Table II

Features of the Dorsal Midbrain Syndrome

1. Limitation of upward eye movements:

Saccades, smooth pursuit, vestibulo-ocular reflex, Bell's phenomenon

2. Lid retraction (Collier's sign): occasionally ptosis

3. Disturbances in downward eye movements:

Downward gaze preference (setting-sun sign) Downward saccades and smooth pursuit may be impaired, but vestibular responses are preserved Down-beating nystagmus

4. Disturbances of vergence eye movements:

Convergence retraction nystagmus (Koerber-Salus-Eischnig syndrome)

Paralysis of convergence Spasm of convergence Paralysis of divergence "A" or "V" pattern exotropia Pseudo-abducens palsy

5. Fixation instability (square-wave jerks)

6. Skew deviation

7. Pupillary abnormalities (light-near dissociation)

findings (Table II). This condition is known by a plethora of names: Parinaud's syndrome, Koerber-Salus-Eischnig syndrome, pretectal syndrome, dorsal midbrain syndrome, and Sylvian aqueduct syndrome. Eyelid abnormalities also occur, such as Collier's tucked lid sign (i.e., lid retraction). Vergence may also be affected. Many of the features of the dorsal midbrain syndrome result from damage of the fibers crossing the posterior commissure, including those from the riMLF and interstitial nucleus destined for their namesakes on the contralateral side. Invariably, damage to other nearby structures may also occur during these lesions, the most important of which are the nuclei of the posterior commissure, the interstitial nucleus of Cajal, the fasciculus retroflexus, and the riMLF. Destruction of the riMLF bilaterally results in complete paralysis of all vertical eye movements (both up and down). Furthermore, as indicated earlier, damage to the interstitial nucleus of Cajal almost always includes damage to the fibers of passage from the riMLF. A single occlusion to the thalamoperfor-ating artery has sometimes led to bilateral infarction of the rostral midbrain-posterior diencephalon near the midline and paralysis of vertical eye movements.

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