Cranial Cavity

Cranial Cavity: Overview - Skull's Inner Sanctum

• Space within the skull (neurocranium); houses the brain & associated structures.
• Boundaries:
  • Superiorly: Calvaria (skullcap).
  • Inferiorly: Skull base (cranial fossae).
• Contents: Brain, meninges (dura, arachnoid, pia mater), CSF, cranial nerves, blood vessels.
• Lined by endosteal layer of dura mater.

⭐ The cranial cavity has an average volume of 1200-1700 cm³; slightly less in females than males. It protects the brain, its primary occupant, from mechanical injury. The rigid skull, however, means any increase in intracranial volume (e.g., hematoma, tumor, edema) can rapidly ↑ intracranial pressure (ICP).

Cranial Fossae: Foramina & Contents - Tri-Level Terraces

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Dura Mater & Venous Sinuses - Brain's Protective Wraps

• Dura Mater: Tough, 2-layered (periosteal, meningeal) outermost meninx.
• Dural Folds:
  • Falx Cerebri: In interhemispheric fissure.
  • Tentorium Cerebelli: Cerebrum/Cerebellum separator.
  • Falx Cerebelli: Between cerebellar hemispheres.
  • Diaphragma Sellae: Roofs pituitary fossa.
• Innervation: CN V (V1, V2, V3), CN X, C1-C3.
• Blood Supply: Middle Meningeal Artery (extradural hematoma risk). and major dural venous sinuses)
• Dural Venous Sinuses: Valveless channels between dural layers.
  • Drain to Internal Jugular Vein.
  • Unpaired: Superior Sagittal (SSS), Inferior Sagittal (ISS), Straight, Occipital.
  • Paired: Transverse, Sigmoid, Cavernous, Superior & Inferior Petrosal.

⭐ Cavernous Sinus: Houses CN III, IV, V1, V2 (lateral wall); CN VI & ICA (medially). 📌 "O TOM CA": O,T,O,M (lat); C,A (med). Infection risk!

Cranial Cavity: Clinical Notes - Skullcap Case Files

• Skull Fractures:
  • Linear: Common, often undisplaced.
  • Depressed: Bone fragment pushed inwards; risk of dural tear, brain injury.
  • Basilar: Skull base involvement. Signs: Battle's sign (mastoid ecchymosis), raccoon eyes (periorbital ecchymosis), CSF rhinorrhea/otorrhea.
• Intracranial Hemorrhages:
  • Extradural Hematoma (EDH): Arterial bleed, typically middle meningeal artery. Lucid interval common. Lens-shaped (biconvex) on CT.

    ⭐ Extradural hematoma is typically caused by rupture of the middle meningeal artery, often due to a fracture at the pterion.

  • Subdural Hematoma (SDH): Venous bleed (bridging veins). Crescent-shaped on CT. More common in elderly and alcoholics.
• Scalp Lacerations: Bleed profusely; involvement of galea aponeurotica can lead to wide gaping of wound edges.
• Cephalohematoma: Subperiosteal bleed in newborns, limited by suture lines; resolves spontaneously weeks later.

High‑Yield Points - ⚡ Biggest Takeaways

• Anterior Cranial Fossa: Frontal lobes; cribriform plate (CN I).
• Middle Cranial Fossa: Temporal lobes, pituitary; cavernous sinus (CN III, IV, V1, V2, VI, ICA).
• Posterior Cranial Fossa: Cerebellum, brainstem; foramen magnum (medulla, vertebral arteries, CN XI spinal roots).
• Epidural hematoma: Middle meningeal artery rupture; biconvex, lucid interval.
• Subdural hematoma: Bridging veins rupture; crescent-shaped.
• Subarachnoid hemorrhage: Ruptured berry aneurysm; thunderclap headache.
• Key Foramina: Optic canal (CN II, ophthalmic a.); Jugular foramen (CN IX, X, XI, IJV).