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292 Disorders of the Auditory System
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C
Figure 6–4. continued
left ear. In addition, both ipsilateral and
contralateral acoustic reflexes were absent
in both ears at all frequencies tested (500,
1000, and 2000 Hz). Severe deficits were
also observed on the Dichotic Digits Test
(8% left, 78% right) and the Dichotic
Rhyme Test (13% left, 20% right), and the
patient was not able to complete the Frequency Pattern Test in either the verbal or
hummed conditions for either ear. Middle
latency response testing was completed
and responses were essentially absent
bilaterally for three electrode sites (Cz, C3,
C4). Both TEOAEs and ABRs also were
administered. The TEOAE results were
normal for both ears (Figure 6–4B) and
the ABRs were totally absent bilaterally
(Figure 6–4C).
Medical Examination
An otolaryngologic examination was unremarkable, as were the results of CT,
MRI, and EEG testing.
Impression
Bilateral ANSD secondary to a likely viral
insult of the seventh and eighth cranial
nerves based on exclusion.
Audiologic Recommendations
and Management
An assistive listening device was suggested along with a wide variety of listening strategies and auditory training. The
patient did obtain an assistive listening
device and reported benefit, particularly
in noise. Routine audiologic monitoring
of the patient’s hearing continues to demonstrate relatively stable thresholds.
Medical Recommendations
and Management
No surgical intervention was recommended,
however, the patient was encouraged to
have routine audiologic follow-up and continued use of the assistive listening device.
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Case 6–5: Auditory Neuropathy
Spectrum Disorder
History
A 4-year-old male presented with parental
concerns regarding his hearing status. The
child had been seen by several audiologists with varying audiologic results. His
parents stated that their child could hear
in a one-on-one situation but required
visual cues (lip-reading) to aid in his
understanding of speech, especially in the
presence of background noise. School staff
also indicated concerns regarding this
child’s hearing. The child had a positive
history of recurrent otitis media resulting in the insertion of PE tubes (since
extruded). The patient reportedly passed
his newborn hearing screening, and his
birth history was unremarkable.
Audiology
An otoscopic check was unremarkable
bilaterally. Results of an initial audiologic
evaluation revealed a mild sensorineural hearing loss bilaterally (Figure 6–5A).
Speech thresholds were in poor agreement
with pure-tone averages for both ears. Of
note is that only an SAT could be obtained
for the right ear as the patient was unable
to identify any spondee words in that ear;
however an SRT could be established for
the left ear. In addition, word recognition performance using an age appropriate test was poor bilaterally (16% right
ear, 64% left ear). Tympanograms demonstrated normal pressure, volume, and
compliance measures bilaterally. DPOAE
were present for both ears (Figure 6–5B).
Given the poor word recognition, it was
recommended that the child undergo an
ABR to evaluate for possible ANSD. The
ABR was completed and yielded absent
click responses bilaterally confirming the
suspicion of ANSD (Figure 6–5C).
Medical Examination
An otolaryngologic examination was unremarkable, as were the results of CT and
MRI scans.
Impression
Bilateral auditory neuropathy spectrum
disorder.
Audiologic Recommendations
and Management
Initially, a trial with hearing aids and
an FM system was recommended. The
patient underwent a trial but no significant benefit was obtained. A cochlear
implant was then recommended for consideration, and the parents elected to
proceed with implantation. Following
implantation, the patient has done very
well. He has begun receiving auditory
training. Both parents and staff reported
significant improvement in his hearing
when wearing the device. Word recognition score for the implanted ear (right
ear) improved from 16% preoperatively to
84% postoperatively.
Medical Recommendations
and Management
Cochlear implantation (right side) with
referral back to audiology following implantation for audiologic management.
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A
Figure 6–5. Pure-tone audiogram and speech recognition scores (A), DPOAEs (B), and ABR trac-
ings (C) for a 4-year-old male with auditory neuropathy spectrum disorder (Case 6–5). continues
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B
Figure 6–5. continues
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C
Figure 6–5. continued
vasculaR looP
syndRome
Introduction
Vascular loops, also referred to as vascular loop syndrome, can affect the auditory nerve. The vascular loop syndrome
was popularized by the work of Peter
Jannetta, a neurosurgeon, in the mid- to
late 1960s (Jannetta, 1967). In this vascular condition, the auditory and adjacent
cranial nerves may be compressed by a
vessel in the CPA and this compression is
believed to result in auditory, vestibular,
and/or facial symptoms. Although this
disorder does not have high visibility and
awareness among most audiologists, it
is an important disorder for audiologists
to consider. The audiologic findings in
patients with vascular loops can be variable and will depend on the degree of
involvement. After surgical decompression, audiologic results often improve
(Møller, 2000). However, more research
with audiologic testing needs to be done
to gain better insight into the auditory
profile associated with this particular
disorder. It has been argued that this disorder can mimic symptoms of Ménière’s
disease and other auditory disorders. This
makes the diagnosis difficult and renders
this disorder controversial in some circles
(see Hain, 2016).
Symptoms
Vascular loops can result in auditory
symptoms of decreased hearing sensitivity, speech perceptual distortions, tinnitus, and hyperacusis. In addition, hemifacial spasm and, in some cases, facial pain
on the side of lesion can be experienced.
This latter symptom is usually related to
the involvement of the trigeminal nerve.
Patients with vascular loop compression
can also present with vestibular symptoms that can be severe in degree in some
patients. Compression effects secondary
to vascular loops can result in many or all
of the symptoms just mentioned, or they
may result in any one of them; however,
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facial spasm and/or pain are the symptoms that are considered most indicative of
the disorder (Bergsneider & Becker, 1995;
Chadha & Weiner, 2008; Møller, 2000).
Incidence and Prevalence
It is important to understand that not all
vascular loops that come into contact with
the auditory nerve in the CPA will result
in auditory symptoms. That is, some vascular loops that are apparently in a position to affect the auditory nerve do not;
therefore, it is difficult to determine the
incidence of auditory compromise associated with vascular loops. Makins, Nikolopoulos, Ludman, and O’Donoghue
(1998) reported that the vascular loop
was in contact with the auditory nerve
in 25% of symptomatic ears and 21% of
asymptomatic ears. Although these data
provide information as to the incidence
of “contact” between vascular loops and
the auditory nerve, they do not address
the percentage of patients with auditory
symptoms. It is also difficult to determine
the incidence of vascular loops that results
in any of the other symptoms mentioned
previously; however, it has been estimated
that trigeminal neuralgia and hemifacial
spasm associated with vascular loops
occur at rates of 0.5 and 0.8 per 100,000
(see Møller, 2000). Lingawi (2003) — who
examined the incidence of vascular loop
contact with the auditory/vestibular,
facial, and trigeminal nerves — noted that
8% of the nerves demonstrated impingement, while 20% showed abutment.
Seventy-two percent of the nerves were
found to be healthy. Of the nerves that
demonstrated impingement, 90.5% were
facial/vestibulocochlear complex, 9.5%
trigeminal, and 2% showed impingement
on all nerves. No bilateral impingements
were detected. Approximately 93% of the
nerves that demonstrated abutments were
at the facial/vestibulocochlear complex.
Etiology and Pathology
It appears that in most cases the vascular
loop originates from the anterior inferior
cerebellar artery (AICA). It is the compression on the eighth nerve and adjacent
nerves, as well as the irritation of these
nerves, that may eventually result in
demyelination of the nerve fibers and the
auditory, vestibular, and/or facial symptoms (Makins et al., 1998). As mentioned
earlier, many people with vessel contact
with cranial nerves in the CPA do not
have symptoms of any sort. For example,
Hardy and Rhoton (1978) found vessel
contact with the trigeminal nerve in 60%
of 50 cadavers examined, none of which
had trigeminal complaints before their
deaths. This suggests that there must be a
constellation of factors present for symptoms to be manifested, and currently it is
not known what factors are necessary to
yield symptoms (Chadha & Weiner, 2008;
Møller, 2000).
Site of Lesion
In vascular loop compression, the site of
involvement is the CPA, more specifically, the porus acusticus or opening of
the internal auditory canal. At this site,
the vascular loop can affect the nerves
exiting the internal auditory canal, which
include the vestibular, auditory, and facial
nerves. The trigeminal nerve can also be
affected by vascular loops; however, this
nerve is generally more rostral than the
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seventh (facial) and eighth (auditory and
vestibular) nerves. Hence, the likelihood
of a slightly different locus for trigeminal
neuralgia associated with vascular loop
compression exists (Møller, 2000). McDermott and colleagues reported results on
vascular loops that were classified based
upon their sites of lesion (McDermott,
Dutt, Irving, Pahor, & Chavda, 2003).
Using an anatomic classification to categorize the loops, these authors reported
that there were 412 type I loops within the
CPA, 202 type II loops at the porus acusticus that extended up to 50% of the internal auditory canal, and 50 type III loops
that extended to greater than 50% of the
internal auditory canal.
Audiology
There has been some evidence pointing
to a midfrequency pure-tone hearing loss
in patients with vascular loop compression. However, many individuals with
this syndrome will demonstrate normal
pure-tone thresholds. Therefore, the hearing thresholds of patients with vascular
loops can be variable. Given the potential
effect of a vascular loop on the auditory
nerve, the ABR is a valuable procedure in
helping to establish a diagnosis of vascular compression. The ABR is often abnormal in patients with vascular loops that
impinge on the auditory nerve. When
abnormalities are noted, the abnormalities typically involve an extension of the
interwave intervals between waves I and
II and/or waves I and III for the involved
side. These findings implicate auditory
nerve involvement, a situation that is
likely to resolve following surgical intervention. After surgery, it is common for
both the auditory symptoms and the ABR
to improve (Møller, 2000).
Møller (2000) also advocates performing acoustic reflex testing in patients
who may have this disorder. Interestingly,
Shinn, Bush, and Jones (2009) reported
a case of vascular loop that yielded
decreased performance on an auditory
processing test battery. The audiologic
testing of these patients garners some
emphasis because radiology (MRI) does
not always prove helpful in documenting
the full effects of vascular compression
in the CPA. If vestibular complaints are
reported, VNG examination should also
be performed.
Medical Examination
As alluded to earlier, vascular loops can
present with symptoms similar to acoustic neuromas or Ménière’s disease as well
as to other neurologic or otologic problems. Hence, otologic/neurologic consults are essential. An extensive case history and an otologic and neurologic exam
should be performed. Ruling in or out a
retrocochlear disorder is done in the usual
manner with appropriate audiologic and
radiologic (usually MRI) procedures (see
Chadha & Weiner, 2008).
Medical Treatment
Although treatment with anticonvulsant
drugs — such as carbamazepine and baclofen — can prove helpful (Hain, 2016),
surgery based on the original approach by
Jannetta (1967) has been the most documented treatment. However, the surgery
is risky as there is the need to expose the
brainstem, which is usually done by a retrosigmoid craniotomy, and should only be
considered in extreme cases. The surgery
results in moving the vessel away from
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the nerve or in some way buffering the
nerve from the vessel (usually by inserting small pieces of Teflon) to prevent the
vessel from migrating back to its original
position (Jannetta, 1967). This is a “decompression” of the nerve and the result is
diminished symptoms. For example,
Bergsneider and Becker (1995) reported
that 22 out of 41 patients with severe vertigo had excellent improvement of symptoms after surgical decompression of the
eighth cranial nerve, and Brackmann,
Kesser, and Day (2001) reported marked
improvement for 16 out of 20 patients
with disabling vertigo and tinnitus following surgical intervention. Part of the
hesitancy in recommending surgery for
vascular loops is believed to be related to
the uncertainty surrounding the diagnosis of this disorder that was discussed earlier. Perhaps the strongest support for the
existence of this syndrome is the relatively
impressive results from surgery. As mentioned earlier, other disorders can result
in symptoms similar to vascular loop
syndrome and more research is needed
to differentiate these other disorders from
vascular loop problems.
Case 6–6: Vascular
Loop Syndrome
History
A 49-year-old female was seen for a central auditory processing evaluation due
to persistent concerns regarding hearing
in her right ear in spite of normal peripheral hearing sensitivity as measured by
routine audiologic tests. This patient
reported that this had been a long-standing concern. Additional audiologic history included constant bilateral tinnitus,
occasional vertigo, and imbalance. She
also reported the need for constant repetition of auditory information, difficulty
hearing in background noise, and poor
localization abilities. Other medical history included migraines with associated
facial weakness and a poor sense of smell.
Audiology
An otoscopic check was unremarkable
bilaterally and results of a comprehensive
audiologic evaluation indicated essentially normal peripheral hearing sensitivity bilaterally (Figure 6–6A). Of note,
however, was an asymmetry between the
right and left ear thresholds on the order
of 10 dB HL across the frequency range.
Word recognition in quiet was excellent
bilaterally.
Five tests of central auditory function
were performed on the patient (Figure
6–6B). They included the Dichotic Rhyme
Test, the Dichotic Digits Test, the Competing Sentences Test, the Duration Patterns
Test, and the Low-Pass Filtered Speech
Test. Results from the auditory processing evaluation demonstrated a right ear
deficit on the Dichotic Digits Test, the
Competing Sentences Test, and the LowPass Filtered Speech Test. Deficits on these
three tests were noted for the ear ipsilateral to the site of lesion (i.e., the right ear).
This not surprising due to the fact that the
site of lesion was at the level of the auditory nerve, inferior to contralateral crossover points. In addition, an unexplained
left ear deficit was also obtained for the
Competing Sentences Test.
An ABR test was also performed
using standard and high repetition rates
for both ears (Figure 6–6C). At a standard stimulus rate (23.3 clicks/sec),
results for the left ear were within normal limits with respect to both absolute and interwave latencies. The right
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A
Figure 6 –6. Pure-tone audiogram and speech recognition scores (A), central auditory behavioral
test results (B), ABR test results (C), and the MRI (D) for a 49-year-old female with a right-sided
vascular loop syndrome (Case 6–6). continues
Figure 6–6. continued
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B–D reproduced with per-
mission from “Correlation of
Central Auditory Process-
, 88(10),
Ear, Nose,
E34–E37. Copyright 2009
ing Deficits and Vascular
Loop Syndrome,” by J. B.
Shinn, M. L. Bush, and R.
O. Jones, 2009,
Ear, Nose, and Throat
& Throat Journal
Journal. continues
B
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