Eberhard Koenig

Spinal arteriovenous malformations and fistulae: clinical, neuroradiological and neurophysiological findings.

SummaryTwenty-six patients with myelographic signs suggestive of a spinal arteriovenous malformation (AVM) were examined neurologically and neurophysiologically. By selective spinal angiography it was possible to differentiate between dural arteriovenous fistulae (dAVF 20 patients) and intradural AVMs (iAVM, 6 patients). Initial complaints were nonspecific and variable, mainly consisting of sensory disorders and muscle weakness. Later, patients suffered involvement of both the upper and lower motor neurons. There was a high percentage of lower motor neuron lesions (95%), especially in dAVF patients, which were mostly of widespread distribution and included several myotomes. Electrophysiological examination regularly revealed lower neuron involvement, frequently with pathological spontaneous activity in several myotomes, pathological sensory-evoked potentials after tibial nerve stimulation, but normal sensory conduction velocities of the sural nerve, indicating sparing of the sensory ganglion. Frequently there was a discrepancy between the localization of the dural fistula or angioma and the spinal level responsible for clinical symptoms. This suggests that it may be the inadequacy of the venous drainage system to cope with the blood volume rather than the AV-shunt that is responsible for the symptoms. An early diagnosis is essential, as removal of the shunt before there has been progression to severe neurological deficits (paraplegia) is the only way to ensure a satisfactory outcome.

The clinical significance of head-shaking nystagmus in the dizzy patient.

The clinical significance of horizontal head-shaking nystagmus (HSN) was evaluated in 85 patients who complained of dizziness and vertigo. This was done by comparison of the horizontal head-shaking test with routine rotatory and caloric vestibular testing. We found that HSN evoked by horizontal head-shaking is a highly sensitive way to detect unilateral vestibular hypofunction. Except in patients with additional central vestibular imbalance or in patients with Menieres disease, the direction of horizontal HSN is highly significant in indicating the side of the lesion, with the fast phase beating toward the intact side. However, horizontal HSN is not specific in distinguishing peripheral hypofunction from more central vestibular imbalances. Peripheral vestibular hypofunction as well as a central asymmetry of the vestibular velocity storage mechanism can each separately or in combination produce horizontal HSN. Thus, while the head-shaking manoeuvre is an excellent bedside-test to detect unilateral vestibular hypofunction, further rotatory and caloric testing is still necessary to clarify the patients condition.

Head-shaking nystagmus during vestibular compensation in humans and rhesus monkeys

Nystagmus evoked after rapid horizontal head-shaking is believed to be a sensitive indication of the existence and location of a unilateral vestibular lesion. Its origin is the directional asymmetry in vestibular responses of the healthy labyrinth (Ewalds second law). For nystagmus to appear after the head has stopped moving, however, the directionally asymmetric responses must have been stored during the head-shaking to be discharged afterwards. Our results confirm the notion that head-shaking nystagmus is most likely generated by a directional preponderance in vestibular responses but only in combination with a functioning central velocity-storage mechanism. If velocity-storage is lost completely, as may occur during the acute phase of a unilateral peripheral vestibular lesion, even a large vestibular preponderance does not lead to head-shaking nystagmus. Thus, to interpret the results of the head-shaking test the condition of the velocity-storage mechanism must be taken into account.

Central spinal cord lesions in stenosis of the cervical canal

Summary34 patients suffering from cervical spondylotic myelopathy confirmed by myelography were examined by delayed CT 6–10 h after myelography. Twelve patients showed bilateral intramedullary collections of contrast medium, predominantly cranial to the stenosis. In these patients males predominated, the duration of clinical symptoms lasted longer although their age was lower. There was no correlation to the degree and the extension of the narrowing of the cervical spinal canal. Half of 20 patients undergoing consecutive decompressive surgery showed intramedullary contrast enhancement, and this was shown again by postoperative MRI in eight. The postoperative clinical and neurophysiological results revealed no change in the majority of patients, but three patients showing intramedullary contrast medium deteriorated in neurophysiological outcome, while only one of the patients in whom intramedullary contrast medium was not noticed got worse.

Oculomotor abnormalities and MRI findings in idiopathic cerebellar ataxia

Extensive oculomotor testing and quantitative MRI evaluation was performed in seven patients with idiopathic cerebellar ataxia without extracerebellar symptoms (IDCA-C) and in ten patients with additional extracerebellar symptoms (IDCA-P). The most severe oculomotor deficits were disturbed smooth pursuit, optokinetic nystagmus and suppression of the vestibulo-ocular reflex (VOR). The symptoms correlated well and consistently with the amount of atrophy of the flocculus and the dorsal vermis. These correlations, however, were not specific, and deficits also correlated with the amount of atrophy of other cerebellar structures. No correlation was found between saccade velocity and brain-stem atrophy or between saccade metrics and atrophy of the dorsal vermis. Although patients with IDCA-P had more severe oculomotor deficits than patients with IDCA-C, the pattern of the oculomotor disturbances was the same for both groups. Thus, eye movement analysis alone is not sufficient to distinguish between patients with pure cerebellar ataxia and those with additional extracerebellar symptoms.

The Effect of Lateral Head Tilt on Horizontal Postrotatory Nystagmus I and II and the Purkinje Effect

The influence of an active lateral head tilt on postrotatory nystagmus I and II (PI, PII) was explored in normal humans. During postrotatory nystagmus the head was tilted laterally either towards the direction of the previous rotation (ipsilateral tilt) or towards the opposite direction (contralateral tilt) or the head was kept erect. Both ipsi- and contralateral head tilts led to a substantially weaker and shorter PI and PII as compared with the trial without head tilt. The time constants of the decline of PI were shortened to the ones observed in the peripheral nerve of animals. The reduction of PI and PII suggests a position-dependent tonic inhibition of the vestibular storage mechanism in the vestibular nuclei probably by the otoliths. The stronger reduction of time constant and cumulative amplitude of PI after contralateral as compared with ipsilateral head tilt may be explained by different combinations of asymmetric responses in canal and otolith afferents.

Fixation suppression of the vestibulo-ocular reflex (VOR) during sinusoidal stimulation in humans as related to the performance of the pursuit system

Fixation suppression (FS) of the vestibulo-ocular reflex (VOR) was tested during passive sinusoidal body rotation with a frequency of 0.1 to 1.0 Hz and stimulus amplitudes ranging from 10 degrees to 240 degrees. To test whether FS can be explained by an internal pursuit signal opposite to the VOR, pursuit and the VOR under different instructional sets were studied. Both pursuit and FS decrease with increasing frequency and stimulus amplitude and seem to be limited by stimulus acceleration. Gains in FS calculated on the basis of the VOR during mental arithmetic correspond closely to the frequency and amplitude dependent pursuit gain, suggesting that an internal pursuit signal plays a major role in VOR suppression.

Impairment of vertical motion detection and downgaze palsy due to rostral midbrain infarction

SummaryWe present two cases with acute onset of vertical gaze palsy, mainly consisting of impaired downgaze and apraxia of downward head movements, together with neuropsychological deficits (hypersomnia, impaired attention and disorders of memory and affective control). CT and MRI revealed bilateral post-ischaemic lesions in the dorsomedial thalamus and the mesodiencephalic junction, dorsomedial to the red nucleus, thus being restricted to the territory of the posterior thalamosubthalamic paramedian artery, which includes the region of the rostral interstitial nucleus of the medial longitudinal fascicle as the main premotor nucleus for the generation of vertical saccades. In our patients, oculographic examination with electro-oculography and magnetic search coil recording showed severe impairment of downward more than upward saccades and only minor deficits of vertical pursuit and the vestibulo-ocular reflex. Visual functions were normal, with one exception: a psychophysical test of motion perception revealed a significant deficit in the detection of vertical movements. This could be due to a central adaptive mechanism which, in order to minimize oscillopsia, might elevate thresholds for vertical motion perception in cases of vertical gaze palsy. As an alternative explanation, lesions within the midbrain tegmentum could have damaged subcortical visual pathways involved in motion perception.

Head position dependent adjustment of the three-dimensional human vestibuloocular reflex

We studied the influence of static head position relative to the rotation axis on the three-dimensional (3-D) vestibuloocular reflex (VOR). By means of a 3-D rotating chair and a 3-D magnetic search-coil system, eye movements were recorded in 6 normal human subjects during sinusoidal rotation about an earth-vertical axis (yaw) with the head positioned at different pitch angles and about an earth-horizontal axis (pitch) with the head positioned at different yaw angles. We confirmed that torsional VOR gain is about 2/3 of horizontal and vertical VOR gain leading to non-collinear axes of eye and head rotation whenever torsional head movement components were present with eye movement axes tilting away from the torsional direction. Despite this non-collinearity of stimulus and eye movement rotation axes there was close to perfect adjustment of the different VOR components depending on the angle between gaze direction and stimulation axis, indicating a vectorial summation of gains obtained for rotations in the major body axes (roll, pitch and yaw). The horizontal and vertical eye movement components followed a cosine function of the angle between the plane of rotation and gaze direction. The torsional component followed a sine function.

Pursuit Opposite to the Vestibulo-ocular Reflex (VOR) during Sinusoidal Stimulation in Humans

Pursuit opposite to a simultaneously activated vestibulo-ocular reflex (VOR) was tested during passive sinusoidal body oscillations (0.1-1.0 Hz, amplitudes 10-80 degrees) about the vertical axis in 4 healthy humans, while subjects were asked to pursue a small target moving in phase with the rotating chair with about half its amplitude relative to the head and 1.5 times its amplitude with respect to space. The decrease in gain of the pursuit opposite to the VOR occurred at lower stimulus frequency, stimulus velocity and stimulus acceleration than pure visual pursuit when gain was calculated in relation to target motion in head coordinates. It resembles that of pure pursuit when calculated in relation to target motion in space (earth coordinates, sum of the displacements of the mirror image and of the chair) thus taking the oppositely directed VOR into account. The data fit the assumption of a linear interaction of the VOR (in counterphase) and pursuit.