Trauma to the Central Nervous System

CNS Trauma Overview - Impact Insights

• Primary Injury: Immediate mechanical damage from impact (e.g., Diffuse Axonal Injury, contusion).
• Secondary Injury: Delayed cascade; key mediators: hypoxia, hypotension, excitotoxicity (glutamate), inflammation, edema.
• Monro-Kellie Doctrine: $V_{intracranial} = V_{brain} + V_{blood} + V_{CSF} + V_{lesion}$ = constant. Explains ↑ICP.
• GCS (Eye, Verbal, Motor): Assesses severity. Mild: 13-15; Moderate: 9-12; Severe: ≤8.

⭐ Secondary brain injury, driven by factors like hypoxia, hypotension, and excitotoxicity, is a major determinant of outcome post-TBI and a key target for neuroprotective strategies.

Skull & Scalp Trauma - Cranial Crack Chronicles

• Scalp Layers 📌 SCALP:
  • Skin
  • Connective tissue (dense)
  • Aponeurosis (galea)
  • Loose areolar tissue (danger area due to spread of infection)
  • Pericranium
• Skull Fractures:
  • Linear: Most common; simple break.
  • Depressed: Bone fragment pushed inwards. Significant if depression >1 bone thickness.
  • Comminuted: Multiple bone fragments.
  • Basilar: Fracture at skull base. Key signs:
    • Battle's sign (mastoid ecchymosis)
    • Raccoon eyes (periorbital ecchymosis)
    • CSF rhinorrhea/otorrhea
    • Hemotympanum

⭐ Basilar skull fractures often present with 'Raccoon eyes' (periorbital ecchymosis) and 'Battle's sign' (mastoid ecchymosis), indicating fracture of the anterior or middle cranial fossa respectively.

Intracranial Hemorrhages - Hemorrhage Hotspots

• Key types of traumatic intracranial bleeds:

⭐ An epidural hematoma (EDH) classically presents with a 'lucid interval' after initial loss of consciousness, followed by rapid neurological decline, and appears as a biconvex (lentiform) hyperdensity on CT scan.

• Intracerebral/Intraparenchymal Hemorrhage: Often associated with coup (at site of impact) and contrecoup (opposite site of impact) injuries. Can be single or multiple. Location varies (frontal/temporal lobes common).

Parenchymal Injury & Sequelae - Core Carnage Consequences

• Concussion: Transient LOC; reversible functional disturbance.
• Contusion: Brain bruise (hemorrhage, necrosis).
  • Coup (impact site) & Contrecoup (opposite site).
• Laceration: Tissue tearing; often with penetrating trauma/depressed skull fractures.
• Diffuse Axonal Injury (DAI):
  • Shearing forces → widespread axonal damage.
  • Punctate hemorrhages (corpus callosum, brainstem).
  • $\beta$-APP stain highlights axonal swellings.

⭐ Diffuse Axonal Injury (DAI) is characterized by widespread damage to axons in the white matter, often not visible on initial CT but a major cause of coma and poor outcome; $\beta$-amyloid precursor protein ($\beta$-APP) immunohistochemistry highlights axonal swellings (retraction balls) within hours to days.

• Herniation Syndromes (↑ICP):
  • Subfalcine: Cingulate gyrus under falx → ACA compression.
  • Transtentorial (Uncal): Uncus through tentorial notch → CN III palsy, PCA compression, Duret hemorrhages.
  • Tonsillar: Cerebellar tonsils through foramen magnum → Brainstem compression (cardiorespiratory arrest). 📌 "CUT the CONE" (Cingulate, Uncal, Tonsillar).

High‑Yield Points - ⚡ Biggest Takeaways

• Epidural Hematoma (EDH): Middle meningeal artery rupture, lucid interval, lentiform (biconvex) CT.
• Subdural Hematoma (SDH): Bridging veins tear, crescentic CT, common in elderly/alcoholics.
• Subarachnoid Hemorrhage (SAH): Ruptured berry aneurysm, "worst headache of life", bloody CSF.
• Diffuse Axonal Injury (DAI): Shearing forces (acceleration-deceleration), widespread axonal damage, often normal CT.
• Brain Herniation: Critical complication of ↑ICP; e.g., uncal, subfalcine, tonsillar.
• Coup-Contrecoup Injury: Brain contusions at impact site and directly opposite_site_