Midbrain syndromes

Isolated oculomotor nerve palsy

• The superior rectus muscle receives innervation from the contralateral nucleus and the efferent fibers pass through the ipsilateral nucleus. Damage to the nucleus will produce difficulty in upgaze in both eyes. Damage to the fascicle will not have this feature.
• Mydriasis is sometimes absent.
• Ptosis and bilateral mydriasis may be observed in infarcts affecting the most medial part of the arterial territory.

Isolated trochlear nerve palsy

• Superior oblique muscle palsy.
• Often involves the region of the trochlear nucleus.

Weber syndrome

Occlusion of P1 segment of posterior cerebral artery is the most common cause and explains why this syndrome is commonly associated with thalamic and occipital lobe signs.

• Ipsilateral oculomotor nerve palsy.
• Contralateral hemiplegia.
• Supranuclear gaze palsy may exist.
• The ipsilateral pupil may be mydriatic or miotic depending on the preservation of sympathetic fibers.
• Contralateral sensory deficit may exist.

Claude syndrome

Paramedian upper midbrain infarction involving the red nucleus and the cerebellothalamic connections that pass through it.

• Ipsilateral oculomotor nerve palsy.
• Contralateral cerebellar signs.

Benedikt syndrome

Paramedian upper-midbrain infarction of the red nucleus.

• Oculomoor nerve palsy.
• Involuntary abnormal movements of the contralateral limbs, most often chorea or tremor.

Nothnagel syndrome

Caused by lesion of the midbrain tectum, involving the oculomotor nerve fascicles and superior cerebellar peduncle.

• Ipsilateral oculomotor nerve palsy.
• Contralateral cerebellar signs.

Supranuclear conjugate vertical gaze palsies

Paramedian or median upper-midbrain infarction. Can be produced by infarction of the territories of the paramedian perforating, superior cerebellar or the paramedian thalamic/mesencephalic arteries.

Proximal paramedian thalamic artery occlusions can produce bilateral infarcts of the thalamus and subthalamus and the paramedian midbrain with more complex semiology.

Upgaze palsy

Unilateral or bilateral midbrain infarctions involving posterior commissure, periaqueductal region or rostral interstitial nucleus of the medial longitudinal fasciculus.

Downgaze palsy

Caused by bilateral infarcts of the upper part of the midbrain.

Combined vertical conjugate gaze palsy

Caused by unilateral or bilateral midbrain infarcts.

Supranuclear disconjugate vertical gaze palsy

Caused by ipsilateral or contralateral unilateral infarcts affecting the upper midbrain.

Distinct forms include mononuclear elevation palsy and vertical one-and-a-half syndrome.

Other ophthalmological presentations

• Skew deviation
• Tonic ocular-tilt reactions
• Pretectal pseudobobbing (V-pattern convergence nystagmus)
• Intermittent corectopia (displacement of the pupil)
• Upper-eyelid retraction
• Ptosis associated with internuclear ophthalmoplegia and dissociated vertical nystagmus
• Convergence-retraction nystagmus
• Seesaw nystagmus
• Dissociated vertical-gaze palsies with asterixis

Midbrain lacunar syndromes

• Pure motor stroke
• Ataxic hemiparesis
• Midbrain locked-in syndrome (tetraplegia but intact voluntary eye movements) - can be produced by bilateral small infarcts in the lateral midbrain

Hemiplegia in PCA infarcts

Proximal PCA occlusions may cause infarction of the lateral upper midbrain resulting in contralateral hemiplegia. The associated hemianopia from involvement of the visual cortex and contralateral hemisensory deficits from posterolateral thalamic involvement may mimic proximal MCA occlusion syndrome.

Abnormal movements and asterixis

Unilateral or bilateral ballistic movements are sometimes caused by subthalamic infarcts.

Cerebellar syndrome

Rostral midbrain infarcts involving the red nucleus may spare the oculomotor fibers and present as a pure cerebellar syndrome with unilateral ataxia of the contralateral limbs.

Top-of-the-basilar syndrome

Ischemia (often bilateral) in rostral midbrain, posterior thalamus, inferior temporal lobes and occipital lobes caused by occlusion of the paramedian perforating branches from the top of the basilar artery.

• Oculomotor and visual deficits.
• Abnormal pupilary response.
• Behavioral abnormalities.
• Consciousness impairment.
• Hallucinations, somnolence, dream-like state.
• Often no motor deficit.

Peduncular hallucinosis

Caused by infarction of the upper-midbrain. Top-of-the-basilar syndrome is one of the more common causes but it may also be caused by ischemic or non-ischemic lesions of the middle cerebellar peduncle, pons or thalamus.

• Vivid, complex, detailed visual hallucinations
• Can occur periodically (often at sundown), continuously or episodically. May persist, become shorter or disappear with time
• Auditory or tactile hallucinations may coexist
• The hallucinations are distinctly different from those occurring in patients with delirium or other psychiatric disorders because the patients are most often aware of the abnormal perceptions.
• Insomnia or inversion of the sleep-wake cycle

Dorsal midbrain syndrome (Parinaud syndrome)

Caused by lesions of the rostral dorsal midbrain affecting the superior colliculi and pretectal structures.

• Paralysis of upgaze with intact other eye movements.
• Abnormal accomodation.
• Normal-to-large pupils with abnormal reflex to light but normal pupillary constriction on convergence.
• Eyelid retraction.
• Convergence-retraction nystagmus.