Anatomy of Wallenberg's Syndrome
The medulla houses the bulk of the vestibular nuclei, including the medial vestibular nucleus (MVN). Other important structures for the control of eye movements in the medulla include the Nucleus Prepositus Hypoglossi, the inferior olivary nuclei, and the inferior cerebellar peduncles1.
Given that the NPH and MVN make up the neural integrator, it can be anticipated that lesions of these structures will result in gaze evoked nystagmus (GEN) on attempted holding of horizontal gaze. This does require that the lesion affecting the dorsolateral medulla extends medially, and hence, GEN may not necessarily be present in Wallenberg's syndrome.
In addition, lesions of the inferior cerebellar peduncle interrupt climbing fibre inputs to the dorsal vermis of the cerebellum leading to excessive inhibition of the fastigial nucleus2. This leads to ipsipulsion, with hypermetric saccades to the side of the lesion, and hypometric saccades to the opposite side.
Lesions of this area, or of the cerebello-pontine angle, may also result in Brun's nystagmus: a combination of nystagmus arising from structures making up the neural integrator (GEN) and a high frequency, small amplitude nystagmus due to vestibular nerve fibre injury or damage to the medial vestibular nucleus, which results in vestibular imbalance.
Lesions affecting the vestibular nucleus can mimic peripheral vestibular lesions with a positive head impulse sign (Video 3 below). In the setting of an acute vestibular syndrome in which a patient has acute vertigo and a spontaneous nystagmus, a normal head impulse test raises suspicion of a central lesion in the brainstem or in the posterior medial cerebellum involving the nodulus and uvula. Other features to distinguish lesions in this region from a peripheral vestibular lesion are discussed further in the section on separating central from peripheral lesions.
Lateropulsion: a tendency to fall or sensation of being pushed towards the affected side (similar to an acute vestibular neuropathy). This is due to a lesion of the inferior cerebellar peduncle. |
| Dysfunction of Ocular Alignment |
| Skew deviation |
| Ocular Tilt Reaction |
| Environmental Tilt: Floor on Ceiling Phenomenon |
| Nystagmus |
| Horizontal, Torsional |
| Mixed horizonal-torsional-vertical |
| See-saw nystagmus |
| Eyelid nystagmus |
| Head nystagmus |
| Smooth Pursuit and Gaze-Holding abnormalities |
| Ipsilateral eye deviation |
| Impaired contralateral smooth pursuit |
| Lateropulsion of pursuit |
| Saccadic abnormalities |
| Ipsipulsion (lateropulsion) |
| Torsipulsion |
| Oblique saccadic trajectories on vertical gaze attempts |
1. Dysfunction of ocular alignment.
An OTR may be present (ipsiversive head tilt, eye lower on the side of the lesion). Ocular torsion may be larger in the lower eye, possibly due to additional involvement of the posterior semicircular canal projections. Spontaneous nystagmus, similar to that of peripheral vestibular lesions, may be horizontal or mixed horizontal-torsional.
Lid nystagmus may also occur with lid twitches synchronized with the fast phase of ocular nystagmus.
The "floor on ceiling" phenomenon is a sensation of environmental tilt, in which the entire room is tilted on its side or even upsidedown; possibly due to dysfunctional vestibular-otolith connection to central structures3.
See-saw nystagmus: This nystagmus is a disjunctive, vertical-torsional nystagmus, one half-cycle of which consists of elevation and intorsion of one eye in conjunction with synchronous depression and extorsion of the other eye; the next half-cycle consists of reversal of these vertical and torsional movements.The usual cause is a lesion compressing the midbrain region, when the nystagmus is pendular. With lateral medullary lesions, however, a jerk see-saw nystagmus may occur3. In the case of the lateral medullary syndrome, the torsional component is conjugate and the fast component beats away from the side of the lesion.
2. Nystagmus
In the lateral medullary syndrome, nystagmus may be due to direct damage to the vestibular nuclei or their cerebellar, semicircular canal, or otolithic connections. Frequently, the medial vestibular nucleus is spared, since the infarction is dorso-lateral, and, if so, neural integrator function and the VOR should be normal, and nystagmus is not a prominent feature, or is absent.
When it does occur, nystagmus is usually positional and is usually horizontal, torsional, or mixed, with torsional, vertical, and horizontal components.
- Horizontal nystagmus beats away from the side of the lesion; the horizontal slow phase is directed toward the side of the lesion and is influenced by different positions of the eyes and by fixation; velocity of drift is faster on contralateral than on ipsilateral gaze.
- Torsional nystagmus is common in Wallenberg's syndrome; the upper pole of the iris beats away from the side of the infarction (link to video #4 below).
- Vertical nystagmus is usually upbeating.
- If there is damage to the MVN-nucleus prepositus hypoglossi complex, gaze-evoked nystagmus (ie, right-beating in right gaze and left-beating in left gaze) will result4.
Gaze-evoked eyelid nystagmus associated with ocular nystagmus has been described, in which a clinically obvious upward jerking of the eyelids occurred synchronously with the fast phase of a gaze-evoked horizontal nystagmus.
Head nystagmus may reflect a lesion in vestibulospinal and reticulospinal projections to cervical motoneurons5.
Head-shaking-induced nystagmus can be ipsilesional (even when spontaneous nystagmus is contralesional), likely resulting from disinhibition of velocity storage connections between the unilateral vestibular nucleus and cerebellar nodulus/uvula4.
Spontaneous nystagmus can have features that are typically thought of as being “peripheral” including having a unidirectional pattern; obeying Alexander’s Law (nystagmus increases in intensity in the direction of the fast phase); and suppressing with visual fixation4. Similarly, if there is involvement of the medial vestibular nucleus, an abnormal head impulse test may be present, since the ipsilateral VOR is deficient.
3. Smooth pursuit and gaze-holding abnormalities
Patients with the lateral medullary syndrome may complain of a sensation of their bodies being “pulled to one side” and may attempt to counteract this “lateropulsion of the body” by leaning toward the opposite side.
Due to the gaze-holding impairment, ocular movements may be similarly affected resulting in lateropulsion (identical to ipsipulsion), which is a conjugate deviation of the eyes toward the side of the lesion. This is best seen with closed lids, and, in particular, a corrective movement may be seen when the eyes are opened, as the eyes refixate on the midline2.
Smooth pursuit eye movements that track targets moving away from the side of the lesion are also impaired in patients with lateral medullary lesions, whereas pursuit toward the side of the lesion is relatively normal1.
The abnormalities of gaze-holding noted in the previous paragraph may also be reflected in saccadic eye movement abnormalities.
Lateropulsion also affects saccades, so that the patient has:
- Hypometric saccades when looking away from the lesion
- Hypermetric saccades were looking towards the lesion
- Vertical saccades tend to deviate towards/ show an oblique trajectory to the side of the lesion (saccadic drift) (notably for upward saccades)3.
- Torsipulsion (i.e. inappropriate torsional “blips”) which may occur during horizontal saccades5.
Inhibitory fibres travelling via the left inferior cerebellar peduncle are damaged, resulting in less inhibition of the left dorsal vermis. There is consequently a greater inhibition of the fastigial nuclei, and less activation of the right sided PPRF.
This results in deficient rightward saccades (contralesional hypometric saccades), and over-active leftward saccades (ipsilesional hypermetric saccades), and ipsilesional ocular lateropulsion.
Ipsipulsion to the left: there is leftward ocular lateropulsion (apparent throughout the video during blinks - during eyelid closure, there is conjugate deviation to the left, and when the eyelids open, the eyes correct back to primary gaze by moving rightwards) is present. There are hypermetric saccades to the left (ipsilateral) and hypometric saccades to the right (contralateral), relating to injury of the climbing fibers traveling through the inferior cerebellar peduncle on the left side.
(vv)Wallenberg.mp4(tt)
From: Gold D. The acute vestibular syndrome with dysarthria, dysphagia, dysphonia, hemi-ataxia, and saccadic dysmetria due to the lateral medullary (Wallenberg) syndrome. Video. [Neuro-Ophthalmology Virtual Education Library: NOVEL Web Site]. 2017.
Available at: https://collections.lib.utah.edu/ark:/87278/s6963fhm
Deviation of the eyes to the left (side of the lesion) under closed eyelids.
Saccadic overshoot to the side of the lesion (ipsipulsion); and undershoot to the right.
(vv)WallenbergZee.mp4(tt)
From: Zee DS. The cerebellum for the neuro-ophthalmologist: A video tutorial of some signs and syndromes to recognize NANOS 42nd Annual Meeting 2016. Retrieved from: https://collections.lib.utah.edu/ark:/87278/s6nw2r5g
Examination shows ipsipulsion: saccadic hypermetria to the right (ipsilesional), hypometria to the left (contralesional) and rightward ocular lateropulsion (ipsilesional) under closed lids, apparent as the eyes shifting left to primary position when the eyes open.
(vv)SaccDysM.mp4(tt)
From: Gold D.Saccadic dysmetria and ocular lateropulsion in lateral medullary stroke. Video. [Neuro-Ophthalmology Virtual Education Library: NOVEL Web Site]. 2016.
Available at: https://collections.lib.utah.edu/ark:/87278/s65176w6
Examination shows ipsipulsion (hypermetric saccades to the left, hypometric saccades to the right, not seen in the video).
There is an ipsilesional (left) hypotropia from skew deviation.
There was also a positive head impulse test, which is typically a "peripheral" sign, although in this case, the positive result was due to left vestibular nucleus involvement6. Note that a positive head impulse test, if seen due to a brainstem lesion, is usually due to involvement of the flocculus in an AICA stroke.
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(vv)Wallenberg2.mp4(tt)
From: Gold D. Wallenberg syndrome in MS. Video. [Neuro-Ophthalmology Virtual Education Library: NOVEL Web Site]. 2016.
Available at: https://collections.lib.utah.edu/ark:/87278/s6ck1p47
Torsional nystagmus. The upper pole of the iris beats away from the side of the infarction; and is clockwise from the examiner's perspective.
A better description would be: " top pole of the eye beating towards the left ear" (since clockwise is ambiguous: some conventions specify that it should be from the patient's perspective.
(vv)TARNROT.mp4(tt)
From: Dieterich M, Tarnutzer AA. Bedside ocular motor testing and vestibular testing. EAN 2020.