39. Cerebrovascular diseases, intracranial haemorhages

Last updated on April 17, 2019 at 18:28

General

The term cerebrovascular disease means any pathological disease of the brain that involves blood vessels. Most of them are acute and cause stroke.

Cerebrovascular diseases can be classified as the following:

  • Stroke
    • Ischaemic stroke / encephalomalacia
      • Based on morphology:
        • Encephalomalacia alba
        • Encephalomalacia flava
        • Encephalomalacia rubra
      • Based on cause:
        • Focal ischaemia
        • Global ischaemia
    • Haemorrhagic stroke / intracranial haemorrhage
      • Intracerebral haemorrhage / cerebral apoplexy
      • Subarachnoid haemorrhage
  • Others
    • Transient ischaemic attack
    • Hypertensive cerebrovascular disease
    • Vasculitis of cerebral arteries
    • Vascular encephalopathy
    • Chronic subdural haematoma

Subdural and epidural haemorrhages are also subtypes of intracranial haemorrhages, but these aren’t cerebrovascular diseases as they are associated with trauma and not an abnormality of the vessels. These are discussed later in this topic.

The hippocampus and Purkinje cells of the cerebellum are the areas most sensitive to hypoxia in the brain, so it is in these areas signs of hypoxia are first seen.

Stroke

A stroke is a clinical diagnosis that involves acute neurological symptoms caused by an acute cerebrovascular event. Common symptoms of a stroke include drooping face, visual problems, hemiplegia and aphasia, but basically any neurological symptoms can occur, depending on which part of the brain is affected. Strokes can be either ischaemic or haemorrhagic in origin. 80% of all strokes are ischaemic, making it the most common type.

A transient ischaemic attack (TIA) is exactly the same as a stroke, except the symptoms last less than 24 hours (often less than 1 hour) and the damage isn’t permanent. People who experience TIAs are at much higher risk of developing strokes later.

Ischaemic stroke (clinical term), encephalomalacia (pathological term) or cerebral infarct (incorrect pathological term) occurs when there is liquefactive necrosis of the brain parenchyme due to ischaemia. The lesions are most commonly focal caused by focal ischaemia, but they can be diffuse (affecting the whole brain) as well.

The most common causes are:

  • Focal ischaemia
    • Embolism
    • Microangiopathy
    • Thrombosis
    • Vasculitis
    • CADASIL
  • Global ischaemia
    • Severe hypotension
    • Hypoxaemia

Most ischaemic strokes are caused by cardiac embolism, often due to atrial fibrillation, myocardial aneurysms or valvular disease. Diabetic microangiopathy may cause obstruction of small brain vessels. This causes many small “infarcts” in the subcortical grey areas called status lacunaris or lacunar stroke.

We distinguish three types of encephalomalacia, the alba, flava and rubra types. Encephalomalacia alba usually occurs when there is a thrombus blocking the arterial supply of a portion of brain parenchyme. The alba type develops into the flava types after a few weeks, as macrophages digest the liquefactive necrosis. Encephalomalacia rubra usually occurs when there is an embolus blocking the arterial supply of the brain. These emboli often lyse, which allows the necrotic area to be reperfused. The reperfused blood causes the redness of this type. Encephalomalacia rubra can also be caused by sinus thrombosis.

Global ischaemia usually damages the hippocampus and Purkinje cells first. Later a special type of infarct called watershed infarct will develop, where the zones most distal to the arteries they’re supplied by become necrotic. This often occurs on the border zone between the area supplied by the anterior and middle cerebral arteries.

People with no brain activity are termed “brain dead”. The brains of these people suffer diffuse, irreversible damage and the brain eventually undergoes autolysis. This phenomenon is called “respirator brain”.

Infarct is a type of coagulative necrosis, while all necrosis of the brain parenchyme is liquefactive. For this reason the term “cerebral infarct” is technically incorrect, and we prefer encephalomalacia instead.

Haemorrhagic stroke occurs when rupture of an artery causes an intracerebral (inside the parenchyme) or subarachnoid (on the surface of the brain) haemorrhage. The haemorrhage increases the intracranial pressure and causes the related symptoms, and it compresses brain parenchyme, causing stroke.

The most common causes are:

  • Intracerebral haemorrhage
    • Hypertension
    • Cerebral amyloid angiopathy
    • Ruptured arteriovenous malformations
  • Subarachnoid haemorrhage
    • Ruptured (berry) aneurysms in the circle of Willis

Rupture of an intracerebral vessel is the cause of intracerebral haemorrhage, also called cerebral apoplexy. The most common cause is hypertension, which weakens the arteries and predisposes them to rupture. Arterial weakness due to amyloid deposition is more frequent in elderly, especially those who suffer from Alzheimer. Ruptured congenital arteriovenous malformations are more frequent in children.

Subarachnoid haemorrhage most commonly occurs due to rupture of so-called berry aneurysms. These aneurysms are saccular and round and are often located in the circle of Willis. The risk for developing these aneurysms is increased in hypertension, smoking, autosomal dominant polycystic kidney disease and collagen disorders like Ehlers-Danlos and Marfan syndrome. The most characteristic symptom is what’s often described as “the worst headache I’ve ever had”.

Traumatic brain injury

Traumatic brain injury (TBI) is physical damage to the brain caused by external impact. The damage is acute in most cases, but there are some cases where there is chronic damage as well. It is most frequent in children, teenagers and elderly. A blow to the head may or may not fracture the skull, and both cases may or may not involve damage to the brain. When the brain is damaged the injuries may involve the parenchyme, the vasculature or both.

There are multiple forms/sequalae of traumatic brain injury:

  • Epidural haematoma
  • Subdural haematoma
  • Contusion
  • Concussion
  • Diffuse axonal injury
  • Chronic traumatic encephalopathy

Epidural haematoma is a bleeding between the dura mater and the skull. It’s often the consequence of blunt force trauma that fractures the skull which rupture the middle meningeal artery, causing it to bleed. Patients usually lose consciousness immediately after the trauma, however it is later regained as a period called the lucid interval starts. During this interval, which lasts minutes to hours, no neurological symptoms are experienced, but after this interval the intracranial pressure elevates and causes neurological symptoms, potentially even tonsillar herniation and death.

Subdural haematoma is a bleeding between the dura and arachnoid maters. Rapid movement of the brain during trauma can rupture the bridging veins, causing a bleeding into the subdural space. People with brain atrophy, like people with neurodegenerative diseases, diabetes or chronic alcoholics, have increased susceptibility for subdural haematoma. When the brain atrophies the bridging veins are stretched, which makes it easier for them to rupture.

Subdural haematomas don’t always cause severe symptoms, especially if they’re small. Especially alcoholics and elderly are prone to multiple minor head traumas, each of which will produce a subdural haematoma that will become organized. The presence of multiple organized subdural haematomas is called chronic subdural haematoma. Previous untreated subdural haematomas are also more prone to rebleeding, which also contributes to this.

A contusion is a type of “bruising” of the brain parenchyme. When an object impacts the head (or vice versa), brain injury may occur at the site of impact, called a coup injury or opposite the site of impact, called a countercoup injury. Contusions are characterised by small haemorrhage, tissue injury and oedema.

A concussion, also known as mild traumatic brain injury, is a state of temporary altered consciousness from head injury without any contusion. The symptoms may last for up to four weeks. There is almost always complete neurologic recovery, but amnesia of the event is often present.

Diffuse axonal injury is a microscopical change in the brain that can occur after trauma. There are no visible changes on imaging. It’s a severe form of traumatic brain injury that may cause altered mental state, potentially coma.

Chronic traumatic encephalopathy was described in topic 36.


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40. Glial central nervous system tumors

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