Vascular Anatomy

Anterior (ICA) MCA & Divisions ACA & AChA/Ophthalmic Posterior Circulation Brainstem Syndromes Venous System Summary

🩸 Anterior Circulation – Internal Carotid & Branches

Internal Carotid Artery (ICA) – Segments & Key Branches ▼

ICA Segments (high-yield)

Segment	Location	Key Points
Cervical	Carotid bifurcation → skull base	No major branches; common site for atherosclerosis
Petrous	Carotid canal (temporal bone)	Protected; small branches to petrous bone & middle ear
Cavernous	Within cavernous sinus	Close to CN III, IV, V1, V2, VI → cavernous sinus pathology
Supraclinoid (Terminal)	After exiting cavernous sinus	Gives off: Ophthalmic, PCom, Anterior Choroidal, ACA, MCA

ICA Stroke – Clinical Pattern

Often = MCA ± ACA territory (if poor collateral flow via ACom/PCom)
Carotid T occlusion: Severe deficit – dense contralateral hemiplegia, hemisensory loss, gaze deviation, aphasia (dominant) or neglect (non-dominant), homonymous hemianopia
Retinal ischemia: Amaurosis fugax or monocular vision loss (ophthalmic artery)
Clue: Ipsilateral monocular blindness + contralateral hemiparesis → think ICA

💎 Board Pearl

“Carotid T” = terminal ICA occlusion at the carotid bifurcation into ACA & MCA → massive MCA ± ACA syndrome + often poor collaterals.

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🧠 Middle Cerebral Artery (MCA) & Divisions

MCA Anatomy & Territories ▼

MCA Segments

M1: Horizontal/sphenoidal segment – from origin to bifurcation/trifurcation
M2: Insular segments (superior & inferior divisions)
M3/M4: Opercular & cortical branches over convexity

Key branches:

Lenticulostriate arteries (from M1): Supply basal ganglia & posterior limb of internal capsule (“arteries of stroke”)
Cortical branches: Lateral frontal, parietal, temporal lobes

Typical MCA Territory Deficit

Contralateral face & arm weakness > leg
Contralateral hemisensory loss (face/arm > leg)
Contralateral homonymous hemianopia (optic radiations)
Dominant hemisphere: Aphasia (Broca/Wernicke/global)
Non-dominant hemisphere: Hemispatial neglect, anosognosia, constructional apraxia
Eyes often deviate toward the lesion in acute phase

MCA Syndromes – M1 Proximal vs Distal vs Divisions

Pattern	Clinical Features	Key Clues / Localization
M1 Proximal (before lenticulostriates)	• Dense contralateral hemiplegia (face, arm, leg) • Contralateral hemisensory loss • Gaze deviation toward lesion • Aphasia (dominant) or neglect (non-dominant) • Often early edema, mass effect	Cortical + deep signs. Internal capsule + cortex involved. Very severe deficit at onset (“devastating MCA stroke”).
M1 Distal (after lenticulostriates)	• Cortical signs prominent (aphasia/neglect, field cut) • Weakness typically less dense (internal capsule spared) • May have mild–moderate face/arm > leg weakness	Cortical signs without profound dense hemiplegia. Think more distal M1 or large M2 branch occlusion.
Superior Division (M2)	• Face & arm weakness prominent • Little or no visual field deficit • Dominant: Broca’s aphasia (nonfluent, good comprehension) • Non-dominant: Mild neglect, motor apraxia	Motor + Broca’s = superior division (dominant). Visual field often spared or mild.
Inferior Division (M2)	• Prominent visual field deficit (HH or quadrantanopia) • Little or no weakness • Dominant: Wernicke’s aphasia (fluent, poor comprehension) • Non-dominant: Severe neglect, anosognosia	Fluent aphasia + HH with minimal weakness = inferior division (dominant). Non-dominant: “classic neglect” pattern.

💎 Board Pearl

Dense hemiplegia + aphasia/neglect → think proximal M1 (cortex + internal capsule).
Fluent aphasia + HH but NO weakness → inferior division MCA.

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🧍 Anterior Cerebral, Anterior Choroidal & Ophthalmic Arteries

Anterior Cerebral Artery (ACA) ▼

Course: From ICA → A1 segment → ACom → A2 pericallosal/callosomarginal branches.

Territory:

Medial frontal & parietal lobes
Leg area of motor & sensory cortex
Anterior corpus callosum & cingulate

ACA Stroke Syndrome:

Contralateral leg weakness > arm/face
Contralateral leg sensory loss
Urinary incontinence
Abulia, akinetic mutism (medial frontal/anterior cingulate)
Frontal release signs (grasp reflex)
Alien limb phenomena (medial frontal/callosal)

Anterior Choroidal Artery (AChA) ▼

Origin: Supraclinoid ICA (classically) – small but high-yield vessel.

Structures supplied:

Posterior limb of internal capsule
Optic tract & lateral geniculate body
Medial temporal lobe (hippocampus)
Globus pallidus

Classic AChA Stroke Triad:

Contralateral hemiparesis (posterior limb IC)
Contralateral hemisensory loss
Contralateral homonymous hemianopia (optic tract/LGN)

Often incomplete in real-life, but exam loves the triad.

Ophthalmic Artery ▼

Origin: First major branch of supraclinoid ICA; enters optic canal with optic nerve.

Supplies: Retina, optic nerve head, orbit.

Clinical:

Amaurosis fugax: Transient monocular vision loss (“curtain coming down”) from retinal ischemia due to carotid disease.
Retinal artery occlusion: Sudden painless monocular blindness; cherry red spot.

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🔄 Posterior Circulation – Vertebrobasilar & PCA

Vertebral & Basilar Arteries – Overview ▼

Vertebral arteries: Join to form basilar at pontomedullary junction.

Key branches:

PICA – posterior inferior cerebellar artery
Anterior spinal artery
AICA – anterior inferior cerebellar artery
SCA – superior cerebellar artery
Paramedian & circumferential branches to brainstem

Posterior Cerebral Artery (PCA) ▼

Origin: Terminal branches of basilar artery.

Territory:

Occipital lobe (primary visual cortex)
Inferomedial temporal lobes
Posterior thalamus
Splenium of corpus callosum

PCA Stroke Syndrome:

Contralateral homonymous hemianopia ± macular sparing
Alexia without agraphia (left PCA + splenium)
Visual agnosia, prosopagnosia (ventral occipitotemporal)
Thalamic pain syndrome (Dejerine–Roussy) if thalamus involved
Bilateral PCA → cortical blindness ± Anton syndrome

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🧲 Brainstem & Cerebellar Stroke Syndromes (Pattern Recognition)

Syndrome	Artery	Localization & Key Features
Lateral Medullary (Wallenberg)	PICA (usually vertebral/PICA)	• Vertigo, nystagmus, nausea • Ipsilateral facial pain/temp loss (trigeminal nucleus) • Contralateral body pain/temp loss (spinothalamic) • Dysphagia, hoarseness, diminished gag (nucleus ambiguus) – “Don’t PICA horse” • Ipsilateral Horner’s, ataxia
Lateral Pontine	AICA (anterior inferior cerebellar)	• Similar to PICA but more facial nucleus involvement • Ipsilateral facial paralysis, ↓ lacrimation, salivation, taste (ant 2/3) • Vertigo, nystagmus • Ipsilateral ataxia • “Facial droop means AICA’s pooped”
Medial Medullary	Anterior spinal (branch of vertebral)	Triad: • Contralateral hemiparesis (corticospinal) • Contralateral dorsal column loss (proprioception/vibration) • Ipsilateral tongue weakness (CN XII) – tongue deviates toward lesion
Locked-in Syndrome	Basilar ventral pons	• Quadriplegia, anarthria • Preserved consciousness & vertical eye movements • Result of bilateral corticospinal & corticobulbar tract involvement
Weber Syndrome	Paramedian midbrain (PCA branches)	• Ipsilateral CN III palsy • Contralateral hemiparesis • Classic midbrain “alternating” hemiplegia
Superior Cerebellar Artery (SCA) stroke	SCA	• Ipsilateral limb ataxia, dysmetria • Nausea, vomiting, nystagmus • Contralateral pain/temp loss (body) • Facial pain/temp may be spared (vs PICA/AICA)

💎 Board Pearl

Posterior circulation strokes often give “crossed findings” – ipsilateral cranial nerve signs with contralateral motor/sensory deficits.

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🩻 Cerebral Venous System – Superficial, Deep & Dural Sinuses

Superficial & Deep Cerebral Veins ▼

Superficial Veins

Drain cerebral cortex and subcortical white matter
Empty mainly into superior sagittal sinus, transverse sinus
Bridging veins traverse subdural space → rupture → subdural hematoma, especially with atrophy/trauma

Deep Venous System

Internal cerebral veins: Drain deep structures (thalamus, basal ganglia, deep white matter)
Join to form the vein of Galen
Vein of Galen → straight sinus → transverse sinus

Dural Venous Sinuses & Clinical Correlates ▼

Major Dural Sinuses

Superior sagittal sinus: Along falx; drains superficial hemispheric veins
Inferior sagittal sinus → straight sinus: Deep midline structures
Transverse & sigmoid sinuses: Exit skull via jugular foramen → internal jugular vein
Cavernous sinus: On either side of sella; ICA + CN III, IV, V1, V2, VI inside/along walls

Cerebral Venous Sinus Thrombosis (CVST)

Risk factors: Hypercoagulable states, pregnancy/postpartum, OCPs, infection
Symptoms: Headache, papilledema, seizures, focal deficits
Superior sagittal sinus thrombosis: Bilateral parasagittal weakness, seizures, ↑ ICP
Lateral (transverse/sigmoid) sinus: Headache, cerebellar signs, raised ICP

Cavernous Sinus Thrombosis

Etiology: Often from facial/sinus infections
Clinical:
- Painful ophthalmoplegia (CN III, IV, VI involvement)
- Decreased corneal reflex (V1)
- Periorbital edema, proptosis
- Often bilateral due to intercavernous connections

💎 Board Pearl

Key venous patterns: • Elderly fall + gradual confusion = subdural (bridging veins).
• Young woman + headache + papilledema + seizure = suspect venous sinus thrombosis.

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