Auditory Brain-Stem Potentials With Unilateral Pontine Hemorrhage Edward J. Hammond, PhD; B. Joe Wilder, MD; Ira J. Goodman, MD; Stephen B. Hunter, MD \s=b\ Although there have been extensive anatomical and physiological studies in animals, the actual neural sources, or e ven the laterality, of some components of auditory brain-stem evoked potentials in humans are uncertain. We studied these responses in a 56-year-old patient who had a clearly demarcated pontine hemorrhage on the right side. The patient Was somnolent, gia with dense left hemiplesigns of involvement of right nerves V, VI, and VII. Stimulation of the left ear (ie, contralateral to the lesion) and cranial evoked a normal series of waves with clearly resolved positive components Peaking at 2.0, 3.3, 4.8 (wave IV), and 6.0 uncertain.' Although anatomical and physiological studies in animals indicate that components occurring after wave III are generated in the brain stem contralateral to the stimulus,12 Chiappa et al" and others6 have pre- sented clinical-physiological correlations in a few patients that suggest a brain-stem source ipsilateral to the stimulated ear. We studied these potentials in a patient who had a unilateral pontine hemorrhage; the results in this study suggest an ipsilateral source for wave V and bilateral source for wave IV. ms (wave V). Stimulation of the right ear (ie, ipsilateral to the lesion) evoked only waves I, III, and IV. These results suggest that a pathway ipsilateral to the stimuear lated is necessary and sufficient for auditory generati wave IVonis generated of wave V and that in bilateral path- ways. (Arch Neurol 1985;42:767-768) A noußh there have been extensive and physiological sti«lies fl?na.tomici»l in animals,1-2 the actual neural s urces, or even the laterality, of some of auditory brain-stem evokPHnentS ed Potentials in humans are From publication July 3,1984. Accepted theforNeurology and Medical Research Service, Veterans Administration Medical Cen- NoDtaUniehpunrlmfdgy,t versity MeColFlHammond, of (Drs odlriecdigenae and the Department of Wilder, and Goodman), of Florida (Dr Hunter), PUniversity athol gy, Gainesvile. PATIENT AND METHODS The patient was 56 years old, somnolent, but easily arousable. He could respond to commands, and was severely dysarthria He had no lateral eye movements; there was intermittent ocular bobbing. He had a good down gaze, with coarse downbeat nystagmus. There was a marked right lower motor-neuron seventh nerve lesion. There was also left hemiparesis, with increased extensor tone on the left; plantar flexion and triple llexion responses were RESULTS Evoked potential waveforms are shown in Fig 2. Stimulation of the left ear evoked a normal complex of waves with clearly resolved positive components peaking at 2.0 ms (wave I), 3.3 ms (wave III), 4.8 ms (wave IV), and 6.0 ms (wave V). Stimulation of the right ear evoked clearly resolved components at 2.1 ms (wave I), 3.75 ms (wave III), and 4.6 ms (wave IV). A wave V was not seen. Fig 1.—Auditory brain-stem evoked potentials in response to independent stimulation of lett and right ears. Two replications are shown. Stimulation of left ear evoked clear waves I, III, IV, and V; stimulation of right ear evoked waves I, III, and IV. CrA, present on the left. Computed tomography showed a unilateral right-sided pontine lesion extending superiorly to the quadrigeminal plate cistern and fourth ventricle. Electroencephalography showed mild diffuse slowing. The unilaterallty of the hemorrhage was confirmed at postmortem examination, which disclosed only a small extension across midline at the level of the trapezoid body (Fig 1). Auditory brain-stem evoked potentials were recorded at bedside (amplifier bandpass: 80 to 1,600 Hz). Stimulus intensity was 85-dB hearing level. Potentials were recorded in response to independent stimu- Cz-A? / Cz-A, Right Ear Stimulation lation of each ear. Rarefaction click rate Electrode linkage was from scalp location C, to each earlohe. An automatic artifact rejection facility was used. was 5/s. Downloaded From: http://archneur.jamanetwork.com/ by a University of California - San Diego User on 06/08/2015 | C2-A, Time, ms Fig 2. Sections of brain taken one week after recordings shown in Fig 1. Left, Level of trigeminal nerve; center, level at midpons; right, level of midbrain just caudal to inferior colliculus. In left section, extension of lesion across midline is seen. — COMMENT This patient had a sharply demarcated right-sided pontine hemorrhage, which extended from just above the pontomedullary junction up to the midbrain (Fig 2). A clear wave I is seen in response to stimulation of either ear. For right ear stimulation, wave II is clearly absent (a normal variant). Wave III is clearly present in response to right ear stimulation; for left ear stimulation, a smaller-amplitude wave (3.3 ms), which could represent wave II or a foreshortened wave III, is seen; this is possibly a reflection of extensive damage at the level of the trapezoid body. Stimulation of the right ear (ie, ipsilateral to the lesion) failed to evoke a wave V, whereas stimulation of the left ear (contralateral to the lesion) evoked a clear wave V. This suggests a brain-stem source for wave V, which is ipsilateral to the stimulated ear. Wave IV was present in response to either left or right ear stimulation. These results are in agreement with clinical data presented by Chiappa et al.3'5 Starr and Squires7 presented topographical mapping studies in response to con- densation click stimuli and arrived at similar conclusions concerning the generator(s) of wave IV. A 1983 study in animals* indicated an ipsilateral source for the P4 wave (analogous to the human wave V). Although the auditory pathway |s commonly thought to be predotf»' nantly crossed, there is an amp'c uncrossed pathway. The anterove11' tral cochlear nucleus projects to bot11 the contralateral and ipsilateral vei>'4 tral nuclei of the lateral lemniscus» which in turn sends third-order fibe1"' to the ipsilateral inferior colliculusIn the primate there is also a pathway of second-order neurons from tn* cochlear nucleus to both ¡psilateri» and contralateral inferior colliculi-1 Alice Cullu and Anne Crawford of the Vet*»" Administration Research Service office and Shirley Dunhar gave secretarial ass1' editorji ans lance. 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