Magnetic resonance imaging assessment of brainstem distortion associated with a supratentorial mass.

Quantitative measurements of brainstem distortion and neural dysfunction were obtained in 25 cases of chronic subdural haematoma. The horizontal and rotational brainstem displacements were measured on axial and coronal MRI in all patients pre-operatively, and brainstem auditory evoked responses (BAERs) were obtained in 11 cases. Logarithmic relationships were noted on both horizontal and rotational displacements of the brainstem and cerebrum. The type of shift changed in the rostro-caudal direction. In the axial plane, the cerebral hemisphere shifts and rotates, the midbrain shifts laterally with no rotation, and the pons shifts minimally but rotates moderately. In the coronal plane, the marked rotation of the cerebral hemisphere and moderate rotation of the brainstem result in midbrain kinking, suggesting a downward displacement of the midbrain. The prolongation of BAER latencies and central conduction times correlated with septum shift. The results of peak-V latency indicated that brainstem rotation in the coronal plane reflects upper brainstem dysfunction most closely. This study presents objective measurements of brainstem displacement shown on MRI, and clarifies the relationships between anatomical and physiological changes in the brainstem that are associated with supratentorial lesions.