Which mechanism best explains the encephalopathy seen in malignant hypertension?

• A Focal vasospasm producing watershed cerebral infarction
• B Cytotoxic oedema from osmotic shifts across the blood-brain barrier
• C Breakthrough of cerebral autoregulation causing hyperperfusion and vasogenic oedema ✓
• D Obstructive hydrocephalus from impaired cerebrospinal fluid absorption

Explanation

Cerebral blood flow stays constant across mean arterial pressures of roughly 60 to 150 mmHg through autoregulatory vasoconstriction. When pressure exceeds the autoregulatory ceiling, arterioles dilate passively and hyperperfusion forces fluid across capillary walls, producing vasogenic oedema and the headache, visual disturbance and seizures of hypertensive encephalopathy. The older vasospasm-ischaemia theory has been abandoned; imaging and animal studies support hyperperfusion, and cytotoxic oedema characterizes infarction rather than this entity.

Reference: Ganong's Review of Medical Physiology, 27th ed.

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