Anatomical feature of the middle cranial fossa in fetal periods: possible etiology of superior canal dehiscence syndrome

Transient connection between the vestibular aqueduct and utricle: A study using sagittal sections of human embryonic heads

BACKGROUND

The aqeductus vestibuli (aqueduct) is believed to connect to the saccule in embryos and adults. However, in embryos, the saccule and utricle are known to communicate widely to provide a common endolymph space "atrium".

METHODS

Using sagittal histological sections from five embryos (crown-rump length or CRL, 14-21 mm), nine early fetuses (CRL 24-35 mm) and 12 midterm and near-term fetuses (CRL 82-272 mm), we revisited the development and growth of the human ear aqueduct.

RESULTS

The atrium took on a thick tube-like appearance as an antero-inferior continuation of the aqueduct, but soon divided into multiple gulfs. Most of the gulfs corresponded to the ampullae of semicircular ducts, while one gulf at the antero-medio-inferior corner corresponded to the future saccule. Notably, in eight of the 14 embryos and early fetuses, the aqueduct ended at the utricle near the primitive ampulla of the anterior (superior) or posterior semicircular duct. Conversely, an embryo of CRL 21 mm was the smallest specimen in which the aqueduct joined the gulf-like saccule. At midterm and near-term, the growing perilymph space separated the aqueduct from the utricle and appeared to push the aqueduct toward the saccule. A topographical change occurred between the embryonic superiorly located utricle and the inferiorly-located saccule to create the antero-posterior arrangement in adults.

CONCLUSIONS

Consequently, the vestibular end of the aqueduct was most likely to migrate anteriorly from the utricle to the saccule at 6-8 weeks possibly due to differential growth of the endothelium. Previous reconstructions of the embryonic aqueduct might be biased by the adult morphology.

Investigation of serum calcium and vitamin D levels in superior semicircular canal dehiscence syndrome: A case control study

Objective

It remains unknown whether calcium metabolism has any effect on the clinical presentation of superior semicircular canal dehiscence (SSCD). Our aim was to analyse the adjusted calcium and vitamin D levels in SSCD patients compared to a control group.

Methods

This was a prospective case-control study performed in a tertiary referral center, university teaching hospital in the UK. It included all new patients with SSCD seen in a dedicated skull base clinic over a 5-year period (2015-2019) compared to a gender and age matched control group. The main outcome of the study was adjusted calcium and Vitamin D levels between the two groups.

Results

A total of 31 SSCD patients were recruited with a matched number of control patients. The mean Vitamin D level on the SSCD group was 44.8 nmoL/l (SD: 20.8) compared to 47.5 nmoL/l (SD: 27.4) on the control group (p = 0.702). Mean Adjusted calcium level was 2.34 mmoL/l (SD: 0.7) for SSCD compared to 2.41 mmoL/l (SD: 0.11) for controls (p = 0.01), being within normal limits for both the SSCD and the control group.

Conclusion

Our study did not identify a link between Vitamin D levels and presence of SSCD. Normal adjusted calcium values were found in both groups. Despite that a statistically significant lower calcium level was found in the SSCD group which could indicate that suboptimal levels of calcium may affect the micro-environment of the otic capsule at the SSC region.

Evaluation of Superior Semicircular Canal Morphology and Its Relationship with Glenoid Fossa Roof Thickness Using Cone Beam Computed Tomography

Purpose

This study aimed to evaluate the bone thickness of the superior semicircular canal (SSC) roof and its relationship with the roof thickness of the glenoid fossa (RGF).

Methods

The cone beam computed tomography (CBCT) images of 280 patients (560 temporal regions) were surveyed. The lowest thickness of the SSC roof was measured and categorized based on the radiological patterns of the Cisneros et al. classification. The thickness of GF and the presence of dehiscence in this part were determined, as well. The relationship between the thickness of the GF roof and the bone thickness covering the SSC was also assessed.

Results

The mean thickness of the SSC roof was 0.93 ± 0.48 mm, with no significant difference among different age groups and genders (p > 0.05). However, superior semicircular canal dehiscence (SSCD) was more prevalent among females over 45 years old. Similarly, the individuals with the dehiscence of the GF roof had a 12.93-fold higher chance of SSCD development.

Conclusions

The results indicated that the thickness of the bone overlying the SSC was significantly related to the roof thickness of the GF. However, an increase in age resulted in no significant change in the bone thickness of the SSC roof. Gender also had no role in changing the thickness of the bone overlying the SSC. Considering the decrease in the thickness of the SSC roof among females over 45 years of age, menopause may be responsible for this occurrence as well as for the increase in the prevalence of SSCD.

Assessment of Metabolic Markers and Osteoporosis in 250 Patients with Superior Semicircular Canal Dehiscence Treated With Middle Fossa Craniotomy

BACKGROUND

Superior semicircular canal dehiscence (SSCD) is caused by bony defects in the osseous shell of the arcuate eminence separating the labyrinth and the intracranial space. This pathologic third window causes hydroacoustic transmission resulting in debilitating symptoms. We examine the pathophysiologic association between metabolic markers, previous medical history, and SSCD symptoms before and after middle fossa craniotomy (MFC) treatment.

METHODS

This study was conducted between March 2011 and September 2020 with patients with SSCD who underwent MFC. We used a Fisher test to compare variables, including bilateral SSCD, second surgery, ear anomaly, osteoporosis, arthritis, vitamin D, and preoperative/postoperative symptoms, and others. Point-biserial correlation analysis was performed to test correlations between continuous variables and categorical variables.

RESULTS

A total of 250 patients with SSCD underwent MFC repair. There was significant postoperative resolution in all symptoms (P < 0.0001). Laboratory 25-hydroxyvitamin D values correlated with preoperative aural fullness (r_pb= 0.29; P = 0.03), and preoperative disequilibrium (r_pb= -0.32; P = 0.02). Serum calcium values correlated with preoperative hearing loss (r_pb= 0.16; P = 0.02). Osteoporosis history (n = 16; 6%) was more prevalent in female patients (P = 0.0001), associated with higher levels of preoperative hearing loss (odds ratio, 4.56; P = 0.02) and higher postoperative hearing loss resolution (odds ratio, 2.89; P = 0.0509).

CONCLUSIONS

Certain metabolic markers may predict SSCD presentation before and after surgery. Previous history of osteoporosis, autoimmune conditions, or arthritis may play a role in SSCD pathophysiology and can help predict clinical outcomes. Future evaluation should take metabolic laboratory values and acquire an exact medical history.

Thinning or dehiscence of bone in structures of the middle cranial fossa floor in superior semicircular canal dehiscence

BACKGROUND

Superior semicircular canal dehiscence (SSCD) is a rare inner ear disorder; currently, it is unknown whether the etiopathology underlying this structural irregularity affects neighboring structures. The goal is to investigate the prevalence of bone thinning in areas of the middle cranial fossa (MCF) floor in SSCD and non-SSCD patients.

METHODS

This retrospective study analyzed 100 patients from March 2011 to June 2017 at a tertiary referral center. 100 patients undergoing 118 SSCD repair surgeries (18 bilateral) were identified. 12 SSCD ears were excluded due to lack of pre-operative computed tomography (CT) scans or history of prior SSCD repair at an outside facility. Non-SSCD ears were identified from routinely-obtained CT scans for temporal bone fracture (fractured sides excluded) for a total of 101 ears; 26 non-SSCD ears were excluded due to lack of high-resolution imaging.

RESULTS

Univariate analyses reveal that SSCD diagnosis is associated with higher rates of geniculate ganglion (GG) dehiscence compared with non-SSCD controls (42.7 vs. 24%; χ²(1) = 9.69,P = 0.008). Individuals with SSCD depicted significantly thinner bone overlying the geniculate ganglion (GG) (0.23 ± 1.2 mm) compared to controls (0.28 ± 1.8 mm, (t(1 6 4)) = 2.1, P = 0.04). SSCD patients presented thinner bone overlying the internal auditory canal (IAC) (0.33 ± 1.3 mm) compared to patients without SSCD (0.46 ± 1.6 mm, (t(2 5 7) = 6.4, P < 0.001).

CONCLUSIONS

The increased prevalence of dehiscence of the MCF in this cohort of SSCD patients compared to non-SSCD patients suggests that the etiology underlying SSCD affects surrounding structures.

The influence of the subarcuate artery in the superior semicircular canal dehiscence and its frequency on stillbirths: illustrative cases and systematic review

Literature describes that on the 25th gestational week the labyrinth is fully formed and with adult size. However, recent studies have shown that the cranial and labyrinth development continues until 3 years of age.

OBJECTIVES

To demonstrate through tomographic study the frequency of semicircular canal dehiscence on nine specimens of stillbirths between 32 and 40 weeks and, through literature review, present another possible etiology for its cause.

METHODS

Tomographic study of the temporal bone of 9 specimens of stillbirths between 32 and 40 weeks.

RESULTS

A frequency of 88.89% of alterations were found in our study, with 44% presenting bilateral alterations and 44% unilateral alteration; 11.11% had no dehiscence.

CONCLUSION

The tomographic study showed superior semicircular canal dehiscence (SSCD) in 88% of the specimens studied, protrusion of the superior semicircular canal (SSC) in all fetuses, and an enlarged SSC that may be caused by the expansion process provoked by the subarcuate artery entering the subarcuate canaliculus, leading to SSCD.

Bone Metabolic Markers in the Clinical Assessment of Patients with Superior Semicircular Canal Dehiscence

BACKGROUND

Superior semicircular canal dehiscence (SSCD) is a bony defect in the osseous shell of the petrous temporal bone. The pathophysiological association between osteoporosis and SSCD remains poorly understood. We investigated the relationship between bone metabolic markers and symptoms in patients with SSCD.

METHODS

We collected patient demographics and clinical parameters for adult patients diagnosed with SSCD on high-resolution computed tomography scans. We used point-biserial correlation analysis to investigate the relationship between bone metabolic markers and symptoms in patients with SSCD. We compared clinical symptoms before and after surgical repair of SSCD through a middle fossa craniotomy using McNemar's test for paired comparisons of binary measures.

RESULTS

We included a total of 99 patients (64 females and 35 males; average age 52 years; 118 surgeries). The level of serum calcium correlated with the need for a second surgery (r_pb = -0.35, P = 0.001). Postoperative calcium supplementation negatively correlated with improvement in dizziness (r_pb = -0.36, P = 0.01). The level of 25-hydroxyvitamin D correlated with preoperative hyperacusis (r_pb = -0.98, P = 0.02) and postoperative autophony (r_pb = 0.96, P = 0.04). Postoperative vitamin D supplementation positively correlated with hearing decline (r_pb = 0.04, P = 0.04) The level of thyroid stimulating hormone correlated with preoperative autophony, amplification, and tinnitus (r_pb = -0.71, r_pb = -0.75, r_pb = -0.70, all P < 0.001).

CONCLUSIONS

Bone metabolic markers could be important in the clinical assessment of SSCD patients and could be potential targets for symptom management.

JB. Evidence of Osteoclastic Activity in the Human Temporal Bone

Bone remodeling within the otic capsule has been reported to be inhibited especially at or near the cochlea, except under some pathological conditions such as otosclerosis, Paget's disease, or mastoiditis, when bone remodeling can occur. Microcavitations found in periosteal and endosteal layers of human temporal bone specimens without otosclerosis, Paget's disease, or inflammation as reported in the current study are consistent with osteoclastic bone resorption. Thirty-three temporal bones from 33 patients were prepared for light microscopy and classified into 4 groups: histologically proven dehiscence of the superior semicircular canal (SSCD) (n = 3, group 1), age 20 years or younger (n = 10, group 2), age 90 years or older and with otosclerosis (n = 10, group 3), and age 90 years or older without otosclerosis (n = 10, group 4). Microcavitation was seen at 7 anatomic locations in the temporal bone in all 4 groups, but not in the cochlea or vestibule. Microcavitation within the temporal bone is likely due to osteoclastic activity, and it is seen in both young and old patients, patients with and without otosclerosis, and in cases with SSCD.

Outcomes of middle fossa craniotomy for the repair of superior semicircular canal dehiscence

Superior semicircular canal dehiscence (SSCD) is a rare defect of the arcuate eminence that causes an abnormal connection between the superior semicircular canal and middle cranial fossa. Patients often present with a variety of auditory and vestibular symptoms. Trigger avoidance is the initial strategy, but surgery may be necessary in debilitating cases. We retrospectively reviewed SSCD patients undergoing repair via a middle fossa craniotomy between March 2011 and September 2015. Forty-nine patients undergoing 58 surgeries were identified. Autophony was the most common symptom at presentation (n=44; 90%). Mean follow-up was 10.9months, with 100% of patients reporting resolution of at least one symptom. Aural fullness was the most commonly resolved symptom following surgical repair (n=19/22; 86%). Hearing loss (n=11/25; 44%) and tinnitus (n=11/38; 29%) were the most common symptoms to persist following surgery. The most common symptom to develop after surgery was disequilibrium (n=4/18; 22%). Upon comparing the overall pre-operative and post-operative groups, the number of patients with autophony (p<0.0001), aural fullness (p=0.0006), hearing loss (p=0.0119), disequilibrium (p=0.0002), sound- and pressure-induced vertigo (p<0.0001), and tinnitus (p<0.0001) were significantly different. Improved clinical outcomes were demonstrated in patients undergoing SSCD repair through a middle cranial fossa approach. The most common presenting symptom (autophony) was also most likely to resolve after surgery. Hearing loss is less amenable to surgical correction. Disequilibrium developed in a small number of patients after repair.

[Dehiscence syndromes : Diagnosis and treatment]

BACKGROUND

Dehiscence syndromes of the semicircular canals are a relatively new group of neurotological disorders. They have a variety of symptoms with hearing/balance involvement. Younger patients have clinically relevant symptoms in only about one third of cases. In addition to etiology and pathogenesis, the present paper describes diagnostic and therapeutic possibilities using a patient series of the authors.

MATERIALS AND METHODS

This nonrandomized prospective study included 52 patients with uni-/bilateral dehiscence syndromes of the superior and/or posterior canal (SCDS/PCDS), diagnosed with high-resolution computed tomography (HR-CT) of the petrous bone. Of 41 patients undergoing surgical therapy for severe symptoms-predominantly vertigo attacks (Meniere-like) and/or falls (Tumarkin crises)-31 received single-sided hearing implants.

RESULTS

Of the 41 patients with transmastoid superior and/or posterior canal occlusion, 30 showed a significant improvement of balance in the Dizziness Handicap Inventory (DHI); the dizzy spells ceased. A positive outcome was correlated with the severity of the preoperative disorder; a poor outcome (nonsignificant increase in DHI, recurrent vertigo of various qualities/frequencies) with the comorbidities vestibular migraine, Menière's disease of the contralateral ear, and a dehiscence size exceeding 4 mm.

CONCLUSION

The more severe the vestibular symptoms, the better the outcome of surgical therapy. Auditory symptoms (nonspecific aural fullness, hyperacusis) do not generally respond well to surgical therapy. Cochlear implants have an additional beneficial effect; comorbidities should be considered as (relative) contraindications.

Superior petrosal sinus causing superior canal dehiscence syndrome

Objective:

To determine signs and symptoms for superior canal dehiscence syndrome caused by the superior petrosal sinus.

Methods:

A review of the English-language literature on PubMed and Embase databases was conducted, in addition to a multi-centre case series report.

Results:

The most common symptoms of 17 patients with superior petrosal sinus related superior canal dehiscence syndrome were: hearing loss (53 per cent), aural fullness (47 per cent), pulsatile tinnitus (41 per cent) and pressure-induced vertigo (41 per cent). The diagnosis was made by demonstration of the characteristic bony groove of the superior petrosal sinus and the ‘cookie bite’ out of the superior semicircular canal on computed tomography imaging.

Conclusion:

Pulsatile tinnitus, hearing loss, aural fullness and pressure-induced vertigo are the most common symptoms in superior petrosal sinus related superior canal dehiscence syndrome. Compared to superior canal dehiscence syndrome caused by the more common apical location of the dehiscence, pulsatile tinnitus and exercise-induced vertigo are more frequent, while sound-induced vertigo and autophony are less frequent. There is, however, considerable overlap between the two subtypes. The distinction cannot as yet be made on clinical signs and symptoms alone, and requires careful analysis of computed tomography imaging.

Relationship between Surgically Treated Superior Canal Dehiscence Syndrome and Body Mass Index

Objective

Examine the association between body mass index (BMI) and superior canal dehiscence (SCD) among patients who have undergone surgical repair for superior canal dehiscence.

Study Design

Retrospective comparison study.

Setting

Neurotology tertiary care center.

Subjects and Methods

Retrospective review of consecutive adult patients evaluated at our institution for SCD syndrome between November 2006 and August 2015. A control group who underwent imaging within the same period for reasons other than SCD was also included. Patient demographics, weight, and height were examined. We performed multiple subgroup analyses to investigate the relationship of BMI, surgery vs no surgery, and correlation between patient BMI and SCD size.

Results

Of the 268 patients with SCD, 99 underwent surgery; 96 of these patients had complete medical records and were eligible for inclusion. Eighty-eight patients were noted to have arcuate eminence defects, and the mean BMI of this surgical cohort was 28.09 ± 5.26 kg/m2. Nonsurgically treated patients with SCD with available data (n = 94) had a mean BMI of 27.97 ± 6.95 kg/m2. A control group of 204 patients who underwent computed tomography for non-SCD-related causes was analyzed, of whom 155 had available data with a mean BMI of 27.91 ± 6.38 kg/m2.

Conclusion

We demonstrate that adult patients who undergo surgery for SCD are not obese (mean BMI <30), and size of dehiscence poorly correlates with BMI. Our observations call into question the proposed theory that patient weight is a risk factor for the development of symptomatic SCD involving the arcuate eminence.

Superior semicircular canal dehiscence syndrome

Superior semicircular canal dehiscence (SSCD) syndrome is an increasingly recognized cause of vestibular and/or auditory symptoms in both adults and children. These symptoms are believed to result from the presence of a pathological mobile "third window" into the labyrinth due to deficiency in the osseous shell, leading to inadvertent hydroacoustic transmissions through the cochlea and labyrinth. The most common bony defect of the superior canal is found over the arcuate eminence, with rare cases involving the posteromedial limb of the superior canal associated with the superior petrosal sinus. Operative intervention is indicated for intractable or debilitating symptoms that persist despite conservative management and vestibular sedation. Surgical repair can be accomplished by reconstruction or plugging of the bony defect or reinforcement of the round window through a variety of operative approaches. The authors review the etiology, pathophysiology, presentation, diagnosis, surgical options, and outcomes in the treatment of this entity, with a focus on potential pitfalls that may be encountered during clinical management.

A radiologic and anatomic study of the superior semicircular canal

OBJECTIVES

The present study sought to determine whether there is a correlation between the prevalence of superior semicircular canal (SSC) dehiscence (SSCD) on temporal CT and population age. The secondary objective was to identify anatomic factors for SSCD by studying SSC diameter and its protrusion into the middle cranial fossa. The aim was to determine the acquired or congenital origin of SSCD (Minor's syndrome).

MATERIAL AND METHOD

A single-center retrospective radiological and anatomic study included 180 CT scans of 354 petrous parts of the temporal bone taken between January and December 2011 in a university hospital center. Bone thickness above the SSC was measured and classified in 4 grades: grade 1, >2.5mm; grade 2, <2.5mm: grade 3, predehiscent; grade 4, dehiscent. SSC diameter was also measured, as was the height of SSC protrusion into the middle cranial fossa.

RESULTS

SSCD was found in 0.8% of cases and predehiscence in 12%. Patients with dehiscence were older; patients with grade 3 or 4 were significantly older than those free of dehiscence (P<0.05). There was no significant difference in SSC diameter according to grade. In grade 1, protrusion was greater than in other subjects, with a significant correlation between age and reduced protrusion (P<0.05).

CONCLUSION

The study demonstrated a correlation between aging and SSCD prevalence. Reduced SSC roof height with age suggests that SSCD may be an acquired phenomenon, related in some way to aging of the base of the skull.

Assessment of superior semicircular canal thickness with advancing age

OBJECTIVE

To determine whether superior semicircular canal dehiscence (SSCD) is more prevalent with advancing age.

STUDY DESIGN

Retrospective observational study.

METHODS

High-resolution computed-tomographic temporal bone scans were identified for patients of all ages and analyzed by two independent assessors. Multiplanar reconstruction was applied, and the thinnest area of temporal bone overlying each superior semicircular canal (SSC) was measured.

RESULTS

A sample of 121 patients was analyzed that contained an almost identical number of male and female patients. In total, 242 temporal bone images were reviewed. Patients' ages ranged between 6 and 86 years. Age was shown to have a significant linear relationship (P < 0.001) such that for every unit increase in age the predicted thickness was reduced by 0.0047 mm.

CONCLUSIONS

The thickness of the SSC decreases with advancing age.

LEVEL OF EVIDENCE

4.

Recent advances in superior semicircular canal dehiscence syndrome

Objective:

This study aimed to review the current advances in superior semicircular canal dehiscence syndrome and to ascertain its aetiology, whether dehiscence size correlates with symptoms, signs and investigation results, the best investigations, and its surgical management.

Methods:

A literature search using the key words ‘superior semicircular canal dehiscence’ was performed using the Allied and Complementary Medicine Database and the Embase, Health Management Information Consortium, Medline, PsycINFO, British Nursing Index, Cinahl and Health Business Elite databases for the period January 2009 to May 2014. Systematic reviews, meta-analyses, randomised controlled trials, prospective and retrospective case series, case reports, and observational studies were included.

Results:

Of the 205 papers identified, 35 were considered relevant.

Conclusion:

The aetiology of superior semicircular canal dehiscence syndrome is unclear. Dehiscence size significantly affects the air–bone gap and ocular vestibular evoked myogenic potential thresholds. Computed tomography evaluation has a high false positive rate. The middle cranial fossa approach is the surgical standard for treating this syndrome; however, the transmastoid approach is gaining popularity.