Author(s)
Douglas J. Totten, MD, MBA
William Schneider, BS
Leah Dauterman, BS McKenzie Stewart
Evan Cumpston, MD
Rick F. Nelson, MD, PhD
Affiliation(s)
Department of Otolaryngology—Head & Neck Surgery, Indiana University, IN, USA; School of Medicine, Indiana University, IN, USA; Indiana University, IN, USA; Department of Neurological Surgery, Indiana University, IN, USA;
Abstract:
Objective: To assess whether development of superior semicircular canal dehiscence (SSCD) may be related to isolated intracranial skull base thinning, global skull bone thinning, or an alternative process.
Study Design: Retrospective cohort study.
Setting: Tertiary referral center.
Patients: SSCD patients with CT IAC and a control cohort matched for age, gender, race, and BMI with minimum of 1 millimeter of bony coverage over superior canal as well as additional cohort of patients with spontaneous cerebrospinal fluid (sCSF) leak.
Main Outcome Measures: Thickness of calvarium and extracranial zygoma in SSCD and control patients as measured using standardized 3D slicer measurements of high-resolution temporal bone computed tomography scans as well as skull base height as measured with calipers at the midpoint of internal auditory canal of SSCD, control, and sCSF leak patients.
Results: 38 SSCD patients (76 SSCD ears) and 55 control patients (110 ears) were assessed. Cohorts were similar in age (SSCD: 56 [SD 14]; control: 56 [10], p=0.41), BMI (SSCD: 30 [8]; control: 31 [9], p=0.81), gender (SSCD: 61% female; control: 65% female), and race (SSCD: 95% White; control: 95% White). 15 (40%) of SSCD patients had bilateral SSCD. Skull base height was also assessed in 83 sCSF leak patients.
Skull base height was massively reduced in SSCD patients compared to controls (4.61 [1.15] mm vs. 2.86 [0.87] mm, p<0.0001) and reduced when compared to sCSF leak patients (3.4 [1.2] mm 2.86 [0.87] mm, p=0.01) despite lower BMI compared to sCSF leak patients (30 [9] kg/m2 vs. 39 [10] kg/m2, p<0.0001). SSCD patients had significantly thinner calvarium (2.35 [0.51] mm vs. 1.93 [0.37] mm, p<0.0001). There was no difference in zygoma thickness (4.71 [0.71] mm vs. 4.54 [0.69] mm, p=0.09). Calvarium-to-zygoma ratio was reduced in SSCD patients (0.26 [0.10] vs. 0.19 [0.08], p=0.011).
Conclusions: SSCD patients have lower BMI than sCSF leak patients yet thinner skull bases than either matched controls or sCSF leak patients. This suggests that, while patients may have global skull thinning, an isolated developmental process impacts the skull base in the pathogenesis of SSCD.
Professional Practice Gap: Etiology of SSCD is poorly understood. This study attempts to elucidate whether SSCD occurs as a result of an isolated skull base defect, a more systemic process, or perhaps a process yet to be explained.
Learning Objective: Patients with SSCD appear to have an isolated developmental skull base abnormality.
Desired Result: Clinicians will gain further understanding regarding the pathophysiology of SSCD prompting additional research into understanding this complex disease process
Level of Evidence: IV
IRB: Indiana University IRB #13133 (approved 10/14/2022)