A patient with malignant hypertension has a blood pressure of 240/140 mmHg and develops encephalopathy and retinal hemorrhages. The cerebral injury occurs because:

• A Chronic adaptation has reset cerebral autoregulation upward, so extreme pressures force excessive flow and disrupt the blood-brain barrier
• B High pressure ruptures pre-existing Charcot-Bouchard microaneurysms
• C Hypertension causes reflex cerebral vasoconstriction leading to watershed infarction
• D Autoregulatory vasoconstriction becomes maximal above a mean pressure near 150 mmHg, beyond which flow rises passively with pressure ✓

Explanation

Cerebral autoregulation maintains constant flow between roughly MAP 60 and 150 mmHg. When mean arterial pressure exceeds the autoregulatory ceiling, vessels can no longer constrict further and flow rises passively, causing endothelial stretch, increased permeability, cerebral edema, and fibrinoid necrosis of arterioles. Charcot-Bouchard aneurysms cause deep intracerebral hemorrhage, a distinct entity. Upward resetting describes chronic compensated hypertension, not the acute breakthrough responsible for encephalopathy.

Reference: Harrison Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.