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Medulla

Function

  • The medulla contains a host of nuclei all tied up with fairly primitive functions such as cardiorespiratory, vomiting centres etc. It also contains the reticular activating system.
  • Medially to the olive and near the midline is the medial lemniscus that carries dorsal column sensation to the thalamus. Vascular supply is by branches of the vertebral artery including the posterior inferior cerebellar artery. PICA as we know classically irrigates lateral medulla.
  • Anteriorly there are median and paramedian perforators from the vertebrals. Lateral medullary syndrome is more commonly due to vertebral occlusion than PICA occlusion of itself.

Medial structures

  • Hypoglossal nerve nucleus controls tongue muscles and the nucleus lies near the midline and exists the posterior fossa through the hypoglossal formina. Each hypoglossal receives bilateral projections from the motor cortex. Unilateral weakness causes the tongue to bend to the weak side. Tongue can be weak and also can be apraxic.
  • Medial lemniscus with crossed fibres from the dorsal column (gracile and cuneate nuclei) on the way to the ipsilateral thalamus
  • Pyramids lie on either side of the midline on the ventral surface and contain the corticospinal motor tracts which are decussating.

Lateral structures

  • Nucleus ambiguus : Receives bilateral cortical innervation from the primary motor cortex. Efferents to IX and X and XI. Concerned with swallowing. Descending nucleus of V: which has its cell bodies within the trigeminal ganglion. Dorsal motor nucleus of X : preganglionic parasympathetic to nerves IX and X. Supplies heart, lungs and abdominal organs.
  • Nucleus solitarus : Lies in the medulla and receives input from VII, IX and X. Part of it is called the gustatory nucleus concerned with taste. Fibres pass from here to the venteroposteromedial nucleus of thalamus.
  • Laterally to the pyramids is the bulge of the inferior olivary nucleus which sends fibres to the cerebellum
  • Vestibular nuclei : four of these lie in floor of the IVth ventricle. Cochlear nuclei : closely associated with vestibular nuclei
  • Inferior cerebellar peduncle with dorsal spinocerebellar, olivocerebellar and cuneocerebellar tracts
  • Lateral spinothalamic tract (spinal lemniscus)
  • Spinal nucleus of V: Fibres concerned with touch, pain and temperature from the face goes to the spinal nucleus of V. Descend from pons down to the medulla.

Vascular Supply

  • Posterior inferior cerebellar artery which supplies the lateral medulla as well as the underside of the cerebellum. Occlusion to the PICA or the vertebral itself will cause an ipsilateral Lateral medullary syndrome.
  • Anterior spinal artery supplies medial structures and if occluded can cause a medial medullary syndrome. Penetrating branches of the vertebral can also supply structures.

Lateral Medullary Syndrome

Introduction
  • Also known as Wallenberg syndrome and due to occlusion of the PICA artery which is a branch of the ipsilateral vertebral artery or the end of it.
  • There is infraction of the posterolateral medulla and damage t those localised structures
  • Not a common type of stroke. The main disability is persisting dysphagia and risk if aspiration.
  • Occlusion of the posterior inferior cerebellar artery (PICA) or the intracranial vertebral artery due to embolism, vertebral dissection, thrombosis
Clinical
  • Damage to the IX, X and XI nerves - dysarthria and dysphagia
  • Sympathetic loss - Ipsilateral Horner's syndrome
  • Abnormal pain and temperature appreciation on the ipsilateral side of face
  • Spinocerebellar tracts - Cerebellar signs in ipsilateral limbs
  • Contralateral spinothalamic loss in limbs and body
  • May be some autonomic dysfunction
Investigations
  • Bloods: FBC/U&E/ESR/CRP/Glucose, lipids
  • ECG/Holter/Echo:Look for AF or evidence for AF
  • MRI/A is best but can occasionally be negative or show occlusion of ipsilateral PICA or Vertebral. It may show a dissection.
Management
  • Aspirin 300 mg 2 weeks then Clopidogrel 75 mg od
  • PEG early for severe dysphagia which can often be removed at 6 weeks
  • Assess particularly for embolic stroke causes
  • Standard ischaemic stroke management and Neurorehabilitation

Medial Medullary Syndrome

Introduction
Clinical
Investigations
Management