Visual suppression test and ocular dysmetria: some electronystagmographic findings relevant to the assessment of size of cerebellopontine angle tumors.

Patients with cerebellopontine angle tumors underwent vestibular examination, testing of voluntary fast and slow conjugate eye movements and of visual-vestibular interaction (visual suppression test--VST) by electronystagmography (ENG). Both spontaneous and evoked nystagmus (Ny) and dysmetric alterations of the voluntary conjugate eye movements are relevant to cerebellopontine pathology. This study shows that ENG may reveal damage to the vestibular brain-stem and archicerebellar structures, the ENG signs of which very often precede the clinical signs of compression. In cranial nerve VIII neuromas vestibular and oculomotor instrumental investigations yield valuable clues for early diagnosis of tumor transition from the otological to the neurosurgical stage.