Journal of

J Neurol (1983) 229:24%254

Neurology © Springer-Verlag 1983

Brainstem auditory evoked potential abnormalities in vascular malformations of the posterior fossa U. W. Buettner, M. St6hr*, and E. Koletzki Neurological Clinic, Eberhard-Karls-Universit~it T0bingen, Federal Republic of Germany

Summary. Recent reports indicate that malformations of arteries and veins in the posterior fossa are a common cause of facial spasm and trigeminal neuralgia. More rarely they may also cause facial nerve paresis and hearing loss. When vascular malformations are present, brainstem auditory evoked potentials (BAEPs) sometimes show abnormalities similar to those usually recorded in patients with tumours in the cerebellopontine angle. In three patients with facial spasm, one with trigeminal neuralgia and one with facial paresis pathologically delayed absolute latencies a n d / o r interpeak latencies of BAEPs associated with vascular malformations were found. It is concluded that those BAEP abnormalities associated with tumours in the posterior fossa may also be caused by vascular malformations. BAEPs are valuable aids to the diagnosis of such malformations. Key words: Brainstem auditory evoked potentials - Vascular malformations Facial nerve spasm - Facial nerve paresis - Trigeminal neuralgia

Zusammenfassung. Malformationen von Arterien und Venen der hinteren Sch~idelgrube k6nnen einen Facialisspasmus oder eine Trigeminusneuralgie verursachen. In selteneren F~illen verursachen sie auch Facialisparesen und H6rminderungen. Bei Vorliegen von GefiiBmalformationen zeigen akustisch evozierte Hirnstammpotentiale (AEHP; BAEP) gelegentlich Abnormalit~iten, die denjenigen bei Patienten mit Kleinhirnbr0ckwinkeltumoren/ihneln. Fiinf Patienten mit Facialisspasmus, Trigeminusneuralgie und Facialisparese hatten pathologische absolute Latenzverz6gerungen und/oder Interpeak-Latenzen im A E H P und eine Gef/iBmalformation. AEHP-Vedinderungen, die tiblicherweise Tumoren der hinteren Sch/idelgrube zugeschrieben werden, k6nnen auch durch GefaBmalformationen verursacht werden. A E H P sind somit niitzlich bei der Lokalisation auch von vaskul/iren Malformationen. Introduction Dandy [5] first suggested that vascular malformations may cause trigeminal neuralgia. Successful treatment by decompression of the proximal roots of the Offprint requests to: Dr. med. U. W. Buettner, Neurologische Universit/itsklinik, Liebermeisterstr. 18-20, D-7400 Ttibingen, BRD * Present address: Neurological Clinic, D-8900 Augsburg, BRD

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fifth, seventh, a n d eighth nerves [1, 6 - 9 , 11] adjacent to elongated arteriosclerotic or a b n o r m a l l y placed arteries a n d veins supports this idea. It m a y therefore be that chronic m i c r o t r a u m a t i z a t i o n by an artery (or vein) in contact with the nerve may cause neuralgia, spasm or even paresis. To our knowledge there is only one published case [14] in which pathological B A E P s were s h o w n to be due to a vascular m a l f o r m a t i o n within the posterior fossa ( a n e u r y s m a l dilatation of the basilar artery). We studied BAEPs in patients with trigeminal neuralgia, facial spasm or progressive facial weakness a n d f o u n d that a b n o r m a l i t i e s are n o t u n c o m m o n .

Methods

Brainstem auditory evoked potentials were recorded with the technique reported by Jewett and Willison [ 10], Stockard et al. [ 15], Starr and Achor [ 13], Robinson and Rudge [ 12], Chiappa et al. [4], and Buettner [2]. The patient sat in a comfortable chair designed for EEG recordings in a quiet room. The position of the head was adjusted for maximum relaxation of the neck muscles. Stimulation was achieved by Nicolet Click/Noise/Tone Stimulators (1001 A, 1002, 1007A) with 70 dBSL rarefaction clicks presented monaurally through shielded earphones (TD 59) at a rate of 11.9 Hz. Recording was done by platinum needle electrodes (Disa 25 C 04) at Cz and Mi/c(vertex positive-up). In case 1 potentials were simultaneously recorded from both mastoid processes, a recording method which has recently been introduced for better understanding of latency and amplitude variabilities between the two sides and to provide a control for the ipsilateral recordings. In the other cases BAEPs were only recorded from the ipsilateral mastoid process. Potentials were averaged by a Toennies four-channel averager. The bandpass of the recording system was set at 100 Hz-3 kHz. The resolution of the averager was 1024 data points. The data were documented using a pen recorder and/or photographs from the oscilloscope. Criteria of normality and normal values in our laboratory are summarized in Table 1. Amplitudes were only evaluated with respect Table 1. Averaged latencies (ms) and limits (3 SD) of brainstem auditory evoked potentials (BAEPs) with monaural 70 dBSL rarefaction "clicks", mastoid electrodes (28 normal subjects) Peak

9 9

<40 yrs >40 yrs < 40 yrs >40 yrs

I

II

III

IV

1.5 (0.5) 1.5 (0.5) 1.5 (0.5) 1.6 (0.5)

2.6 (0.5) 2.6 (0.5) 2.6 (0.5) 2.6 (0.5)

3.5 (0.5) 3.6 (0.5) 3.6 (0.5) 3.6 (0.5)

4.7 4.6 4.7 4.7

V

(0.6) (0.6) (0.6) (0.5)

Interpeak latencies (IPL) I-II

I-III

I-V

III-V

1.1 (0.4)

2.0 (0.4)

3.85 (0.6)

1.8 (0.5)

I-V

III-V

Interpeak side differences I-II <0.3

Side differences of single peaks < 0.5 Amplitude relation IV-V/I > 1.0

I-III <0.4

<0.4 [ms]

<0.4

5.3 5.5 5.4 5.5

(0.5) (0.5) (0.5) (0.6)

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249

to the relation of the peaks I V - V / I of the same side. Amplitude side differences were considered only in conjunction with latency abnormalities. Side differences of latencies [of interpeak latencies (IPL) and single peaks] were calculated from the mean of absolute differences plus 3 SD.

Case reports Among 32 subjects referred to our clinic with the diagnosis of trigeminal neuralgia, facial spasm, or progressive facial nerve paresis five patients were found to have both pathologically delayed latencies of BAEPs and a vascular malformation in the posterior fossa, confirmed by CT a n d / o r angiography (a further case with proved vascular malformation, but only slight abnormality of the BAEP is not included in these case reports). The abnormal BAEPs and vascular malformations were thought to be causally related to the cranial nerve pathology. There were seven patients with BAEP abnormalities, who showed no abnormality on CT scan. In these cases no further inVasive investigations were done. The aetiology of the BAEP abnormalities and the patients' complaints could not therefore be determined in these cases.

Case 1. A 55-year-old woman had suffered from left-sided hemifacial spasm for 2 years. Neurological examination revealed ptosis and slight paresis of the facial nerve on the left, but no disturbance of hearing. CT and angiography showed marked elongation of the basilar artery and further abnormalities of both superior cerebellar arteries. BAEPs (Fig. 1) showed a delayed IPL I - I I I on the left, suggesting a lesion between the cochlear nerve and the superior olive. Case 2. A 53-year-old man had complained of progressive left hemifacial spasm for some years. Angiography revealed a coiling of the distal vertebral and basilar arteries. No abnormalities were found on clinical examination. Operative decompression of the facial nerve led to complete recovery. Intraoperatively additional coiling of the posterior inferior cerebellar artery was seen. BAEPs (Fig. 2) showed a delayed IPL I - I I I on the left side (preoperatively), whereas latencies on the right side were normal.

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Fig. 1. A 55-year-old woman with left hemifacial spasm; 70 dBSL monaural rarefaction clicks. Simultaneous recording from the right and left mastoid. Note the prolonged interpeak latencies (IPLs) I - I I I on the left. The IPL I - I I I on the right and I-V on both sides are at the upper limit of normality. Left (ipsilateral recording): I--1.4; I I - - 2 . 9 ; I I I - - 4 . 0 ; IV--5.1; V--5.8. Right (ipsilateral recording): I--1.5; I I - - 2 . 9 ; III--3.9; IV--5.1; V - - 6 . 0

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left

4.4

2--fz-S. I right •

5

lores

Fig. 2. A 53-year-old man with left hemifacial spasm; 70 dBSL monaural rarefaction clicks, mastoid recording. Note the delayed IPL I-III on the left side. Left: I--1.4; I1--2.6; 1II--4.1; IV--5.4; V--5.9. Right: I--1.5; II--2.5; 111--3.8; IV--4.9; V--5.9

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Fig. 3. A 43-year-old man with right hemifacial spasm and delayed IPLs I-III on both sides. Parameters as in Fig. 2. Left: I--1.7; 1I--2.9; II1--4.3; IV--5.5; V--?. Right: I--1.8; 11--3.4; III--4.4; IV--5.3; V--?

BAEP abnormalities in vascular malformations

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left right Fig. 4. A 46-year-old man with trigeminal neuralgia with preoperative and postoperative recordings showing pathologically delayed latencies on the left side and badly reproducible peaks IV and V on the right side. The last recording shows some improvement of amplitude and latency on the left side. Parameters as in Fig. 2, except that in all recordings more than 8000 averaging periods were necessary to evoke the potentials. Left: 1--1.9; II--?; Ill--4.3; IV---?; V--6.2. Right: I--1.4; II--3.0; II1--4.1; IV--5.1; V--5.8 (preoperatively)

Case 3. A 43-year-old man with hemifacial spasm on the right and otherwise normal neurological examination exhibited a pathologically delayed IPL I - I I I of the BAEPs (Fig. 3) on both sides. CT scan, except for an ectatic basilar artery, showed no further abnormalities. There has been no operative intervention. Case 4. A 46-year-old man had been treated for trigeminal neuralgia of the second and third branches on the left some years previously by thermocoagulation of the Gasserian ganglion. On admission attacks were frequent and extremely painful. BAEPs showed pathologically delayed latencies on the left from the first peak on (traces 2 and 3 more prominently than trace 1), and a pathologically low amplitude relation of IV-V/I on the right, suggesting an additional brainstem lesion. IPLs I - I I I on both sides were prolonged on the right or at the upper limit on the left respectively (Fig. 4). Angiography and subsequent operation revealed elongated loops of the inferior and superior cerebellar arteries on the left. Decompression of the nerve rootlets and interposition of muscle tissue completely relieved the patient's pain. Pre- and early postoperative (Fig. 4) recordings of BAEPs initially did not show a significant change of latencies, although amplitudes improved. Five months later a shortening of IPL I - I I I could be seen on the left, but the pathological delay and low amplitude of peaks IV and V on the right as compared to peak I of the same trace cannot easily be explained. Case 5. A 67-year-old man presented at the first admission with a peripheralparesis of the right facial nerve. The CT scan (Fig. 5) revealed a much enlarged and elongated basilar artery, which was thought to be compressing the nerve. Evoked potentials from the trigeminal nerve [3, 16] and BAEPs were both abnormal. BAEPs on the right and left (Fig. 6) showed prolonged IPLs I-III, suggesting demyelination of the eighth nerve.

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Fig. 5. A 67-year-old man with progressive peripheral paresis of the right facial nerve. CT demonstrates the elongated ectatic basilar artery

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BAEP abnormalities in vascular malformations

253

Discussion Patients with trigeminal neuralgia, facial spasm and facial paresis may show abnormal BAEPs. It was recently demonstrated [1, 6, 8, 11] that these symptoms can be caused by malformations of arteries or veins in the posterior fossa. BAEP abnormalities with a delay beginning with the first or second peak and a prolonged IPL I - I I I are often associated with either tumours of the cerebellopontine angle [14] or multiple sclerosis. The results presented here indicate that vascular malformations are able to cause a similar abnormality. It is therefore necessary to consider this possibility in every case presenting with symptoms of cranial nerve involvement, such as hearing loss, progressive facial paresis, trigeminal nerve paresis or neuralgia, facial spasm and, more rarely, neuralgia of the glossopharyngeal nerve. BAEPs are particularly useful in patients with trigeminal neuralgia, facial spasm and facial paresis, which may be caused by ectasia or aneurysm of arteries or veins in the cerebellopontine angle. Such malformations may cause localized demyelination through prolonged pulsating pressure, leading in turn to a delay of neuronal conduction with axonal damage (blockage) and reduced amplitude. Similar findings were reported by Stfhr et al. [ 17], who demonstrated a delay of the sensory potential evoked by trigeminal nerve stimulation in patients with trigeminal neuralgia. Different types of BAEP abnormalities have been recorded: 1. Delay of all waves, including the first peak, combined with reduced amplitude, presumably caused by a lesion of the cochlea or the ganglion scarpae. 2. A prolonged IPL I-III, usually on both sides, indicating a lesion of the eighth nerve near the brainstem or the lower brainstem itself. 3. Reduction of amplitude of the IV/V-complex, e.g. in case 4, which may be due to an additional vascular lesion in the upper brainstem. With increasing experience of posterior fossa operations [7], in which the nerve is released from vascular compression, BAEPs and trigeminal SEPs are of particular interest. Both may help to localize the lesion and later to decide the need for a microsurgical intervention within the cerebellopontine angle. Abnormal BAEPs are only indicative of a lesion of the auditory pathway (clinically evident in only two of our cases, one of which exhibited normal BAEPs). Therefore 13 cases withpathological BAEPs out of 32 shows the investigation to be very sensitive in the detection of brainstem lesions. Although in seven cases (with pathological BAEPs) neuroradiological methods (CT scan) did not reveal posterior fossa pathology, only further invasive studies or operative procedures (not available in these cases) could decide whether these BAEPs were falsepositive. Two conclusions may be drawn: 1. In cases of progressive hearing loss, progressive facial paresis, trigeminal neuralgia, and facial spasm, BAEPs may show abnormalities which indicate the location of the pathological process. 2. BAEP abnormalities with a delay of the first peak or a prolonged IPL I - I I I are often associated with tumours of the cerebellopontine angle or multiple sclerosis. However, vascular malformations are able to mimick the same

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B A E P a b n o r m a l i t i e s a n d therefore should be considered as a possible cause of the a b n o r m a l i t y , especially when C T does n o t reveal a t u m o u r in the posterior fossa. A n g i o g r a p h y m a y t h e n show that vascular m a l f o r m a t i o n is the cause of the symptoms.

References 1. Auger RG, Piepgras DG, Laws ER, Miller RH (1981) Microvascular decompression of the facial nerve for hemifacial spasm: clinial and electrophysiologial observations. Neurology (NY) 31:346-350 2. Buettner UW (1982) Akustisch evozierte Potentiale. In: St6hr M, Dichgans J, Diener HC, Buettner UW. Evozierte Potentiale. Springer, Berlin Heidelberg NewYork, S 325-390 3. Buettner UW, Petruch F, Scheglmann K, St6hr M (1982) Diagnostic significance of cortical somatosensory evoked potentials following trigeminal nerve stimulation. In: Courjon J, Maugui~re F, R6vol M (eds) Clinical applications of evoked potentials in neurology. Raven Press, New York, pp 339-345 4. Chiappa KH, Gladstone KJ, Young RR (1979) Brain stem auditory evoked responses: studies of wave form variations in 50 normal human subjects. Arch Neurol 36:81-87 5. Dandy WE (1934) Concerning the cause of trigeminal neuralgia. Am J Surg 24:447-455 6. Hardy DG, Rothon AL (1978) Microsurgical relationships of the superior cerebellar artery and the trigeminal nerve. J Neurosurg 49:669-678 7. Jannetta PJ (1977) Observations of the etiology of trigeminal neuralgia, hemifacial spasm, acoustic nerve dysfunction and glossopharyngeal neuralgia. Definite microsurgical treatment and results in 117 patients. Neurochirurgia 20:145-154 8. Jannetta PJ, Abbasy M, Maroon JC, Ramos FM, Albin MS (1977) Etiology and definite microsurgical treatment of hemifacial spasm. J Neurosurg 47:321-328 9. Jannetta PJ, Rand RW (1966) Transtentorial subtemporal retrogasserian neurectomy in trigeminal neuralgia by microsurgical technique. Bull Los Angeles Neurol Soc 31:93-99 10. Jewett DC, Williston JS (1971) Auditory evoked far fields averaged from the scalp of humans. Brain 94:681-696 11. Oberbauer RW, Heppner F, Schr6ttner O (1982) Die mikrochirurgische Dekompression des N. trigeminus im Briickenwinkel. Nervenarzt 53 : 110-113 12. Robinson K, Rudge P (1978) The stability of the auditory evoked potentials in normal man and patients with multiple sclerosis. J Neurol Sci 36:147-156 13. Starr A, Achor LJ (1975) Auditory brain stem response in neurological diseases. Arch Neurol 32:761-768 14. Stockard J J, Stockard JE, Sharbrough FW (1980) Brain stem auditory evoked potentials in neurology; methodology, interpretation, clinical application. In: Aminoff MJ (ed) Electrodiagnosis in clinical neurology. Churchill Livingstone, NewYork, pp 370--413 15. Stockard JE, Stockard J J, Westmoreland B, Corfits JL (1979) Brainstem auditory-evoked responses--normal variation as a function of stimulus and subject characteristics. Arch Neurol 36: 823-831 16. St6hr M, Petruch F (1979) Somatosensory evoked potentials following stimulation of the trigeminal nerve in man. J Neurol 222:95-98 17. St6hr M, Petruch F, Scheglmann K (1981) Somatosensory evoked potentials following trigeminal nerve stimulation in trigeminal neuralgia. Ann Neurol 9:63-66 Received December 20, 1982