GENERAL NEUROLOGY
Parinaud syndrome
Updated on 03/06/2024, published on 31/05/2024
- Parinaud syndrome is caused by disturbance of the midbrain tectum and is characterized by upward gaze palsy, convergence retraction nystagmus, light-near dissociation, and bilateral lid retraction
- syndrome is named after French ophthalmologist Henri Parinaud; synonyms: dorsal midbrain syndrome, Sylvian aqueduct syndrome, pretectal syndrome
Anatomy and pathophysiology
- the vertical gaze center lies in the rostrodorsal portion of the midbrain and involves several key structures:
- rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF)
- the interstitial nucleus of Cajal (INC)
- the nucleus of Darkschewitsch
- the nucleus of the posterior commissure (involved in downward gaze)
- oculomotor nucleus complex (CN III)
- Parinaud syndrome leads to upward gaze paresis due to riMLF and INC lesion; downgaze is relatively preserved; it is typically only affected by large space-occupying lesions or bilateral lesions
- light-near dissociation (pupils accommodate but do not react to light) is due to damage to the pretectal and Edinger-Westphal nuclei or the decussating fibers of the pretectal nucleus in the posterior commissure
- convergence-retraction nystagmus – due to abnormal burst activity in the pretectal area, causing intermittent co-contraction of the medial recti (convergence) + simultaneous superior and inferior rectus (retraction) during attempted upward gaze
- bilateral lid retraction (Collier sign) due to loss of the supranuclear inhibitory input to the third nerve nucleus; the levator palpebrae superioris receives constant stimulation via the oculomotor nerve, resulting in lid retraction
- riMLF is a crucial structure involved in the control of vertical eye movements
- located in the rostral part of the midbrain, near the junction of the midbrain and the diencephalon, adjacent to the medial longitudinal fasciculus (MLF)
- primarily responsible for initiating and coordinating rapid vertical eye movements (saccades)
- receives inputs from various cortical and subcortical regions involved in the control of eye movements, including the frontal eye fields and superior colliculus
- sends direct excitatory inputs to the oculomotor (III) and trochlear (IV) nuclei, which innervate the extraocular muscles responsible for vertical eye movements
- riMLF works in conjunction with other nuclei, such as the interstitial nucleus of Cajal (INC), to integrate and execute vertical eye movements
- lesions in the riMLF can lead to vertical gaze palsy, particularly affecting the ability to perform vertical saccades
- INC plays a critical role in the control of eye movements, particularly in maintaining vertical gaze and contributing to the stabilization of eye position
- it integrates signals from the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) for vertical saccades and smooth pursuits and is involved in the vestibulo-ocular reflex (VOR)
- receives input from various brainstem structures involved in eye movement control, such as the superior colliculus and the riMLF
- sends projections to the oculomotor and trochlear nuclei, which innervate the extraocular muscles responsible for vertical eye movements (superior and inferior rectus, superior and inferior oblique muscles)
- the nucleus lies in the periaqueductal gray matter ventral to the aqueduct at the level of the superior colliculi
- it has two major components:
- a medially situated parasympathetic nucleus, the so-called Edinger-Westphal nucleus (or accessory autonomic nucleus), which innervates the intraocular muscles (the sphincter pupillae muscle and the ciliary muscle)
- a larger and more laterally situated nuclear complex for four of the six extraocular muscles (the superior, inferior, and medial rectus muscles and the inferior oblique muscle). There is also a small nuclear area for the levator palpebrae muscle
Etiology
- ischemic stroke – occlusion of pretectal perforators or dorsal penetrating branches from the posterior cerebral artery (PCA) incl. quadrigeminal artery
- vascular causes are more common among elderly populations
- external compression (hydrocephalus, pineal tumors, aneurysm)
- brainstem tumors (glioma), hemorrhage, or infections (e.g., toxoplasmosis)
- multiple sclerosis
- PSP
- Whipple’s disease (GIT disturbances, dementia, uveitis)
Clinical presentation
- upward gaze palsy (“sunset” eyes)
- light-near dissociation
- normal or slightly dilated pupils
- no light reaction with preserved reaction to accommodation (pseudo Argyll-Robertson pupil)
- convergence-retraction nystagmus during convergence
- eyelid retraction (Collier sign)
Differential diagnosis
- bilateral paralysis of the muscles elevating the eyeball (RS and Ol – “double elevator palsy”)
- pseudo-dorsal midbrain syndrome in myasthenia gravis
- local causes of upward movement limitation due to orbital lesions (thyroid eye disease, Brown’s syndrome of the superior oblique tendon)
- congenital or age-related limitation of upward movement