Evoked potentials in basilar artery thrombosis: correlation with clinical and angiographic findings

Evaluation of patients with vertigo of vertebrobasilar insufficiency origin using auditory brainstem response, electronystagmography, and transcranial Doppler

OBJECTIVES

Vertigo can be a manifestation of underlying vertebrobasilar stroke in older adults. The study objectives were to investigate the correlation, sensitivity, and specificity of the auditory brainstem response (ABR), electronystagmorgraphy (ENG), and transcranial Doppler (TCD) collectively to distinguish between vertigo due to vertebrobasilar insufficiency (VBI) and vertigo due to non-VBI.

DESIGN

Prospective experimental study comparing ENG, ABR, and TCD battery findings between two groups of patients with vertigo and a control group.

STUDY SAMPLE

Participants included 14 patients with vertigo of VBI origin, 14 patients with vertigo of non-VBI, and 11 matched controls.

RESULTS

Participants with VBI had more abnormal findings in the ENG (86%), TCD (72%), and ABR (64%) compared to the non-VBI group (64%, 21%, and 7%, respectively) and the control group. The combined battery revealed positive correlations, 64% sensitivity, and 84% positive predictive value (PPV) in the VBI group, and 100% specificity with lack of correlations in the non-VBI group.

CONCLUSIONS

The modest sensitivity and PPV helps with early detection of VBI, thus preventing risk of vertebrobasilar stroke in 84% to 64% of patients. The 100% specificity in the non-VBI group rules out VBI, thus reducing the referral rate for unnecessary, diagnostic evaluations and ineffective treatment.

Stroke attributable to acute basilar occlusion

Acute basilar artery occlusion carries a high risk of disabling stroke or death. Fast recanalization of the vessel is the mainstay of the therapy. Recanalization may be achieved by intravenous or intra-arterial administration of thrombolytics. These procedures are currently used as life-saving interventions, despite the low level of evidence supporting their efficacy, because of the bad prognosis of the disease. Intravenous thrombolysis may be started earlier, but it is less often used, mainly for historic reasons; intra-arterial measures are possibly more effective in achieving recanalization but require extra time before they can be started and demand a considerable amount of resources. The basilar artery does not recanalize in approximately one third of patients; this result has not been modified over the past two decades by these treatments and probably will not change. Combined mechanical and intra-arterial thrombolysis may be more efficient in achieving basilar artery recanalization, but the impact of this combined intervention on the final outcome has not been evaluated. Because time is critical, as in every stroke, implementation of a specific treatment protocol for this condition, including one of the aforementioned treatments, and eventual transfer to a secondary-care unit will save time and improve prognosis.

Evaluation of vertigo by auditory brain stem response

The authors examined the hypothesis that abnormal patterns of the auditory brain stem response (ABR) could supplement the neuro-otological evaluation and assist in localizing the site of vestibulocerebellar dysfunction. This project is based upon the fact that the sources of waves I through V have been regionally identified. Absent or delayed patterns can be referenced to the normal data, and the site of a lesion generating vertigo can be established. We found absence of waves or prolonged interpeak latencies in 25% of the vertiginous subjects with normal hearing and magnetic resonance images of the brain. We conclude that in selected cases, lesions affecting the vestibular system can influence the ABR, and the electrophysiological tests of audition may suggest regionalization of the dysfunction in the hindbrain and midbrain.

A lateral mass fracture of C1 associated with left vertebral artery and mid-basilar artery occlusion

Extreme acceleration and deceleration forces as well as axial loading are exerted at the occipito-cervical junction of drivers involved in high-velocity motor vehicle accidents, especially with fastened seatbelts. Injury at this level, usually lethal, can go unrecognized despite modern emergency management of the unconscious patient. A precise neurologic and radiographic workup of damage to this area is often not possible or overlooked in the initial phase of such severe trauma. We describe a patient with multiple injuries who sustained a left vertebral artery occlusion associated with a left-sided lateral mass fracture of C1 and a basilar artery occlusion resulting in a locked-in syndrome after an automobile accident.

Medical technology assessment EEG and evoked potentials in the intensive care unit

We review the principal aspects of EEG and evoked potential (EP) neuromonitoring in the intensive care unit. The electrophysiological methods allow functional assessment of comatose patients and can be used (a) as a help to diagnose the origin of coma, (b) as a means to predict outcome, and (c) for monitoring purposes. The combination of the EEG and long-, middle-, and short-latency EPs allows widespread assessment of the cerebral cortex, the brain-stem, and the spinal cord. The EEG and the EP interpretation first requires taking into account non-neurological factors that may interfere with the recorded activities (sensory pathologies, toxic or metabolic problems, body temperature). The sensitivity and the specificity of any neurophysiological technique depend on the etiology of coma. Anoxic comas are associated with a predominantly cortical involvement, while the cortical and brain-stem functions are to be taken into account to interpret the EEG and the EPs in head trauma. The EEG and the EPs can be used to differentiate the comas due to structural lesions from those of metabolic origin, to confirm brain death and help to diagnose psychogenic unresponsiveness or a de-efferented state. While the prognostic value of the EEG is markedly hampered by the widespread use of sedative drugs, it has been possible to design efficient systems based on early- and middle-latency multimodality evoked potentials in anoxic and traumatic comas and, more generally, in all comas associated with an increase of the intracranial pressure. Continuous neuromonitoring techniques are currently under development. They have already been proven useful for the early detection and for the prevention of subclinical seizures, transtentorial herniation, vasospasm, and other causes of brain or spinal-cord ischemia.

Influence of extreme head rotations on brainstem auditory evoked potentials (BAEP)

The influence of extreme head rotations on BAEP was studied in 47 patients who had vertebral artery angiogram. Patients with and without unilateral hypoplasia of the vertebral artery (VA) lumen were identified and all patients were further divided into two groups: with and without hypertension. The subjects underwent a BAEP examination in three head positions: neutral position, extreme right and extreme left rotation. In the subgroup of patients with hypertension and unilateral VA hypoplasia, and following the rotation away from the non-hypoplastic vessel a statistically significant decrease in the PV wave amplitude and prolonged PV wave latency was found. Head maneuvers in subjects with normal blood pressure or in hypertensive patients with symmetrical VA did not cause significant changes in BAEP. These results document the effect of head rotation in subjects with potentially impaired collateral flow. An increase in the PV wave latency and decrease in its amplitude may reflect subtle changes in the brainstem perfusion in hypertensive patients. These changes maybe due to a reduced capacity to compensate for dynamic obstruction of VA following the head rotations.

The temporal relationship between the brainstem and primary cortical auditory evoked potentials

Many methods are employed in order to define more precisely the generators of an evoked potential (EP) waveform. One technique is to compare the timing of an EP whose origin is well established with that of one whose origin is less certain. In the present article, the latency of the primary cortical auditory evoked potential (PCAEP) was compared to each of the seven subcomponents which compose the brainstem auditory evoked potential (BAEP). The data for this comparison was derived from a retrospective analysis of previous recordings of the PCAEP and BAEP. Central auditory conduction time (CACT) was calculated by subtracting the latency of the cochlear nucleus BAEP component (wave III) from that of the PCAEP. It was found that CACT in humans is 12 msec which is more than double that of central somatosensory conduction time. The interpeak latencies between BAEP waves V, VI, and VII and the PCAEP were also calculated. It was deduced that all three waves must have an origin rather more caudally within the central auditory system than is commonly supposed. In addition, it is demonstrated that the early components of the middle latency AEP (No and Na) largely reside within the time domain between the termination of the BAEP components and the PCAEP which would be consistent with their being far field reflections of midbrain and subcortical auditory activity. It is concluded that as the afferent volley ascends the central auditory pathways, it generates not a sequence of high frequency BAEP responses but rather a succession of slower post-synaptic waves. The only means of reconciling the timing of the BAEP waves with that of the PCAEP is to assume that the generation of all the BAEP components must be largely restricted to a quite confined region within the auditory nerve and the lower half of the pons.

When is Isolated Vertigo a Harbinger of Stroke?

Isolated vertigo is usually a distressing though benign clinical entity. Recently, however, it has been recognized that in a subset of patients isolated vertigo may be a harbinger of vertebrobasilar stroke. Recognition of this “at risk” subgroup may be difficult. Brainstem auditory evoked potentials (BAEPs) are usually normal in patients with vertigo from labyrinthine disease.

We describe a patient with isolated vertigo, in whom BAEPs were abnormal, and who subsequently developed an anterior inferior cerebellar artery territory infarct.

BAEP testing might lead to early recognition of those patients at risk for catastrophic stroke, and prompt appropriate investigation and treatment to prevent this outcome.

Monitoring therapeutic efficacy of decompressive craniotomy in space occupying cerebellar infarcts using brain-stem auditory evoked potentials

Brain-stem auditory evoked potentials (BAEPs) have been used to gauge effects of brain-stem dysfunction in humans and animal models. The purpose of this study was to evaluate the usefulness of BAEP in monitoring patients undergoing decompressive surgery of the posterior fossa for space occupying cerebellar infarcts. We report on serial BAEP recordings in 11 comatose patients with space occupying cerebellar infarcts undergoing decompressive craniotomy. BAEP studies were performed within 12 h after admission, 24 h following surgery and prior to extubation. BAEP signals were analyzed using latency determination and cross-correlation. Following surgery, 9 patients regained consciousness; 2 patients persisted in a comatose state and died subsequently. BAEP interpeak latency (IPL) I-V assessed prior to surgery exceeded normal values in all patients in whom it could be reliably measured (N = 9). Following decompressive surgery BAEP wave I-V IPL normalized in 5 patients, but remained prolonged despite dramatic clinical improvement in 4 patients. We prospectively computed the coefficient of cross-correlation (MCC) of combined ipsilateral BAEP trials after right and left ear stimulation. In all patients increasing MCC was associated with clinical improvement. Unchanging or decreasing MCC indicated poor outcome. We conclude that serial BAEP studies are an appropriate perioperative monitoring modality in patients with space occupying cerebellar infarcts undergoing decompressive surgery of the posterior fossa. Our study suggests advantages of cross-correlation analysis as an objective signal processing strategy; relevant information can be extracted even if BAEP wave discrimination is impossible due to severe brain-stem dysfunction.

Multimodality evoked potentials (auditory, somatosensory and motor) in coma

Auditory brainstem responses (ABRs) have proved to be significantly related to outcome, both in severe head injury and brain hemorrhage. Nevertheless, the usefulness of ABR is limited by the anatomic extent of the investigated pathways. The combined use of ABRs and somatosensory evoked potentials (SEPs) improves the outcome prediction in comparison to the use of only one modality. It mainly decreases the rate of false negatives, since patients with severe hemispheric damage sparing the brain stem may have a poor outcome despite normal ABRs. The use of motor evoked potentials (MEPs) from magnetic transcranial stimulation is also significantly related to outcome: it appears to be far superior to the clinical evaluation of motor responses, while the combined use of MEPs and SEPs gives a new opportunity of checking sensorimotor dysfunction. ABRs and SEPs may also be useful tools in the confirmation of brain death, the kernel of which is the assessment of brainstem death: they allow to check lemniscal pathways, which cannot be properly evaluated by clinical examination, and provide an objective confirmation of absence of brain stem activity.

Visual evoked potentials and electroretinography in brain-dead patients

Visual evoked potentials and electroretinograms were elicited by light-emitting diode stimulation and recorded simultaneously, with cephalic and noncephalic references, in 30 normal subjects and in 30 brain-dead patients. A characteristic pattern was found in the group of patients: when a cephalic reference was used for both visual evoked potentials and the electroretinogram, the a- and b-waves of the electroretinogram were recognized in all patients, and visual evoked responses consisted of waves with inverse polarity, similar morphologic characteristics, the same latency, and less amplitude than those of the electroretinogram. When a noncephalic derivation was chosen for the electroretinogram and visual evoked potentials, electroretinogram did not change in either morphologic features or latency, whereas the visual evoked potential channel showed no response. Only in two cases was it possible to record waves in the visual evoked potential lead with a noncephalic reference, showing a spread of the electroretinogram to the occipital area, with a considerably reduced amplitude. These results suggest that, although contamination of visual evoked potential records by the spread of the electroretinogram to the occipital area could occur, it is easy to confirm the absence of a true cortical visual response in brain-dead patients by means of a noncephalic reference. This pattern clearly confirms that in the visual pathways of brain-dead patients, electrical activity is confined to the retina.

Sudden bilateral hearing impairment in vertebrobasilar occlusive disease

BACKGROUND

Bilateral hearing impairment is rare in vertebrobasilar occlusive disease.

SUMMARY OF COMMENT

Between 1986 and 1991, we encountered seven patients (four men, three women; median age, 61 years; range, 46-71 years) who had sudden bilateral hearing impairment among 503 patients with vertebrobasilar occlusive disease. The main initial neurological symptoms were sudden bilateral hearing impairment, tinnitus, and vertigo. Acute labyrinthitis or Ménière's disease was the initial diagnosis until subsequent brain stem or cerebellar signs appeared. Brain stem auditory evoked potentials were abnormal bilaterally in six patients but had unilateral attenuation of the IV-V complex in the remaining one patient. Computed tomographic scans in all six patients showed multiple hypodense lesions in the brain stem and the cerebellum. Cerebral angiography showed complete occlusion on both vertebral arteries in one patient, occlusion on the left with small caliber on the right in another, and severe stenosis on both sides in a third. There was no opacification of internal auditory arteries in these three patients. The remaining patient had arteriosclerotic changes with faint opacification of the bilateral internal auditory arteries. Five patients had a poor prognosis, with locked-in state in four and severe truncal ataxia in one.

CONCLUSIONS

We conclude that sudden bilateral hearing impairment in vertebrobasilar occlusive disease is more common than previously recognized and that it may indicate a grave prognosis.

The combined monitoring of brain stem auditory evoked potentials and intracranial pressure in coma. A study of 57 patients

Continuous monitoring of brainstem auditory evoked potentials (BAEPs) was carried out in 57 comatose patients for periods ranging from 5 hours to 13 days. In 53 cases intracranial pressure (ICP) was also simultaneously monitored. The study of relative changes of evoked potentials over time proved more relevant to prognosis than the mere consideration of "statistical normality" of waveforms; thus progressive degradation of the BAEPs was associated with a bad outcome even if the responses remained within normal limits. Contrary to previous reports, a normal BAEP obtained during the second week of coma did not necessarily indicate a good vital outcome; it could, however, do so in cases with a low probability of secondary insults. The simultaneous study of BAEPs and ICP showed that apparently significant (greater than 40 mm Hg) acute rises in ICP were not always followed by BAEP changes. The stability of BAEP's despite "significant" ICP rises was associated in our patients with a high probability of survival, while prolongation of central latency of BAEPs in response to ICP modifications was almost invariably followed by brain death. Continuous monitoring of brainstem responses provided a useful physiological counterpart to physical parameters such as ICP. Serial recording of cortical EPs should be added to BAEP monitoring to permit the early detection of rostrocaudal deterioration.

Transcranial magnetic stimulation in pontine infarction: correlation to degree of paresis

Transcranial magnetic stimulation was performed in 20 patients with pontine infarction who had initially some degree of hemiparesis. Only patients with a well defined lesion on magnetic resonance imaging that was appropriate for the neurological signs were included. Recordings were made from the abductor pollicis brevis muscle (APB) bilaterally. The degree of hand paresis was estimated clinically and related to the following parameters: central motor conduction time (CMCT), interside latency difference of total latency, and amplitude ratio of affected to unaffected side. Increasing degree of paresis was associated with increasing latency parameters and decreasing amplitude ratio. In the four patients with severe paresis a low amplitude response could be evoked and CMCT was delayed by up to 10 ms. When the paresis had resolved at the time of transcranial magnetic stimulation CMCT was normal. However, amplitude ratio was less than 100% in all but one patient, with most of the values ranging between 40% and 60%, which indicates a subclinical pyramidal tract lesion. Median nerve sensory evoked potentials (SEP) and related interside latency difference to amplitude ratio N20/P25 were also recorded. In contrast to TCMS, decreased amplitude ratio of SEP was not associated with delayed latency. Clinically, the mild degree of and good recovery from paresis in ventral pontine infarction was remarkable.

Brain-stem auditory evoked potentials and brain death

BAEP records were obtained from 30 brain-dead patients. Three BAEP patterns were observed: (1) no identifiable waves (73.34%), (2) an isolated bilateral wave I (16.66%), and (3) an isolated unilateral wave I (10%). When wave I was present, it was always significantly delayed. Significant augmentation of wave I amplitude was present bilaterally in one case and unilaterally in another. On the other hand, in serial records from 3 cases wave I latency tended to increase progressively until this component disappeared. During the same period, wave I amplitude fluctuations were observed. A significant negative correlation was found for wave I latency with heart rate and body temperature in 1 case. Two facts might explain the progressive delay and disappearance of wave I in brain-dead patients: a progressive hypoxic-ischaemic dysfunction of the cochlea and the eighth nerve plus hypothermia, often present in brain-dead patients. Then the incidence of wave I preservation reported by different authors in single BAEP records from brain-dead patients might depend on the moment at which the evoked potential study was done in relation to the onset of the clinical state. It is suggested that, although BAEPs provide an objective electrophysiological assessment of brain-stem function, essential for BD diagnosis, this technique could be of no value for this purpose when used in isolation.

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.

Neuroradiological, neurophysiological and anatomopathological study of a case of locked-in syndrome

We report an anatomoclinical case of locked-in syndrome together with the neuroradiological and neurophysiological findings. MRI confirmed its value in the diagnosis of posterior cranial fossa pathology while the neurophysiological work-up (BAEPs, SEPs, MAPs and TEPs) revealed that the lesion may have broader functional implications than may be gauged from the neuroradiological and pathological evidence. Evoked potentials may therefore be of considerable importance in pinpointing brainstem lesions.

Clinical features of proven basilar artery occlusion

Our study describes the early symptoms and signs of 85 patients with either basilar artery occlusion or bilateral distal vertebral artery occlusion documented by selective angiography. The most common prodromal symptoms were vertigo, nausea, and headache, which occurred during the 2 weeks before the stroke. Angiographic findings of 49 patients were classified into proximal, middle, and distal basilar artery occlusions. Twenty-two of these patients had additional vertebral artery lesions. A fourth group was composed of 36 patients with bilateral distal vertebral artery occlusion without opacification of the basilar artery through a vertebral artery injection. Onset was sudden in 20 patients; sudden, but preceded by prodromal symptoms in 11 patients; and progressive in 54 patients. Patients with progressive strokes often had bilateral vertebral artery occlusions. Most patients with acute onset had occlusion of the middle and distal basilar artery. An embolic origin of basilar artery occlusion from an arteriosclerotic vertebral artery lesion was assumed to be an important mechanism. An embolus reaching the basilar artery may not necessarily reach the top of the artery, but may also become lodged more proximally.

The effects of experimental brain-stem ischaemia on brain-stem auditory evoked potentials in primates

We related intracranial auditory brain-stem evoked potentials (BAEPs) to the surface BAEP using a model of focal brain-stem ischaemia. In 17 baboons anaesthetised with alpha-chloralose, BAEPs were recorded bilaterally at the mastoids and in the caudal lateral lemniscus (LL) and inferior colliculus (IC), in response to monaural click stimulation. Electrodes at these sites were each connected to the positive input of a differential amplifier, and one other electrode, placed at the vertex, was connected to all the negative inputs. Measurements of local cerebral blood flow (CBF) by hydrogen clearance were made at the LL and IC sites. The LL wave form contained 5-7 positive peaks, the second (B wave) being dominant and coinciding with the negative wave II of the surface BAEP. Following graded ischaemia, produced by basilar artery occlusion and controlled hypotension, the latency changes of these two peaks were significantly correlated, as were those of the third wave (C wave) of the LL response and the surface wave III. In the IC, the contralateral wave form contained 4 positive waves (A-D) and a later, dominant, slow negative wave; changes in its peak latency and those of the slow negative surface wave were similarly correlated. The thresholds of local CBF for increases in latency of waves B and C in the LL were similar (12-15 ml/100 g/min), but in the IC the thresholds were 20, 30-35 and 20-24 ml/100 g/min for the B, C and slow negative waves, respectively. Our data indicate that a gradient of sensitivity to ischaemia is present along the brain-stem auditory pathways; this could explain the earlier change of the late, rather than early, BAEP components as reported in clinical cases involving brain-stem lesions.

Auditory evoked potentials in vertebrobasilar transient ischemic attacks

Brainstem auditory evoked potentials (BAEPs) are affected by stroke or migraine in the vertebrobasilar arterial system. Some studies have reported BAEP changes in vertebrobasilar transient ischemic attacks (TIAs), but others have shown no alterations. We recorded BAEPs in 35 patients with TIAs in the vertebrobasilar system who did not have a stroke, other neurologic disease or significant hearing loss. Thirty patients were recorded after resolution of symptoms, while five individuals still had some resolving signs or symptoms. TIA patients as a group had longer interpeak latencies, but I-III, III-V, and I-V latencies were not significantly longer than in controls. Wave V was significantly longer in latency and lower in amplitude in TIA patients, however. The patients whose TIAs had resolved at absolute and interpeak latencies were within normal limits, but three of five had interpeak latencies at or above three standard deviations beyond the normal mean in the still symptomatic group. One of these was later tested and found to be within normal limits. BAEPs after subsidence of symptoms may add little to the evaluation of vertebrobasilar ischemia, but further AEP analysis may show more definitive differences of diagnostic use. The occasional BAEP abnormality during the resolving transient ischemia supports the recently suggested continuum between ischemia and infarction in the vertebrobasilar territory.

Sensorimotor and auditory central conduction time in locked-in syndrome

Motor evoked potentials (MEPs) following magnetic cortical stimulation, somatosensory evoked potentials from median nerve (SEP) and auditory brain-stem responses (ABR) were recorded in a patient with locked-in syndrome during the acute and chronic phases of the clinical course. During the acute phase both ABR and SEP were normal. The MEP from the right upper limb showed a delayed and low voltage potential, while that from the left upper limb was absent. The CT scan showed a ponto-mesencephalic hypodensity. In the chronic phase the MEP from the left upper limb had reappeared and showed a normal latency, while the one from the right upper limb worsened; at that time a new small left fronto-parietal hypodensity had appeared on CT scan. The combined use of MEP, SEP and ABR was able to confirm that the brain-stem damage involved the pyramidal but spared the lemniscal pathways, while MEP changes during the clinical course appeared to reflect both clinical and radiological findings.