Welcome to Stroke Education.CO.UK

Learning objectives

  • What is the thalamus and related structures
  • What does it do and clinical effects of damage
  • What is blood supply and risk of stroke

    Subthalamic nuclei

    Part of the basal ganglia. Damage here can lead to dyskinesias and hemiballismus and associated motor disorders.

    Axial cross section Note that anatomical diagrams show the orientation of the skull facing down and imaging such as MR and CT show the skull looking up. It makes more sense to get use to the radiological presentation of anatomy.

    Thalamus

    This is the largest mass of cell bodies within the nervous system. The thalamus may be affected by both haemorrhage and infarction involving the posterior cerebral artery and its branches. It is a large paired egg shaped structures sitting opposite each other across 3rd ventricle. Contains discrete collections of neuronal cell bodies called nuclei. Separated by a y shaped internal lamina. All but the reticular nucleus send fibres to the cortex. Receives all sensory stimuli (except olfactory) including from the cerebellum, spinal cord and cranial nerves. Bilateral thalamic strokes can cause amnesia as well as hypersomnolesence. Others cause hemisensory loss. Thalamic damage can also lead to so called thalamic pain syndromes where patients experience severe often sharp neuropathic pain in the corresponding contralateral side and it is notoriously hard to treat satisfactorily and causes much morbidity. It contains several discrete thalamic nuclei

    • Medial dorsal thalamus
    • Anterior thalamus
    • Back of thalamus
      • Lateral Geniculate body: Fibres from the optic tracts
      • Medial Geniculate body: fibres from inferior colliculus
    • lateral thalamus
      • Dorsal nucleus
      • Ventral nucleus

    Pons

    Ventrally rather bulbous due to large cell groups and fibres running transversely between large pontine nuclei and the cerebellum. Laterally lies the bulging middle cerebellar peduncle. The pontine nuclei mediate fibres coming from cerebral cortex to the cerebellum. The VI, VII, VIII and V nerves all leave ventrally. As its name suggests it is bridge like and like any bridge it is a major crossover centre for fibres carrying signals bidirectionally from above and below and communication with the cerebellum. Like any bridge it covers the CSF filled 4th ventricle which separates it from the cerebellum with its vermis and hemispheres which sit tightly behind.

    The Pons contains the Corticospinal fibres, Corticopontine fibres, Pontocerebellar fibres and Raphe nuclei. The lower Pons contains the Nucleus of VI, Nuclei of VII, Facial nerve, Superior salivatory Gustatory. The facial nerve and abducent nerve are closely associated as the exiting VII nerve loops around the nucleus of VI. Also contained is the Medial lemniscus (carries contralateral dorsal column), Spinothalamic tract (carries pain and temperature) and Middle cerebellar peduncle which contains fibres from c/L pons to cerebellum.

    Medial structures

    • Medial longitudinal fasciculus
    • VI (Abducent) nerve nucleus and fibres
    • Genu of VII (Facial) closely associated with VI
    • Medial lemniscus (carries contralateral dorsal column)
    • Corticospinal tract

    Lateral structures

    • Facial nucleus VII and nerve fibres
    • Spinal nucleus and tracts of V
    • Lateral spinothalamic tract (spinal lemniscus)

    Vascular supply is from the basilar artery which lies anteriorly and provides median and paramedian perforators. Short circumferential branches irrigate more laterally and laterally including the middle cerebral peduncle is supplied by branches of the superior cerebellar and anterior inferior cerebellar arteries.

    Medulla

    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. PIC 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.
    • 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 : 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 is from the 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. Medially the anterior spinal artery if occluded can cause a medial medullary syndrome. Penetrating branches of the vertebral can also supply structures.

    Structural anatomy

  • BRAIN PARENCHYMA
  • Pia: The most closely adherent and inner layer is the pia which is closely related to the surface of the brain sulci and gyri. It is very delicate and vascular covering the brain and spinal cord.
  • Subarachnoid space: Blood vessels lie in this plane and it is the plane of bleeding for berry aneurysms. Terminates at S2 in sacral vertebra
  • Arachnoid: It is separated from the arachnoid by the subarachnoid space. It is delicate but non vascular.
  • Subdural space: traversed by bridging veins which can bleed. Potential space in the spinal cord.
  • Dura: Above this lies the dura mater. Between the arachnoid and dura mater is the subdural space where bleeds due to the shearing of veins may be seen.
  • Extra (Epi)dural space: between the skull and dura lies the extradural space. Contains meningeal arteries and veins. The dura matter is adherent to the skull at areas where bones fuse which limits the spread of blood with extradural haemorrhage. Convex shaped bleeds on CT. In the cord injection of this space may be used to cause anaesthesia.
  • SKULL PERIOSTEUM

    Fibrous Membranes

    • Falx cerebri which is a vertical membrane that separates right and left cerebral hemispheres. If there is a rapidly expanding unilateral cerebral space occupying lesion or extraaxial lesion (EDH or SDH) can force the uncus of the temporal lobe under the falx.
    • Falx cerebelli separate the right and left lobes of the cerebellum.
    • Tentorium cerebelli lies between occipital cortex and superior surface of cerebellae. This helps enclose the cerebellum within the bony and membrane bound posterior fossa where for example a large cerebellar haematoma needs evacuation before it can cause an acute rise in pressure compressing the brainstem or causing hydrocephalus.

    Herniation syndromes - seen in the context of rising ICP in the comatose patient. These are all neurosurgical emergencies and demand rapid escalation.

    • Subfalcine: the brain is pushed under the falx separating right and left cortices. There may be compression and stroke involving the anterior cerebral artery with contralateral leg weakness. The lateral ventricles and brain midline will be distorted and shifted and can be seen on CT.
    • Transtentorial: A supratentorial mass or pressure gradient forces the uncus of the temporal lobe down beneath the tentorium 'tent' can result in an ipsilateral oculomotor paresis (dilated pupil, ptosis, down and out pupil) and compression of the posterior cerebral artery giving contralateral hemianopia. The shift forces the opposing cerebral peduncle against the edge of the tentorium causing contralateral hemiparesis to the peduncle. The indentation of the tentorium edge causes kernohan's notch on the opposite cerebral peduncle. This is a false localising sign.
    • Transforaminal: the brainstem and cerebellar tonsils are forced down into the foramen magnum. Pressure on the medulla leads to apnoea and death

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