Anatomy, Head and Neck, Basilar Artery

Article Author:
Oluwaseun Adigun
Article Editor:
Scott Dulebohn
Updated:
9/19/2018 9:58:31 PM
PubMed Link:
Anatomy, Head and Neck, Basilar Artery

Introduction

The basilar artery (Latin: arteria basilaris) contributes the posterior component of the circle of Willis and supply contents of the posterior cranial fossa. It arises from the confluence of two vertebral arteries at the medullo pontine junction, to ascend through the basilar sulcus on the ventral aspect of the pons. It provides arterial supply to the brainstem, cerebellum, and contributes the posterior part of the circle of Willis through the posterior cerebral arteries. Clinical manifestations of basilar artery pathology range from the impaired level of consciousness, cranial nerve deficits, cerebellar dysfunctions, and motor and sensory dysfunctions. A cerebrovascular accident involving the basilar artery may result in characterized clinical syndromes, notable among them are the “locked-in syndrome” and the “top-of-the-basilar syndrome.”

Structure and Function

 The basilar artery branches into the following arteries:

  • Pontine arteries: Paramedian perforating arteries supplying the Pons
  • Right and left anterior inferior cerebellar artery (AICA): supplies inferior aspect of the cerebellum including the inferior and middle cerebellar peduncles. The AICA mostly gives off the labyrinthine (internal auditory) artery
  • Right and left Superior cerebellar artery: supplies the superior aspect of the cerebellum
  • Right and left posterior cerebral artery: contributes the posterior component of the circle of Willis.

Embryology

At around day 28 of embryonic life the brain receives arterial supply from the primitive carotid artery via the carotid-vertebrobasilar anastomosis, formed by three longitudinal neural arteries (named after the accompanying nerves):

  • Primitive trigeminal artery
  • Primitive hypoglossal artery
  • Primitive pro-atlantal artery.

This primitive anastomosis begins to disintegrate sequentially to pave the way for the definitive arterial circulation of the central nervous system (CNS).

At day 29:

  • The paired longitudinal neural artery on both sides of the hindbrain unites in the midline to form the Basilar arterial plexus
  • The basilar arterial plexus communicates anteriorly and cranially via the posterior communicating arteries and caudally with the vertebral arteries.

Days 30 to 35:

  • The basilar artery and vertebral arteries assume more mature distribution and morphology.
  • The basilar artery providing the posterior contribution to the circle of Willis via the posterior cerebral artery and the vertebral arteries which continue as the paravertebral anastomosis of the cervical intersegmental arteries of C1 to C7.

Nerves

As the basilar artery courses through the basilar sulcus on the ventral aspect of the pons, it travels adjacent to the abducens nerve at the lower pontine border and the oculomotor nerve as it ascends more cranially.

Physiologic Variants

Some commonly documented variations in basilar artery distribution include:

  • Persistent carotid-basilar artery anastomosis: Several cadaveric studies put the incidence rate to less than 0.5%. A persistent trigeminal artery is the most commonly documented persistent carotid-basilar artery anastomosis, followed by the persistent hypoglossal artery. Other persistent carotid-basilar artery anastomoses are persistent primitive otic artery and persistent primitive pro-atlantal intersegmental artery
  • Fenestrated basilar artery: duplication of portions of the basilar artery, commonly the lower segments have been documented with variable prevalence rates, but autopsy prevalence rate as high as 5 % has been reported. It predisposes to basilar artery aneurysm
  • Labyrinthine artery: also called the internal auditory artery, typically arises from the AICA but may arise from the basilar artery in about 15% of cases
  • Hypoplastic basilar artery: A very rare condition often seen alongside a persistent carotid-basilar artery anastomosis
  • Posterior inferior cerebellar artery: Mostly a branch of the vertebral artery but may arise from the basilar artery in about 10% of cases.

Surgical Considerations

Surgical recanalization using stent-assisted angioplasty or traditional angioplasty is an option in the management of high-grade basilar artery stenosis with poor response to medical thrombolysis. However, varying mortality and morbidity rates following surgery remains a disincentive.

Clinical Significance

Basilar Artery Aneurysms

These accounts for about 5% of intracranial aneurysms, but the most common of the aneurysm of the posterior circulation. Symptoms vary as the size of an aneurysm; these include headaches, visual disturbances, nausea, vomiting and loss of consciousness. Aneurysms of less than 15 mm may be asymptomatic. A basilar artery aneurysm may rupture causing a subarachnoid hemorrhage; this may be heralded by a sudden and severe headache described as "thunderclap." Patient may describe it as "worse headache of my life".

Basilar Artery Thrombosis

This refers to a cerebrovascular accident or stroke due to occlusion of the basilar artery by a thrombus. The risk factors are like in any other cerebrovascular accident. Implicated risks include atherosclerosis promoting factors like hypertension, hyperlipidemia, cigarette smoking, obesity, diabetes, coronary artery disease, among others. Clinical manifestation often corresponds to level and degree of occlusion ranging from hemiparesis, quadriparesis, ataxia, dysphonia, dysarthria, oculomotor palsy, and abducens palsy. These may present as groups of signs and symptoms recognized as distinct clinical syndromes:

  • Top-of-the-basilar syndrome: occlusion is in the rostral part of the basilar artery, resulting in ischemia affecting the upper brainstem and the thalamus. Clinical manifestations include behavioral changes, hallucinations, somnolence, visual and oculomotor disturbances.
  • Locked-in syndrome: Occlusion is at the proximal and middle part of the basilar artery, sparing the tegmentum of the pons. The patient is thus conscious and oculomotor function is preserved but other voluntary muscles of the body are affected hence patient cannot move and cannot talk, but consciousness is evidenced by vertical eye movement which is an oculomotor function.
  • Pontine warning syndrome: This is a basilar artery atherosclerotic disease characterized by motor and speech disturbances that occur in a wax and wane manner, e.g., recurrent on-and-off attacks of hemiparesis and dysarthria. It is indicative of an imminent basilar artery branch occlusion with infarction of the supplied region.

Vertebrobasilar Insufficiency

Transient occlusion of the vertebrobasilar system resulting in reversible ischemia manifesting as temporary cerebellar or brainstem dysfunctions commonly as follows: vertigo, diplopia, dysarthria, ataxia, confusion, and sudden fall due to knee weakness called a “drop attack." It also is called the beauty parlor syndrome after the early 1990s incidence of stroke in victims noticed to have hyperextended their necks at the wash basin for a prolonged time at the salon. The underlying pathology is chiefly an atherosclerotic pathology of the vertebrobasilar system, made only worse by the associated triggers most notorious of them is sudden change in position, especially from prolonged sitting to an errect position, this should however not be confused with positional change associated with Benign Paroxsymal positional vertigo (BPPV)

Other Issues

MRI with Angiography : This is the preferred imaging study, as it afford a more sensitive delineation of areas of ischemia as well as areas of stenosis within the vertebrobasilar circulation.