Maj Rishi PokhrelDept of Anatomy

NAIHS

Circle of Willis

(Circulus Arteriosus)• Polygonal anastomotic channel•Base of brain (interpeduncular fossa)•2 sets of arteries

– Int Carotid - Frontal & parietal lobes and parts of temporal & occipital lobes

– Vertebrobasilar - brainstem, cerebellum, parts of temporal &occipital lobes

CIRCLE OF WILLIS (Circulus Arteriosus)•Functions

–Equalizes blood flow to different parts of brain–If 1 arterial system occluded, bld. passes via communicating As to prevent infarction

Branches:•Anteromedial: from ant cerebral & ant communicating As

•Paired Anterolateral: from ant & mid cerebral As•Paired Posterolateral: from post cerebral A•Posteromedial: from post cerebral & post comm. A

Cortical & Central ArteriesCortical Arteries• Arise from ant, mid & post Cerebral As• Ramify on pia, form anastomoses• Supply grey matter & subjacent white matter• Are in 2 sets• Short cortical-extend upto middle of grey matter• Long cortical – 3-4cm long, run upto superficial white matter

- NOT actual end-arteries

Central Arteries• Branches of Circle of Willis• Penetrate base of brain• Supply int capsule, thalamus & basal ganglia• Arranged in 4 sets

– Antero med– paired anterolat– Paired posterolat– Postero med

• Both central & cortical As are surr. by pial sheath upto pre-capillary level

Lenticulostriate Arteries• Clinically - most important

• Central branches of MCA

• Pierce ant perforated substance & enter white matter

• Pass through lentiform nucleus to reach int. capsule

• Supply upper part of int capsule, lentiform & caudate nuclei

• Some are long, slender, thin-walled & prone to rupture in hypertension-called Charcot’s arteries of cerebral hemorrhage.

BLOOD BRAIN BARRIERExists at capillary level, from inside to outside

consists of:• endothelial cells of capillaries with tight

junctions• Basement membrane of endothelial cells• Perivascular extensions of astrocytes• Intercellular space filled with tissue fluid• Neuronal cell membrane

Cerebral cortex – segmental supply

Regional arterial supply of Brain•Brain stem:

– Medulla oblongata: branches of vertebral, ant & post spinal, PICA and basilar A which enter along ant med fissure and post med sulcus. Vs supplying central substance enter along with rootlets of CN IX, X, XI and XII. Additional supply is from pial plexus of same A.

– Pons: basilar A, AICA and PICA. Direct br from basilar A enter along ventral median groove, others enter along CN V, VI, VII, VII and from pial plexus.

– Midbrain: PCA, SCA and basilar A, crura by Vs entering their med and lat sides. Med Vs also supply sup-med part of tegmentum including CN III nucleus ; lat Vs - lat part of crus and tegmentum. Colliculi by 3 Vs on each side from PCA and SCA. Additional supply to crura, colliculi and their peduncles comes from post-lat group of central br of PCA.

•Cerebellum: by PICA, AICA and SCA, which from superficial plexus on cortical surface, anastomosis b/w deeper sub-cortical branches has been postulated. Choroid plexus of 4 th ventricle is supplied by PICA.

•Optic chiasma, tract and readiation: Chiasma – by ACA but median zone depends on rami from ICA reaching it via pituitary stalk. Tract; ant choroidal and post comm A. Radiation: deep br of MCA and PCA.

• Diencephalon: – Thalamus: br from post comm A, PCA and basilar A; contribution from ant chorodial A is

doubtful.– Median br from post choroidal A: supplies post commissure, habenular region, pineal

gland and medial parts of thalamus including pulvinar.– Hypothalamus: Small central br from circle of willis and its br.– Pituitary gland: hypophyseal br of ICA– Lamina terminalis: ACA and ant comm A– Choroid plexus of 3rd and lat ventricles: br from ICA and PCA.

• Basal ganglia: majority from striate A from roots of ACA & MCA which enter brain from ant perforated substance and also supply internal capsule.

– Caudate Nu: additional supply from ant and post choroidal A– Post-inf part of lentiform complex: thalamo-striate br of PCA.– Ant choroidal A, preterminal br of ICA supply both segments of globus pallidus and caudate Nu,

ligation of this VS (known by serendipity) alleciates the symptoms of parkinson’s disease by infarction of globus pallidus (lead to initiation of pallidotomy).

• Internal Capsule: by central br of circle of willis and its br, mainly med and lat striate A which come from either ACA or ACA and also supply basal ganglia.

– Lateral striate A: ant limb, genu and most of post limb. Commonly involved in ischemic and hemorrhagic stroke.

– Charcot’s A of cerebral hemorrhage : larger striate br of MCA.– Medial strate A: br of proximal part of MCA or ACA supplies ant limb, genu and basal ganglia.– Ant choroidal A from ICA: contributes to ventral part of post limb and retrolentiform part of int

capsule.

Applied anatomy

Lateral medullary syndrome

Medial medullary syndrome

Lateral medullary syndrome of Wallenberg

• Occlusion of PICA• Posterolateral part of medulla is damaged• Involvement of

– spinal nuc & tract of V nerve – ipsilateral loss of pain & temp from face & forehead

– spinal lemniscus (lat spinothalamic tract) – contralateral loss of pain & temp from body below face

– Nucleus ambiguus – paralysis of muscles of soft palate, pharynx & larynx- dysarthria & dysphagia

– Vestibular nuclei- giddiness • Crossed hemianesthesia

Medial Medullary Syndrome• occlusion of ant spinal artery which supplies

medial part of medulla• Involvement of• CN XII nucleus – ipsilateral LMN paralysis of

tongue ; deviated to affected side• Pyramidal fibres - contralateral UMN paralysis• Medial lemniscus (post column fibres) –

contralateral loss of fine touch & discrimination• Crossed motor paralysis

Pontine Hemorrhage• Pontine arteries rupture • Hyperpyrexia – thermoregulatory mechanism disrupted• Pinpoint pupils – contraction of sphincter pupillae • Coma – reticular formation lesion• Contralateral UMN paralysis – pyramidal fibres involved

Pons•Raymond’s syndrome: Alternating abducent hemiplegia (lesion in medial cranial part of pons)•Milalard Gubler syndrome: Alternating facial hemiplegia (lesion in medial caudal part of pons)•Lesions in lateral part of mid pons: alternating trigeminal hemiplegia

Midbrain•Weber’s syndrome: crossed III CN hemiplegia•Benedikt’s syndrome: https://en.wikipedia.org/wiki/Benedikt_syndrome

•Parinaud’s syndrome: https://en.wikipedia.org/wiki/Parinaud%27s_syndrome

Veins on Superolateral surface of cerebrum

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