Transmastoid Superior Semicircular Canal Plugging: A Prospective Analysis of Surgical Outcomes

Abstract

Objectives: To assess the outcomes of the transmastoid superior semicircular canal plugging in patients with superior semicircular canal dehiscence (SSCD). Study design: Prospective cohort study. Setting: Tertiary, university center. Patients: Patients with SSCD undergoing transmastoid superior semicircular canal plugging within a 30-month period. Interventions: Transmastoid superior semicircular canal occlusion. Main outcome measures: We documented the surgical technique, pre-and postoperative (3-month review) dizziness handicap inventory scores, average hearing thresholds, lowfrequency air-bone gap, six-canal video head-impulse-test responses, improvement of the auditory symptoms and complications. Results: Out of 30 patients with SSCD, 11 patients (12 ears) were enrolled with an average age 41.17 years (range 32-65 years). Oscillopsia resolved in all patients; DHI score improved from 56.7 (range 22-84) preoperatively to 25.83 (10-46) postoperatively ( p ¼ 0.001), while out of the nine patients with troublesome auditory symptoms, five patients noticed an improvement. The average pre-and postoperative hearing thresholds were 15.2 dB (range 3-32.5 dB) and 14.17 dB (range 5-30 dB) ( p ¼ 0.73), respectively. The average pre-and postoperative low-frequency air bone gap was 12.3 dB (range 5-20 dB) and 9.4 dB (range 0-20 dB), respectively ( p ¼ 0.24) (Table 1). There were no major complications; two patients developed postoperative benign paroxysmal positional vertigo. Conclusion: Transmastoid plugging of the superior semicircular canal can safely and significantly improve the vestibular symptoms of the patients with SCDS, as well as the auditory symptoms in a substantial number of patients in a hearing-preservation way.

Impaired Vestibulo-Ocular Reflex on Video Head Impulse Test in Superior Canal Dehiscence: “Spontaneous Plugging” or Endolymphatic Flow Dissipation?

“…Namely, CHL was restored (<15 dB) in half of the cases, while a residual ABG ≥15 dB could still be detected in half of them. An→ SNHL, either transient or persistent, was detected in a significant number of patients, consistent with data available in the literature [3,[11][12][13][14][16][17][18]22,25,54,55]. Overall, the VEMP threshold normalized and amplitudes decreased, which was consistent with a restoration of the physiological impedance of the inner ear [10,13,21,23,25].…”

“…Interestingly, all patients showed either ipsilesional or contralesional spontaneous nystagmus with variable torsional components in the first days after surgery, which exhibited a spontaneous reversal of direction in the following days in six of the patients, behaving similarly to MD [56]. Even the onset of both SNHL and ipsilesional PSC-BPPV in the post-operative period supports the hypothesis of a transitory perturbation of the whole inner ear, leading to damage to the cochlear hair cells and dislodgement of otoconia from the utricle, respectively [22,54,59]. While HSC-VOR gain fully recovered in all cases, PSC function restored only in some of them.…”

“…The improvement of the aforementioned symptoms and the restoration of instrumental abnormalities after surgical plugging of the canal, irrespective of the technique adopted, strongly support this assumption. In fact, despite developing a vestibulo-ocular reflex (VOR) gain impairment for the affected canal, SSC plugging has been demonstrated to be an effective treatment for disabling symptoms due to a TMWM through a restoration of a physiological two-window system, thus resulting in ABG closure, normalization of electrophysiological measurements, and the receding of sound/pressure-induced vertigo [1,3,6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. On the contrary, a different mechanism other than TMWM has been implied to explain the reduced VOR gain values for the affected SSC after head impulses, as is often measured in patients with wide-sized SCD either with a magnetic-scleral search coil or, more commonly, through the video head impulse test (vHIT) [2,9,[26][27][28][29].…”

Development of semicircular canal occlusion

“…In 1998, Minor et al (1998) first reported eight cases of SCDS, and since then, many cases of SCDS have been reported (Steenerson et al, 2020;de Wolf et al, 2021;Kontorinis and Gaggini, 2021;Nieto et al, 2021;Ellsperman et al, 2022). The incidence of SCDS is low and its pathogenesis is unknown, and it may be related to head trauma, infection, and pathological changes in the middle ear or adjacent structures (Rosowski et al, 2004;Ward et al, 2017;Mau et al, 2018).…”

Postmastoidectomy Hyperacusis Syndrome: Clinical Features and Treatment

“…This usually involves performing a cortical mastoidectomy with preservation of the bony external auditory canal. This is the case, for example, in patients with pulsatile tinnitus who are undergoing surgery to obliterate a sigmoid sinus diverticulum or repair dehiscence over the sigmoid sinus (3) or in patients with intractable benign paroxysmal positional vertigo (BPPV) or superior semicircular canal dehiscence syndrome who undergo transmastoid plugging of the affected semicircular canal (4,5).…”