Incidence and Clinical Implications of Superior Semicircular Canal Dehiscence with Encephalocele
Objective: This study aims to determine the incidence and clinical significance of superior semicircular canal dehiscence in patients with tegmen encephalocele.
Study Design: This study is a retrospective chart review.
Setting: This study was performed at tertiary care neurotology practice.
Patients and Methods: A retrospective chart review of patients with a history of tegmen encephalocele repair was performed, searching for a concomitant finding of superior semicircular canal dehiscence. A total of 66 patients demonstrating a middle cranial fossa encephalocele were identified. After exclusion criteria (absence of a preoperative CT scan) were applied, 54 cases of patients between 29 and 81 years of age were found who underwent an encephalocele repair either via a transmastoid or middle cranial fossa approach and had a high-resolution preoperative CT scan from January 2009 to June 2014 at a tertiary care neurotology practice. Demographics, body mass index, computed tomography results, intraoperative findings and postoperative hearing results were assessed. Statistical analysis was performed analyzing correlations between body mass index (BMI), presence of encephalocele, presence of superior semicircular canal dehiscence, and hearing loss.
Results: The incidence of radiographic presence of a superior semicircular canal dehiscence in patients with a tegmen encephalocele was 42.6% (31 of 54 cases) over a 5-year period. Intraoperatively, superior semicircular canal dehiscence was identified in 74% of patients with a preoperative radiographic diagnosis. The incidence of postoperative hearing loss in patients with concomitant superior semicircular canal dehiscence was 10.5%.
The average BMI for all patients was 31.92 kg/m2. The average BMI for patients with encephalocele plus superior canal dehiscence vs encephalocele alone was 28.68 compared with 34.44 kg/m2.
Conclusion: We found a very high incidence of superior semicircular canal dehiscence (42.6%) in patients undergoing middle cranial fossa encephalocele repair. During encephalocele repair, either by a middle cranial fossa or a transmastoid approach, it is important to recognize the presence of a superior semicircular canal dehiscence to prevent postoperative sensorineural hearing loss and vertigo. It is our recommendation to obtain high resolution CT scans using both Stenver and Poschl views in all patients undergoing repair of middle cranial fossa encephaloceles to document the presence of a superior semicircular canal dehiscence. Repair of both defects at the time of surgery can be routinely performed.
The high average BMI in patients with encephalocele and encephaloceles plus a superior semicircular canal dehiscence may help in elucidating the pathophysiology of these two disorders, as increased intracranial pressure may lead to thinning of the bone over the tegmen and superior semicircular canal.