A patient with a brain abscess has marked perilesional white matter edema on MRI. Dexamethasone dramatically reduces the edema and mass effect. This improvement occurs because the edema is:

• A Cytotoxic, with glucocorticoids blocking cellular Na+/K+-ATPase failure
• B Vasogenic, with glucocorticoids restoring blood-brain barrier integrity and reducing extracellular fluid leakage ✓
• C Interstitial, with glucocorticoids increasing CSF reabsorption at the arachnoid villi
• D Osmotic, with glucocorticoids lowering plasma sodium toward isotonic levels

Explanation

Peritumoral and peribacterial edema is vasogenic: increased vascular permeability allows protein-rich fluid into the extracellular space, chiefly white matter. Glucocorticoids reduce this leakage by decreasing capillary permeability and restoring tight junction function, hence their dramatic benefit around tumors and abscesses. Cytotoxic edema from ischemic cell swelling involves intracellular fluid accumulation with an intact barrier, so steroids do not help, which is the key distinction examiners test.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.