[Unilateral supranuclear abducens palsy in a pineal tumor].

A 13-year-old boy complained of frequent headaches and diplopia on rightward gaze. A CT scan demonstrated hydrocephalus and a non-homogeneous enhancing mass in the pineal area, leading to a diagnosis of pineal tumor. The physical examination revealed no abnormalities. On neurological examination, there were a right homonymous hemianopsia and slight choked disc in both optic fundi. His right eye was slightly adducted on primary gaze. On right lateral gaze, his right eye could not move beyond the midline and showed gaze paretic nystagmus, whereas his left eye could move fully in all directions. The abducens palsy could be overcome by the oculocephalic maneuver or caloric test. Interestingly, his right eye could abduct when his left eye was covered. From these finding, this was labelled a supranuclear abducens palsy. The convergent nystagmus was observed. Rightward OKN (quick phase to right) of the right eye was abolished with and without the left eye covered, while leftward OKN of the right eye was preserved. Pursuit to right was disturbed. After removal of the tumor, the gaze palsies disappeared. It is postulated that the supranuclear lateral gaze palsy was caused by impairment of supranuclear control by involvement of lateral gaze pathways to gaze center coursing near the oculomotor nucleus.