Brainstem auditory evoked potential abnormalities and magnetic resonance imaging in posterior fossa lesions

Brainstem auditory evoked potentials (BAEPs) were evaluated in a series of 15 patients with extra-axial cerebello-pontine angle tumors (3 cases), demyelinating plaques (11 cases), and intra-axial tumor (1 case), verified by magnetic resonance imaging (MRI). A satisfactory correlation between the location of the lesions and the type of BAEP abnormalities was found in 11 cases. In 2 other cases, definite MRI brainstem lesions located outside the acoustic pathways were associated with normal BAEPs. In the opposite situation (2 cases of BAEP abnormalities with normal MRI), the inability of MRI to detect demyelinating lesions may be due to the temporal evolution of the lesions themselves. The results of this BAEP-MRI comparative study confirm that BAEP is a sensitive diagnostic tool in revealing brainstem dysfunction, although its localizing power appears to be debatable. The most satisfactory MRI/BAEP topodiagnostic correlation was found with lesions involving the acoustic nerve in its intracranial tract or the caudal pons and bulbopontine junctions.