Non-traumatic Neurological Emergencies

Acute Stroke Imaging - Brain Attack Basics

• Goal: Rapidly differentiate ischemic vs. hemorrhagic stroke; guide reperfusion therapy. "Time is Brain!"
• Initial Imaging: Non-Contrast CT (NCCT)
  • Primary: Exclude hemorrhage (hyperdense).
  • Early ischemic signs: Loss of grey-white differentiation, sulcal effacement, hyperdense MCA sign.
  • ASPECTS score (0-10) on NCCT for MCA stroke.
• Ischemic Stroke Workup:
  • MRI: Gold standard.
    • DWI: Positive within minutes.
    • ADC map: Confirms restricted diffusion.
  • CTA: Detects Large Vessel Occlusion (LVO).
  • CTP: Identifies core infarct vs. penumbra (target for reperfusion).

⭐ DWI hyperintensity with corresponding ADC hypointensity signifies restricted diffusion, visible within minutes (<30 min) of acute ischemic stroke onset.

CNS Infections - Brain Invaders

• Bacterial Meningitis:
  • CT: Often normal; may show hydrocephalus, basal cistern effacement. Post-contrast: meningeal enhancement.
  • MRI: Superior for leptomeningeal enhancement (FLAIR, T1+C); DWI for restricted diffusion of pus in sulci.
• Viral Encephalitis (Herpes Simplex - HSV):
  • Typically affects temporal lobes, insula.
  • CT: Early stages often normal; later may show hypodensity, edema.
  • MRI: Characteristic T2/FLAIR hyperintensity, DWI restriction, petechial hemorrhages.
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• Brain Abscess:
  • CT/MRI: Central area of liquefaction necrosis, surrounded by a thick, enhancing rim and vasogenic edema.
  • DWI: Central restricted diffusion is key for pyogenic abscess.
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  • ⭐ DWI restriction in the core of a pyogenic abscess is typical.

• Tuberculous Meningitis:
  • Features: Thick basal meningeal enhancement, hydrocephalus, tuberculomas (ring-enhancing lesions). Infarcts common due to associated vasculitis.

Seizures & Status - Electric Storms

• Imaging Goal: Identify structural causes (e.g., tumor, stroke, infection, malformation) or complications.
• New-onset seizure: Non-contrast CT (NCCT) head initially to exclude acute bleed/mass.
• MRI: Superior for subtle epileptogenic lesions (e.g., mesial temporal sclerosis, cortical dysplasia, encephalitis).
• Status Epilepticus: May show reversible cortical/subcortical DWI restriction, T2/FLAIR hyperintensity, ↑perfusion; hippocampal changes common.

⭐ MRI is superior to CT for detecting subtle epileptogenic lesions; CT is often first-line in emergency new-onset seizures to exclude acute bleed/mass effect immediately threatening life or requiring urgent neurosurgical intervention (e.g. large hematoma, hydrocephalus).

Raised ICP & Hydrocephalus - Pressure Cooker Brain

• Raised ICP: Symptoms: Headache, vomiting, papilledema. Late: Cushing's triad. CT findings: Effaced sulci, compressed ventricles/cisterns.
• Hydrocephalus: ↑CSF volume causing ventricular dilatation (Evan's Index > 0.3).
  • Acute sign: Transependymal CSF flow (periventricular lucency on CT / T2 hyperintensity on MRI).
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  • ⭐

    Transependymal CSF seepage (periventricular lucency on CT / T2 hyperintensity on MRI) indicates acute/uncompensated hydrocephalus.

• Differentiating Types:

Other Vascular Crises - Vessel Vendettas

⭐ The "empty delta sign" on contrast-enhanced CT is a classic finding in superior sagittal sinus thrombosis.

High‑Yield Points - ⚡ Biggest Takeaways

• AIS: NCCT head first (no bleed); MRI (DWI) is most sensitive for early infarct.
• ICH: NCCT shows type, location, mass effect; CTA for underlying vascular causes.
• SAH: NCCT for acute blood; Angiography (CTA/DSA) vital for aneurysms.
• CVT: MRV/CTV are diagnostic; look for "empty delta sign" on CECT.
• CNS Infections: Contrast MRI for complications (e.g., abscess); DWI is key for herpes.
• PRES: MRI (FLAIR/T2) shows posterior reversible edema, typically parieto-occipital.