Brainstem Anatomy
- The brainstem is divided transversely into the midbrain, pons and medulla
- All the cranial nerve nuclei save I and II lie in the brainstem
- Midbrain:
- III (oculomotor)
- Pre-tectal and Edinger-Westphal nucleus (consensual light reflex)
- II → pre-tectal nucleus → projections to bilateral Edinger-Westphal nuclei (parasympathetic nuclei of III) → ciliary ganglion → pupil constriction
- IV (trochlear), the only cranial nerve which decussates
- Pons
- V (trigeminal)
- VI (abducens)
- VII (facial)
- VIII (vestibulocochlear)
- Medulla
- IX (glossopharyngeal)
- X (vagus)
- XI (spinal accessory)
- XII (hypoglossal)
- The midline structures of the brainstem are:
- Motor (pure) nuclei: III, IV, VI and XII
- Medial longitudinal fasciculus
- Motor (corticospinal) tract, which decussates in the lower medulla
- Medial lemniscus (proprioception and vibration), which decussates in the middle medulla
- The lateral structures of the brainstem are:
- Sensory nucleus of Vth nerve
- Spinothalamic tract (pain and temperature, decussates immediately in lower cord)
- Spinocerebellar tract (proprioception from limbs to cerebellum), ipsilateral (does not cross)
- Sympathetic pathway, ipsilateral
Midbrain Syndromes
- Weber’s syndrome
- Ipsilateral third nerve palsy
- Contralateral hemiparesis (involvement of cerebral peduncle containing corticospinal fibres which decussate in the medulla)
- Benedikt’s syndrome (posterior cerebral artery)
- Ipsilateral third nerve palsy
- Contralateral chorea, athetosis, tremor or cerebellar ataxia (involvement of the red nucleus which receives projections from the contralateral hemisphere and projects to the ipsilateral cerebellum)
- Claude’s syndrome (posterior cerebral artery)
- Ipsilateral third nerve palsy
- Contralateral ataxia (involvement of the superior cerebellar peduncle)
- Parinaud’s syndrome
- Typically caused by tumours of the pineal gland
- Compress on the vertical gaze centre, resulting in vertical gaze palsy
- Vertical Doll’s not affected as the lesion is supra-nuclear
- Irregular pupils
- Eyelid retraction
- Convergence nystagmus on upward gaze
- Loss of accommodation
Pontine Syndromes
- Raymond’s syndrome
- Ipsilateral sixth nerve palsy
- Contralateral hemiparesis (corticospinal tract which decussates in medulla)
- Millar-Gubler’s syndrome
- Ipsilateral abducens nerve palsy
- Ipsilateral facial nerve palsy with loss of corneal reflex
- Contralateral hemiparesis
- ± contralateral loss of vibration / proprioception
- Lateral pontine syndrome (anterior inferior cerebellar artery)
- Ipsilateral loss of pain and temperature from face (sensory trigeminal)
- Loss of ipsilateral corneal reflex (sensory trigeminal)
- Contralateral loss of pain and temperature from limbs (spinothalamic tract)
- Ipsilateral lower motor neuron facial weakness (course of nerve)
- Ipsilateral sensorineural hearing loss (vestibulocochlear nerve)
- Ipsilateral Horner’s syndrome (descending sympathetic pathway)
- One-and-a-half syndrome
- Conjugate horizontal gaze palsy in one direction (involvement of ipsilateral abducens)
- Internuclear ophthalmoplegia in the other eye
- Bilateral lesion (locked-in syndrome)
- Quadriplegia
- Aphonia
- Bilateral facial and abducens nerve palsy
- Spares oculomotor and trochlear nerves (lesion below midbrain)
Medullary Syndromes
- Medial medullary syndrome (Dejerine’s syndrome – distal vertebral artery / proximal anterior spinal artery)
- Spares face
- Ipsilateral tongue weakness (tongue deviates towards side of lesion)
- Contralateral hemiparesis (may be variable depending on location of lesion in relation to decussating corticospinal tract fibres)
- Contralateral loss of vibration / proprioception
- Pain and temperature from limbs not affected
- Lateral medullary syndrome (Wallenberg’s syndrome – vertebral artery / posterior inferior cerebellar artery)
- Ipsilateral ataxia (spinocerebellar tract and inferior cerebellar peduncle)
- Ipsilateral loss of pain and temperature sensation in face (spinothalamic tract of trigeminal nerve)
- Contralateral loss of pain and temperature sensation from limbs (spinothalamic tract)
- Ipsilateral Horner’s syndrome (sympathetic fibres)
- Ipsilateral reduced gag reflex (vagus nerve)
- Dysphagia, dysarthria (bulbar palsy)
Differential Diagnosis of Brainstem Syndromes
- Vascular (ischaemic / haemorrhagic stroke)
- Inflammatory (e.g. demyelination in multiple sclerosis, acute disseminated encephalomyelitis)
- Brainstem encephalitis (Bickerstaff’s encephalitis)
- Central pontine myelinolysis
- Trauma
- Neoplastic (brainstem gliomas / ependymomas)
- Arnold-Chiari malformation
- Syringobulbia