Hypertension And Cerebrovascular Disease

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Next to age, the most important factor predisposing to cerebral infarction or haemorrhage is hypertension. The risk is equal in males and females and is proportional to the height of blood pressure (diastolic and systolic).

Normotensive subject Chronic hypertensive subject

Cerebral blood flow is normally maintained over a wide range of blood pressure - AUTOREGULATION (sec page 75)

HYPERTENSIVE ENCEPHALOPATHY

In hypertension, a shift of this curve results in: relative protection from hypertensive encephalopathy

HYPERTENSIVE ENCEPHALOPATHY

greater vulnerability to falls in blood pressure with the

_________risk of infarction in the boundary zones or watershed areas between vascular territories.

Mean arterial blood pressure

The pathological effects of sustained hypertension are:

- Charcot Bouchard microaneurysms -» INTRACEREBRAL HAEMORRHAGE (from perforating vessels)

- Accelerated atheroma and thrombus formation -» INFARCTION (large vessels)

- Hyalinosis and librin deposition -» INFARCTION (lacunes - small vessels) HYPERTENSIVE ENCEPHALOPATHY

An acute, usually transient, cerebral syndrome precipitated by sudden severe hypertension. The excessive blood pressure may be due to malignant hypertension from any cause, or uncontrolled hypertension in glomerulonephritis, pregnancy (eclampsia) or phaeochromocytoma.

The mechanism is complex: Cerebral resistance vessels

Elevated BP (breakthrough of autoregulation)

SPASM

FORCED DILATATION — and INCREASED VASCULAR PERMEABILITY

MICROINFARCTION PETECHIAL HAEMORRHAGE

OEDEMA

Clinical features: Headache and confusion precede convulsions and coma. Papilloedcma with haemorrhages and exudates are invariably found. Proteinuria and signs of renal and cardiac failure are common. Diag/iosis: CT scanning shows widespread white matter low attenuation and excludes other pathology. MRI confirms increased brain water content and SPECT shows hyperperfusion adjacent to these changes. Treatment: a precipitous fall in blood pressure can result in retinal damage and watershed infarction. Gradually reducc blood pressure with i.v. nitroprusside or hydralazine. Reserve peritoneal dialysis for resistant cases. N.B. With treatment full recovery is usual. Without treatment death occurs.

BINSWANGER'S ENCEPHALOPATHY (Subcortical arteriosclerotic encephalopathy ■

A rare disorder in which progressive dementia and pseudobulbar palsy are associated with diffuse hemisphere demyclination. The CT scan shows areas of periventricular low attenuation, often also involving the external capsule. The pathological changes were previously attributed to chronic diffuse oedema, but the recent finding of a high plasma viscosity in these patients suggests that this, in conjunction with hypertensive small vessel disease, could produce chronic ischaemic change in central white matter.

Subclinical forms of this disease may exist as this CT scan appearance is occasionally found in asymptomatic patients. MRI appears more sensitive in establishing radiological diagnosis.

SAE)

Periventricular low attenuation

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