Brainstem syndromes, most of them with awkward names

   

The midbrain syndromes

There is a significant overlap between the midbrain syndromes: Weber’s, Benedikt’s, Claude’s and Nothnagel’s.

Weber’s syndrome

Weber’s syndrome is a crossed midbrain syndrome. Other names for the syndrome are midbrain stroke syndrome and superior alternating hemiplegia.

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It is typically caused by an ischemic or hemorrhagic stroke. The midbrain receives its blood supply from the vertebrobasilar circulation, from the branches of the basilar, posterior cerebral and superior cerebellar arteries. Weber’s syndrome caused by the stroke most often comes with signs of stroke in other parts of the vertebrobasilar system, rarely as an isolated syndrome. Other possible causes of Weber’s syndrome are tumors, aneurysms, and demyelination.

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Close relationship between abducens nucleus and facial nerve

   

The abducens (CN VI) nucleus is located in the caudal part of the pons. It lies just under the floor of the fourth ventricle, medial to the sulcus limitans.

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The nucleus contains two main groups of neurons: motor neurons and interneurons. It contains also a third group, a small number of neurons that send their axons to the flocculus of the cerebellum.

Motor neurons of the abducens nucleus form the ipsilateral abducens nerve (the sixth cranial nerve, CN VI). Abducens nerve is a pure motor nerve and innervates the lateral rectus muscle of the ipsilateral eye. The main function of the muscle is to abduct the eye.

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