CEREBROVASCULAR DISEASE

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chapter 10

Cerebrovascular Disease

Cerebrovascular disease (CVD) is one of the commonest problems encountered in clinical neurology. Hippocrates (460–375 BCE) is credited with introducing the concept of apoplexy (derived from the Greek word for seizure, apoplēxia, in the sense of being struck down) to describe patients with stroke. He is also credited with the statement ‘it is difficult to cure a mild case of apoplexy and impossible to cure a severe case’. This essentially is still the case today and thus the focus should be on primary and secondary prevention. The epidemiology of stroke is discussed in Appendix E.

MINOR STROKE OR TRANSIENT ISCHAEMIC ATTACK: DOES THE DEFINITION MATTER?

Patients with symptoms of cerebral ischaemia that have lasted less than 24 hours have been arbitrarily defined as suffering from a transient ischaemic attack (TIA) while patients with symptoms that last more than 24 hours have been designated as having had a stroke [1]. A term that has come and gone is the reversible ischaemic neurological deficit (RIND), which was defined as symptoms lasting more than 24 hours and less than 6 weeks. However, cerebral infarction can be demonstrated on diffusion-weighted MRI (dwMRI) in patients with symptoms lasting less than 24 hours [2, 3] and may predict the subsequent risk of stroke developing in patients who have had what is currently defined as a TIA [4]. This has led some authorities to recommend a change in the definition of TIA [5, 6].

There are essentially two types of patients with cerebral ischaemia:

• those with minor symptoms that may or may not resolve within a defined period

• those with cerebral ischaemia associated with a severe and disabling neurological deficit.

In the former group prompt assessment and institution of appropriate treatment provides an opportunity to prevent the severe stroke [7]. The risk of stroke after TIA or minor stroke is similar (see Table 10.1), once again suggesting that the separation between TIA and minor stroke is arbitrary and of little clinical value. Thus, all patients with minor symptoms of cerebral ischaemia, regardless of how long the symptoms last, should be treated as a matter of urgency.

TABLE 10.1

The subsequent risk of stroke after TIA and minor stroke (95% confidence intervals in brackets) [11]

Forty percent of patients who subsequently suffer a stroke after a TIA will do so within the first 7 days; in 17% the TIA will be on the day of the stroke while in 9% it will be on the day prior [8]. Unfortunately, many patients ignore minor symptoms and do not seek urgent medical advice. The opportunity to prevent stroke is lost. The subsequent risk of early stroke after minor cerebral ischaemia is greatest with severe carotid stenosis and in patients with repeated or crescendo TIAs, the ‘capsular warning syndrome’ [9, 10].

• All patients with minor cerebral ischaemia should be evaluated as a matter of urgency.

• Recurrent stereotyped TIAs indicate a tight stenosis that could be either a large artery or a perforating vessel.

The principles of management of patients with CVD are simple and at the same time complex as many patients have more than one potential underlying pathological cause [12]. Patients can present with a cerebral infarct one time and an intracerebral haemorrhage the next [13, 14]. The symptoms and signs of a small intracerebral haemorrhage can be identical to a cerebral infarct of a similar size in the same area and many patients have coexistent medical problems that make the choice of subsequent therapy difficult.

This chapter will discuss the general principles of diagnosis, investigation and management of the more common manifestations of CVD and as such is far from comprehensive. For more detail the reader is referred to one of the many excellent books on the subject [15–20]. There are many websites that also help the clinician keep abreast of the latest developments (e.g. http://www.cochrane.org/reviews/en/topics/93_reviews.html, http://www.strokeassociation.org/presenter.jhtml?identifier=1200037, http://www.strokecenter.org/).

PRINCIPLES OF MANAGEMENT

The principles of management are shown in Figure 10.1. As treatment is currently largely disease-specific and different diseases affect different regions, accurate localisation of the problem within the cerebral hemispheres, brainstem or cerebellum is essential. A detailed knowledge of the basic principles of neuroanatomy, which were outlined in Chapter 1, ‘Clinically oriented neuroanatomy’, particularly the concept of the meridians of longitude and the parallels of latitude, is absolutely essential in this respect and a review of Chapter 1 and Chapter 4, in particular the ‘Rule of 4’ of the brainstem would be useful before reading further.

FIGURE 10.1 Principles of management of patients with cerebral vascular disease (CVD)

Carotid territory refers to cerebral ischaemia in the distribution of the main artery at the front of the neck: the carotid and its branches, the anterior and middle cerebral arteries. Vertebrobasilar territory refers to the arteries at the back of the neck: the two vertebral that coalesce to form the basilar arteries and the branches of the basilar artery, the posterior inferior cerebellar artery, the anterior inferior cerebellar artery, the superior cerebellar artery and the posterior cerebral arteries, and the small paramedian perforating vessels that arise from the basilar artery.

It could be argued that modern diagnostic facilities (and yet to be developed technology), such as CT scans, MRI scans, duplex carotid ultrasound, transthoracic and trans-oesophageal echocardiography, can readily establish if a patient has CVD, differentiate between haemorrhage and infarction, localise the exact site of the lesion, determined if it is lacunar infarction and most likely establish the aetiology. The difficulty with this approach is that not everybody has access to such facilities, the tests are not always positive in patients who are clinically suspected to have CVD (particularly patients with transient symptoms) and both asymptomatic cerebral infarction [21] and asymptomatic carotid stenosis are not uncommon. Therefore, a careful history and, in the presence of abnormal neurological signs, a detailed neurological examination remain the essential tools in management of patients with CVD.

DECIDING THE PROBLEM IS CEREBRoVASCULAR DISEASE

Cerebral vascular disease should be suspected when a patient presents with the sudden or subacute onset of a focal neurological deficit associated with loss of function. The neurological deficit is usually of sudden onset within minutes if not quicker, particularly with an embolic source from the heart or from atherosclerotic vascular disease in one of the major extracranial vessels. Other modes of onset include stepwise stuttering (related to thrombosis rather than embolism) or fluctuating deficit [22, 23].

There a number of common presentations including:

• Vertebrobasilar territory ischaemia

• Ataxia, nausea and vomiting with or without vertigo: cerebellar infarction or haemorrhage

• Dysphagia, dysarthria and ataxia: lateral medullary syndrome (almost always on an ischaemic basis)

• Pure motor hemiparesis affecting arm and leg: paramedian pontine syndrome (almost always on an ischaemic basis)

• Horizontal diplopia looking to one side: unilateral internuclear ophthalmoplegia (almost always on an ischaemic basis)

• Hemianopia: occipital infarction (almost always on an ischaemic basis)

• Carotid territory ischaemia

• Transient or permanent monocular visual loss: retinal ischaemia (almost always on an ischaemic basis)

• Non-fluent dysphasia and right-sided hemiparesis: dominant hemisphere frontal lobe (almost always on an ischaemic basis)

• Fluent dysphasia with or without a hemianopia: dominant parietal or temporal lobe

• Left-sided weakness and neglect, with or without hemianopia: non-dominant parietal lobe

• Pure motor hemiparesis affecting the face, arm and leg equally: lacunar infarct deep within the cerebral hemisphere

Note: The lacunar syndromes are ischaemic in more than 80% of cases.

There should be an increased level of suspicion in older patients when there are one or more of the risk factors listed above or when other manifestations of atherosclerotic vascular disease such as coronary artery or peripheral vascular disease are present.

Imaging in cerebrovascular disease

Apart from transient ischaemic attacks that last less than 3–4 hours, current imaging technology such as CT scanning and magnetic resonance imaging (MRI) can, in the great majority of patients, confirm the diagnosis of CVD, differentiate between haemorrhage and ischaemia and usually determine the exact site of the cerebral ischaemia within the central nervous system.

It is important to remember that CVD can occur:

• at any age, even in childhood

• in patients without currently recognised risk factors for stroke

• with symptoms that do not always develop suddenly.

CT scan of the brain is often normal in the first 6 and sometimes up to 24 hours after cerebral infarction; MRI can detect changes as early as 1.5 hours after ischaemia [24]. Diffusion-weighted MRI (dwMRI; see Figure 10.2) has a sensitivity of > 90–95% for detecting early (within the first 6 hours after onset) ischaemic changes as opposed to CT scan with a sensitivity of only 70–75% [1, 25].

FIGURE 10.2 DwMRI showing lacunar A and larger artery infarction B

The longer the deficit takes to develop the less one can be certain clinically that the problem is CVD.

A normal dwMRI does not exclude cerebral ischaemia under the following circumstances:

• when performed in the first few hours

• for small lacunar infarcts in the brainstem, deep hemisphere or cortex [1].

DwMRI should be performed within the first week after onset as the changes are transient and this helps to differentiate long-standing old ‘asymptomatic’ ischaemic changes from acute cerebral infarct.

DIFFERENTIATING BETWEEN HAEMORRHAGE AND ISCHAEMIA

• Extradural haematoma (due to rupture of an artery, usually the middle meningeal) and acute subdural haematoma (due to rupture of veins that cross the subdural space) are rarely confused with cerebral ischaemia; both present with the rapid onset of a depressed conscious state.

• A chronic subdural haematoma, on the other hand, can be confused with stroke as it often presents with a non-specific hemiparesis particularly in the elderly [26].

• Subarachnoid haemorrhage (SAH) presents in most patients with the sudden onset of a very severe headache, nausea and vomiting with or without depression of the conscious state. Although SAH is usually discussed under the heading of CVD it rarely presents with a stroke. Occasional patients will have a focal neurological deficit if bleeding occurs into the brain.

• A small intracerebral haemorrhage in the same location within the hemisphere or brainstem as an infarct will result in identical neurological symptoms and signs, and, very rarely, resembles lacunar syndromes [27].

Clues that may help differentiate haemorrhage from infarction

MORE IN KEEPING WITH ISCHAEMIA

• Antecedent transient ischaemic attack(s) with the same symptoms prior to the stroke would indicate ischaemia rather than haemorrhage. For example, repeated stereotyped episodes of weakness affecting the face, arm and leg are typical of the capsular warning syndrome, invariably on the basis of lacunar infarction [10, 31].

• The neurological deficit gradually spreads from one part of the body to the rest. For example, if it initially involves the arm and then spreads to the face and subsequently the leg, it is more likely to be ischaemic in origin.

• Spontaneous improvement within the first few hours favours ischaemia rather than haemorrhage.

HAEMORRHAGIC STROKE

Intracranial haemorrhage can occur into the extradural, subdural or subarachnoid spaces or be intracerebral or intraventricular (see Figure 10.3). Each site of haemorrhage is associated with a different symptom complex and results from different causes.

FIGURE 10.3 CT scans showing the different types of intracranial haemorrhages: A extradural, B subdural, C subarachnoid, D intracerebral and E intraventricular

Extradural haematoma

Extradural haematoma results from a severe head injury and is almost invariably associated with a fractured skull.

The patient may be comatose from the start or deteriorate within minutes to hours with severe headache, vomiting, a hemiparesis and subsequent coma.

Treatment is essentially surgical evacuation but up-to-date recommendations regarding management of head injuries can be found on the National Neurotrauma Society website (http://www.neurotraumasociety.org/book.asp).

Subdural haematoma

Acute subdural haematoma usually results from trauma to the head although at times the trauma may appear trivial, for example striking one’s head on the corner of a cupboard. On the other hand, almost half of patients with chronic subdural hematomas will not have a history of trauma. There is an increased risk of chronic subdural haematoma in patients on anticoagulants.

Subdural haematoma presents with headache, nausea, confusion and hemiparesis and, if acute, a depressed conscious state. In the elderly, hemiparesis may not be a feature [26]. A classic triad with a reduced conscious state, a dilated pupil ipsilateral to the haematoma (related to a 3rd nerve palsy) and a contralateral hemiparesis indicates life-threatening transtentorial herniation and is a surgical emergency. Occasionally, chronic subdural haematomas are bilateral and may present with an apraxic gait similar to the gait disturbance that occurs with frontal lobe pathology (see Chapter 5, ‘The cerebral hemispheres and cerebellum’).

Acute and large chronic subdural haematomas require surgical evacuation, but some chronic subdural haematomas resolve with conservative treatment. Hyperventilation and mannitol are used to reduce raised intracranial pressure.

ISCHAEMIC CEREBROVASCULAR DISEASE

Ischaemic stroke accounts for the great majority of patients with CVD. When managing a patient with ischaemic stroke one needs to consider whether the ischaemia relates to arterial or, much less likely, venous disease. In patients with cerebral ischaemia related to arterial disease it is important to differentiate between small vessel disease within the parenchyma due to occlusion of small perforating vessels and large artery disease that is most likely to be embolic in origin either from the heart, the arch of the aorta or the large arteries in the neck (see Figures 10.6 and 10.7).

Is it large artery, small vessel or cerebral venous disease?

Differentiating between large artery and small vessel disease can be very difficult. Access to diffusion-weighted MRI in the first week after stroke enables differentiation between large vessal and small vessel ischaemia. Small vessel disease is often referred to as the lacunar syndrome where occlusion of very small vessels is usually due to lipohyalinosis and that of slightly larger ones is due to atheromatous or embolic occlusion of the

MANAGEMENT of INTRACRANIAL HAEMORRHAGE

• Extradural and acute subdural haematomas. Surgical evacuation.

• Chronic subdural haematomas. Can be treated conservatively, although many will require surgical evacuation.

• Subarachnoid haemorrhage. Transfer as a matter of urgency to a neurosurgical unit with expertise in the management of SAH. The management is complex and includes the timing of intervention, the method of occluding the aneurysm, with options of direct surgical clipping (the traditional method) or endovascular intervention [37], and the management of the cerebral vasospasm that occurs as a result of irritation by the subarachnoid blood and resulting secondary cerebral infarction.

• Intracerebral haemorrhage [38]. If the ICH is small it can be managed conservatively. Treatment of larger ICHs consists of ventilatory support, blood pressure control, reversal of any preexisting coagulopathy, intracranial pressure monitoring, osmotherapy, fever control, seizure prophylaxis, treatment of hyerglycaemia and nutritional supplementation [39]. Despite these measures there is some doubt that mortality is reduced [40]. The only study of mannitol failed to show any benefit at 3 months [41]. The role of surgery is clearly established [42] with cerebellar haemorrhages, but the role of surgery in hemisphere haemorrhages is less well defined.

Current guidelines [37] recommend:

• Protamine sulfate should be used to reverse heparin-associated ICH, with the dose varying and related to the time from cessation of heparin.

• Patients with warfarin-associated ICH should receive intravenous vitamin K to reverse the effects of warfarin and treatment to replace clotting factors.

• Treatment of patients with ICH related to thrombolytic therapy includes urgent empirical therapies to replace clotting factors and platelets.

• Patients with acute primary ICH and hemiparesis/hemiplegia should have intermittent pneumatic compression for prevention of venous thromboembolism.

• After documentation of cessation of bleeding, low-dose subcutaneous low-molecular-weight heparin or unfractionated heparin may be considered in patients with hemiplegia after 3–4 days from onset.

• Patients with an ICH who develop an acute proximal venous thrombosis, particularly those with clinical or subclinical pulmonary emboli, should be considered for acute placement of a vena cava filter.

• Cerebellar haemorrhage > 3 cm, posterior fossa decompression and/or a ventricular drain to treat the secondary hydrocephalus.

• Lobar clots within 1 cm of the surface, evacuation of supratentorial ICH by standard craniotomy might be considered.

• The routine evacuation of supratentorial ICH by standard craniotomy within 96 hours of ictus is not recommended (see possible exception above for patients presenting with lobar clots within 1 cm of the surface).

• There is insufficient data on the role of decompressive craniectomy to improve outcome in ICH.

original penetrating vessel [36]. Although many lacunar syndromes have been described, the advent of sophisticated imaging has revealed that large artery territory infarcts can mimic many of the clinical features of these syndromes.

The most common and more likely features that reflect small vessel disease lacunar syndromes are pure motor hemiparesis and pure sensory loss affecting the contralateral face, arm and leg equally. This usually reflects involvement of the deep hemisphere, in particular the internal capsule and less likely the paramedian brainstem, although in this situation the face may not be affected if the infarct is below the mid pons.

The value of the lacunar syndromes is that they usually identify patients with small vessel disease. The pure motor hemiparesis is where the degree of weakness is similar in the face, arm and a leg and is not associated with any dysphasia, visual field loss or visual inattention; sensory symptoms or signs including sensory inattention; and the three parietal sensory signs described in Chapter 5, ‘The cerebral hemispheres and cerebellum’, stereognosis, graphaesthesia or 2-point discrimination. There are a number of other lacunar syndromes, such as ataxic hemiparesis (also referred to as crural paresis and homolateral ataxia), dysarthria clumsy hand syndrome and the sensorimotor stroke, but the same clinical features can occasionally be seen in large artery ischaemia. The advent of CT and MRI has allowed detection of many more lacunar infarcts and highlighted that the clinical features can be very varied, and these have been referred to as ‘atypical lacunar syndromes’ [43].

The risk factors associated with small vessel disease are virtually identical to those associated with large vessel disease, although lacunar infarcts are more common in patients with long-standing hypertension and diabetes. It is not uncommon for patients with a lacunar infarct to have multiple potential causes for ischaemia, such as an ipsilateral internal carotid artery stenosis or a cardiac source for embolism [12].

The presence of dysphasia, visual field disturbances and the cortical sensory signs as described in Chapter 5, ‘The cerebral hemispheres and cerebellum’, all indicate involvement of the cortex and, therefore, are related to large artery disease. An epileptic seizure associated with the stroke would also indicate cortical involvement and large artery disease.

Internuclear ophthalmoplegia (see Chapter 4, ‘The cranial nerves and understanding the brainstem’) can occur as an isolated phenomenon and can either be uni- or bilateral. It occurs with ischaemia of the median longitudinal fasciculus and usually in the setting of ostial atheroma affecting a paramedian pontine perforating artery, which may also be associated with more significant basilar artery atheroma.

CEREBRAL VEIN THROMBOSIS

Cerebral vein thrombosis is very rare. In the cerebral venous system blood drains from the cortical veins into the superior sagittal sinus and, together with the straight sinus, these drain into the torcular herepholi which then drains into the internal jugular veins via the lateral sinuses (see Figure 10.5).

FIGURE 10.5 Cerebral venous system Reproduced with permission from ‘Cardiogenic stroke’ by PC Gates, HJM Barnett, MD Silver, in Stroke: Pathophysiology, Diagnosis and Management, edited by HJM Barnett et al, 1986, Churchill Livingstone, Figure 35.1, p 732 [44]

The resultant clinical syndrome depends on which part of the venous system is affected [44].

• Lateral sinus usually results in intracranial hypertension, resembling idiopathic (IIH) or benign intracranial hypertension (BIH) with raised intracranial pressure causing headache and papilloedema.

• Superior sagittal sinus thrombosis may also result in idiopathic intracranial hypertension but more often it causes severe headache, focal or generalised convulsions and a focal neurological deficit, predominantly hemiparesis due to associated cortical vein thrombosis.

• Cavernous sinus thrombosis presents with unilateral periorbital pain, impaired ocular movements, proptosis (protruding eye) and chemosis (conjunctival oedema and erythema).

• The deep venous system (the straight sinus and its tributaries) is very rare and presents with headache, vomiting, fever and a depressed conscious state.

IF IT IS A LARGE ARTERY DISEASE, WHAT IS THE VASCULAR TERRITORY OF THE CEREBRAL ISCHAEMIA?

The reason for differentiating between ischaemia in the carotid territory and ischaemia in the vertebrobasilar territory relates to the different management currently recommended for atherosclerotic vascular disease causing stenosis of the extracranial vessels. In addition, asymptomatic vascular disease is not uncommon and the risk of subsequent cerebral ischaemia is very different when the vascular disease is symptomatic compared to when it is asymptomatic.

At times it can be difficult to differentiate between anterior and posterior circulation ischaemia. As discussed in Chapter 2, ‘The neurological history’, many neurological symptoms and signs are non-specific in terms of their ability to localise a problem to a particular part of the nervous system, while others accurately identify the part of the nervous system affected. A hemiparesis affecting the arm and leg with or without the involvement of the ipsilateral side of the face; unilateral sensory abnormalities affecting the primary sensory modalities of pain, temperature, vibration and proprioception; and dysarthria are all non-specific symptoms with poor localising value, other than to say the lesion is in the CNS above the level of the uppermost signs. If the face, arm and leg are affected this clearly places the problem above the level of the 7th nerve nucleus in the pons but cannot localise it any more accurately. A hemiparesis affecting the arm and a leg in the absence of any other signs can occur with lesions in the contralateral brainstem or hemisphere.

Carotid territory ischaemia: Visual field defects and dysphasia, together with the parietal cortical signs discussed in Chapter 5, ‘The cerebral hemispheres and cerebellum’, would indicate the involvement of the cerebral hemispheres.

Vertebrobasilar territory ischaemia: The presence of bilateral weakness or sensory disturbance suggests that the brainstem is affected whereas diplopia or vertigo associated with a weakness or sensory disturbance clearly indicates that the problem is in the brainstem. Nausea, vomiting and an inability to stand are not pathognomonic for CVD, but when these symptoms are due to cerebral vascular disease it almost invariably points to cerebellar infarction or haemorrhage.

Symptoms of cerebral ischaemia in two different vascular territories within a short period of time indicate that the likely source is proximal, either the heart or the arch of the aorta.