Cross-sectional Anatomy: Brain and Head

Axial Brain Anatomy (CT/MRI) - Slice & Dice Insights

• Supratentorial Structures:
  • Lobes: Frontal, parietal, temporal, occipital.
  • Basal ganglia: Caudate, putamen, globus pallidus.
  • Thalamus, internal capsule.
  • Ventricles: Lateral, third.
• Infratentorial Structures:
  • Cerebellum, brainstem (midbrain, pons, medulla).
  • Fourth ventricle.
• Density/Intensity:
  • CT: Grey (hyperdense) vs. White (hypodense).
  • MRI T1: White (hyperintense), Grey (hypointense).
  • MRI T2/FLAIR: Grey (hyperintense), White (hypointense).

⭐ Internal Capsule: Posterior limb is a common site for lacunar infarcts, causing pure motor hemiparesis.

Coronal & Sagittal Brain Anatomy - Profile & Portrait Views

• Coronal (Frontal/Portrait View): Slices brain from front to back.
  • Visualizes: Cerebral hemispheres, ventricles (frontal horns, bodies), basal ganglia, hippocampus, temporal lobes.
  • Key for: Pituitary gland, cavernous sinuses, temporal lobe epilepsy assessment.
• Sagittal (Lateral/Profile View): Slices brain from side to side.
  • Mid-sagittal: Corpus callosum, brainstem, cerebellum, pituitary stalk, 3rd/4th ventricles.
  • Parasagittal: Shows structures lateral to midline.

⭐ The "empty sella sign" on sagittal MRI, where the sella turcica appears filled with CSF, can be a normal variant or indicate intracranial hypertension or pituitary atrophy.

Ventricular System & Cisterns - Brain's Fluid Network

• Ventricular Pathway (CSF Flow):

  • Lateral Ventricles (paired) → Foramina of Monro
  • → Third Ventricle → Cerebral Aqueduct (of Sylvius)
  • → Fourth Ventricle → Foramina of Luschka (2 lateral) & Magendie (1 medial)
  • → Subarachnoid Space (cisterns & over convexities) → Arachnoid granulations

• Key Cisterns (CSF Pools):

  • Suprasellar: Contains optic chiasm, Circle of Willis.
  • Interpeduncular: Between cerebral peduncles, anterior to midbrain.
  • Quadrigeminal: Posterior to midbrain; contains great cerebral vein of Galen, pineal gland.
  • Cisterna Magna (Cerebellomedullary): Largest; beneath cerebellum, posterior to medulla.
  • Cerebellopontine Angle (CPA): Houses CN VII & VIII.

⭐ Effacement of the perimesencephalic cisterns (e.g., ambient, quadrigeminal) can be an early sign of transtentorial herniation; crucial to identify on imaging!

Cerebral & Cerebellar Vasculature - Brain's Blood Flow

• Arterial Supply:

  • Circle of Willis: Anastomotic polygon at brain base; ensures collateral flow.

  • Major Arteries & Territories:

    • ACA: Medial cortex (frontal, parietal); leg-foot motor/sensory.
    • MCA: Lateral cortex; Broca's, Wernicke's; face-arm motor/sensory.
    • PCA: Occipital lobe (vision); thalamus, midbrain.

  • Cerebellar Arteries: PICA, AICA, SCA (from vertebrobasilar). 📌 PICA AIN'T SCARED (Posterior Inferior, Anterior Inferior, Superior Cerebellar Arteries).

• Venous Drainage:
  • Superficial veins → Superior Sagittal Sinus (SSS).
  • Deep veins (Int. Cerebral V., Great Vein of Galen) → Straight Sinus.
  • Dural Sinuses (SSS, Straight, Transverse, Sigmoid) → Internal Jugular V. (IJV).

⭐ MCA territory infarcts are most common, often affecting speech (aphasia) and contralateral face/arm motor/sensory function.

Skull Base, Sinuses & Orbits - Head's Bony Framework

• Skull Base Foramina (Key):
  • Cribriform Plate: CN I
  • Optic Canal: CN II, Ophthalmic A.
  • Foramen Ovale: CN V3 (Mandibular)
  • Jugular Foramen: CN IX, X, XI, IJV
• Paranasal Sinuses (PNS): 📌 FESM (Frontal, Ethmoid, Sphenoid, Maxillary).
  • Drain via meati; Osteomeatal Complex (OMC) vital for drainage.
• Orbits: 7 bones (📌 "My Friendly Zebra Likes Eating Salty Peanuts": Maxilla, Frontal, Zygomatic, Lacrimal, Ethmoid, Sphenoid, Palatine).
  • Contents: Globe, Extraocular Muscles (EOMs), CN II-VI.
• Mastoids: Air cells in temporal bone; risk of mastoiditis.

⭐ The sphenoid sinus provides a common surgical corridor to the pituitary gland (transsphenoidal approach).

High‑Yield Points - ⚡ Biggest Takeaways

• Internal Capsule: Identify anterior limb, genu (corticobulbar), and posterior limb (corticospinal tracts).
• Circle of Willis: ACoA & PCoA are frequent sites for berry aneurysms.
• Ventricular Obstruction: Aqueduct of Sylvius stenosis is a key cause of non-communicating hydrocephalus.
• Basal Ganglia: Caudate atrophy (Huntington's), putaminal changes (Wilson's disease, CO poisoning).
• Vascular Territories: MCA infarcts are most common; distinguish ACA (leg weakness) & PCA (hemianopia) strokes.
• Cavernous Sinus: Houses CN III, IV, V1, V2, VI and ICA; susceptible to thrombosis/tumors.