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Midbrain 2. NEOPLASMS- DORSAL MIDBRAIN SYNDROME (PARINAUD'S SYNDROME) A Sample Case: A 6 year old boy was noticed by his mother to have developed pubic hair and an enlarged penis. The neurologic examination revealed a bilateral paralysis of upward gaze and a questionable weakness of convergence. The pupils constricted upon convergence but not in response to light. Explanation - When due to a tumor of the pineal gland this syndrome may be marked by precocious puberty primarily occurring in males; the tumor secretes hCG (human chorionic gonadotrphic hormone) which causes testosterone production. The neurologic manifestation of this syndrome is primarily the inability to move the eyes vertically upward but is not invariably associated with paralysis of downward gaze. The lesion occurs in the dorsal part of the superior colliculus and so is associated with the region of oculomotor nuclei, pretectal nuclei,. posterior commissure, and the vertical gaze center associated with the rostral MLF. There may be changes in pupillary responses (fixed pupils in response to light but which constrict in accommodation) and often there is eyelid retraction and a lag in elevating the lid. Often there is no evidence of paralysis of individual ocular muscles. This syndrome occurs with injury to the superior colliculus, pretectal area, and posterior commissure. It occurs in encephalitis, and in tumors of the pineal gland, posterior 3rd ventricle, and midbrain. A vascular etiology is occlusion of the collicular branches of the posterior choroidal artery which is a branch of the posterior cerebral artery.
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