Abstract
Vestibular schwannoma and superior semicircular canal dehiscence are both uncommon entities, especially when present in the same ear. Here we illustrate how both of these pathologies can be repaired through the same surgical exposure, of the middle cranial fossa, with complete preservation of the cochlear nerve function and relief of symptoms caused by canal dehiscence.
1
Introduction
Several diseases of the lateral skull base may present with hearing loss. The main pathologies include benign and malignant neoplasms, acute and chronic infections, or dehiscence of the skull base and semicircular canals. Vestibular schwannoma (VS) is the most common tumor that causes sensorineural hearing loss . Superior canal dehiscence (SSCD) has also been described to cause decrease in hearing by dissemination of the acoustic energy through a mobile third window created by the dehiscence . We describe a case report of a patient that presented with symptoms of hearing loss and dizziness and was found to have both of these rare pathologies in the same ear.
2
Case reports
A 40-year-old white female presented with a 12-week history of left ear tinnitus and autophony. Moreover, she complained of dizziness provoked by loud sounds. Her past medical history included asthma and Hashimoto’s thyroiditis.
On physical examination she had normal bilateral cranial nerve examination and her outer ear canals and eardrums assessment revealed no pathology. When asked to perform Valsalva maneuver, patient reported a slight shift of the visual scene and dizziness. The Weber fork exam lateralized to the left ear, and the Rinne test was positive bilaterally. Audiologic testing demonstrated a mixed low frequency mild to moderate left-sided low frequency hearing loss ( Fig. 1 ). Patient was also found to have presence of stapedius reflex on the affected side.
Due to asymmetric unilateral hearing loss, a magnetic resonance imaging (MRI) with gadolinium was obtained demonstrating a 0.8 × 0.4 × 0.4 cm homogeneously enhancing mass iso- to hypointense on T2-weighted images within the left internal auditory canal fundus, most compatible with an intracanalicular VS ( Fig. 2 ). Moreover, a concomitant left SSCD was suspected on MRI. Patient opted not to have further computer tomography imaging done. Thus, SSCD was diagnosed based on physical examination, audiometric results and MRI.
Given that this patient was recently diagnosed, and following an algorithm for incidentally diagnosed VS based on Hoa et al. , treatment options that were offered to the patient included observation, stereotactic radiosurgery, or surgical resection. Taking into account her refractory and sometimes incapacitating symptoms caused by SSCD, and given patient’s good residual hearing, the patient opted not to wait but instead wanted to proceed with the surgery. Since both, the excision of the intracanalicular VS and a plugging procedure for SSCD, could be achieved during the same operation, the patient elected to undergo a left middle cranial fossa approach.
After performing temporal craniotomy, the dura was elevated off the floor of the middle fossa and canal dehiscence was identified. The dura was then further elevated anteriorly, where geniculate ganglion was also clearly dehiscent. The roof of the internal auditory canal was drilled out and dura was opened allowing tumor identification. Tumor was seen to be arising from the inferior vestibular nerve ( Fig. 3 ). At this stage the superior canal dehiscence was packed with bone wax and tumor was then removed en-bloc using microsurgical technique. Abdominal fat graft was placed into the cranial defect. There were no complications observed during the intraoperative and postoperative period.
After 1 month, the patient reported a complete relief of dizziness, oscillopsia and autophony. There was also a partial reduction of the intensity of tinnitus in her left ear. At three month follow up, the audiogram demonstrated closure of the gap and a significant improvement of pure tone thresholds at all frequencies with word recognition score at 96% ( Fig. 4 ).
2
Case reports
A 40-year-old white female presented with a 12-week history of left ear tinnitus and autophony. Moreover, she complained of dizziness provoked by loud sounds. Her past medical history included asthma and Hashimoto’s thyroiditis.
On physical examination she had normal bilateral cranial nerve examination and her outer ear canals and eardrums assessment revealed no pathology. When asked to perform Valsalva maneuver, patient reported a slight shift of the visual scene and dizziness. The Weber fork exam lateralized to the left ear, and the Rinne test was positive bilaterally. Audiologic testing demonstrated a mixed low frequency mild to moderate left-sided low frequency hearing loss ( Fig. 1 ). Patient was also found to have presence of stapedius reflex on the affected side.
