Eye examination of a patient revealed lack of downward gaze and loss of convergence but has normal pupillary reactions to light. What is the MOST probable location of the lesion?
In this patient the lesion is most probably located at the level of inferior colliculus. Features of lesion at the level of inferior colliculus are normal pupillary reactions to light, lack of downward gaze and loss of convergence. It could be due to lesions of the pineal gland, multiple sclerosis, vascular diseases or Wernicke's encephalopathy. Lesions in the collicular region is caused by pressure and distoion of underlying structures in the midbrain and not by damaged to specific pathways traversing the colliculi. It can produce any combination of impaired upward gaze, impaired downward gaze, pupillary abnormalities or loss accommodation reflex can occur. The general name for the clinical picture produced is called Perinaud's syndrome. Ref: Textbook of Ophthalmology edited by Sunita Agarwal, page 284.
Optic chiasm
Inferior colliculus
Superior colliculus
Edinger Westphal nucleus