NORMAL ARTERIAL AND VENOUS ANATOMY OF BRAIN AND ITS TERRITORIES

DR. DEV LAKHERA

Imaging techniques

Arterial anatomy of brain, variants and

territories Anterior circulation

Circle of Willis

Posterior circulation

Venous anatomy of brain

IMAGING TECHNIQUES

Digital Subtraction Angiography (DSA).

Computed Tomography Angiography (CTA).

Magnetic Resonance Angiography (MRA).

DSA

Endovascular interventional procedures.

Follow-up DSA after aneurysm and AVM treatment.

Negative CTA, in order to exclude a small fistula.

CT Angiography

Anatomy and pathology

Contrast enhanced CT angiography

Adv over MR Angiography Quicker and easier to perform Can be used in MR

contraindications

MR Angiography

Contrast enhanced MR angiography-

Non-contrast enhanced MR angiography-

1. time of flight2. phase contrast

Adv: Can be done without contrast

Time-of-flight (non-contrast) MR angiogram, axial view

Intracranial circulation

Intracranial circulation

Anterior circulation

Intracranial part of ICA

Posterior circulation Vertebrobasil

ar Trunk

CCA bifurcates at C4 vertebral body

Complex course

7 segments and 3 genu

Anterior circulation

Internal Carotid artery

Seven segments, C1–C7 C1- Cervical segment C2- Petrous segment C3- Lacerum segment C4- Cavernous segment C5- Clinoid segment C6- Ophthalmic segment C7- Communicating segment

Cervical segment

Course – crosses behind and medial to ECA

No named branches

ICA ECA

Petrous segment C2 ICA –intraosseous

enters carotid canal in petrous temporal bone.

exits at petrous apex Branches

• Vidian artery (artery of pterygoid canal) anastomoses with external carotid artery (ECA) • Caroticotympanic artery (supplies middle ear)

Axial CT

Posterior genu as it courses anteromedially into the cavernous sinus

ICA courses along the basisphenoid bone

• Through cavernous sinus proper turns superiorly • Form grooves under anterior clinoid process •Curve upwards towards dural ring• Enter subarachnoid space

Posterior genu

Carotid sulcus

Anterior genu

Cavernous ICA

Cavernous ICA Major branches

- Meningohypophyseal trunk (arises from posterior genu, supplies pituitary, tentorium and clival dura)

- Inferolateral trunk arises from horizontal segment, supplies cavernous sinus (CS) dura / cranial nerves;

Clinoid segment C5

•Between proximal , distal dural rings of cavernous sinus

•Ends as ICA enters subarachnoid space near anterior clinoid process

•No important branches

Ophthalmic segment C6

Extends from distal dural ring at superior clinoid to just below posterior communicating artery (PCOM) origin Branches –

•Ophthalmic artery •Superior hypophyseal artery

Anterior clinoid process

C6

Normal ICA variants

Aberrant ICA

Persistent stapedial artery

Embryonic carotid-basilar anastomosis.

Aberrant ICA

Involution of normal cervical ICA

Enter through posterior wall of middle ear cavity and crosses MEC and joins horizontal segment

Can present as a retrotympanic vascular mass

Persistent stapedial artery

embryonic stapedial artery persists postnatally arises from the C2 (petrous) ICA

PSA passes through the stapes footplate and doubles the size of the anterior (tympanic) facial nerve segment

MMA arises from PSA

Persistent embryonic carotid-basilar anastomosis.

Variants – Persistent Trigeminal Artery •In utero – embryonic trigeminal artery supplies basilar artery before the PCOM and vertebral artery develops

course – arise when ICA exits carotid canal and enters cavernous sinus

Runs posterolaterally along trigeminal nerve 41%

Crosses over / through dorsum sella before joining basilar artery

Connects ICA to vertebrobasilar system

trident shape on lateral DSA

PCOM is absentSupply entire vertebrobasilar circulation distal to anastomosis

Saltzmann type Ι

• Fetal PCA and I/L P1 segment absent • Fill superior cerebral arteries (SCA) with

posterior cerebral arteries (PCA ) fills via patent PCOM

Saltzmann type ΙΙ

•Increased incidence of intracranial aneurysms / malformations•Increased importance in transphenoidal surgery

CIRCLE OF WILLIS

Ring of vessels

Connects the anterior and posterior circulation

Important source of collateral circulation

Normal MR Angiogram

Anterior cerebral artery Medial branch of

supraclinoid ICA

Runs in interhemispheric fissure

3 segments

Three segments A1 (horizontal): origin

from the ICA to the anterior communicating artery (ACOM). ~14 mm in length

A2 (vertical): from ACOM to the bifurcation.

A3 (cortical branches): distal to the bifurcation.

ACA TERRITORY

• Anterior two-thirds of the medial surface of the hemisphere

• Small wedge along the inferomedial frontal lobe

• Cortex over the top of the hemisphere vertex

Segments M1: horizontal segment from the origin

to bifurcation/trifurcation

M2: insular segment from bi/(tri)furcation to circular sulcus of insula where it makes hairpin bend to continue as M3

M3: opercular branches (those within the Sylvian fissure);

M4: cortical segment

Middle cerebral artery

MCA territories

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 lobe and occipital lobe (via PCA).

Posterior cerebral artery

P1: from it origin at the termination of the basilar artery to posterior communicating artery (PCOM), within interpeduncular cistern.

P2: from the PCOM around the mid-brain to ambient segment

P3: segment with the quadrigeminal cistern

P4: cortical segment

MR Angiography

The PCA territory

occipital lobe

posterior third of the

medial and the

posterolateral surfaces of

the hemisphere

inferior surface of the

temporal lobe

Variants 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 (fetal

PCOM) ~20%

infundibular dilatations of the PCOM origin ~10% (range 5-15%)

Duplicated ACOM Fenestrated ACOM

Fetal origin of posterior cerebral artery

The posterior cerebral artery (PCA) arises directly from internal carotid artery (ICA) on right side. The right P1 segment is hypoplastic.

Vertebrobasilar system V1 (EXTRAOSSEOUS) SEGMENT: enters

the C6 transverse foramen V2 (FORAMINAL) SEGMENT:

V3 (EXTRASPINAL) SEGMENT. VA exits the C1 transverse foramen

V4 (INTRADURAL) SEGMENT. VA becomes intradural, it courses superomedially behind the clivus and in front of the medulla

anterior and posterior spinal arteries medullary perforating branches. PICA

Basilar artery At pontomedullary junction Terminates in the interpeduncular

cistern give 2 PCAs

AICA SCA Pontine Labyrinthine

Territory

Cerebellum, midbrain, posterior thalami, occipital lobes, most of the inferior and posterolateral surfaces of the temporal lobe, and upper cervical spinal cord

Normally left vertebral artery is dominant 50 %

Origin from aortic arch

No connection with basilar artery

Fenestration / Partial duplication

Variants

Normal Venous Anatomy

Two major components

Dural venous sinuses

Cerebral veins Superficial Deep

Dural sinuses

Superficial cerebral veins (Sup, middle, inf) drain in to sagittal sinus

CSF drains into it via arachnoid granulations

The two TSs are frequently asymmetric, with the right side typically larger than the left.

Hypoplastic and even atretic segments are common

Arachnoid granulations

Superficial cortical veins

Cavernous Sinus

irregularly shaped, heavily trabeculated/compartmentalized venous sinuses

lie along the sides of the sella turcica

Tributaries draining into the CSs Superior/inferior ophthalmic veins Sphenoparietal sinuses

Deep system of veins Internal cerebral veins-

Anterior and middle cerebral veins join to form basal vein.

(1) medullary veins (2) subependymal veins (3) deep paramedian veins

Great cerebellar vein a/k/a vein of galen.

Internal carotid angiogram

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