CNS Blood Supply Flashcards
What proportion of CO is received by brain?
What proportion of O2 does it use?
17%
20%
Describe the intracranial course of the carotid artery
Enters the skull in the middle cranial fossa beside the dorsum sellae of the sphenoid.
Carotid siphon- anterior, superior at medial ACP, enters subarachnoid space and courses posteriorly below optic nerve turning upwards lateral to optic chiasm
Divides into terminal branches below anterior perforated substance
Which artery supplies the neurohypophysis?
Inferior hypophyseal
What do the superior hypophyseal arteries supply?
Enter the median eminence of the hypothalamus.
Break up into capillary loops into which hypothalamic releasing factors gain access.
The capillary loops drain through small hypophyseal portal veins into the capillaries of the anterior lobe.
Where is the ophthalmic artery given off?
Immediately after the ICA enters the subarachnoid space
What structures are supplied by the ophthalmic artery?
Eye and other orbital contents
Frontal area of the scalp
Frontal and ethmoid paranasal sinuses
Parts of the nose
What are the branches of the ophthalmic artery?
DR MCLESSI
D: dorsal nasal artery
R: (central) retinal artery
M: muscular artery
C: ciliary arteries (long, short and anterior)
L: lacrimal artery
E: ethmoidal arteries (anterior and posterior)
S: supraorbital artery
S: supratrochlear artery (frontal artery)
I: internal palpebral artery
Which of the branches of the ophthalmic artery supply the nose?
Anterior and posterior ethmoidal
Passage of the anterior choroidal artery
Posterior- along optic tract, choroid fissue at medial edge of temporal lobe
Branches to optic tract, uncus, amygdala, hippocampus, globus pallidus, lateral geniculate body and ventral part of the internal capsule.
Terminal branches→ choroid plexus in temporal horn anastomosing with posterior choroidal
Neurological deficit with ICA occlusion
Blindness of ipsilateral eye
Loss of contralateral half of visual field.
Contralateral hemiplegia and hemianopia with global aphasia
Neurological deficit with anterior choroidal occlusion
Contralateral hemiplegia and sensory abnormalities (internal capsule)
Contralateral homonymous heminaopia
Passage of MCA
Runs deep in the lateral sulcus between the frontal and temporal lobes
What branch of the ACA is given off just proximal to the AComm?
Medial striate artery (recurrent artery of Heubner)
What is supplied by the recurrent artery of Heubner?
aka Medial striate artery
Penetrates the anterior perforated substance to supply the ventral part of the head of the caudate nucleus, the adjacent part of the putamen and the anterior limb and genu of the internal capsule
Branches of the ACA
Ascends in the longitudinal fissure and bends backwards around the genu of the corpus callosum.
Supplies medial part of the orbital sufrace of frontal lobe including the olfactory bulb and tract.
Continues along the upper surface of the corpus callosum as the pericallosal artery and a large branch, the callosmarginal artery follows the cingulate sulcus.
Why does a unilateral MCA lesion cause no loss of hearing even though the auditory cortex is including in the MCA territory?
Due to the bilateral cortical projection.
Why does a lesion in the internal capsule not cause aphasia?
Because the connections of the language areas with the contralateral hemisphere are intact.
Features of anterior cerebral artery occlusion
Contralateral paralysis of leg and perineum.
May have urinary incontinence caused by inadequate perineal sensation.
May also have contralateral facial weakness due to corticofugal fibres.
Infarction of olfactory lobe may cause anosmia.
Mental confusion and dysphasia may result ?due to loss of function in the prefrontal cortex, cingulate gyrus and SMA
How does the vertebral artery enter the subarachnoid sapce?
Pierces the atlanto-occpital membrane then the arachnoid and dura mater at the foramen magenum
Whence does the single anterior spinal artery arise?
From a contribution from each vertebral artery.
From what do the posterior spinal arteries arise
Either as a branch of the vertebral or PICA.
Passage of PICA
Irregular course between medulla and cerebellum.
Branches of PICA
Distributed to posterior parts of the cerebellar hemisphere, inferior vermis, central nuclei of cerebellum and choroid plexus of the fourth ventricle.
There are also important medullary branches to the dorsolateral medulla
Under which layer of meninges do the CNS arteries lie?
Subarachnoid
Where do the vertebral arteries unite?
Pontomedullary junction
What structures are supplied by PCA?
Midbrain
Occipital lobe
Where does the anterior spinal artery originate?
Anterior to the medulla from two contributory branches of the vertebral artery.
Structures supplied by PICA
Lateral medulla
Posteroinferior cerebellum
What proportion of SC is supplied by ASA?
Anterior 2/3rds
How do segmental arteries enter the SC?
Via the spinal nerves, divide into anterior and posterior radicular arteries passing down the ventral and dorsal spinal roots.
How many posterior spinal arteries are there?
What is their origin?
2
Vertebral arteries or from PICA
What are 3 important contributory arterial systems to the segmental supply of the spinal cord?
Deep cervical artery
Intercostal
Lumbar
What is the most important contributory artery to the anterior spinal artery?
Artery of Adamkiewicz/Great Medullary Artery (direct supply from the aorta).
Mostly on left.
What are the two watershed zones of the spinal cord supplied by the anterior spinal artery?
What is the clinical significance of this?
T4
L1
These are the most common areas to infarct in the compromise of anterior spinal arterial supply.
What is the watershed zone of the posterior spinal arteries?
T1-3.
Origin of AICA
Variable, arises from basilar or vetrebral
Structures supplied by AICA
Anteroinferior cerebellum
Lateral pons
Which artery supplies the middle ear?
Origin?
Labyrinthine artery
Basilar or from AICA
SCA supplies
Superior cerebellum.
Portion of midbrain.
Where does the internal carotid pierce dura mater to enter the subarachnoid space?
Medial to anterior clinoid process
Ophthalmic artery branches
DR MCLESSI
First and second last branches of the mnemonic are the terminal branches
Dorsal nasal artery
Retinal artery
Muscular artery
Cilliary arteres (long, short and anterior)
Lacrimal artery
Ethmoidal arteries (anterior and posterior)
Supraorbital artery
Supratrochlear artery
Internal palpebral artery
Which blood vessel is the most common site for Berry aneurysm?
AComm
C1 carotid
Cervical portion
From the carotid bifurcation to the carotid foramen of the skull base
No branches
C2 carotid
Petrous portion
From the carotid foramen to the posterior edge of the foramen lacerum in the carotid canal.
One branch:
Caroticotympanic artery
[vidian artery occasionally]
Branches of the second carotid segment
Petrous portion
Caroticotympanic and vidian
C3 carotid
Lacerum segment
Small portion where the ICA passes over the foramen lacerum
C4 carotid
Cavernous segment
From the foramen lacerum (petrolingual ligament) to the anterior clinoid process
Multiple branches including
Meningohypophyseal trunk
Inferolateral trunk.
Medial trunk or McConnell’s artery goes to the capsule of the pituitary gland.
Branches of the fourth segment of the carotid
Cavernous segment
Meningohypophyseal trunk
Inferolateral trunk
McConnel’s capsular artery
(small capsular arteries to the wall of the cavernous sinus)
Branches of the meningohypophyseal trunk
Tentorial artery (AKA Bernasconi and Cassinari artery)
Dorsal meningeal artery
Inferior hypophyseal artery
Bernasconi and Cassinari artery
Tentorial artery
Branch of the meningohypophyseal trunk (D)
McConnell’s artery
They arise from the medial wall of the cavernous ICA distal to both the meningohypophyseal trunk and the inferolateral trunk.
C5 carotid
Clinoid segment
Between the proximal and distal dural rings
Branches of the external carotid
Superior thyroid
Ascending pharyngeal
Lingual
Facial
Occipital
Posterior auricular
Maxillary
Superficial temporal
C6 carotid
Ophthalmic segment
From the distal dural ring to the PComm
Two important branches:
Ophthalmic
Superior hypophyseal
Important branches of the sixth segment of the internal carotid
Ophthalmic segment
Ophthalmic artery
Superior hypophyseal artery
C7 carotid
Communicating segment
From the PComm artery to the bifurcation of the ICA into the ACA and the MCA
Branches are
PComm
Anterior choroidal
Branches of the 7th segment of the carotid
PComm
Anterior choroidal
Classification of the ACA
Can be grossly divided into precommunicating and postcommunicating segments based on its relation to the AComm
Can also be divided into 5 segments
A1 ACA
From the bifurcation to the AComm
A2 ACA
From the AComm to the junction of the rostrum and genu of the corpus callosum
Recurrent artery of Heubner may arise from either the junction of A1/2 or from A1 or A2
A2 segment normally gives off the frontopolar and the orbitofrontal artery
A3 of the ACA
Travels around the genu of the corpus callosum and becomes A4 after turning sharply.
Highly variable branches including the callosomarginal which may divide into the anterior, middle and posterior internal frontal arteries. These 3 arteries may also arise directly from the A3 segment.
The pericallosal artery may also arise from the segment or be a direct continuation of the ACA
A4/5 segments of ACA
Run over the body of the corpus callosum
Separated from each other via a vertical line running over the callosal surface
A4 gives off the paralobular central artery.
A5 gives off superior and inferior internal parietal arteries.
M1 of the MCA
The sphenoidal or horizontal segment
From the origin of the MCA to the bifurcation into a superior and inferior trunk.
Lateral lenticulostriate arteries arise from this segment
M2 of the MCA
Insular segment
Runs in the depth of the Sylvian fissure from its bifurcation.
M3 of the MCA
Opercular segment
From the depths of the Sylvian fissure on its posterior segment to the surface
M4 of the MCA
Cortical segment
Starts at the surface of the Sylvian fissure and gives off multiple branches travelling to the cortical surfaces of the cerebral hemispheres.
V1 of the vertebral artery
Subclavian to C6 transverse foramina
V2 of the vertebral artery
Vertebral segment
From C6 to C2
V3 of the vertebral artery
Extradural segment, from C2 to the foramen magnum
V4 of the vertebral artery
Intradural segment
From its entry to the dura of the foramen magnum to its unification with the contralateral vertebral artery and formation of the basilar
Branches of basilar
AICA
Labyrinthine
Pontine
SCA
P1 of the PCA
Precommunicating
From the bifurcation of the basilar to the junction of the PComm
Gives off multiple perforators to the diencephalon and anterolateral midbrain.
P2 of the PCA
Ambient segment
From PComm to posterior edge of the midbrain.
Lateral posterior choroidal artery and thalamogeniculate arteries
P3 of PCA
Quadrigeminal segment
From the posterior edge of the midbrain to the calcarine anterior limit of the calcarine fissure.
Posterior temporal artery, Parieto-occipital and calcarine artery, Posterior pericallosal artery
Two main superficial veins of the cranium
Superior vein of Trolard
Inferior vein of Labbe
Vein of Trolard
Drains from Sylvian fissure to SSS
Vein of Labbe
Drains from Sylvian fissure to transverse sinus
What are the major deep veins
Internal cerebral vein
Vein of Galen
Basal vein of Rosenthal
Internal cerebral vein
Receives the thalamostriate vein at the foramen of Monro and the septal vein
Basal vein of Rosenthal
Drains the base of the brain from the anterior perforated substance to the internal cerebral vein
Joins to form the vein of Galen
Vein of Galen
Formed by the internal cerebral and basal vein of Rosenthal
Joins with ISS to form straight sinus
Function of BBB
Stabilises internal environment of CNS
Protects CNS from endogenous and exogenous toxins and bacteria
Maintains concentration of neurotransmitters
Types of capillaries
Continuous (tight)
Fenestrated
Sinusoidal
What are the special features of the endothelial cells of neurovascular capillaries
Tight junctions between cells
Demonstrate very low levels of transcellular vesicular transport
No fenestrations
P-glycoproteins (ATP dependent pumps that pump lipid-soluble toxins out of CNS)
Basement membrane (contains pericytes)
Astrocyte foot processes against BM release substances which stimulate endothelial cells to produce occludins and other factors that promote type junctions
What substances cannot cross BBB?
Plasma proteins or plasma protein-bound substances
Highly charged molecules/polar/water-soluble molecules
Toxic substances
Which substances can cross the BBB?
Small molecules
Non-polar/lipid soluble molecules
Specific facilitative transporters (e.g. for glucose)
Which glucose transporters are present in CNS capillaries?
GLUT-1
(independent of insulin)
Components of the blood-CSF barrier?
Fenestrated endothelial cells without tight junctions.
BM of endothelial cells
BM of ependymal cells
Specialised ependymal cells (choroidal epithelial cells) which possess tight junctions
Under which circumstances is BBB disrupted?
Physiological:
Circumventricular organs
Neonates
Pathological:
Trauma
Inflammation/infection
Irradiation
Neoplasm
Hypertensive encephalopathy
High altitude (hypoxia can damage BBB)
All cause vasogenic oedema
What is bounded superiorly by the anterior commissure and inferiorly by the optic chiasm?
Lamina terminalis of the third ventricle
What are the periventricular organs?
Sensory:
Vascular organ of lamina terminalis (OVLT)
Area postrema
Subfornical organ
Median eminence
Secretory:
Posterior pituitary
Subcommissural organ
Pineal gland
What is the embryological significance of the lamina terminalis?
Derives from cranial neuropore
What is the arrangement of capillary endothelial lining at the periventricular organs?
Fenestrated (except subcommissural)
Why is the BBB broken in the median eminence?
To allow carriage of regulatory peptides from hypothalamus to pituitary
Why is the BBB broken at the OVLT?
Senses presence of peptides in blood including AngII and IL-1
Contains osmoreceptors
Interacts with supra-optic nucleus promoting the release of ADH
Function of subfornical organ?
Contains neurones sensitive to AngII
Acts as thirst centre and centre for regulation of fluid balance.
Connected with OVLT
Why is BBB broken at pineal gland
To allow secretion of melatonin into blood
Function of subcommissural organ?
Not clearly established
No fenestrated capillaries
In other species secretes glycoproteins into the ventricular system to form Resiner’s fibres/threads which keep the system open. ?Aetiology of congenital cerebral aqueduct stenosis
Location of area postrema
Two centres
Lower portion of floor of fourth ventricle
Function of area postrema
Emetogenic substances
Connected with dorsal nucleus of vagus and nucleus of tractus solitarius which together are called the dorsal vagal triangle
Known as chemoreceptor trigger zone
At what point is the PCA joined by the PComm?
The lateral margin of the interpeduncular cistern.
Structures supplied by the PCA?
Posterior part of the cerebral hemispheres
Thalamus
Midbrain
Other deep structures including the choroid plexus and walls as lateral and third ventricles
P1 Segment of PCA
Precommunicating segments
Extends from the basilar bifurcation to the junction with the PCommA
What is meant by a fetal P1 configuration
In which the P1 has a smaller diameter than the PComA and the PCA arises predominantly from the carotid artery
In what proportion of hemispheres is a fetal PComm arrangement found?
1/3rd of hemispheres
Relationship of the oculomotor to PCommA
Passes below and slightly lateral to the PComA if a normal configuration is present.
If a fetal pattern is present, P1 is longer and the nerve courses beneath or medial to the communicating artery
What are the 4 constant branches of P1?
Thalamoperforating artery (enters the brain through the posterior perforated substance)
Medial posterior choroidal artery
Branch to quadrigeminal plate
Rami to the cerebral peduncle and mesencephalic tegmentum.
Extent of the P2 segment
Begins at the PCommA
Lies within the crural and ambient cisterns, terminating laterally to the posterior edge of the midbrain.
Divided into an anterior and posterior part
Anterior part of P2
P2A or crural/peduncular segment as it courses around the cerebral peduncle in the crural cistern
Posterior part of P2
P2P or ambient/lateral mesencephalic segment because it courses lateral to the midbrain in the ambient cistern
Passage of P2A
Begins at PCommA and courses between the cerebral peduncle and uncus that forms the medial and lateral walls of the crural cistern and inferior to the optic tract and basal vein that crosses the roof of the cistern to enter the proximal portion of the ambient cistern
Passage of P2P
Commences at the posterior edge of the cerebral peduncle at the junction of the crural and ambient cisterns.
Passes between the lateral midbrain and the parahippocampal and dentate gyri which form the medial and lateral wallls of the ambient cistern below the optic tract, basal vein and geniculate bodies.
P3 Segment
Quadrigeminal segment
Proceeds posteriorly from the posterior edge of the lateral surface of the midbrain and ambient cistern to reach the lateral part of the quadrigeminal cistern and ends at the anterior limit of the calcarine fissure.
What is the quadrigeminal point
The point where the PCAs from each side are nearest is referred to as the collicular or quadrigeminal point.
P4 Segment
Includes the cortical branches.
Begins at the anterior end of the calcarine sulcus
What are the 3 categories of PCA branches
Central perforating branches to the di and mesencephalon
Ventricular branches to the choroid plexus and walls of the lateral and third ventricles and adjacent structures
Cerebral branches to the cortex and splenium of the corpus callosum
Perforating branches of the PCA
Divided into direct and circumflex arteries
Direct:
Thalamoperforating arteries (P1)
Thalamogeniculate and peduncular perforating arteries (P2)
Circumflex arteries of the PCA
Encircle the brainstem for a variable distance before entering the diencephalon and mesencephalon and divided into long and short groups dependent on how far they course around the brainstem.
Through which transverse foramen of the cervical vertebra does the vertebral artery pass?
C1-6
How many segments of the vertebral artery are there?
4 segments
Extent of V1
Prevertebral.
From its origin at the subclavian artery to C6
Extent of V2
Vertebral segment
Runs within the transverse foramen from C6 to C2
Extent of V3
Extradural segment
From C2 to the foramen magnum
Extent of V4?
From the entry into the dura of the foramen magnum until its jucntion with the contralateral vertebral artery where it forms the basilar.
What are the collateral branches of the vertebral arteries?
Anterior meningeal artery
Posterior meningeal artery
Posterior spinal artery
Branches of the vertebral artery
ASA
PICA
Features of the anterior spinal artery?
Formed from two branches oiginating from each of the VAs prior to their union as the basilar artery.
Runs in the surface of the anterior median fissure of the spinal cord, supplies blood to the anterior 2/3rds.
Features of PICA
Supplies the posterolateral medulla, the fourthh ventricle and the posteroinferior cerebellar hemispheres
Level of termination of the basilar artery?
Interpeduncular cistern
Branches of the basilar
AICA
Labyrinthine
Pontine
SCA
Number of segments of PCA?
4 segments
Extent of P1
Pre-communicating segment
From the bifurcation of the basilar artery to the junction of PComm
Gives off multiple perforators to the thalamus, hypothalamus, subthalamus and the anterolateral segment of the midbrain.
Extent of P2
Ambient segment
From the junction of the PComm to the posterior edge of the midbrain.
Some of the PCA branches at this segment are the lateral posterior choroidal artery and thalamogeniculate arteries.
Extent of the P3 segment
Quadrigeminal segment
From the posterior edge of the midbrain to the anterior limit of the calcarine fissure.
The branches of this segment supply the posteroinferior temporal lobe (posterior temporal artery)
Occipital lobe (parieto-occipital artery and calcarine artery
And the posterior segment of the corpus callosum (posterior pericallosal artery)
Extent of P4 segment
Terminal segment
Anatomy of Alexia without Agraphia
Cerebral hemispheric infarction
Left occipital region plus splenium of the corpus callosum.
Due to infarction of Callosal branches
Pure word blindness, can write but not read
Alexia without agraphia
Signs and symptoms of alexia without agraphia
Can write but not read
May have contralateral homonymous hemianopia
Balint Syndrome
Oculomotor ataxia
Bilateral loss of voluntary but not reflex eye movements
Bilateral optic ataxia- poor visual-motor coordination
Asimultagnosia- inability to understand visual objects
Anatomy of Balint syndrome
Bilateral parietal occpital lobe infarct due to bilateral PCA stroke
Claude Syndrome
Ipsilateral CN3
Contralateral ataxia of arm and leg.
Marked ataxia differentiates from Benedikt’s
Anatomy of Claude syndrome
Contralateral ataxia due to infarction of midbrain tegmentum secondary to PCA occlusion.
May also have ipsilateral oculomotor palsy with contralateral tremor and ataxia due to involvement of decussation of superior cerebellar peduncle
Anton Syndrome
Cortical blindness
Bilateral visual loss
Unawareness or denial of blindness
Anatomy of Anton syndrome
Bilateral PCA occlusion or top of basilar occlusion
Due to bilateral occipital lobe involvement
Unilateral Occpital PCA stroke
Conralateral homonymous heminaopia with macular sparing
Due to infarction of occipital and infero-medial temporal lobes
Dejerine Roussy Syndrome
Thalamic pain syndrome
Due to thalamoperforator branch infarction
Causes hemisensory loss- all modalities then development of intractable hemi-body pain
Weber Syndrome
Basal midbrain stroke
Contralateral weakness of arm and leg due to corticospinal tract involvelent
Ipsilateral CN3 palsy
Benedikt syndrome
Paramedian midbrain syndrome
Ipsilateral CN3 palsy
Cerebellar ataxia with choreoathetotic movements (red nucleus)
May involve contralateral hemiparesis due to involvement of corticospinal tract.
Artery of Davidoff and Scheter
The artery of Davidoff and Schechter (ADS) is a dural branch that arises from the posterior cerebral artery and supplies the falcotentorial junction. It is usually not identified on angiography except when enlarged in the setting of dural AVFs, meningiomas, or, rarely, cerebellar tumours
Normal CBF
50ml/100g/min
Vertebral artery dominance
Left side 50%
Right side 25%
Non-dominance 25%
The left vertebral artery arises from the aorta in what proportion of patients?
5%
What proportion of the population have a hypoplastic vertebral artery?
40%
Structures supplied by superior thyroid artery
Larynx and upper thyroid
Anastomoses with the thyrocervical trunk
Structures supplied by and anastomoses:
Ascending pharyngeal
Nasopharynx, oropharynx and middle ear
CNs IX-XI
Meninges
Vertebral artery branches
Structures supplied by and anastomoses:
Lingual artery
Tongue and floor of mouth
Structures supplied by and anastomoses:
Facial artery
Face, palate, lips
Angular branch of the facial artery anastomoses with the orbital branch of the ophthalmic
Structures supplied by and anastomoses:
Occipital artery
Posterior scalp, upper cervical musculature, posterior fossa and meninges
Anastomoses with the vertebral artery
Structures supplied by and anastomoses:
Posterior auricular artery
Pinna, EAC, scalp
Structures supplied by and anastomoses:
Superficial temporal
Scalp and ear
Structures supplied by and anastomoses:
Maxillary
Deep face
Gives off MMA and accessory meningeal
Anastomoses with inferolateral trunk, ophthalmic and petrous carotid via ethmoidal and vidian branches
Subsegmentation of the intracavernous ICA
Ascending portion (entrance into the cranium to the genu)
Posterior genu (between C5 and C3 segments)
Horizontal portion (between the genu)
Anterior genu
Remainder of intracavernous ICA segment
Location of the cervical ICA
Larger than ECA
Located in the lateral pharyngeal space
Initially posterolateral to the ECA but becomes medial to enter the carotid canal anteromedial to the IJV
Location of the petrous ICA
Enters the caroid canal of petrous temporal bone
Lies behind the eustachian tube
Segments of petrous ICA
Vertical sgment (10mm)
Horiztonal (20mm), exits the petrous apex superior to the foramen filled lacerum
Caroticotympanic artery
Embryonic hyoid artery remnant
Arises near the genu of the petrous ICA passes superiorly
When aberrant can cause retrotympanic pulsatile mass
Anastomoses with inferior tympanic artery (ECA)
Supplies middle and inner ear
MHT branches
Italian artery (tentorial)
Inferior hypophyseal
Dorsal meningeal
Structures supplied by:
Tentorial artery
Tentorium
Structures supplied by:
Inferior hypophyseal artery
Neurohypophysis
Structures supplied by:
Dorsal meningeal artery
CN VI and clivus
Structures supplied by:
Inferolateral trunk
Inferolateral cavernous sinus wall, tentorium, CN III, IV, VI, V ganglion
Anastomoses with the maxillary artery and MMA
Medial trunk of cavernous sinus
Present in 28% of the population
Anterior capsular artery- medially over sellar roof
Inferior capsular artery- inferomedially to the sellar floor
Supplies anterior and inferior pituitary
Ophthalmic artery branches
DR MCLESSI
D: dorsal nasal artery
R: (central) retinal artery
M: muscular artery
C: ciliary arteries (long, short and anterior)
L: lacrimal artery
E: ethmoidal arteries (anterior and posterior)
S: supraorbital artery
S: supratrochlear artery (frontal artery)
I: internal palpebral artery
Aneurysms of ophthalmic artery
Arise from the superior wall of the ICA distal to the OA origin, project superiorly and may abut the CN II
Structures supplied by the superior hypophyseal artery
Adenohypophysis and the infundibulum
Tuber cinereum
Inferior surface of the optic chiasm and CN II
Course of the SHA
Arises from the posteromedial ophthalmic ICA beneath CN II
SHA aneurysms
Project inferiorly and medially
Course of PCommA
Arises from the posterior wall of the ICA and passes posterolaterally above CN III to join the P1 segment of PCA
Structures supplied by PComm
Posterior hypothalamus
Anterior thalamus
STN
Posterior limb of internal capsule via seven perforators that are equally distributed along the vessel length and course superomedially to their targets
PComm Aneurysms
Normally arise from the posterior wall of the ICA immediately distal to the PComm origin and point towards CNIII
PComm is typically inferomedial to the aneurysm and the anterior choroidal artery is superior lateral
What proportion of population has variant PComm?
Categories of PComm variation
50%
Absent or hypoplastic
Fetal
Infundibulum
What proportion of the population have an absent or hypoplastic PComm?
30%
What proportion of population have fetal PComm
20%
(PComm A same diameter as P1)
PComm infundibulum
Funnel-shaped dilatation of the PComm <2mm
PComm arising from dome of a pyramidal dilatation
Differentiated from aneurysm does which does not come off tip
Structures supplied by the medial proximal striate branches of A1
1-12 perforators
Optic nerve and chiasm
Anterior hypothalamus
Septum pellucidum
Anterior commissure
Pillars of the fornix and the anteroinferior striatum
NB Medial DISTAL lenticulostriate artery= recurrent artery of Heubner
AComm perforators
2 or more arise from the AComm to supply:
Infundibulum
Chiasm
Subcallosal area
Preoptic hypothalamus
Include the subcallosal artery and medial artery of the corpus callosum
AComm aneurysms
Usually arise at the point where the dominant A1 bifurcates and point towards the contralateral side
Branches of A2
Heubner (A1)
Orbitofrontal artery
Frontopolar artery
Anterior internal frontal artery
Branches of A3
Callosomarginal artery
Pericallosal artery
Middle internal frontal artery
Posterior internal frontal artery
Paracentral artery
Superior parietal artery
Inferior parietal artery
What proportion of the population have an MCA bifurcation
50%