1 A Case Study Review Superior Semicircular Canal Introduction Dehiscence (SSCD) and the This Case Study Review Paper is based on Recurrence of Benign the poster presentation of the International Vestibular Conference, Chicago, IL, 2018. Paroxysmal Positional Vertigo The paper begins with a review of Superior (BPPV) Following Head Semicircular Canal Dehiscence (SSCD) and the recurrence of Benign Paroxysmal Trauma Positional Vertigo (BPPV). SSCD was first described in 1998 by Minor Bridgett D Wallace1-3, Bradford B Melancon4,5, and colleagues as related to several patients Michele L Frizell6, Natalie F Hiddemen7 having symptoms of disequilibrium and 360 Balance & Hearing sound- or pressure-induced vertigo with Austin, TX 78731 nystagmus in the plane of the superior semicircular canal. High resolution computed Correspondence to: Bridgett Wallace at [email protected] tomography (HCRT) of the temporal bone revealed a bony dehiscence (absence of bone) 1360 Balance & Hearing, Owner, Austin, TX. 2360 over the superior semicircular canal1. As Neuro Health, Director of Clinical Education, Austin, more patients with SSCD were recognized, TX. 3Bertec, Director of Education, Columbus, OH. 4360 Balance & Hearing, Director of Audiology, Austin, TX. additional symptoms were identified such as 5Auditory Specialists of Austin, Department of hearing internal noises transmitted to the Audiology, Austin, TX. 360 Balance & Hearing. 6360 affected ear and tinnitus. This became Balance & Hearing, Vestibular Testing Specialist & referenced as Super Canal Dehiscence Clinical Practice Manger, Austin, TX. 7360 Balance & Hearing, Director of Clinical Education, Austin, TX. Syndrome (SCDS) due to either the thinning and the absence of bone overlying the superior semicircular canal facing toward the dura of the middle cranial fossa2. Minor and colleagues theorized that SSCD acts as an additional window for the vestibular system, which allows noise and/or pressure changes to result in vestibular symptoms2. Normally, sound pressure enters the oval window (via the stapes) and exits at the round window. SSCD, however, results in the pressure entering at the oval window but is then transmitted through the labyrinth instead of the cochlea, resulting in vestibular associated symptoms. Benign Paroxysmal Positional Vertigo (BPPV) was first described by Barany as 2 early as 19213. BPPV is a common inner ear disorder due to abnormal stimulation of the semicircular canals, which results in brief spells of positional vertigo. There are two forms of BPPV including canalithiasis and cupulolithiasis3. BPPV most commonly affects the posterior canal. However, it may affect any of the semicircular canals and any combinations of multiple canals simultaneously. The presence of SSCD and a high recurrence of BPPV has not yet been addressed in the literature. Prevalence/Etiology of SSCD and BPPV Figure 1: Representation of SSCD5 SSCD The prevalence of thinning or absence of bone occurs in 2% of the population and it is BPPV estimated that 50% of those with SSCD have As previously noted, BPPV is the most bilateral involvement2. The etiology of SSCD common vestibular disorder that causes true is unknown. There are currently 2 theories: vertigo, accounting for approximately 50% of (1) congenital and acquired. It is believed cases reported in older adults6. BPPV can that congenital is the most common cause occur spontaneously in many patients, so the and that symptoms typically do not occur etiology may not always be known. However, until later in life, which was typically related BPPV has long been associated to otolith to head trauma or a significant pressure dysfunction3,6 due to several triggers. The alternating event such as barometric most common causes of BPPV include head pressure trauma. Figure 1 demonstrates the trauma, inner ear infection, anterior area affected in the superior semi-circular vestibular artery ischemia, prolonged bed canal either by a dehiscence or thinning. rest and other vestibular disorders (e.g., Gianoli and Soileau further theorized Meniere’s Disease and Vestibular alterations of intracranial pressure resulted Migraines)7,8. Figure 2 demonstrates the in an increased compliance of the middle and displaced otoconia in both the posterior and oval window. If pressure changes were horizontal canal. significant enough, the disruption of the windows would result in a middle ear perilymphatic fistula4. 3 Diagnosis SSCD In the clinical setting, it is recommended to produce a range of different frequency tones at different intensities with an audiogram while wearing video goggles or Frenzel lenses to monitor eye movements – observing for nystagmus. This finding is not observed in all patients nor is the nystagmus always in the Figure 2: Representation of BPPV5 plane of the superior semi-circular canal. Another clinical test is a closed-glottis Valsalva (or negative pressure test), which has been found to produce an upbeating Symptoms of SSCD and BPPV nystagmus and with a torsional component SSCD beating away from Some of the most common symptoms of SSCD include bone conduction hyperacusis (hearing internal noises transmitted loudly to the affect ear), pulsatile tinnitus (rhythmical noise that beats at the same rate of the the affected ear. For example, a clockwise person’s heart rate), sound- or pressure- torsion (upbeating and towards the left) induced vertigo, and autophony (the indicates a right SSCD while a counter- unusually loud hearing of the one’s own clockwise torsion (upbeating and to the right) voice). suggests a left SSCD. A Valsalva can also be performed with pinched nostrils that has In reference to our case study poster been known to result in a downbeating presentation, the patient had no reports of nystagmus and the torsional component is hearing loss or pulsatile tinnitus. However, towards the affected ear (e.g., clockwise he did report notable sensitivity to loud indicates left SSCD while counter-clockwise noises. Upon further questioning, he reported suggests the right)9. Closed-glottis Valsalva is that the symptoms were not just irritating preferred over pinched-nose since the latter but resulted in an exacerbation of dizziness increases middle ear pressure. and feeling like he could fall. A comprehensive audiogram can be very BPPV helpful even in the absence of hearing loss. BPPV is characterized by brief episodes of One of the most common findings is a large true vertigo (spinning) induced by changing air-bone gap at the lower frequencies (250, the head position – typically, in the plane of 500 and 1000 Hz). the involved semicircular canal(s) but can occur in multiple positions. Often times This is a pattern typically associated with nausea, unsteadiness and/or a residual otosclerosis, which is a disease of the middle dizziness accompanies the more intense and inner ear bones. The ossicles become knit vertigo. together and do not transmit sound as well, resulting in a conductive hearing loss. The displacement of the otoconia (also However, with otosclerosis, reflexes and the referred to as “ear crystals or rocks”) from tympanograms are abnormal, whereas with the utricle to the semicircular canal(s) is the SSCD, these components of the audiogram most recognized cause of BPPV related are frequently normal10. symptoms. 4 In reference to our case study poster patient’s cVEMP and oVEMP findings. In the presentation, an audiogram was right ear, the patient had abnormal findings recommended due to the exacerbation of in both VEMPs. The combination of the symptoms with loud sounds. Figure 3 patient’s symptoms and diagnostic findings demonstrates an example of the audiogram warranted an ENT referral. Also, of note is shown in our poster presentation. It reveals a that his abnormal oVEMPs bilaterally are conductive hyperacusis hearing loss pattern, consistent with otolith dysfunction. Otolith which can be suggestive of otosclerosis. dysfunction is correlated with high However, reflexes and tympanograms were recurrences of BPPV11. WNLs. This pattern is strongly suggestive of a SSCD. It has also been known that the “A- pattern” of tympanograms can be elevated in the affected ear. Figure 3: Audiogram of 36 y.o. male diagnosed with SSCD. Figure 4a: Representation of abnormal cVEMP on the right side due to an absent P1-N1 waveform and non-reproducible waveforms in oVEMP as well as an atypical P1-N1 waveform. Vestibular Evoked Myogenic Potentials (VEMPs) are considered a reliable vestibular test in identifying SSCD because it quantifies sound sensitivity. The cervical VEMP (c- VEMP), measures saccule function while ocular VEMP (o-VEMP) measures utricle function. In SSCD, VEMPs are frequently abnormal. More recently, there is a growing argument that o-VEMPs provide a higher level of sensitivity and specificity than c- VEMPs9,10. In reference to our case study poster presentation, Figures 4a and 4b represent the 5 identification of canal involvement as well as type of BPPV will not be discussed. However, there is a plethora of information regarding the assessment and treatment of BPPV via research articles, textbooks and/or educational training modules. The following is a link to updated document addressing BPPV Best Practice Guidelines: http://www.neuropt.org/docs/default- source/csm-2018-handouts/handout_bppv- best-practice_2017-revised- cpg_final.pdf?sfvrsn=6165443_4. Figure 4b: Representation of normal P1-N1 wave in the left ear for cVEMP but abnormal oVEMP on the left due to non- reproducible waveforms. Treatment of SSCD and BPPV The accepted diagnostic criteria for SSCD are Historically, the most recognized form of based on the combination of CT evidence, treatment for SSCD is surgical repair or symptoms and abnormal transmission of occlusion. Surgical options include repair pressure via a third mobile window. Imaging through a middle fossa craniotomy or a transmastoid approach, transcanal for confirming a SSCD is a high-resolution coronal temporal bone CT with 1-mm sliced reinforcement of the of the oval and round windows, and/or a combination of both13. thickness12. Currently, there are no medical guidelines that support conservative, medical treatment. It is estimated that about 50% of the population pursue surgery10. As noted by Dr.