Quantitative analysis of reversible dysfunction of brain-stem midline structures caused by disturbance of basilar artery blood flow with the auditory brain-stem responses

To clarify the effects of disturbances in basilar artery blood flow, basilar artery angiospasm was induced in 2 cats and 4 guinea pigs and auditory brain-stem responses (ABRs) were continuously recorded preceding, during and following the angiospasm. The angiospasm caused specific ABR changes in that waves II (P2-N2) and III (P3-N3) were attenuated without any corresponding amplitude reduction of P4. Those changes were equivalent following stimulation of either ear. Moreover, the ABR changes gradually recovered within 5 h. On the basis of the animal experiments, 52 patients with subarachnoid hemorrhage, supratentorial tumor showing increased intracranial pressure or hydrocephalus were selected for repeated ABR examinations. ABR abnormalities similar to those observed in the animal experiment were obtained especially from the patients exhibiting grade 3 or 4 symptomatology with subarachnoid hemorrhage. In these cases, the wave III to wave IV-V amplitude ratio was significantly decreased. In some cases the ABR abnormalities and the wave III to wave IV-V amplitude ratio recovered as the clinical course improved. These results support the conclusion that specific ABR changes (wave III to wave IV-V amplitude ratio) reflect transient ischemic dysfunction of the midline portion of the brain-stem caused by disturbances of basilar artery blood flow.     

Auditory brain-stem responses in brain death.

Auditory brain-stem responses were measured by far-field recording techniques in 27 patients fulfilling the criteria of brain death. The responses were either absent or consisted of the presence of just the initial component (Wave I). Wave I, when present, was of normal amplitude but prolonged in latency. Four patients were followed over several days from a state of coma with evidence of preserved brain-stem and cerebral functions to a clinical state compatible with brain death. Auditory brain-stem responses were initially intact and then showed a decrease in amplitude and a prolongation of latency of the later components until finally Wave I was alone. Auditory brain-stem responses are an objective measure of one of the sensory pathways traversing the brain-stem and can be used to evaluate the functional states of the brain-stem in patients in whom the question of brain death has been raised.     

Is the auditory brain-stem response (ABR) effective in the assessment of post-traumatic coma?

The aim of the present study is to evaluate the capacity of ABRs to detect the limit between reversible dysfunction and irreversible damage to the brain-stem after severe head injuries. ABRs were recorded in 40 severely head-injured patients, strictly selected on the basis of clinical and CT scan findings and the absence of otologic disease. The interpeak latency of waves V-I (IPL V-I) was calculated and compared to that recorded in 19 healthy control subjects. The distribution curve for IPL V-I in surviving patients was analysed. The overall mortality was 47.5%; all the patients showing an IPL V-I greater than 4.48 msec died or remained vegetative, while all but 2 of the patients with IPL V-I less than 4.48 msec survived. The IPL V-I was significantly different from normal value in surviving patients, showing a brain-stem dysfunction in reversible post-traumatic coma. The 95% confidence limits for the mean IPL V-I in the surviving population were 4.08 and 4.24 msec. Our results confirm the high prognostic accuracy of ABR (P less than 0.001) and suggest the hypothesis that 95% of survivors have an IPL V-I ranging between 3.82 and 4.50 msec.     

Auditory brain-stem responses in hydrocephalic patients

Auditory brain-stem response (ABR) was measured in 40 patients (80 ears) with confirmed hydrocephalus. Eighty-eight percent of these patients showed some form of ABR abnormality. Responses indicative of brain-stem dysfunction consisted of prolonged I-V interwave latency (38%), reduced V/I amplitude ratio (33%), and abnormalities in wave-shape of components III (27%) and V (53%). In addition, 70% of the patients had elevated ABR thresholds; 45% had responses in excess of 20 dB HL and the remaining 25% had no ABR activity. The etiology of the hydrocephalus, head circumference and brain-stem symptoms were not associated with particular ABR abnormalities. Communicating hydrocephalus correlated significantly with both prolonged I-V conduction time and absence of ABR activity, compared with non-communicating hydrocephalus. Four of the 9 patients retested showed ABR improvement on follow-up; one patient showed deterioration. The results were compared to our prior studies of ABR in 60 post-meningitic patients and in 100 severely neurologically impaired institutionalized children in whom the incidence of intrinsic brainstem abnormalities was one-third and two-thirds that of the hydrocephalic group, respectively. The results of this study suggest that ABR can be used to document clinically unsuspected brain-stem pathology that may accompany hydrocephalus. Auditory brain-stem dysfunction is likely to complicate the assessment of hearing sensitivity in hydrocephalic patients.     

Clinical correlates of brain-stem auditory evoked potential variables in multiple sclerosis. Relation to click polarity.

The correlations between clinical signs and BAEP latency, amplitude and dispersion variables were investigated in 98 multiple sclerosis patients. A new dispersion variable, the wave IV-V "shape ratio" (SR IV-V), correlated most strongly with brain-stem signs (i.e., nystagmus). Severely reduced wave IV-V amplitude was frequently found in patients with vertical nystagmus or internuclear ophthalmoplegia, and interpeak latency (IPL) III-V correlated most strongly with cerebellar dysfunction (i.e., ataxia). The results may reflect different localizing ability among the various BAEP variables. The association between ataxia and increased IPL III-V was significantly stronger for BAEP to C clicks than to R clicks. Patients with abnormal BAEPs to one polarity (C or R) but not to the other, had significantly more clinical dysfunction than patients with normal BAEPs to both C and R clicks. Hence, C vs. R discordance may be interpreted to indicate possible brain-stem dysfunction.     

经菱形窝切除脑干海绵状血管瘤

目的探讨28例经菱形窝入路切除的脑干海绵状血管瘤的适应证、手术技巧及术中注意点。方法术中采取坐位,枕下正中开颅,广泛打开小脑延髓裂;在脑干表面有色素沉淀或膨隆处,或在B超、导航引导、术中颅神经监护下切开脑干,病变暴露后清除血肿,然后切除病变,保留含铁血黄素沉淀的胶质组织。结果28例中有21例位于桥脑;术中发现脑干表面有含铁血黄素沉淀21例,其中脑干表面膨隆9例;所有病变位于脑干背侧;随访期间:症状和体征较术前改善的19例,保持术前水平的5例,加重、出现新的颅神经症状、或其他神经功能障碍(共济失调、运动障碍、感觉障碍)共4例。MRI随访未见病变残留或复发。结论经菱形窝入路主要适于桥脑部、且位于背侧的海绵状血管瘤;脑干表面的含铁血黄素沉淀和(或)膨隆是脑干的安全进入区,术中结合神经电生理监测、B超以及导航是手术成功的关键;术中尽可能全切病变,但保留含铁血黄素沉淀的胶质组织。     

Chronic effects of phenytoin on brain-stem auditory evoked potentials in man.

The effects of phenytoin (PHT) on brain-stem auditory evoked potentials (BAEPs) were studied in 65 epileptic patients who received long-term PHT monotherapy at therapeutic and supra-therapeutic levels with no clinical evidence of brain-stem toxicity. Abnormal BAEPs were found in 7.5% and 33.3% of patients with therapeutic and supra-therapeutic PHT levels respectively. Serum PHT levels had a trend towards a positive relationship with the I-V interpeak latency (IPL), and a significant negative relationship with the amplitudes of waves I and V. At supra-therapeutic levels, both I-V and I-III IPLs were significantly prolonged while at therapeutic levels only I-III IPLs were prolonged. The absolute latency of wave I was prolonged in both the therapeutic and the supra-therapeutic groups. These results suggest that PHT acts both peripherally on either the auditory nerve or the cochlea, and centrally on brain-stem conduction.     

Brain-stem auditory evoked potentials in children with brain-stem or cerebellar dysfunction

Brain-stem auditory evoked potentials (BAEPs) were recorded in 23 children who had signs of brain-stem or cerebellar dysfunction. In patients with brain-stem gliomas, BAEPs were abnormal in all except one, in whom involvement of the brain-stem auditory pathway was limited to the midbrain tectum. The BAEPs were normal in neuronal ceroid lipofuscinosis, but abnormal bilaterally in inheritable leukoencephalopathies. All patients with Leigh's encephalopathy had BAEP abnormalities; in two, abnormalities occurred before the appearance of lesions on computed tomographic scan. Patients with Friedreich's ataxia and giant axonal dystrophy had abnormal BAEPs, but the test was normal in a child with similar neurologic findings with vitamin E deficiency. Patients with diffuse metabolic encephalopathies had variable findings. Thus, BAEP abnormalities are nonspecific for various disease processes but are frequently seen in neoplastic and neurodegenerative diseases, with primary white matter or extensive brain-stem involvement.     

Auditory brain-stem evoked potentials in patients undergoing dialysis

Auditory brain-stem evoked potentials (ABEPs) and pure-tone audiograms were obtained for 38 patients with renal failure, undergoing dialysis, before and after a dialysis session, and for 40 healthy normal subjects. Blood chemistry was also evaluated for each patient before and after dialysis. ABEP abnormality (using 10/sec click rate) was observed for 24% of the patients, rising to 44% when 55/sec measures were included. Abnormalities included prolongations of peak latencies for both click rates, and prolongation of interpeak latency differences. Pre-dialysis calcium was significantly different between patients with or without ABEP abnormality. In addition to this chronic effect on ABEPs, an acute effect of the dialysis session was found. Blood chemistry data, ABEP latencies and I-III interpeak latency differences were significantly different before, as compared to after dialysis. The acute effect of dialysis on blood calcium levels correlated with its effect on latencies of peaks III and V at 10/sec click rate, and on peaks I and V latency at 55/sec. These results may indicate the types of dysfunction revealed by increased stimulus rate measures.     

Auditory brain-stem responses in adrenomyeloneuropathy

We studied three patients with adrenomyeloneuropathy. Complete audiologic assessment was obtained: two patients showed unimpaired peripheral hearing and one showed a mild high-frequency hearing loss. Auditory brain-stem responses were abnormal in both ears of all subjects, with one subject showing no response above wave I, and the other two having significant wave I to III and wave III to V interval prolongations. We concluded that auditory brain-stem response testing provides a simple, valid, reliable method for demonstrating neurologic abnormality in adrenomyeloneuropathy even prior to evidence of clinical signs.     

Unusual pattern of somatosensory and brain-stem auditory evoked potentials after cardio-respiratory arrest

Two patients in coma after cardio-pulmonary arrest showed bilateral absence of all brain-stem auditory evoked potentials contrasting with normal brain-stem reflexes and normal somatosensory cortical evoked potentials. In both patients pre-existing dysfunction of peripheral auditory structures could be ruled out. Subsequent neuropathological analysis showed that the anoxic-ischaemic lesions were restricted to Sommer's sector and the Purkinje cells. These unusual data suggest the hypothesis that a severe hypoxic-ischaemic insult may impair cochlear function and interfere with the activation of the intact auditory pathways.     

Auditory brain-stem responses in blepharospasm

The auditory brain-stem response (ABR) has been reported to detect abnormalities in both the auditory pathways and in adjacent structures. Ten of 35 consecutive patients with blepharospasm were found to have abnormal ABRs involving poor form and delayed peak latency of positive components III or V. Abnormal ABRs in approximately 30% of patients with essential blepharospasm suggest pathology in the brain-stem of a substantial proportion of patients with this form of cranial-cervical dystonia.     

Origin of N18 and P14 far-fields of median nerve somatosensory evoked potentials studied in patients with a brain-stem lesion

Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded in 3 patients with a brain-stem or medullary lesion documented by clinical and CT or MRI evidence. The positive P14 and negative N18 scalp far-fields were preserved. The results suggest that P14 reflects the spike volley in caudal medial lemniscus, and that the N18 neural generators are located in the medulla, probably in the dorsal column nuclei and/or the accessory inferior olives.     

Subacute brain-stem encephalitis

A 65 year old man developed progressive signs of pontine and medullary dysfunction with striking bilateral paralysis of lateral gaze, dysarthria, dysphagia, and ataxia. A respiratory death occurred seven months from the onset. Pathological examination revealed focal brain-stem changes of perivascular lymphocytic cuffing, microglial infiltration, glial nodules, and neuronophagia. No underlying malignancy or general disease impairing immunity mechanisms was discovered.     

Brain-stem involvement in multiple sclerosis: a comparison between brain-stem auditory evoked potentials and the acoustic stapedius reflex

Summary Brain-stem auditory evoked potentials (BAEPs) and the acoustic stapedius reflex (ASR) were recorded in 68 patients with definite, probable and possible multiple sclerosis (using the definitions of McAlpine). The high incidence of abnormal results, 68% and 60%, respectively, pointed to the diagnostic value of these two measures in detecting brain-stem dysfunction. Combination of the methods increased the diagnostic yield to 85%. Since in part the same brain-stem generator sites underlie BAEPs and the ASR, it was considered that a study of their correlation might serve to increase the reliability and validity of these techniques. There was 71% agreement overall between results from the two measures. Furthermore, 72% of the joint BAEP and ASR abnormalities corresponded in detection of the brain-stem lesion site. It was concluded that the combined approach may supply powerful, complementary information on brain-stem dysfunction, which may aid in establishing the diagnosis of multiple sclerosis.This study was supported by the M. Sackler Foundation for Multiple Sclerosis Research     

脑干及小脑病变的质子磁共振波谱研究

目的探讨质子磁共振波谱（^1HMRS）分析对脑干及小脑病变的诊断价值。方法对15例健康志愿者和18例脑干及小脑病变患者分别进行^1HMRS采集,定量分析N-乙酰天门冬氨酸（NAA）、肌酸（Cr）和胆碱（Cho）代谢物的变化。结果肿瘤组NAA／Cr、NAA／（Cho＋Cr）的比值低于非肿瘤组,且两者都低于对照组,有显著的统计学差异（P〈0．05）;肿瘤组Cho／Cr的比值高于非肿瘤组,且两者都高于对照组,有显著的统计学差异（P〈0．05）。结论^1HMRS对脑干和小脑病变的定性诊断及预后评估有重要价值。     

Auditory brain-stem response in zitter rats with genetic spongiform encephalopathy.

Zitter rats with genetic spongiform encephalopathy and hypomyelination developed an abnormal auditory brain-stem response (ABR) before the appearance of spongy lesions in the central nervous system (CNS). The ABR abnormalities were characterized by a dual peak of wave I, with a longer latency than in normal rats, and decreased or absent waves III and IV. Hypomyelination in both peripheral and central nerves may have been responsible for these abnormalities. The slow negative wave became wide and obscure with aging. These changes accompanied age-dependent progression of spongy changes in the CNS. These findings suggest that at least two mechanisms, one involving hypomyelination and the other causing spongy lesions, are responsible for the brain-stem auditory pathway dysfunction in zitter rats.     

Anesthesia effects: auditory brain-stem response

Auditory brain-stem responses (ABRs) were measured in the awake state and with ketamine and xylazine anesthesia in adult gerbils. Surface recorded vertex-positive components of the ABR were analyzed with respect to the awake and anesthetized states as a function of stimulus frequency. ABR thresholds were not altered with ketamine/xylazine. Small increases in peak latency were associated with anesthesia for all components except wave P1. Increases in absolute latency were progressively greater for successive peaks, reaching an average shift of 0.41 msec for wave P6. Amplitude changes with anesthesia were more variable, with increases generally seen for waves P4 and P6. Significant anesthesia effects on peak latency and amplitude were independent of stimulus frequency. These data confirm previously reported ABR sensitivity to non-barbiturate anesthesia. Direct comparisons of ABR interpeak intervals or amplitude ratios from awake versus anesthetized animals must account for the effects of barbiturate and non-barbiturate agents. However, the stability of response threshold and the small magnitude of latency and amplitude changes with a ketamine and xylazine regimen demonstrate that accurate electrophysiological measures of hearing sensitivity and auditory brain-stem activity can be obtained in anesthetized animals, provided that temperature and other parameters are maintained within normal physiological limits.     

Auditory brain-stem responses in Marcus Gunn ptosis

The auditory brain-stem response (ABR) can detect anomalies both in the auditory pathways and in structures adjacent to these pathways. Patients with Duane's retraction syndrome, associated with hypoplasia of the abducens nerve in the brain-stem, and patients with hemifacial spasm, due to compression of the facial nerve in the brain-stem, have been found to have abnormal ABRs. Marcus Gunn ptosis with 'jaw winking' is considered to be due to misconnection of oculomotor, trigeminal and other cranial nerves. Suspecting that perhaps some 'jaw-winking' phenomena may be due to detectable brain-stem anomalies we tested 7 patients with Marcus Gunn ptosis. Three of the patients demonstrated abnormal ABRs indicative of pontine pathology.     

Stereotaxic biopsy of brain-stem tumours in children

Stereotaxic biopsies were performed in a series of 14 patients with clinical and computed tomographic evidence of a brain-stem lesion. Seven of these cases were in the paediatric age group (under 15 years of age). Biopsies were obtained by means of the Leksell stereotaxic system, through the transcerebellar (three cases) or transfrontal route (four cases). A definite tumour diagnosis could be obtained in all cases. No patients were subjected to open biopsy, as the further management of their tumours did not warrant surgery. One patient developed transient oculomotor nerve palsy. There was no mortality related to the biopsy procedure in this series. The biopsy technique and its utility and safety are discussed.Presented at the XVII Annual Meeting of the International Society for Pediatric Neurosurgery, Bombay 1989