Citation: Isolated Aplasia of Lateral Semicircular Canal. American Research Journal of Otolaryngology; 1(1): 1-6.
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We aim to review the recent literature about inner ear embryology and discuss the audio vestibular findings in a patient with isolated lateral semicircular canal (LSCC) aplasia. Patient presented with dizziness for the past two years along with lightheadedness and spinning sensations. Radiological and vestibular test results are reviewed. Isolated lateral semicircular canal aplasia is a problem of embryological origin, it may manifest itself with audio vestibular complaints in late ages.
Keywords: Semicircular canals; Sensorineural hearing loss; Dizziness; Vestibular labyrinth
INTRODUCTION
Aplasia of lateral semicircular canal (LSCC) is the most
common congenital labyrinthine anomaly. LSCC aplasia is the result of
incomplete partition from vestibular anlage [1].Usually aplasia of semicircular
canal (SCC) cases are seen in association with syndromic or non-syndromic
congenital anomalies of cochlea [2,3,4]. The LSCC is the last of the three SSCs
which develops during the fetal period, and temporal bone histopathologist
suspected that is why it is the most common labyrinthine anomaly[ 5]. Our
report reviews the recent literature about inner ear embryology and discusses
the audio vestibular findings in a patient with isolated LSCC aplasia.
CASE PRESENTATION
A 46-year-old woman presented with dizziness for the past two years with lightheadedness and spinning sensations. Her dizziness was characterized with spontaneous episodes which last seconds. Between episodes she felt normal. She could tell when she was going to have an attack as it starts with a pressure feeling in her head. She has history of severe migraine headaches and her mother had left sided Meniere’s disease. Otoscopic examination was normal. Pure tone air and bone conduction audiometry revealed normal low frequency hearing, falling to a moderately-severe mid-frequency sensorineural hearing loss, improving to mild high frequency sensorineural hearing loss, slightly poorer for her right ear at 1000 and 6000-8000 Hz (Figure 1). There was a very weak spontaneous nystagmus to the right, which was barely noticeable at right gaze under examination with video Frenzel goggles. Vibration to mastoid triggered brisk right beating nystagmus. Caloric test revealed left unilateral labyrinthine weakness (Figure 2). VEMP (vestibular evoked myogenic potentials) showed normal response at the right but there was no response at left (Figure 3). Radiological assessment with Computerized Tomography (CT) and Magnetic Resonance imaging (MRI) showed us left LSCC aplasia (Figure 4A-B, 5A-B, 6A-B). No cochlear malformation was seen in either side. The internal auditory canal and the cerebellopontine angle were strictly normal.
DISCUSSION
The development of the vestibular system is made up with Fgf
(fibroblast growth factor) , RA (Retinoic acid) and Wnt signaling. RA and Fgf
continue to pattern the ear at otic vesicle stages to set up sensory,
neurogenic and non-neural domains in ventral otic epithelium. Fgf promotes,
while RA restricts, the otic expression of otx1b, which has a conserved role in
formation of the horizontal semicircular canal [6]. By week 5, dorsomedial part
of the otic vesicle grows in order to form the utricle and semicircular canals.
Towards the ventrocaudal area the pars sacculocochlearis develops, due to
constitute the cochlear duct and saccule [2]. By week 6, the SCCs and the
cochlea can be identified. Presumably, the SCC malformation is the result of an
abnormal fusion during embryological development. Kiernan et al. showed that
SCC development is encoded in the proximal portion of chromosome 4 near the
centromere [7].
There is no consensus about caloric response findings in
LSCC aplasia patients though clinicians predict to see a non-responsive ear
[8]. Some will be seen, as in our case, to be responsive in the presence of
significant weakness. Thus this suggests lateral canal may not be the sole area
responsible for the caloric response [9].
A compensated peripheral vestibular nystagmus is often
suppressed by visual fixation but could be seen during examination with Frenzel
goggles. The response to vibration of mastoid can be helpful. Another use of
vibration is in evaluating Meniere patients after gentamicin injection a brisk
nystagmus towards the good ear confirms the gentamicin effect weeks after the
injection. Without goggles no nystagmus would be seen in normal subjects until
the frequency of oscillation approaches 1 Hz or the peak velocity is greater
than 60°/s [10].
Patients with aplasia may also present with episodic spells
as in our patient. There is an MRI study reported 76.7% endolymphatic hydrops in
the aplasia group compared to 27.8% in the control group (P < 0.001) [11].
Histopathologic reports do not support these MRI findings [2]
Sensorineural hearing loss is usually seen in association
with LSCC malformations in the presence of cochlear abnormally but a number of
LSCC patients presented with conductive hearing loss are also reported [12].
Our patient’s imaging cochlear characteristics are normal, but she has
significant bilateral high frequency hearing loss. Although in migraineurs,
auditory symptoms are not as common as vestibular symptoms, this issue must be
considered as hearing loss can be seen in some migraineurs [13,14]. Fluctuating
or permanent sudden sensorineural hearing loss has been described in
migraineurs, and these patients characteristically had concomitant with
neurological phenomena (such as retinal migraine, hemiplegia, and/or visual
aura) as a result of vasospasm. The other explanation is concurrent organ of
Corti lesions (Alexander’s dysphasia/aplasia) might be present, mostly at the
basal turn of cochlea and leading to her hearing loss. Thus, in her hearing
mostly high frequencies are affected. Given the severe labyrinthine abnormally
this explanation is more likely possible.
CONCLUSION
Aplasia of lateral semicircular canalis the most common
congenital labyrinthine anomaly. Although aplasia of LSCCis a congenital
anomaly, it may develop by giving symptoms in olderages. Therefore, aplasia of
LSCC should not be forgotten in patients with complaints of dizziness in older
ages.
Informed Consent
Written informed consent was obtained from the patient for publication of this case report and accompanying images.
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