[Visual illusion with 90-degree forward rotation on the sagittal plane due to acute paramedian pontine infarction]

We report an unusual and dramatic type of visual illusion, a 90-degree forward rotation of vision on the sagittal plain in 2 cases of acute paramedian pontine infarction. At initial neurological examination, they were both alert and well-oriented. The one case had slight right lateral gaze palsy, left motor paresis and hallucinose pédunculaire, and the other case had slight right gaze palsy, right Horner's syndrome, slight left sensory deficit and left limb ataxia. They complained that they felt as if they themselves, the bed, the floor and the ceiling were standing vertically, although actually they were lying on the bed horizontally. The sensation of the 90-degree rotation of vision frequently occurred as soon as they awoke or opened their eyes, and continued for a few minutes. The illusion disappeared within several days after the onset of the pontiue infarction. These visual symptoms may be contributed to imbalance of the integrated processing among the vestibular, visual and somatosensory systems resulting from the brainstem lesion involving the vestibulo-cortical network fibers, or may be considered as dysfunction of the ascending reticular activating system similar to the mechanism of hallucinose pédunculaire.