Posterior circulation ischaemic stroke and TIA:

Diagnosis, investigation, and secondary prevention

Introduction

• One Fifth of all TIA’s and ischemic attacks are in the territory of the vertebrobasilar circulation.

• They are associated with high risk of early recurrent stroke.

• Secondary prevention is important.• There are particular challenges in diagnosis,

investigations and treatment.

Anatomy

• Vertebral Artery – Has an intracranial and extra cranial part. Lumen diameter(3-5mm)

• Unilateral hypoplasia (<= 2mm) is present in 25% of normal individuals(MRA). But it is more commonly seen in patients with posterior circulation stroke.

• This suggests that the narrowing was caused by atherosclerosis, in these patients.

• PICA(Posterior inferior cerebellar artery) is a branch of INTRACRANIAL vertebral artery.

• In up to 20% cases it may arise EXTRACRANIALLY.

• Rarely it may arise from basilar artery.

Basilar artery-Branches

• AICA(Anterior inferior cerebellar artery)• Pontine arteries.• Superior cerebellar arteries• Posterior cerebral artery.

• For each of these arteries, anatomical variants have been described.

PCA(Posterior cerebral artery)

• Arise as terminal bifurcation of basilar artery.• In 50% of population, Internal carotids

significantly contribute to the posterior circulation via the PCOMs.

• In 10% of population, The P1 segment is absent and PCA is exclusively supplied by the internal carotids.

Disease mechanisms.

• Cardioembolism.

• Large artery atherosclerosis.

• Small Artery disease.

• Atherosclerosis OFTEN occurs at or near the ORIGIN of the vertebral artery.

• Also occurs in distal vertebral artery and basilar arteries.

• Atherosclerotic narrowing by itself rarely causes ischemia- In a registry only 13 0f 407 patients had hemodynamically significant atherosclerotic obstruction.

• THROMBOEMBOLISM from the site of arterial stenosis seems to be the predominant cause of ischemia.

Small vessel disease- Lacunar infarcts

• Lipohyalinotic thickening of vessels in the background of hypertension.

• Focal atherosclerosis of the penetrating vessel.

• Patients with lacunar infarcts have been found to have co-existng large artery atheroscleroseis, and/or cardioembolic source.

• Vertebral artery dissection is an important cause of posterior circulation stroke in the young.

Clinical features.(Sample size of 407 patients)

Symptoms• Dizzyness (47%)• Unilateral Limb weakness(41%)• Dysarthria (31%)• Headache (28%)• Nausea & vomitnig (27%)

Signs• Unilateral limb weakness (38%)• Gait ataxia (31%)• Unilateral Limb ataxia (30%)• Dysarthria (28%)• Nystagmus (24%)

• The findings may also occur in isolation. Notably,..

• Isolated vertigo.• Isolated Cranial nerve palsies.• Internuclear ophthalmoplegia.• Ptosis• Dysphagia, dysarthria• Deafness

• Labyrinthine artery (branch of AICA) supplies the inner ear.

• Occlusion may lead to symptoms of vertigo and hearing loss.

• In patients with isolated symptoms, there are no clinical signs that can reliably differentiate between cerebellar and brainstem ischemia and a non-vascular cause of the isolated symptoms.

Posterior circulation TIA and risk for stroke.

• Isolated TRANSIENT brainstem symptoms were 12 times more frequent in the 90 days before vertebrobasilar stroke. (when compared to carotid stroke)

• 30 times more frequent during the preceding 2 days.

Accuracy of clinical diagnosis

• Sensitivity (54-.2% - 70.8%)• Specificity (84.4% - 89.9%)

• In a study in which three independent neurologists diagnosed the most likely vascular territory.

Investigations

• MRI is more sensitive than CT. Especially in the brainstem.

• Particularly if diffusion weighted imaging is done during the acute phase.

• However they can be negative for clinically definite posterior circulation infarcts, particularly small brainstem infarcts.

• Duplex- Ultrasound is less sensitive in detecting vertebral artery stenosis

• CT Angiography and Contrast Enhanced MR Angiography allow visualisation of the entire vertebrobasilar arterial tree.

• CE-MRA has the highest sensitivity and specificity.

Risk of recurrent stroke after an ischemic event.

• In the ACUTE phase, there is a higher risk of EARLY recurrent stroke after vertebrobasilar events, when compared to carotid ischemic events.

• These patients have high prevalence of vertebrobasilar stenosis, which itself is associated with high prevalence of recurrent stroke

• Risk of recurrence during the first year, however was similar in both vertebrobasilar and carotid TIA.

• In patients with vertebrobasilar TIA, the absolute risk of stroke at 1 year was 17.1%

Secondary Prevention.

• Similar to that of stroke in general.• Clopidogrel Alone or Aspirin-Dipyridamole

combination is recommended.

• Evidence from trials suggest that Aspirin-Clopidogrel combination is more effective, with an acceptable risk factor profile for EARLY prevention of recurrent stroke.

• i.e for the first few months after the ischemic event to cover the period of increased risk.

• Blood pressure lowering is beneficial in most patients.

• Aggressive blood pressure reduction is to be avoided in patients with bilateral vertebral artery stenosis, severe unilateral stenosis, or severe basilar artery stenosis, as it increases the risk of recurrent stroke.(SBP<140mmHg)

Endovascular treatment

• Angioplasty and/or stenting.• No evidence from RTC’s to identify whether it

is superior to best medical treatment.• The only Completed RTC had 16 patients,

which is too small a number to draw strong conclusions.

Surgical management.

• Surgery is rarely undertaken to treat vertebral artery stenosis, when compared to carotid endarterectomy.

• Surgical access is less easy in vertebral artery stenosis.

Future directions.

• Better diagnostic aids are needed for the benefit of a substantial minority of cases.

• New factors are needed to differentiate reliably between CVA and Non-vascular causes of isolated and transient neurological symptoms.

• Randomised controlled trials are needed to identify whether intervention with stenting can reduce the risk of stroke in cases of symptomatic vertebral artery stenosis.