Visual environmental rotation: a novel disorder of visiospatial integration.

A 70-year-old man experienced an unusual disorder of visual perception after undergoing a ventriculoperitoneal shunt for normal-pressure hydrocephalus. The disorder was characterized by transient episodes of 90 degrees rotation of the visual environment, rather than the retinotopic visual field. This phenomenon is different from standard visual allesthesia and may have been caused by disordered integration of vestibular and visual inputs to the posterior parietal cortex or perseveration of a pre-existing environmental memory trace.