Abstract
Three-dimensional eye movements (scleral search coil system) were recorded in a patient with a surgically acquired perilymph fistula of the left horizontal semicircular canal. Spontaneous horizontal pendular nystagmus was found to be related to the heart rate and may be caused by pressure transfer of blood pulses to the labyrinth. In addition, a contralesional horizontal jerk nystagmus was elicited by Valsalva maneuver, indicating that Ewald’s first law may not only be valid for excitation but also for inhibition.
Perilymph fistulas (PLF), rare disorders characterized by paroxysmal vertigo,1 are caused by abnormal connections between the perilymph space of the labyrinth and the CSF or the middle ear. Depending on the location of the abnormal connection, PLF are classified as inner (to the CSF)2 and, more commonly, as outer types (to the middle ear).3 An important diagnostic test for the outer type of PLF is the Valsalva maneuver. By pressing against the closed nostrils,4 the tympanic pressure increases and may cause a jerk nystagmus (JN) and rotational vertigo in case of a PLF.
We report on a patient with an outer PLF of the left horizontal semicircular canal who presented with a spontaneous horizontal pendular nystagmus (PN) associated with horizontal head oscillations and a Valsalva-induced contralesional horizontal JN. Two main question were addressed:
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1. Is PN caused by a transfer of pulsatile pressure from the vascular system to the labyrinth?
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2. Is Ewald’s first law5 valid not only for canal excitation6 but also for inhibition?
Case report.
A 74-year-old woman with a history of a cholesteatoma in the left ear presented with intermittent pain of the left ear and otorrhea of 2 weeks’ duration. A cholesteatoma of the same left ear was found to be the cause and was surgically removed. Immediately after surgery, the patient had rotational vertigo (increased by swallowing or Valsalva maneuver), vomiting, a falling tendency to the left, but also slow horizontal pendular oscillopsia and a pulse-synchronous tinnitus in the left ear. Surgical exploration showed a fistula from the left middle ear to the horizontal semicircular canal, which was surgically closed by soft tissue. One day after the closure of the fistula, the patient presented without vertigo and tinnitus. The neurologic examination was normal except for a hypacusis of the left ear. The audiogram showed hypacusis of the left ear for air, but not for bone conductance. Routine laboratory examination yielded values within normal limits.
Methods.
After the patient had given her informed consent, three-dimensional eye and head movements were recorded by using a scleral search coil system (CNC Seattle; Skalar, Delft, 500 Hz Sampling Rate). The eye coil data were calibrated using fixation spots and a gimbal system to calibrate torsion.7,8⇓ Rightward, upward, and clockwise eye movement directions from the point of the subject were defined as positive.
Three-dimensional eye and head positions were recorded in a head-fixed and a head-free condition in the dark by using the following paradigms: 1) spontaneous, 2) visually guided, and 3) evoked eye movements by Valsalva maneuver or retroauricular fingertip pressure. In addition, conventional electro-oculography (EOG) was used for simultaneous recording of the ECG.
Helical, high-resolution CT (reconstruction 1 mm) of the temporal bones was performed on a somatom CT scanner (Siemens Medical Systems, Munich/Erlangen, Germany). MRI was performed out on a 1.5-Tesla MRI unit (Siemens Magnetom Symphony) by using a T1-weighted spin-echo sequence, a T2-weighted turbo-spin-echo sequence, and a T2-weighted gradient echo sequence (3d-CISS).
Results.
The CT scan of the temporal bones after surgery of the cholesteatoma of the middle ear showed an interruption of the wall of the left horizontal semicircular canal (figure 1, A [arrow]).
Figure 1. High-resolution CT (A) of the temporal bones after surgery of the left-sided cholesteatoma. Note the defect in the prominentia of the left horizontal semicircular canal (white arrow). MRT 3d-CISS-sequence (B) of the temporal bone shows that both horizontal semicircular canals are normally filled with liquid. It does not show the fistula as the CT scan does (arrow). Note the granulation tissue (star) next to the left horizontal semicircular canal.
MRI showed normal signal intensities in the horizontal semicircular canals, but could not show the fistula (see figure 1, B [arrows]). The postoperative granulation tissue in the middle ear was directly adjacent to the canal (star).
Immediately after cholesteatoma surgery, the patient showed clinically two types of nystagmus: First, a clinically visible, conjugate, purely horizontal spontaneous PN (estimated amplitude, 3–4 degrees) was observed in the light, which increased without fixation (Frenzel’s glasses). Concomitantly the patient noticed slow horizontal sinusoidal oscillopsia of about 1 Hz. PN was not observed during the Valsalva maneuver. Second, a horizontal JN to the right was elicited during the Valsalva maneuver or direct retroauricular pressure on the tamponade. All other oculomotor performance (including saccades and smooth pursuit) was normal.
One week after surgery, when PN had decreased in amplitude, three-dimensional search coil recordings of the right eye were performed in darkness in the head-fixed condition:
Spontaneous horizontal PN (figure 2, A) had a mean amplitude of 1.07 ± 0.76 degrees with a small torsional component of 0.34 ± 0.12 degrees and a frequency 0.92 Hz.
Figure 2. Recordings of eye (A, B, D) and head (C) positions in the dark: three-dimensional search coil recordings of the right eye show spontaneous pendular (A) nystagmus and pressure-induced JN (B; horizontal bar: Valsalva maneuver) 1 week after surgery (Ev: vertical, Eh: horizontal, and Et: torsional eye position; ccw: counterclockwise, cw: clockwise). In C, spontaneous head oscillations are shown 1 week after surgery. The horizontal head position trace of purely horizontal head oscillations of approximately 1 degree is shown. There were no oscillations in the torsional and vertical planes (not shown). (D) Phase relationship of heart rate (ECG; gray line) and oscillations of the horizontal eye position as recorded by EOG (black line) 4 days after the cholesteatoma operation. Both are phase-locked at the same frequency (dashed line as reference).
Horizontal JN (see figure 2, B) to the right (mean amplitude of 1.82 ± 0.60 degrees) with a small positive torsional component (mean amplitude, 0.43 ± 0.12 degrees) and a frequency of 2.84 ± 0.42 Hz was elicited by the Valsalva maneuver (see figure 2, B [bar]) or by retroauricular pressure (not shown). After Valsalva maneuver, the nystagmus direction reversed for about half a second (see figure 2, B [arrows]).
In the head-free condition, there were horizontal head oscillations without concomitant PN with a mean amplitude of 1.0 ± 0.19 deg, and a frequency of 1.0 ± 0.08 Hz (see figure 2, C).
Eye velocity vectors of JN and PN were compared with the horizontal semicircular canal sensitivity axes (figure 3 [dashed lines]) as reconstructed from anatomical data of the horizontal canals.9 The velocity vectors of both types of nystagmus align with the axes of the left horizontal semicircular canal and show a contralesional (right) nystagmus direction, indicating an inhibitory vestibular response.3
Figure 3. The eye velocity vectors of the PN (A, C) and of the Valsalva-induced JN (B, D) are compared with the optimal stimulation axes of the horizontal semicircular canals9 (dotted lines). PN aligns approximately (A, C), and the JN aligns closely (B, D) with the horizontal semicircular canal axes. The excitatory direction of the axes of the horizontal semicircular canals are indicated by symbols (dot: right; triangle: left semicircular canal) and are opposite to the direction of slow compensatory eye movements (HCl, HCr: horizontal semicircular canal left, right; cw: clockwise, ccw: counterclockwise torsion; VELH, VELV, VELT: horizontal, vertical, and torsional eye velocity).
To evaluate the temporal relationship of the heart rate and PN, ECG and horizontal EOG were recorded simultaneously (see figure 2, D) 4 days after surgery. PN and ECG had the same frequency of 0.98 Hz (fast fourier analysis) and a fixed phase-relationship (see figure 2, D). Eye position maximum (zero eye velocity) is approximately at the T wave of ECG.
Discussion.
Evidence of an outer type of surgically acquired PLF arises from 1) the onset of symptoms immediately after surgery, 2) imaging, 3) the Valsalva and direct pressure–induced horizontal JN in the horizontal canal plane, and 4) the disappearance of the symptoms after closure of the fistula.
Pendular nystagmus has not been observed with PLF so far. It may be a new, rare clinical sign of PLF. Evidence that PLF causes PN additionally comes from the alignment of the eye movement velocity vectors with the sensitivity axis of the left semicircular canal. Moreover, PN is fixed in phase and frequency with the ECG (see figure 2, D). This phase-locked behavior with respect to the ECG suggests a transfer of pressure from the vascular system to the labyrinth. Two possible mechanisms are 1) transfer of the systolic blood pulsation via the PLF to the inner ear or 2) transfer of venous blood pulsation via the cochlear aqueduct.
According to Ewald’s first law, selective single semicircular canal stimulation causes eye movements in the plane of the canal.5 It was found that it is valid during excitation of the semicircular canals, such as in an inner type PLF of the posterior canal2,6⇓ or during benign paroxysmal positioning vertigo of the posterior canal (BPPV).10 We present evidence that the law is also valid during inhibition of the semicircular canal deriving from the alignment of the elicited JN velocity with the sensitivity vector of the left horizontal canal in our patient and the contralesional direction of the nystagmus. The direction of nystagmus with respect to the manipulated ear depends on the endolymphatic flow in the semicircular canal3 and indicates in our case an inhibition of the left horizontal semicircular canal.
Acknowledgments
Supported by Deutsche Forschungsgemeinschaft (DFG).
Acknowledgment
The authors thank J. Benson for carefully reading the manuscript.
- Received December 1, 2000.
- Accepted February 24, 2001.
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