Auditory brain stem responses (ABR) in patients with acute severe closed head injuries. The use of a grading system

Impact of mild traumatic brain injury on auditory brain stem dysfunction in mouse model

The auditory brainstem response (ABR) is an electrophysiological test that examines the functionality of the auditory nerve and brainstem. Traumatic brain injury (TBI) can be detected if prolonged peak latency is observed in ABR measurements, since latency measures the neural conduction time in the brainstem, and an increase in latency can be a sign of pathological lesion at the auditory brainstem level. The ABR is elicited by brief sounds that can be used to measure hearing sensitivity as well as temporal processing. Reduction in peak amplitudes and increases in latency are indicative of dysfunction in the auditory nerve and/or central auditory pathways. In this study we used sixteen young adult mice that were divided into two groups: sham and mild traumatic brain injury (mTBI), with ABR measurements obtained prior to, and at 2, 6, and 14 weeks after injury. Abnormal ABRs were observed for the nine TBI cases as early as two weeks after injury and the deficits lasted for fourteen weeks after injury. Results indicated a significant reduction in the Peak 1 (P1) and Peak 4 (P4) amplitudes to the first noise burst, as well as an increase in latency response for P1 and P4 following mTBI. These results are the first to demonstrate auditory sound processing deficits in a rodent model of mild TBI.

Avaliação eletrofisiológica da audição em indivíduos após traumatismo cranioencefálico

OBJETIVO: caracterizar o potencial evocado auditivo de tronco encefálico e de longa latência em pacientes pós traumatismo cranioencefálico, comparando-os com indivíduos normais. MÉTODO: estudo clínico transversal realizado com 20 indivíduos audiologicamente normais divididos em dois grupos pareados por idade e sexo: a) 10 indivíduos que sofreram traumatismo cranioencefálico (grupo pesquisa); b) 10 indivíduos sem qualquer tipo de alteração neurológica (grupo controle). Foram submetidos à avaliação audiológica básica, ao potencial evocado auditivo de tronco encefálico e ao potencial evocado auditivo de longa latência (P300). RESULTADOS: observou-se no potencial evocado auditivo de tronco encefálico, latências absolutas das ondas I, III e V e intervalo interpico I-III mais prolongados no grupo pesquisa do que no grupo controle, sendo estatisticamente significante para as latências absolutas das ondas I e III à direita e para a onda III e intervalo interpico I-III à esquerda. A amplitude das ondas I, III e V na orelha direita e das ondas III e V na orelha esquerda foram maiores no grupo controle. Em relação ao P300, o grupo pesquisa apresentou maior latência e menor amplitude em ambas as orelhas, sem significância estatística, quando comparado ao grupo controle. CONCLUSÃO: indivíduos que sofreram traumatismo cranioencefálico apresentam alterações no potencial evocado auditivo de tronco encefálico e não apresentam diferenças significantes no potencial evocado auditivo de longa latência (P300) quando comparados a indivíduos sem lesões cerebrais.

Audiological deficits after closed head injury

BACKGROUND

Damage to the peripheral auditory structures has long been recognized as a common component of head injury. It is estimated that a majority of patients with skull trauma have resultant hearing impairment. Damage to the peripheral and/or central auditory pathways can occur as a primary or secondary injury. Considering the high incidence of hearing loss, it was considered worthwhile to conduct an in-depth investigation by administering a comprehensive audiological test battery on head-injured patients.

METHOD

The sample population consisted of 290 subjects with closed head injury (study group) and 50 subjects with otologically normal subjects (control group). The subjects in the study group were further divided into mild (n = 150), moderate (n = 100), and severe (n = 40) category on the basis of Glasgow Coma Scale score. The audiological assessment consisted of pure tone audiometry, speech audiometry, tympanometry, acoustic reflex testing, auditory brain stem response audiometry, and middle latency response audiometry.

RESULTS AND CONCLUSIONS

It is concluded that there is higher prevalence of hearing impairment in the study group compared with control group. Majority of the patients who incur hearing loss after closed head injury have mild degree of hearing impairment. A significant difference between the study and control group observed on majority of the auditory brain stem response and middle latency response parameters studied.

Appearances are deceptive? long-term cognitive and central auditory sequelae from closed head injury ¿Las apariencias engañan? Secuelas cognitivas y auditivas centrales a largo plazo después de un traumatismo cráneo-encefálico cerrado

The purpose of the present study was to examine possible signs of long-term cognitive and/or central auditory sequelae seven to eleven years after a closed head injury (CHI) of sufficient severity to cause scull fracture and/or brain contusion. Another purpose was that this investigation should be carried out in a group of recovered trauma victims with, to the individual, no known or minimal sequelae. A computer-based set of five cognitive tests and three central auditory tests were used in a group of formerly brain-injured patients who considered themselves as well recovered. Most of the participants did not report any signs of cognitive or auditory impairment. Tests of working memory capacity, verbal information processing speed, phonological processing and verbal inference-making ability were used. Auditory brain response (ABR), distorted speech audiometry (interrupted speech), and phase audiometry were used to test central auditory function. The initial severity of brain damage, i.e. status when the patient arrived at the emergency ward, was estimated with Swedish Reaction Level Scale (RLS). Cognitive shortcomings after CHI were demonstrated in a high percentage (59%, 13/22) of the cases seven to eleven years after the injury. Central auditory processing disorders (APD) were also demonstrated in a fairly high percentage (58%, 11/19) of the subjects. None of the correlations between RLS and the results on cognitive and central auditory tests reached statistical significance. However, there was a correlation between cognitive performance and the results on the central auditory tests used in this investigation. Eighty percent (8/10) of those participants with pathologies on ABR and/or phase audiometry and/or IS also failed on one or more of the cognitive tasks, compared to 44% (4/9) among those with no signs of APD. It is possible, many years after CHI, to observe cognitive shortcomings and APD in a relatively high percentage of CHI cases that are subjectively considered to be fairly well recovered. The cognitive tasks used in the study have proved to be a sensitive method to discover cognitive impairments. Long-term cognitive sequelae and APD could not be predicted from RLS scores.

Short-Term Pathophysiologic Changes and Histopathologic Findings of the Auditory Pathway after Closed Head Injury, Using a Rabbit Model

Hearing impairment is a well-known consequence of closed head injury (CHI). The aim of this study was to elucidate the pathogenesis of CHI-induced hearing loss, using a rabbit model. Twelve New Zealand white rabbits were divided into two groups of 6. In the first group, CHI was induced mechanically, whereas the rabbits of the second group served as controls. Baseline distortion product otoacoustic emissions (DPOAEs), contralateral suppression (CS) of the DPOAEs and auditory brainstem response (ABR) were obtained. The same measurements were performed in the first group after CHI. Three hours later, the animals were sacrificed and their brain was excised and subjected to histopathologic examination. Mean I-III ABR latencies were increased and DPOAE amplitudes and CS values were reduced in the trauma group after CHI, at a statistically significant level. Histopathologic examination of the temporal lobe and brainstem showed multiple hemorrhagic and necrotic areas, with edema in the surrounding region. The vestibulocochlear nerve was severely damaged at its emerging site at the brainstem. In conclusion, both peripheral and central involvement of the auditory pathway was found after CHI. Otoacoustic emissions in conjunction with ABR may provide significant information on both peripheral and central auditory function.

Brainstem auditory-evoked potentials as an objective tool for evaluating hearing dysfunction in traumatic brain injury

Because of the violent nature of traumatic brain injury, traumatic brain injury patients are susceptible to various types of trauma involving the auditory system. We report a case of a 55-yr-old man who presented with communication problems after traumatic brain injury. Initial results from behavioral audiometry and Weber/Rinne tests were not reliable because of poor cooperation. He was transferred to our service for inpatient rehabilitation, where review of the initial head computed tomographic scan showed only left temporal bone fracture. Brainstem auditory-evoked potential was then performed to evaluate his hearing function. The results showed bilateral absence of auditory-evoked responses, which strongly suggested bilateral deafness. This finding led to a follow-up computed tomographic scan, with focus on bilateral temporal bones. A subtle transverse fracture of the right temporal bone was then detected, in addition to the left temporal bone fracture previously identified. Like children with hearing impairment, traumatic brain injury patients may not be able to verbalize their auditory deficits in a timely manner. If hearing loss is suspected in a patient who is unable to participate in traditional behavioral audiometric testing, brainstem auditory-evoked potential may be an option for evaluating hearing dysfunction.

Long-term objective and subjective audiologic consequences of closed head injury

During a period of 5 years, a total of 47 patients, 16-60 years of age, with major closed head injury (CHI) were admitted to 2 Swedish medical centres. Seven to 11 years after injury, 25 of them (mean age 40.8 years; range 25-59 years) were evaluated using peripheral and central auditory tests, and most of them also completed 2 questionnaires concerning self-assessed hearing ability and quality of life. Twenty-two patients did not participate in the long-term follow-up tests: 15 were excluded for medical reasons and 4 did not wish to participate; an additional 2 were impossible to trace and 1 had died. As many as 68% of patients (17/25) demonstrated abnormalities on 1 or more of the audiometric tests, 14 on pure-tone audiometry (p < 0.02) and/or central audiometric tests (3 on central tests only and 2 on pure-tone audiometry only). Four out of six patients with available early post-traumatic audiograms showed a significant progressive deterioration. As a group, their assessments of hearing ability and quality of life were equal to or better than those of the controls. These results may indicate that a higher priority should be given to obtaining an early audiologic evaluation of every CHI patient than is the rule today. The impact of post-traumatic progress and central lesions on social hearing at an advanced age is highlighted.

Audiological findings following head trauma

Traumatic head injury is the principal cause of death and serious physical disability in adolescents and young adult. Hearing loss is a common sequela of head trauma. The results of pure tone and auditory brain-stem response (ABR) assessment of minor head injury revealed that 20 per cent of these cases showed impairment of hearing including both conductive and sensorineural hearing loss mostly in the high frequencies loss. ABR findings showed a significant difference of absolute wave V latency and interwave (III-V) latencies at repetition rate 11.1 click/sec., and a highly significant difference at a repetition rate of 51.1 click/sec., compared with the control group. In severe head injury, conductive hearing loss was found in only one case, in which a longitudinal fracture of the temporal bone was identified radiologically. No ABR could be recorded at a repetition rate of 11.1 click/sec. in either ear of this case; this patient died a few days later. Three cases were found with a mixed sensorineural hearing loss; one of them showed a longitudinal fracture radiologically. ABR findings in two cases showed prolongation of wave V and I-V interwave latencies, and the third case showed absence of ABR recording. In comatose patients, an ABR grading system is a more sensitive index of brainstem dysfunction than the simple division of normal versus abnormal ABR waves and interwave latencies. Presence or prolongation of wave V and interwave latency I-V even in one ear is of good prognostic value in the comatosed patient.