AKA
- Dorsal midbrain syndrome
- Sylvian aqueduct syndrome
- Pretectal syndrome
- Koerber-Salus-Elschnig syndrome.
Definition
- Upward gaze palsy +
- Convergence retraction nystagmoid (not a true nystagmus) +
- Light-near dissociation +
- Bilateral lid retraction
Aetiology
- Lesions affecting structures in the dorsal midbrain
- Most common
- Vascular (Infarction & Hemorrhage)
- Elderly
- Tumors (most common)
- Pineal region tumours
- Pineocytoma and germinoma account for up to 40%
- Younger
- Demyelination
- Inflammation
- Infection
- Trauma
- Hydrocephalus
- Children:
- Obstructive hydrocephalus causing more than 10mmHg pressure difference between supra and infra tentorial compartment. Causes distortion of midbrain leading to caudal midbrain dysfunction.
- Arteriovenous malformations
Pathophysiology
- Involvement of the structures of the dorsal midbrain produce the findings.
Up gaze palsy
- Damage of the vertical gaze center
- Consist of
- Rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) AND
- Responsible for vertical saccades
- Interstitial nucleus of Cajal (INC) AND
- Controls other vertical eye movements including vertical gaze holding and skew deviation
- Its connections.
- Both of these nuclei lie in close proximity to the cerebral aqueduct and decussate in the posterior commissure.
- Their presence in the posterior commissure makes them particularly susceptible to unilateral space occupying lesions and elevated cerebrospinal fluid pressures.
- Downgaze is relatively preserved in PS until late in the disease due to its bilateral innervation and is typically only affected by large space occupying lesions or bilateral lesions.
Convergence retraction nystagmoid
- Damage of the midbrain supranuclear fibers.
- These fibers normally exert an inhibitory effect on the third nerve nucleus, thereby preventing activation of the extraocular muscles innervated by CN3.
- Retraction due to:
- Superior and inferior rectus muscles receive constant stimulation, resulting in retraction of the globe.
- Involuntary retraction
- Stimulation of the medial rectus muscles causes it to overpower the lateral rectus
- Lateral rectus innervate by CN6 lives in pons
- Not a true nystagmus
- Does not have a rhythm
Light-near dissociation
- Light reflex (defect)
- Pathway goes thru the Pretectal nucleus which is damage in Parinauds
- Near accommodation (still working)
- Pathway goes thru LGN into optic radiations, therefore avoiding pretectal nucleus
Bilateral lid retraction (Collier sign)
- Due to loss of the supranuclear inhibitory input to the third nerve nucleus → no inhibitory effect of the supranuclear fibers → Levator palpebrae superioris receives constant stimulation via the oculomotor nerve, resulting in lid retraction.
- Like convergence retraction nystagmus
Presentation
General
- The full PS triad of up gaze palsy, convergence retraction nystagmus, and light-near dissociation may only be seen in up to 65% of cases.
Up gaze palsy
- Most common initial presentation (87-100%)
- Limited upward gaze often leads to a preference for downward gaze in primary position and is described as the setting-sun sign.
Convergence-retraction nystagmus
- Description: Irregular, oscillatory movements of the eyes, particularly with upward gaze and saccades upward.
- Involuntary convergence and globe retraction are also most evident on upward gaze.
- 35-88%
Light-near dissociation
- Presents with poor bilateral pupillary constriction in response to light, but preserved constriction with convergence.
- 65-96%
Collier’s sign (bilateral lid retraction)
- 20-40%
Other signs & symptoms
- Ataxia
- Exotropia
- Convergence insufficiency
- Papilledema
- Diplopia
- Blurry vision
- Oscillopsia
- Nausea
- Vomiting
Outcome
- Depends on aetiology
- Correction of hydrocephalus with CSF shunting may lead to a complete resolution of all symptoms.
- Full resolution of symptoms following tumor resection is rare, with only around 12% of patients experiencing complete resolution.
- Even with treatment, most patients continue to experience at least some residual ocular motility disturbances.
Management
- For obstructive hydrocephalus aetiology in paediatrics (see above)
- Shunt
- Resolution of complex symptoms after shunt revision was often slow.
- In some cases, a transient paradoxical aggravation of clinical symptoms was observed after shunt revision, despite improved radiological findings and normal or subnormal ICP levels.
- Inversion of the pressure gradient (lower supratentorial pressure) was observed after shunt revision because the shunt only drained the supratentorial system, and the infratentorial compartment remained excluded.
- ETV
- Was performed in 11 cases and allowed resolution of the symptoms and withdrawal of the shunt.
- As the "ideal solution" and "best treatment" because it re-equilibrates CSF pressure across the tentorium by restoring free communication between the supratentorial and infratentorial compartments
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