Basilar artery stroke

  Basilar artery stroke

Basilar artery is the most important artery in the posterior circulation. It is formed at the pontomedullary junction by the combination of both vertebral arteries. It lies on the ventral

surface of the pons and, along  its course,  it gives off its median, paramedian, short, and long circumferential branches.The branch of the basilar artery with the larger circumference is the anterior inferior cerebellar artery. It normally arises at the junction of the proximal and middle thirds of the basilar artery and supplies the lateral pontine tegmentum, brachium pontis or middle cerebellar peduncle, flocculus, and a small part of the anterior cerebellum. The internal auditory artery usually arises from the anterior inferior cerebellar artery; however, it may also arise as a direct branch of the basilar artery.

The terminal branch of the basilar artery is the posterior cerebral artery (PCA);  which mainly  supplies the midbrain, the thalamus, and the medial aspect of the temporal and occipital lobes. Proximal to its bifurcation into the terminal branches (ie, PCA), the basilar artery gives off the superior cerebellar arteries that supply the lateral aspect of the pons and midbrain and the superior surface of the cerebellum. The clinical manifestations depend on the location of the occlusion, the extent of thrombus, and the collateral flow. If the proximal segment of the basilar artery is occluded and the occlusion resulted from a slowly progressive stenosis, collateralization occurs within the cerebellum into the circumferential branches of the basilar artery. In  most cases of distal (top of the basilar) or proximal (vertebrobasilar junction) occlusions which  are due to embolism either from a cardiac or an arterial source. On the other hand, midbasilar artery occlusion is typically the result of atherothrombosis. Arterial dissections are very rare and usually involve the vertebral artery and occasionally extend to the basilar artery .

  •     Clinical presentation 
    • An abnormal level of consciousness and motor signs, such as hemiparesis or quadriparesis (usually asymmetric), are seen
    • Bulbar and pseudobulbar signs are the most common findings  .
    • Pupillary abnormalities, oculomotor signs, and pseudobulbar manifestations (ie, facial weakness, dysphonia, dysarthria, dysphagia) are common
                                              . The syndromes more commonly associated with basilar artery occlusion are:
      • Locked-in syndrome: It is caused by infarction of the basis pontis secondary to occlusive disease of the proximal and middle segments of the basilar artery, which leads to quadriplegia. Because the tegmentum of the pons is spared, the patient has a spared level of consciousness, preserved vertical eye movements, and blinking.
          • Top-of-the-basilar syndrome:  it is the manifestation of upper brainstem and diencephalic ischemia  which is caused by occlusion of the l basilar artery, usually by an embolus. Patients present with changes in the level of consciousness.  visual symptoms such as hallucinations and/or blindness is common. Third nerve palsy and pupillary abnormalities are also frequent. Motor abnormalities include abnormal movements or posturing.
        • Oculomotor signs are common. They usually reflect involvement of the vertical gaze center in the midbrain or the abducens nucleus, the horizontal gaze center located in the paramedian reticular formation contiguous to the abducens nucleus, and/or the medial longitudinal fasciculus. Lesions to these structures result in the following:

          • Ipsilateral abducens palsy
          • Ipsilateral conjugate gaze palsy
            • Internuclear ophthalmoplegia
            • One-and-a-half syndrome caused by a lesion simultaneously affecting the paramedian reticular formation and the medial longitudinal fasciculus, resulting in ipsilateral conjugate gaze palsy and internuclear ophthalmoplegia
            • Ocular bobbing, which localizes the lesion to the pons: This is characterized by a brisk downward movement of the eyeball with a subsequent return to the primary position.
            • Skew deviation.
                                                                              Other reported signs of pontine ischemia include limb shaking, ataxia (usually associated with mild hemiparesis), facial weakness, dysarthria, dysphagia, and hearing loss.
                           Medical care
                                              Patients with unstable  neurological symptoms, decreased level of consciousness, active cardiac or respiratory  conditions, hemodynamic instability, or a need for interventional therapies (eg, thrombolysis) must be admitted to a neurological intensive care unit.Every effort should be made to maintain a normal intravascular volume by administering isotonic solutions.. Dobutamine should be used with caution and with close monitoring of the cardiac index because it can often cause vasodilatation and hypotension.  Management of the airway is  importantl.Endotracheal intubation is recommended in most patients to keep their airway clear while maintaining normal ventilation. Tissue plasminogen activator (tPA) is the only pharmaceutical agent used  for the treatment of acute ischemic stroke within the first 3 hours of onset. . In some cases Angioplasty with or without stent placement has been performed to treat patients with atherosclerotic stenosis or to mechanically dislodge thrombi. The combination of intravenous thrombolysis with consecutive on-demand endovascular mechanical thrombectomy may allow for early treatment initiation with high recanalization.Recanalization of the basilar artery is key to the successful treatment of basilar artery thrombosis and for improving its prognosis.

Article publié pour la première fois le 22/10/2011

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