Third Window Lesions

Posterior Semicircular Canal Dehiscence with Vestibulo-Ocular Reflex Reduction for the Affected Canal at the Video-Head Impulse Test: Considerations to Pathomechanisms

Posterior semicircular canal dehiscence (PSCD) has been demonstrated to result in a third mobile window mechanism (TMWM) in the inner ear similar to superior semicircular canal dehiscence (SSCD). Typical clinical and instrumental features of TMWM, including low-frequency conductive hearing loss (CHL), autophony, pulsatile tinnitus, sound/pressure-induced vertigo and enhanced vestibular-evoked myogenic potentials, have been widely described in cases with PSCD. Nevertheless, video-head impulse test (vHIT) results have been poorly investigated. Here, we present six patients with PSCD presenting with a clinical scenario consistent with a TMWM and an impaired vestibulo-ocular reflex (VOR) for the affected canal on vHIT. In two cases, an additional dehiscence between the facial nerve and the horizontal semicircular canal (HSC) was detected, leading to a concurrent VOR impairment for the HSC. While in SSCD, a VOR gain reduction could be ascribed to a spontaneous "auto-plugging" process due to a dural prolapse into the canal, the same pathomechanism is difficult to conceive in PSCD due to a different anatomical position, making a dural herniation less likely. Alternative putative pathomechanisms are discussed, including an endolymphatic flow dissipation during head impulses as already hypothesized in SSCD. The association of symptoms/signs consistent with TMWM and a reduced VOR gain for the posterior canal might address the diagnosis toward PSCD.

Photon-counting CT allows better visualization of temporal bone structures in comparison with current generation multi-detector CT

PURPOSE

To compare photon-counting CT (PCCT) and multi-detector CT (MDCT) for visualization of temporal bone anatomic structures.

METHODS

Thirty-six exams of temporal bones without pathology were collected from consecutive patients on a MDCT, and another 35 exams on a PCCT scanner. Two radiologists independently scored visibility of 14 structures for the MDCT and PCCT dataset, using a 5-point Likert scale, with a 2-month wash-out period. For MDCT, the acquisition parameters were: 110 kV, 64 × 0.6 mm (slice thickness reconstructed to 0.4 mm), pitch 0.85, quality ref. mAs 150, and 1 s rotation time; for PCCT: 120 kV, 144 × 0.2 mm, pitch 0.35, IQ level 75, and 0.5 s rotation time. Patient doses were reported as dose length product values (DLP). Statistical analysis was done using the Mann-Whitney U test, visual grading characteristic (VGC) analysis, and ordinal regression.

RESULTS

Substantial agreement was found between readers (intraclass correlation coefficient 0.63 and 0.52 for MDCT and PCCT, resp.). All structures were scored higher for PCCT (p < 0.0001), except for Arnold's canal (p = 0.12). The area under the VGC curve was 0.76 (95% CI, 0.73-0.79), indicating a significantly better visualization on PCCT. Ordinal regression showed the odds for better visualization are 354 times higher (95% CI, 75-1673) in PCCT (p < 0.0001). Average (range) of DLP was 95 (79-127) mGy*cm for MDCT and 74 (50-95) mGy*cm for PCCT (p < 0.001).

CONCLUSION

PCCT provides a better depiction of temporal bone anatomy than MDCT, at a lower radiation dose.

CRITICAL RELEVANCE STATEMENT

PCCT provides a better depiction of temporal bone anatomy than MDCT, at a lower radiation dose.

KEY POINTS

1. PCCT allows high-resolution imaging of temporal bone structures. 2. Compared to MDCT, the visibility of normal temporal bone structures is scored better with PCCT. 3. PCCT allows to obtain high-quality CT images of the temporal bones at lower radiation doses than MDCT.

Proposal for a Unitary Anatomo-Clinical and Radiological Classification of Third Mobile Window Abnormalities

Introduction: An increased number of otic capsule dehiscence (OCD) variants relying on the third window pathomechanism have been reported lately. Therefore, a characterization of the anatomical structures involved and an accurate radiological description of the third window (TW) interface location have become essential for improving the diagnosis and appropriate therapeutic modalities. The purpose of this article is to propose a classification based on clinical, anatomical, and radiological data of third mobile window abnormalities (TMWA) and to discuss the alleged pathomechanism in lesser-known clinical variants.

Materials and Methods: The imaging records of 259 patients who underwent, over the last 6 years, a high-resolution CT (HRCT) of the petrosal bone for conductive hearing loss were analyzed retrospectively. Patients with degenerative, traumatic, or chronic infectious petrosal bone pathology were excluded. As cases with a clinical presentation similar to those of a TW syndrome have recently been described in the literature but without these being confirmed radiologically, we thought it necessary to be integrated in a separated branch of this classification as “CT - TMWA.” The same goes for certain intralabyrinthine pathologies also recently reported in the literature, which mimic to some extent the symptoms of a TW pathology. Therefore, we suggest to call them intralabyrinthine TW-like abnormalities.

Results: Temporal bone HRCT and, in some cases, 3T MRI of 97 patients presenting symptomatic or pauci-symptomatic, single or multiple, unilateral or bilateral OCD were used to develop this classification. According to the topography and anatomical structures involved at the site of the interface of the TW, a third-type classification of OCD is proposed.

Conclusions: A classification reuniting all types of TMWA as the one proposed in this article would allow for a better systematization and understanding of this complex pathology and possibly paves the way for innovative therapeutic approaches. To encompass all clinical and radiological variants of TMWA reported in the literature so far, TMWAs have been conventionally divided into two major subgroups: Extralabyrinthine (or “true” OCD with three subtypes) and Intralabyrinthine (in which an additional mobile window-like mechanism is highly suspected) or TMWA-like subtype. Along these subgroups, clinical forms of OCD with multiple localization (multiple OCD) and those that, despite the fact that they have obvious characteristics of OCD have a negative CT scan (or CT – TMWA), were also included.

Acoustic streaming resulting from compression of the cochlear bony capsule

Acoustic streaming resulting from the time-harmonic compression of the cochlear capsule is examined in this paper. The cochlear pressure is expressed as an integral equation in the cochlear partition velocity. Rapid spatial variation in the velocity of the cochlear partition requires one to treat high-order fluid modes within the cochlear fluid. Hence, evanescent pressure modes are needed in the analysis. Asymmetry in the oval and the round window velocity is shown to give rise to a pressure gradient across the cochlear partition. The time-average fluid motion is obtained using the method of matched asymptotic expansions in conjunction with numerical evaluation of the outer flow field.

Superior Semicircular Canal Dehiscence by Superior Petrosal Sinus: Proposal for Classification

OBJECTIVES

This study aimed to present 3 different clinical stages in patients presenting with superior semicircular canal dehiscence (SSCD) by the superior petrosal sinus (SPS). A specific 3-class classification based on clinical, radiological, and audio-vestibular arguments is proposed.

MATERIALS AND METHODS

We retrospectively compared clinical and radiological findings in 3 patients with different degrees of audio-vestibular dysfunction in whom the imagery evocated the diagnosis of SSCD by SPS. Imaging sensitivity was improved by combining inner ear high-resolution computed tomography (HRCT) scan and magnetic resonance imaging in fusion, allowing us to compare and corroborate clinical and audio-vestibular findings in each case with the imagery.

RESULTS

HRCT and 3T inner ear fusion imaging highlighted a direct contact and/or compression between SPS and the membranous superior semicircular canal (SSC). We propose a new classification of SSCD by SPS. Class "A" corresponds to an HRCT image with a "cookie bite" and thin bone still covering the SSC. Class "B" corresponds to a "cookie bite" image with confirmed contact between the SPS wall and the membranous SSC in MRI labyrinthine sequences. Class "C" type corresponds to a "cookie bite" image, contact, and obvious compression of the membranous SSC by SPS on MRI sequences.

CONCLUSION

Anatomical systematization is needed for daily practice. This classification of SSCD by SPS would contribute to a better understanding of the wide variety and variability in the occurrence and onset of symptoms.

Rare Disorders of the Vestibular Labyrinth: of Zebras, Chameleons and Wolves in Sheep's Clothing

The differential diagnosis of vertigo syndromes is a challenging issue, as many - and in particular - rare disorders of the vestibular labyrinth can hide behind the very common symptoms of "vertigo" and "dizziness". The following article presents an overview of those rare disorders of the balance organ that are of special interest for the otorhinolaryngologist dealing with vertigo disorders. For a better orientation, these disorders are categorized as acute (AVS), episodic (EVS) and chronic vestibular syndromes (CVS) according to their clinical presentation. The main focus lies on EVS sorted by their duration and the presence/absence of triggering factors (seconds, no triggers: vestibular paroxysmia, Tumarkin attacks; seconds, sound and pressure induced: "third window" syndromes; seconds to minutes, positional: rare variants and differential diagnoses of benign paroxysmal positional vertigo; hours to days, spontaneous: intralabyrinthine schwannomas, endolymphatic sac tumors, autoimmune disorders of the inner ear). Furthermore, rare causes of AVS (inferior vestibular neuritis, otolith organ specific dysfunction, vascular labyrinthine disorders, acute bilateral vestibulopathy) and CVS (chronic bilateral vestibulopathy) are covered. In each case, special emphasis is laid on the decisive diagnostic test for the identification of the rare disease and "red flags" for potentially dangerous disorders (e. g. labyrinthine infarction/hemorrhage). Thus, this chapter may serve as a clinical companion for the otorhinolaryngologist aiding in the efficient diagnosis and treatment of rare disorders of the vestibular labyrinth.

Beyond Tympanomastoidectomy: A Review of Less Common Postoperative Temporal Bone CT Findings

Postoperative temporal bone imaging after surgical procedures such as ossiculoplasty, tympanomastoidectomy, cochlear implantation, and vestibular schwannoma resection is often encountered in clinical neuroradiology practice. Less common otologic procedures can present diagnostic dilemmas, particularly if access to prior operative reports is not possible. Lack of familiarity with the less common surgical procedures and expected postoperative changes may render radiologic interpretation challenging. This review illustrates key imaging findings after surgery for Ménière disease, superior semicircular canal dehiscence, temporal encephalocele repairs, internal auditory canal decompression, active middle ear implants, jugular bulb and sigmoid sinus dehiscence repair, and petrous apicectomy.

Inner-Ear Disorders Presenting with Air-Bone Gaps: A Review

Air-bone gaps (ABGs) are commonly found in patients with conductive or mixed hearing loss generally due to outer- and/or middle-ear diseases such as otitis externa, tympanic membrane perforation, interruption or fixation of the ossicular chain, and chronic suppurative otitis media. ABGs can also be found in correlation with inner-ear disorders, such as endolymphatic hydrops, enlarged vestibular aqueduct syndrome, semicircular canal dehiscence, gusher syndrome, cochlear dehiscence, and Paget disease's as well cerebral vascular anomalies including dural arteriovenous fistula. The typical clinical presentation of inner-ear conditions or cerebral vascular anomalies causing ABGs includes audiological and vestibular symptoms like vertigo, oscillopsia, dizziness, imbalance, spinning sensation, pulsatile or continuous tinnitus, hyperacusis, autophony, auricular fullness, Tullio's phenomenon, and Hennebert's sign. Establishing a definitive diagnosis of the underlying condition in patients presenting with an ABG is often challenging to do and, in many patients, the condition may remain undefined. Results from an accurate clinical, audiological, and vestibular evaluation can be suggestive for the underlying condition; however, radiological assessment by computed tomography and/or magnetic resonance imaging is mandatory to confirm any diagnostic suspicion. In this review, we describe and discuss the most recent updates available regarding the clinical presentation and diagnostic workup of inner-ear conditions that may present together with ABGs.

The Forgotten Second Window: A Pictorial Review of Round Window Pathologies

The round window serves to decompress acoustic energy that enters the cochlea via stapes movement against the oval window. Any inward motion of the oval window via stapes vibration leads to outward motion of the round window. Occlusion of the round window is a cause of conductive hearing loss because it increases the resistance to sound energy and consequently dampens energy propagation. Because the round window niche is not adequately evaluated by otoscopy and may be incompletely exposed during an operation, otologic surgeons may not always correctly identify associated pathology. Thus, radiologists play an essential role in the identification and classification of diseases affecting the round window. The purpose of this review is to highlight the developmental, acquired, neoplastic, and iatrogenic range of pathologies that can be encountered in round window dysfunction.