Large vessel occlusion

Large vessel occlusion (LVO), also termed proximal large vessel occlusion (PLVO), describes occlusion of a proximal and large-sized intracranial artery resulting in impending acute ischemic stroke. The definition of large vessel occlusion varies significantly among clinical trials of endovascular clot retrieval ^1,2.

Definition

One consensus definition of ‘large vessel’ suggests intracranial arteries with a luminal diameter of >2.0 mm ¹. This is in-keeping with occlusion of the following arteries, which are generally included within the definition of large vessel occlusion across multiple large clinical trials ^1-4:

• intracranial internal carotid arteries

• M1 segments of the middle cerebral arteries

• basilar artery

• intracranial vertebral arteries

It should be noted that anatomical anomalies of these proximal arteries may have an impact on their inclusion under the luminal diameter definition of ‘large vessel’, such as hypoplasia (e.g. hypoplastic vertebral artery) or duplication (e.g. duplicated middle cerebral artery), which may render the luminal diameter to be <2.0 mm ¹. Regardless of this, expert consensus is to include occlusion of these arteries in the definition of large vessel occlusion because the occlusion is still of a proximal intracranial artery ¹.

The M2 segments of the middle cerebral arteries can be highly variable in angioarchitecture between patients (1.1-2.1 mm) and thus, its definition as a large- or medium-sized vessel is a subject of conjecture ¹. In instances of a dominant M2 segment whereby the artery can have a luminal diameter of >2.0 mm, if occluded, this may be classified as a large vessel occlusion ¹. Indeed, some patients with M2 segment occlusions were included in the original randomized control trials concerning endovascular clot retrieval ³. However, in many instances, the vessel diameter is <2.0 mm and occlusion would thus be better classified as a medium vessel occlusion (MeVO) ^1-5.

Similarly, the A1 segments of the anterior cerebral arteries and the P1 segments of the posterior cerebral arteries can also be variable in angioarchitecture between patients and thus, are also a subject of definitional conjecture ^1-3. Depending on the exact size of the vessel occluded, these may variably be defined as either large vessel occlusions or medium vessel occlusions (MeVO) ^1-3.

Clinical importance

• large vessel occlusion accounts for up to 38% of acute ischemic stroke ⁶

• identifying large vessel occlusions on neuroimaging is vital in the work-up and management of acute ischemic stroke as these patients may be eligible for endovascular clot retrieval ³