Neuroanatomy of Stroke: Vascular Territories & Syndromes

• These notes summarize the clinical neuroanatomy of stroke, focusing on vascular territories involved, specific stroke syndromes, and diagnostic imaging.

Classification of Stroke by Vascular Territory

• Anterior Circulation Stroke (Carotid System): Includes involvement of the MCA (Middle Cerebral Artery), ACA (Anterior Cerebral Artery), and ICA (Internal Carotid Artery).
• Posterior Circulation Stroke (Vertebrobasilar System): Involves the PCA (Posterior Cerebral Artery) and PICA (Posterior Inferior Cerebellar Artery).

Anterior Circulation Stroke - MCA Obstruction

• The superior division M2/M3, a right-side lesion, causes left hemiparesis predominantly affecting the upper limb and face more than the lower limb
• Right hemisensory deficit is also observed in the upper limb and face
• Cortical sensory signs are present
• Left sensory inattention/hemineglect can occur, along with right gaze preference.
• If the inferior division M2/M3 is damaged on the right side, it can cause left hemianopia.
• Sensory association areas include left cortical sensory signs impacting the upper limb and face more than the lower limb, and sensory inattention/hemineglect
• M1 blockage impacts all of the above internal capsule and genu, it results total contralateral hemiplegia + lower facial UMN paralysis, upper limb = face = lower limb

Why UL/Face > LL in MCA Strokes

• The upper limb and face areas in the brain converge via the corona radiata.
• Infarction in the MCA territory directly affects these areas.
• Oedema can secondarily affect lower limb neurons.

Sub-Cortical - Lacunar Infarcts

• Lacunar infarcts occur in subcortical areas, including the internal capsule, thalamus, midbrain, and pons.
• Results from small vessel disease affecting perforating branches of cerebral arteries, such as the lenticulostriate and pontine arteries
• Lesions are smaller than 2cm and located in deep grey and white matter.
• Lacunar syndromes include pure motor stroke. It effects the posterior limb/brainstem, resulting in pure motor stroke.
• Pure sensory stroke is derived from the sensory fibbers in thalamus/IC- Pure sensory stroke.
• The genu of internal capsule and adjacent posterior limb/cerebral peduncle cause dysarthria and clumsiness, and the midbrain/pons results in ataxic hemiparesis.

CT Appearance of Infarcts

• Non-contrast CT scans are commonly used in acute stroke to exclude hemorrhagic stroke.
• Hemorrhagic strokes appear white (hyperdense) on CT, while water, fat, and air appear black (hypodense).
• Infarcts lead to accumulation of water in brain tissue (oedema), resulting in a loss of grey-white matter differentiation
• Appearance of hypodensity may take several hours after stroke onset.
• Thrombus or embolus may appear as a hyperdense shadow inside a vessel.

Anterior Circulation Stroke - ACA Obstruction

• A2 territory strokes result in contralateral weakness and sensory deficits affecting the lower limb more than the upper limb and face
• It causes urinary incontinence.

Why LL > UL/Face in ACA Strokes

• The lower limb territory is primarily affected in ACA strokes.
• These strokes often lead to a condition where the patient can't walk but hand function is preserved.

Stroke & Incontinence

• Micturition is initiated by the detrusor reflex regulated by the pontine micturition center, which coordinates detrusor contraction and internal sphincter relaxation.
• Frontal micturition controls PMC and spinal reflexes
• Bilateral lesions of the medial frontal micturition center may cause urinary incontinence by disinhibiting pontine and spinal micturition centers.
• Unilateral lesions may lead to transient urinary incontinence.

Obstruction of Internal Carotid

• Complete obstruction leads to extensive infarct involving the ACA and MCA territories/cortical
• Symptoms may include contralateral hemiparesis involving the face, upper limb, and lower limb
• Similar to an internal capsule lesions

Posterior Circulation Stroke - PCA Obstruction

• Lesions in the region cause stroke in the distal P2 and proximal PCA
• Distal P2 Occlusion affects the occipital cortex causing contralateral homonymous hemianopia with macular sparing
• Proximal PCA occlusion affects the midbrain causing crossed hemiparesis/hemisensory loss
• Damage causes ipsilateral CN III palsy with contralateral long tract involvement

Brainstem CVD

• Lesions typically affect multiple structures, including cranial nerve nuclei and long tracts.
• Unilateral lesions affect ipsilateral cranial nerves at the level of the lesion and long tracts carrying sensory and motor signals
• They can cause ipsilateral cranial nerve palsy and contralateral long tract signs such as crossed hemiparesis or crossed hemisensory loss.
• Altered consciousness and vomiting commonly occur with reticular formation/vestibular nuclei involvement.

Brainstem Lesions - Rule of 4

• Rule used to diagnose brain stem strokes
• Four cranial nerves located above the pons
• Four structures in the midline beginning with M: motor pathway, motor nuclei, medial lemniscus, medial longitudinal fasciculus.
• Four structures to the side, or lateral: spinocerebellar pathway, spinothalamic pathway, spinal nucleus of the 5th cranial nerve.
• Four motor nuclei in the midline are affected by three, four, six, and twelve motors.

Examples of Brainstem Stroke Syndromes

• Weber's Syndrome involves the anterior midbrain which has an ipsilateral (IL) oculomotor nerve palsy, contralateral (CL) lower facial palsy + contralateral spastic UL and LL paresis
• Medial Pontine Syndrome has lesion 1, which causes the inability to abduct the left eye + right spastic UL and LL weakness.
• It can also has lesion 2: left sided hemi facial paralysis + inability to abduct the left eye + right spastic UL and LL weakness.

Medial Medullary Syndrome

• Injuries impacts the cranial nerves, hypoglossal nerve, and DCML causing deviation of tongue to ipsilateral side on protrusion + Ipsilateral wasting and fasciculations
• Injuries impacts the Pyramid resulting in contralateral spastic paresis of UL and LL.

Lateral Medullary (Wallenberg) Syndrome

• Vertigo, vomiting, and nystagmus are common.
• Ipsilateral pharyngeal, palatal, laryngeal muscle paralysis
• Effects include contralateral pain temp
• Damage can cause Iipsilateral Horner's Syndrome and ipsilateral cerebellar signs

Summary Presentation of Anterior vs Posterior Circulation Stroke

• Anterior circulation stroke includes Hemiparesis and Hemisensory loss
• MCA cortical infarct – Face & Arm > Leg if cortical
• ACA cortical infarct - Leg> Face & Arm if cortical
• Internal capsule infarct is a dense hemiplegia (UL=LL=Face)
• Can also cause Hemianopia/Qudrantonopia
• Aphasias/Sensory inattention/Hemineglect/ and Ipsilateral gaze preference
• Posterior Circulation stroke often has Contralateral Crossed Hemiparesis & Hemisensory loss,
• Cranial nerve palsy signs and Hemianopia.
• Can also have Cerebellar signs - Ataxia/Nystagmus

Collateral Circulation in Brain

• Primary Collateral Circulation:
  • Circle of Willis supports A2, P2
  • but does NOT support MCA occlusions
• Secondary Collateral circulation found in Cortical branches & ICA and ECA, Ophthalmic & Superficial temporal arteries; Cerebral As & Meningeal, Occipital As
• Penetrating branches generally lack collaterals

Conditions from Stroke

• Artherosclerosis- plaque build ups
• Embolism - clot from body travels and gets lodged
• SAH - bleeding between the brain and the arachnoid layers

Sub Arachnoid Haemorrhage (Non-traumatic)

• Bleeding into the subarachnoid space
• Caused by rupture of Berry aneurysms
• Signs & Symptoms include
  • Small bleeds cause diluted in CSF
  • Large bleeds causes blood in CSF causing cerebral vessel irritation causing
  • Severe sudden headache
  • Altered/loss of consciousness
  • Nausea/vomiting
  • Neck stiffness
  • Kernig sign
  • Seizures

Meningeal Irritation

• Neck stiffness derived from passive neck flexion
• Kernig Sign: supine patient with hips and knees flexed, passive extension of the knee results in stimulation of nerve roots.
• Brudzinski's sign is flexion of knees when neck is flexed

SAH – Complications & Ix

• Global cerebral ischaemia – due to cerebral vasospasm
• Hydrocephalus – Obstructive hydrocephalus is derive from blood clots
• Conditions can cause Raised intracranial pressure which can lead to Cerebral herniation & Death
• Negative CT & still high suspicion may be the cause

Intracerebral Haemorrhage

• Is when blood vessel rupture occurs in the brain parenchyma
• Is causes by blood traps with disrupt neurological functions (amyloid vasculopathy)
• Is cause a pressure effect
• May cause expanded hemorrhage which can act as mass
• Ischemia causes Increased intracranial pressure causing the Cerebral herniation