Neuroanatomy for Radiologists

Cerebral Hemispheres & Lobes - Brainy Bits & Bobs

• Two hemispheres (L/R), linked by Corpus Callosum.
• Key Sulci: Central Sulcus (Rolandic), Lateral Fissure (Sylvian).
• Lobes (F-POTI): 📌 Frontal, Parietal, Occipital, Temporal, Insula.
  • Frontal: Motor control, executive function, Broca's area (expressive speech).
  • Parietal: Somatosensory input, spatial awareness, part of Wernicke's area.
  • Temporal: Auditory processing, memory, olfaction, Wernicke's area (receptive speech).
  • Occipital: Vision.
  • Insula: Deep lobe; autonomic control, emotion, interoception.

⭐ The Central Sulcus separates the Frontal Lobe (containing precentral gyrus/motor cortex) from the Parietal Lobe (containing postcentral gyrus/somatosensory cortex).

Ventricular System & CSF Pathways - Fluid Highways

• Network of four CSF-filled cavities: Two Lateral Ventricles, Third Ventricle, Fourth Ventricle.

• CSF Production: Primarily by choroid plexus in lateral & third ventricles. Rate: ~20 mL/hr (total 400-500 mL/day). Normal volume: 125-150 mL.

• CSF Circulation Pathway:

• CSF Absorption: Via arachnoid granulations into dural venous sinuses, mainly Superior Sagittal Sinus.

• 📌 Foramina: Luschka = Lateral; Magendie = Median.

⭐ The Aqueduct of Sylvius, being the narrowest segment, is a critical chokepoint; its obstruction is a common cause of non-communicating hydrocephalus.

Brainstem & Cerebellum - Control Central Hub

• Brainstem: Midbrain, Pons, Medulla. Relay station; CN nuclei (III-XII).
  • Midbrain: CN III, IV. Cerebral peduncles, tectum, substantia nigra.
  • Pons: CN V-VIII. Middle cerebellar peduncles (MCPs), basilar artery.
  • Medulla: CN IX-XII. Pyramids, olives. Vital centers (cardiac, respiratory).
• Cerebellum: Vermis, hemispheres. Coordination, balance, motor learning.
  • Peduncles (SCP, MCP, ICP) connect to brainstem segments.
  • Common lesions: Infarcts, tumors (medulloblastoma, astrocytoma).

⭐ Posterior Inferior Cerebellar Artery (PICA) infarct causes Wallenberg (Lateral Medullary) Syndrome.

Cerebral Vasculature - Brain's Blood Lines

• Circle of Willis: Key arterial anastomosis at brain's base ensuring collateral flow.
  • Formed by: Internal Carotid Arteries (ICAs) & Vertebral arteries (via Basilar artery).
  • Components: AComA, PComAs, ACAs (A1 segments), PCAs (P1 segments), ICA termini.
• Major Arterial Territories:
  • ACA (Anterior Cerebral Artery): Medial cerebral hemispheres (frontal, parietal lobes). Contralateral leg > arm motor/sensory loss.
  • MCA (Middle Cerebral Artery): Lateral hemispheres, insula, parts of temporal/parietal lobes. Contralateral arm/face > leg weakness, aphasia (dominant), neglect (non-dominant).

    ⭐ The MCA is the most frequently occluded artery in stroke.

  • PCA (Posterior Cerebral Artery): Occipital lobes, medial temporal lobes, thalamus. Contralateral homonymous hemianopia.
• Dural Venous Sinuses: Collect venous blood, drain into Internal Jugular Veins (IJVs).
  • Major sinuses: Superior Sagittal, Transverse, Sigmoid Sinuses.

Key Sulci, Gyri & Tracts - Navigating Brain Folds

• Landmark Sulci (Fissures):
  • Central Sulcus (Rolandic): Divides frontal (motor) & parietal (sensory) lobes.
  • Sylvian Fissure (Lateral): Separates temporal from frontal & parietal; houses MCA.
  • Parieto-occipital Sulcus: Medial; separates parietal & occipital lobes.
  • Calcarine Sulcus: Medial occipital; primary visual cortex.
• Functionally Critical Gyri:
  • Precentral Gyrus: Primary motor cortex.
  • Postcentral Gyrus: Primary somatosensory cortex.
  • Superior Temporal Gyrus: Auditory cortex, Wernicke's area.
• Major White Matter Tracts:
  • Corticospinal Tract: Descending motor pathway.
  • Corpus Callosum: Largest commissure; connects hemispheres.
  • Arcuate Fasciculus: Connects Broca's & Wernicke's areas.

⭐ The genu of the corpus callosum connects frontal lobes; the splenium connects occipital/temporal lobes. Lesions cause specific disconnection syndromes.

High‑Yield Points - ⚡ Biggest Takeaways

• Circle of Willis: Note common variants; PCOM/ACOM are key aneurysm sites.
• MCA territory infarcts: Most frequent; affect motor, sensory, language.
• Basal ganglia: Caudate, putamen, globus pallidus; recognize calcification/signal changes.
• CSF flow: Obstruction causes hydrocephalus; aqueductal stenosis is a key cause.
• Cranial nerves: Know pathways & foramina; CN III palsy links to PCOM aneurysm.
• Dural venous sinus thrombosis: Look for empty delta sign or dense clot.
• Key sulci/gyri: Central sulcus, Sylvian fissure, pre/postcentral gyri are vital landmarks.