Head            

ARTERY & VEINS

Discuss the anatomy of the Middle Cerebral Artery and variants (30 marks)

• Larger, lateral terminal branch of supraclinoid ICA

4x SEGMENTS OF MCA

1. Horizontal (M1) segment (ICA bifurcation —> MCA bifurcation and termination at Sylvian fissure)

• Origin: terminal ICA bifurcation
• Lies lateral to optic chiasm, behind olfactory trigone
• Courses laterally under anterior perforated substance
• Usually bi- or trifurcates just before Sylvian fissure
• Termination: Post bifurcation trunks enter Sylvian fissure then turn upwards in a gentle curve (MCA “genu”)
• **Has 2 branches**
• 5-15x Perforating branches (medial and lateral lenticulostriate arteries)
  • medial lenticulostriate supply = internal capsule, caudate nucleus, medial basal ganglia
  • lateral lenticulostriate supply = lentiform nucleus, caudate, claustrum, external capsule
• anterior temporal artery
  • supply anterior temporal lobe

2. Insular (M2) segments (Terminates: apex of Sylvian fissure)

• Runs deep in Sylvian fissure and along insular – superior and inferior divisions
• 6-8x “stem” arteries arise from post bifurcation trunks, course superiorly within Sylvian fissure, ramify over the surface of insula
• Termination: top of Sylvian fissure = “top loops of M2 segment delineate apex of Sylvian fissure” = “angular artery with Sylvian point”
• No branches

3. Opercula (M3) segments (Terminates: exit Sylvian fissure)

• Origin: top of sylvian fissure, course inferolateral through sylvian fissure
• Termination: Exit sylvian fissure at surface of brain
• No branches

4. Cortical (M4) segments

• Exit Sylvian fissure and ramify over lateral surface of hemisphere
• **Has 11 branches**

Cortical branches (M4 segments) (from inferior to superior to posterior)

• Orbitofrontal (lateral frontobasal) artery
• Prefrontal arteries

• Precentral (prerolandic) artery – Runs between precentral and central sulci
• Central sulcus (rolandic) artery – Runs within central (rolandic) sulcus
• Postcentral sulcus (anterior parietal) artery – Runs in postcentral, then intraparietal sulcus

• Posterior parietal artery
  • Exits posterior end of sylvian fissure
  • Runs posterosuperiorly along supramarginal gyrus

• Angular artery (most posterior)
  • Most posterior branch exiting sylvian fissure
  • Runs posterosuperiorly over transverse temporal gyrus
• Temporooccipital artery
  • Runs posteroinferiorly in superior temporal sulcus
• Posterior temporal artery –
  • Extend inferiorly from sylvian fissure
  • Cross superior, middle temporal gyri
• Middle temporal artery
• Anterior temporal artery

VASCULAR TERRITORY

Cortical branches

• Considerable variation in the territory of individual branches
• Most common pattern
  • Supply most of lateral surface of cerebral hemispheres except for superior convexity (ACA) and inferior temporal gyrus
  • Anterior tip of temporal lobe (variable)

Penetrating branches

• Medial lenticulostriate arteries (a few arise from proximal MCA)
  • Medial basal ganglia, caudate nucleus
  • Internal capsule
• Lateral lenticulostriate arteries
  • Lateral putamen, caudate nucleus
  • External capsule

VARIANTS

• High variability in branching patterns
• “Early” MCA bi- or trifurcation (within 1 cm of origin)
• Anterior choroidal coming from M1
• True anomalies (hypoplasia, aplasia) rare
• MCA duplication seen in 1-3% of cases (comes off ICA)
  • Large branch arises from distal ICA just prior to terminal bifurcation
  • Parallels main M1
• Accessory MCA (comes off ACA)
  • Arises from anterior cerebral artery A1 proximal or distal
  • High association with saccular aneurysm
• Fenestrated MCA