Diffusion-weighted imaging (DWI) in acute ischemic stroke shows restricted diffusion because:
- A Vasogenic edema increases extracellular water movement
- B Blood breakdown products create magnetic field inhomogeneity
- C Cytotoxic edema causes cell swelling, reducing extracellular space and water diffusivity ✓
- D Loss of blood-brain barrier increases free water diffusion
Correct answer: C. Cytotoxic edema causes cell swelling, reducing extracellular space and water diffusivity
Explanation
In acute ischemic stroke, failure of the Na+/K+ ATPase pump due to ATP depletion causes ionic cytotoxic edema — water shifts into the intracellular compartment, leading to cell swelling and reduction of the extracellular space. This restricts the random Brownian motion (diffusion) of water molecules, appearing bright on DWI and dark on ADC maps. Vasogenic edema (seen in later stages) actually increases apparent diffusion. Hemosiderin creates susceptibility artifact on T2*, not DWI restriction.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.