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Structured Approach to Localisation of Stroke

Based on Bradley and Daroff's Neurology in Clinical Practice and Localization in Clinical Neurology, 8e

STEP 1 - THE FUNDAMENTAL FRAMEWORK: TWO CIRCULATIONS

Before anything else, classify every stroke into one of two circulations. This single step halves your differential immediately.

	Anterior (Carotid) Circulation	Posterior (Vertebrobasilar) Circulation
Vessels	ICA, MCA, ACA, anterior choroidal, ophthalmic	Vertebral, basilar, PICA, AICA, SCA, PCA
Territory	Frontal, parietal, temporal (most), basal ganglia, internal capsule	Brainstem, cerebellum, occipital, inferior temporal, thalamus
Key clues	Language (left), neglect (right), arm > leg weakness, retinal symptoms	Diplopia, dysphagia, dysarthria, ataxia, crossed deficits, vertigo

STEP 2 - ANATOMICAL LEVEL: WHERE IN THE NEURAXIS?

Work systematically from cortex down. Each level has a signature.

Level 1 - Cerebral Cortex

Signature features:

Higher cortical functions affected (aphasia, apraxia, agnosia, neglect, hemineglect)
Cortical sensory loss (astereognosis, agraphesthesia, two-point discrimination impaired)
Contralateral homonymous visual field defect (if occipital or parietal-occipital involvement)
Jacksonian march or focal seizures may occur at onset
No "crossed" deficits (cranial nerve on one side + limb on the other)
Face + arm > leg weakness (MCA territory) OR leg > arm weakness (ACA territory)

Differentiating cortical from subcortical: Cortical strokes produce cortical signs (aphasia, neglect, agnosia). Pure motor or pure sensory deficits without cortical signs suggest subcortical or lacunar pathology.

Level 2 - Subcortical White Matter / Internal Capsule / Basal Ganglia

Signature features:

Pure motor hemiparesis (posterior limb of internal capsule): face + arm + leg equally affected
No cortical signs (no aphasia, no neglect, no visual field defect)
Lacunar syndromes dominate (see Step 4)
Homogeneous, equal weakness - the "capsular stroke" pattern
Striato-capsular infarction (proximal MCA lenticulostriate branches): large area, may have cortical signs if extensive

Level 3 - Brainstem

Signature features - the crossed deficit:

Ipsilateral cranial nerve palsy + contralateral limb weakness/sensory loss
This crossing pattern is pathognomonic of brainstem localization
Specific level determined by which cranial nerve is involved:
- CN III palsy → midbrain
- CN VI or VII palsy → pons
- CN IX, X, XII palsy → medulla

Other brainstem clues: Horner syndrome (any level), internuclear ophthalmoplegia (medial longitudinal fasciculus, pons), "one-and-a-half" syndrome (pons), bilateral limb signs, impaired consciousness with small lesions.

Level 4 - Cerebellum

Signature features:

Ipsilateral limb ataxia (cerebellar connections are ipsilateral)
Gait ataxia, truncal ataxia
Nystagmus (horizontal or direction-changing)
Dysarthria (scanning speech)
NO weakness, NO sensory loss (pure cerebellar lesion)
Vermis lesions: truncal ataxia, gait ataxia
Hemispheric lesions: ipsilateral limb dysmetria, dysdiadochokinesia
Beware: large cerebellar infarcts can cause obstructive hydrocephalus and herniation

STEP 3 - VASCULAR TERRITORY SYNDROMES: ANTERIOR CIRCULATION

3A - Middle Cerebral Artery (MCA) - Most Common Stroke Territory

Anatomy: MCA gives lenticulostriate branches (subcortical) and cortical branches (superior and inferior divisions).

Complete MCA Occlusion (main stem):

Contralateral hemiplegia (face + arm > leg)
Contralateral hemisensory loss
Contralateral homonymous hemianopia
Left MCA: Broca's aphasia (superior division) or Wernicke's aphasia (inferior division) or global aphasia (complete occlusion)
Right MCA: Hemispatial neglect, hemi-inattention, constructional apraxia, anosognosia (denial of deficit)
Gaze deviation toward the lesion (frontal eye field involvement)
Dysarthria

Superior Division MCA:

Broca's aphasia (left hemisphere): non-fluent, effortful speech, preserved comprehension
Contralateral face + arm weakness > leg
No homonymous hemianopia

Inferior Division MCA:

Wernicke's aphasia (left): fluent, paraphasic, impaired comprehension
Contralateral superior homonymous quadrantanopia ("pie in the sky")
Contralateral neglect (right hemisphere)

MCA Lenticulostriate (Subcortical):

Contralateral hemiparesis with little sensory involvement
Pure motor stroke (one cause) - see lacunar section
Striatocapsular infarction: hemiplegia, hypesthesia, visual field defect, transient aphasia

3B - Anterior Cerebral Artery (ACA)

Territory: Medial surface of the frontal and parietal lobes, anterior corpus callosum, anterior internal capsule.

Syndrome:

Contralateral leg > arm weakness (homunculus: leg is on the medial surface)
Contralateral leg > arm sensory loss
Gait apraxia, urinary incontinence (frontal lobe)
Bilateral ACA occlusion (rare): Akinetic mutism - patient lies with eyes open, follows visual stimuli but is mute and akinetic; caused by bilateral cingulate gyrus infarction
Transcortical motor aphasia (left ACA): non-fluent speech, preserved repetition (unlike Broca's)
Grasp reflex, snout reflex (frontal release signs)
Callosal disconnection syndrome (anterior corpus callosum): left hand apraxia, alien hand syndrome

3C - Anterior Choroidal Artery

Arises from the ICA just distal to the posterior communicating artery.

Classic triad (incomplete in most cases):

Contralateral hemiplegia (posterior limb, internal capsule)
Contralateral hemisensory loss (thalamus, posterior limb)
Contralateral homonymous hemianopia (lateral geniculate body, optic tract, retrolenticular internal capsule)

3D - Internal Carotid Artery (ICA)

Occlusion findings depend on collateral flow:

If good collaterals: may be silent
If poor collaterals: MCA + ACA territory infarction (massive hemispheric stroke)
Ipsilateral monocular visual loss (amaurosis fugax or permanent): ophthalmic artery involvement - this is a hallmark of ICA disease
Contralateral hemiplegia, hemisensory loss
Ipsilateral Horner syndrome (sympathetic fibers travel with ICA)

STEP 4 - LACUNAR SYNDROMES (Small Vessel / Penetrating Artery Occlusion)

Lacunar infarcts are small (< 15 mm), deep, caused by lipohyalinosis or microatheroma of penetrating arteries. Five classic syndromes:

Syndrome	Location	Features
Pure Motor Hemiplegia	Posterior limb internal capsule OR pons OR corona radiata	Face + arm + leg equal weakness, NO sensory, NO cortical signs - most common lacunar syndrome
Pure Sensory Stroke	Thalamus (ventral posterolateral nucleus)	Contralateral hemisensory loss all modalities, NO motor deficit; described by C.M. Fisher
Sensorimotor Stroke	Posterior limb internal capsule + thalamus, or thalamocapsular	Motor + sensory, no cortical signs
Ataxic Hemiparesis	Pons OR posterior limb internal capsule OR corona radiata	Ipsilateral cerebellar ataxia + contralateral hemiparesis, leg > arm; "homolateral ataxia and crural paresis"
Dysarthria-Clumsy Hand	Pons OR internal capsule genu	Dysarthria + facial weakness + contralateral hand clumsiness/weakness

Key principle: Lacunar syndromes have NO aphasia, NO visual field defect, NO cognitive change, NO hemineglect - absence of cortical signs with pure motor or sensory deficit points strongly to lacune.

STEP 5 - POSTERIOR CIRCULATION SYNDROMES

5A - Posterior Cerebral Artery (PCA)

Territory: Occipital cortex, inferior temporal lobe, thalamus (penetrating branches), midbrain.

Cortical PCA (P2 segment onwards):

Contralateral homonymous hemianopia - the signature finding; macular sparing common (macular cortex has MCA collaterals)
Left PCA: Alexia without agraphia (patient cannot read but can write - disconnection of visual cortex from language areas), anomic aphasia, visual agnosia
Right PCA: Prosopagnosia (failure to recognize faces), topographical disorientation
Bilateral PCA occlusion: Cortical blindness - patient is blind but denies it (Anton syndrome = cortical blindness + anosognosia); Balint syndrome (bilateral parieto-occipital) = optic ataxia + ocular apraxia + simultanagnosia

Penetrating PCA (thalamo-perforating branches):

Aphasia (left pulvinar involvement)
Global amnesia (bilateral hippocampal-parahippocampal)
Akinetic mutism
Dejerine-Roussy syndrome (thalamic pain syndrome): Contralateral sensory loss all modalities + severe contralateral dysesthesias/thalamic pain + vasomotor changes + transient hemiparesis + choreoathetoid movements; caused by thalamogeniculate branch occlusion

MRI showing PICA territory infarction with left lateral medullary infarct

T2-weighted MRI: posterolateral medullary infarct + small cerebellar infarct in PICA territory (Bradley and Daroff's Neurology)

5B - Thalamic Infarction Syndromes

The thalamus receives blood from 4 vascular regions:

Territory	Vessel	Syndrome
Posterolateral	Thalamogeniculate (P2 segment PCA)	Pure sensory stroke, sensorimotor stroke, Dejerine-Roussy syndrome
Anterior	Polar/tuberothalamic artery (posterior communicating)	Amnesia, confusion, personality change, aphasia (left), neglect (right)
Paramedian	Thalamo-perforating artery (P1 segment PCA)	Profound amnesia, vertical gaze palsy, somnolence; Bilateral = artery of Percheron occlusion: bilateral paramedian thalamic infarction with coma
Dorsal (pulvinar)	Posterior choroidal arteries	Language disturbance (left), neglect (right), visual field defects

Artery of Percheron: A single thalamoperforating artery arising from the P1 segment supplying both paramedian thalami. Occlusion causes bilateral thalamic infarction with coma or hypersomnolence, profound amnesia, and vertical gaze palsy - all without motor signs.

5C - Vertebrobasilar Territory - Brainstem Syndromes

The "Crossed Deficit" Rule:

Ipsilateral CN palsy + contralateral hemiplegia/hemisensory loss = brainstem lesion, level determined by CN involved.

MIDBRAIN (CN III, IV)

Weber Syndrome (ventral midbrain - cerebral peduncle):

Ipsilateral CN III palsy (ptosis, dilated pupil, "down and out" eye)
Contralateral hemiplegia

Benedikt Syndrome (tegmentum midbrain - red nucleus):

Ipsilateral CN III palsy
Contralateral tremor, ataxia, choreoathetosis (red nucleus involvement)

Parinaud Syndrome (dorsal midbrain - superior colliculus, pretectal area):

Upgaze palsy (vertical gaze paresis)
Convergence-retraction nystagmus on attempted upgaze
Light-near dissociation of pupils
Often from posterior thalamo-midbrain perforator or posterior circulation stroke

Claude Syndrome (combination of Benedikt + superior cerebellar peduncle):

CN III palsy + contralateral cerebellar ataxia

PONS (CN V, VI, VII)

Millard-Gubler Syndrome (ventral pons):

Ipsilateral CN VI palsy (lateral gaze palsy, diplopia)
Ipsilateral CN VII palsy (lower motor neuron facial weakness)
Contralateral hemiplegia

Foville Syndrome (tegmental pons, PPRF + CN VI nucleus):

Ipsilateral horizontal gaze palsy (eyes deviate away from lesion - in cortical stroke eyes deviate toward lesion)
Ipsilateral CN VII palsy
Contralateral hemiplegia
Key diagnostic point: In pontine strokes, gaze deviation is away from the lesion (PPRF destroyed); in cortical/hemispheric strokes, gaze deviation is toward the lesion (FEF pushes eyes to the opposite side)

One-and-a-Half Syndrome (paramedian pons - PPRF + MLF):

Ipsilateral gaze palsy (PPRF/CN VI nucleus lesion)
Ipsilateral internuclear ophthalmoplegia (MLF lesion)
Net result: only the contralateral eye can abduct; all other horizontal movements are lost

Locked-In Syndrome (bilateral ventral pons - bilateral corticospinal and corticobulbar tracts):

Complete quadriplegia and anarthria
Preserved consciousness, preserved vertical eye movements (RIMLF spared)
Patient communicates only by blinking or vertical eye movements

MEDULLA (CN IX, X, XI, XII)

Lateral Medullary Syndrome (Wallenberg Syndrome) - PICA or vertebral artery occlusion:

This is the most clinically important posterior circulation syndrome. Caused by occlusion of the PICA or vertebral artery, producing an infarct in the posterolateral medulla.

Structure damaged	Feature
Spinothalamic tract	Contralateral loss of pain and temperature (limbs and trunk)
Descending trigeminal nucleus	Ipsilateral facial loss of pain and temperature
Vestibular nuclei	Vertigo, nausea, vomiting, nystagmus
Nucleus ambiguus (CN IX, X)	Ipsilateral palatal palsy, dysarthria, dysphagia, hoarseness
Descending sympathetic fibers	Ipsilateral Horner syndrome (ptosis, miosis, anhidrosis)
Inferior cerebellar peduncle / cerebellum	Ipsilateral limb and gait ataxia
Solitary nucleus / dorsal vagal nucleus	Hiccups

Classic "crossed sensory deficit": Ipsilateral face loss of pain/temperature + contralateral body loss of pain/temperature (thermoanalgesia). Motor power is characteristically SPARED (corticospinal tracts are in the ventral medulla, not affected in lateral medullary syndrome).

Medial Medullary Syndrome (Dejerine's Anterior Bulbar Syndrome) - ASA or vertebral artery branch:

Structure	Feature
Corticospinal tract (pyramids)	Contralateral hemiplegia (spares face)
Medial lemniscus	Contralateral loss of discriminative touch, vibration, proprioception
CN XII (hypoglossal nerve)	Ipsilateral tongue weakness/atrophy (tongue deviates toward lesion)

5D - Cerebellar Artery Territories

Artery	Territory	Key Syndrome
PICA (Posterior Inferior Cerebellar Artery)	Posteroinferior cerebellum + lateral medulla	Wallenberg syndrome (lateral medullary); cerebellar infarct causing vertigo, ataxia, possible obstructive hydrocephalus
AICA (Anterior Inferior Cerebellar Artery)	Anteroinferior cerebellum + lateral caudal pons	Ipsilateral CN VII + VIII involvement (facial palsy + deafness + tinnitus) + lateral pontine syndrome + ipsilateral Horner; AICA infarct should be suspected when lateral pontine features accompany hearing loss
SCA (Superior Cerebellar Artery)	Superior cerebellum + lateral rostral pons	Ipsilateral cerebellar ataxia (severe), ipsilateral Horner, ipsilateral CN IV palsy, contralateral hemisensory loss (spinothalamic), ipsilateral CN V partial deficit; contralateral loss of pain/temperature

STEP 6 - SPECIAL LOCALIZING CLUES: CLINICAL PEARLS

Visual Field Defects - Localizing Value

Defect	Localization
Monocular blindness	Retina or optic nerve (ipsilateral) - anterior to chiasm
Bitemporal hemianopia	Optic chiasm
Contralateral homonymous hemianopia	Optic tract, LGN, optic radiation, occipital cortex
Superior quadrantanopia ("pie in sky")	Inferior optic radiation, temporal lobe (Meyer's loop)
Inferior quadrantanopia ("pie in floor")	Superior optic radiation, parietal lobe
Macular-sparing hemianopia	Occipital cortex (MCA/PCA boundary zone at occipital pole)

Gaze Deviation Lateralizing Rule

Gaze deviation	Meaning
Eyes deviate TOWARD the hemiplegia side	Cortical/hemispheric stroke (FEF pushes eyes to the opposite hemisphere's territory, i.e., away from lesion, but patient presents with eyes toward ipsilateral side to lesion) - eyes look "away" from the hemiplegic limbs but "toward" the lesion
Eyes deviate AWAY from hemiplegia	Pontine stroke (PPRF destroyed; contralateral PPRF pulls eyes to that side)

Practical rule: "The eyes look toward a cortical stroke and away from a pontine stroke."

Language as a Lateralizing Tool (Left Hemisphere = Dominant in 90%)

Aphasia Type	Localization	Key Features
Broca's (expressive)	Left inferior frontal (Broca's area, BA44/45), superior MCA division	Non-fluent, telegraphic, effortful; comprehension intact; patient aware of deficit
Wernicke's (receptive)	Left posterior superior temporal (BA 22), inferior MCA division	Fluent, paraphasic, neologisms; comprehension severely impaired; patient unaware
Global	Large left hemisphere (Broca + Wernicke areas both)	Non-fluent + poor comprehension + poor repetition
Conduction	Left arcuate fasciculus (connects Broca and Wernicke)	Fluent, good comprehension, severely impaired repetition; paraphasic errors
Transcortical Motor	Left frontal (ACA territory, anterior to Broca's)	Non-fluent, but repetition preserved (unlike Broca's)
Transcortical Sensory	Left parieto-occipital (posterior watershed)	Fluent, poor comprehension, repetition preserved (echolalia)
Alexia without agraphia	Left PCA territory (left occipital cortex + splenium of corpus callosum)	Cannot read, can write; disconnects right visual cortex from language areas

Hemispatial Neglect

Right hemisphere (usually right parietal or frontoparietal) causes left hemispatial neglect
Patient ignores left side of space, left side of body
Line bisection test: bisects to the right of midline
Much more severe and persistent with right hemispheric strokes than left

Horner Syndrome Localizing Value in Stroke Context

Central Horner (hypothalamus to ciliospinal center of Budge, C8-T2): Any stroke affecting the lateral hypothalamus, lateral brainstem (especially lateral medullary), or cervical cord
In posterior circulation stroke: Ipsilateral Horner + ipsilateral ataxia + ipsilateral CN palsy = lateral brainstem involvement
Horner syndrome without anhidrosis suggests post-ganglionic; with anhidrosis (face and body) suggests pre-ganglionic or central

STEP 7 - CORTICAL vs. SUBCORTICAL vs. BRAINSTEM DIFFERENTIATION TABLE

Feature	Cortical	Subcortical/Lacunar	Brainstem	Cerebellar
Aphasia	YES (left)	NO	NO (except peduncle lesions)	NO
Neglect	YES (right)	NO	NO	NO
Visual field defect	YES (hemianopia)	NO (unless thalamocapsular)	YES (rare cortical blindness)	NO
Face + arm + leg equal weakness	Rarely	YES (capsular)	YES (with CN palsy)	NO
Crossed deficits	NO	NO	YES - hallmark	NO
Cerebellar signs	NO	NO	Possible (peduncle)	YES (ipsilateral)
Consciousness affected	If large	Rarely	YES if basilar	Late (herniation)
Seizures at onset	Possible	Rare	NO	NO

STEP 8 - THE OCSP (OXFORD/BAMFORD) CLINICAL CLASSIFICATION

A practical bedside classification requiring no imaging:

Category	Criteria	Vascular Territory
TACI - Total Anterior Circulation Infarct	All 3: motor/sensory deficit + cortical sign + homonymous hemianopia	Complete MCA or ICA territory
PACI - Partial Anterior Circulation Infarct	2 of 3 above, or cortical sign alone	MCA branch territory
LACI - Lacunar Infarct	Pure motor, pure sensory, sensorimotor, or ataxic hemiparesis; NO cortical signs	Small perforating artery
POCI - Posterior Circulation Infarct	Any of: brainstem, cerebellar, bilateral motor/sensory, crossed deficit, isolated hemianopia	Vertebrobasilar

Clinical utility: TACI has worst prognosis (60% dead or dependent at 1 year); LACI best (10-15% dead or dependent). OCSP classification predicts functional outcome, etiology, and recurrence risk.

STEP 9 - INTEGRATING THE APPROACH - BEDSIDE ALGORITHM

SUDDEN FOCAL DEFICIT
        ↓
1. CORTICAL SIGNS? (aphasia, neglect, visual agnosia, cortical sensory loss)
   YES → Cortical involvement → Anterior (MCA/ACA/PCA) or large vessel
   NO  → Subcortical / brainstem / cerebellum
        ↓
2. CROSSED DEFICIT? (ipsilateral CN + contralateral limb)
   YES → BRAINSTEM (identify CN → level: III=midbrain, VI/VII=pons, IX/X/XII=medulla)
   NO  → Not brainstem
        ↓
3. CEREBELLAR SIGNS WITHOUT WEAKNESS?
   YES → Cerebellar (identify artery by co-features: PICA=lateral medulla, AICA=hearing, SCA=high ataxia)
   NO  → Continue
        ↓
4. PURE MOTOR / PURE SENSORY / ATAXIC HEMIPARESIS?
   YES → LACUNAR - no cortical signs confirm
   NO  → Continue
        ↓
5. VISUAL FIELD DEFECT?
   Hemianopia + language → MCA (left) or PCA (left or right)
   Hemianopia alone, macular sparing → PCA
   Monocular → Retinal / optic nerve (carotid territory)
        ↓
6. ARM > LEG WEAKNESS → MCA
   LEG > ARM WEAKNESS → ACA
   Equal face + arm + leg → Internal capsule / pons

STEP 10 - IMAGING CORRELATION

Syndrome	Expected Imaging Finding
MCA territory	CT: wedge hypodensity frontal-parietal-temporal; loss of insular ribbon; MRI DWI: bright cortical + subcortical
Lacunar	CT: small deep hypodensity (often missed acutely); MRI: small DWI-bright lesion < 15mm in basal ganglia, capsule, pons, thalamus
PCA	CT: occipital hypodensity; MRI DWI: occipital, thalamic, and hippocampal involvement
Lateral medullary (Wallenberg)	CT: often normal; MRI T2/DWI: posterolateral medullary hyperintensity; may see vertebral/PICA poor flow void
Basilar artery occlusion	CT: "dense basilar" sign; CT angiography: cut-off at basilar; MRI: bilateral pontine, thalamic, occipital DWI changes
Artery of Percheron	MRI: butterfly-shaped bilateral paramedian thalamic DWI lesion; may see mesencephalic involvement

SUMMARY MEMORY AID

MCA (left): Aphasia + contralateral face/arm hemiplegia + hemianopia
MCA (right): Neglect + anosognosia + contralateral hemiplegia
ACA: Leg > arm + frontal release signs + akinetic mutism (bilateral)
PCA: Hemianopia (macular sparing) + alexia without agraphia (left) + thalamic pain
Lacune: Pure motor / pure sensory / sensorimotor / ataxic hemiparesis - NO cortical signs
Wallenberg: Crossed sensory (ipsilateral face / contralateral body) + Horner + dysphagia + ataxia + NO motor weakness
Medial medulla: Contralateral hemiplegia (spares face) + contralateral dorsal column loss + ipsilateral tongue palsy
Pons (ventral): Locked-in / one-and-a-half / eyes deviate away from lesion
Midbrain: CN III palsy + contralateral hemiplegia (Weber) or tremor (Benedikt)
Thalamus (paramedian, bilateral): Artery of Percheron → coma + amnesia + vertical gaze palsy - NO motor deficit

Sources: Bradley and Daroff's Neurology in Clinical Practice; Localization in Clinical Neurology, 8e (Brazis et al.)

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