferior colliculi
• Below the colliculi, the superior cerebellar peduncles converge to form the superior boundary of the fourth ventricle
• CNIV nerve emerges just superior to the inferior colliculus
• Tectum is posterior to the cerebral aqueduct
Tegmentum
• Runs through the pons and medulla oblongata
• Contains all the brainstem nuclei
Cerebral peduncles:
• Composed of the large ascending and descending tracts that run to and from the cerebrum
• Separated by an interpeduncular fossa
• CNIII nerve emerges from between the peduncles anteriorly and passes between the PCA and SCA
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Midbrain: relations
* Anterior: interpeduncular cistern
| * Posterior: quadrigeminal cistern
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Midbrain: vasculature
```
Arterial supply:
• PCA
• Superior cerebellar arteries
Venous drainage:
• Posterior mesencephalic veins to the great cerebral vein (of Galen)
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Optic pathway
* Optic nerve → Optic chiasm → Optic tract → Lateral geniculate nucleus → Optic radiation → Visual cortex
* Lateral geniculate nucleus is a sensory nucleus in the thalamus of the brain
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Pituitary gland
• Together with the hypothalamus are the main endocrine interface between the CNS and the rest of the body
• Situated in the pituitary fossa of the sphenoid bone
• Divided into anterior pituitary and posterior pituitary
o anterior pituitary: responsible for synthesis and secretion of adrenocorticotropic hormone, luetinizing hormone, follicle stimulating hormone, thyroid stimulating hormone, growth hormone, prolactin
o posterior pituitary: direct extension of the hypothalamus and is responsible for secretion of oxytocin and ADH
• Anterior pituitary is glandular (adenohypophysis)
• Posterior pituitary is collection of axons (neurohypophysis)
• Anterior lobe is adherent with the posterior lobe by a narrow zone called the pars intermedia
• Covered superiorly by a dural reflection called the diaphragma sella
• Connected to the hypothalamus by the infundibular stalk
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Pituitary gland: relations
* Inferior: body of sphenoid, sphenoid sinus
* Superior: diaphragma sellae, suprasellar cistern, optic chiasm, AComA, circle of Willis
* Lateral: cavernous sinus (and contents: OTOMCA), Meckels cave
* Anterior: anterior intercavernous sinus
* Posteriorly: posterior intercavernous sinus
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Pituitary gland: vasculature
Arterial supply:
• Superior hypophyseal artery gives rise to hypophyseal portal system
• Inferior hypophysial artery (from meningohypophyseal trunk)
• A capillary bed in the infundibulum gives rise to portal vessels to the anterior lobe
Venous drainage:
• Cavernous and intercavernous sinuses
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Pituitary gland: innervation
* Anterior lobe produces hormones in response to release factors carried from the the hypothalamus by the hypophyseal portal veins
* Posterior lobe is made of nerve fibres whose cell bodies lie in the hypothalamus
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Pituitary gland: variant anatomy
* Hypoplasia
* Hyperplasia
* Duplication
* Incomplete diaphragma sella: allows CSF to enter the pituitary fossa giving an empty sella sign
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Septum pellucidum
* Thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles
* Runs as a sheet from the corpus callosum down to the fornix
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Cavum Septum Pellucidum
• Normal variant CSF space between the leaflets of the septum pellucidum
• Sometimes called the 5th ventricle
• CSP is present in the normal foetus, but over 85% of them fuse by 3-6 months of age
o persists in ~15% of the adult population
• Often confused with cavum vergae which is situated posterior to the anterior columns of the fornix
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Cavum Vergae
• Along with CSP, CV is a persistence of the embryological fluid-filled space between the leaflets of the septum pellucidum
• Sometimes called the 6th ventricle
• CV is the posterior extension of the CSP
o posterior to the anterior columns of the fornix, lying inferior to the splenium of the corpus callosum
• Not uncommon to have both persistent CSP and CV together
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Cavum Velum Interpositum
• Dilated CSF space involving the velum interpositum
o velum interpositum is a small membrane containing a potential space just above and anterior to the pineal gland which can become enlarged to form a cavum velum interpositum
• Extends below the splenium of the corpus callosum and the column of the fornix, and above internal cerebral veins
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Spinothalamic tract
The spinothalamic tract (also known as anterolateral system or the ventrolateral system)
Sensory pathway from the skin to the thalamus (VPL).
Ventral posterolateral nucleus -> cortex of the postcentral gyrus.
Two adjacent pathways
- Anterior (Crude touch)
- Lateral (Pain + temperature)
In the spinal cord
- Segmental organization (cervical, thoracic, lumbar, and sacral)
- Arranged from most medial to most lateral respectively
- The pathway decussates at the level of the spinal cord (approx 1 level above entry)
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Temporal lobe
• The temporal lobe is one of the four lobes of the brain
• Involved in memories, language comprehension, and emotion association
• Can be divided into two main sections:
o neocortex: comprised of standard cerebral cortex
o mesial temporal lobe (limbic lobe): includes the hippocampus, amygdala, parahippocampal gyrus
• Divided into 6 gyri by 5 sulci which are oriented parallel to the Sylvian fissure (order from superolateral to inferomedial):
o superior temporal gyrus
o superior temporal sulcus
o middle temporal gyrus
o inferior temporal sulcus
o inferior temporal gyrus
o lateral occipitotemporal sulcus
o lateral occipitotemporal gyrus
o collateral sulcus
o lingual gyrus
o calcarine sulcus
o hippocampal gyrus
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Thalamus
* Thalamus is a paired and symmetrical structure in the brain
* Main part of the diencephalon
* Pathway through which signals are sent from cerebrum to midbrain via the cerebral peduncles and vice versa
* Four parts (HEP D): hypothalamus, epithalamus, prethalamus and dorsal thalamus
* Thalamus is connected to the spinal cord via the spinothalamic tract
* Involved in consciousness, arousal, the level of awareness and activity, relaying sensory information, regulating sleep-wake cycle
* Thalami usually connected via interthalamic adhesion
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Thalamus: vasculature
• All are branches of the PCA
o posterior communicating artery
o paramedian thalamic-subthalamic arteries
o thalamogeniculate arteries
o posterior (medial and lateral) choroidal arteries
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Thalamus: Relations
* Medial: forms lateral wall of the 3rd ventricle, pineal gland
* Anterior: basal ganglia
* Lateral: internal capsule
* Posterior: occipital horn of the lateral ventricle
* Inferior: red nucleus, midbrain, substantia nigra
* Superior: anterior horn of the lateral ventricle, corpus callosum
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Thalamus: variants
* Artery of Percheron (rare): single arterial trunk arises from the PCA to supply both thalami
* Interthalamic adehesion (80% of people)
