CASE #4: 15 year old female with a right superior semicircular canal dehiscence secondary to a prominent superior petrosal sinus in the middle fossa and normal tegmen

This is a 15 year old otherwise healthy girl who presented with a history of right-sided aural fullness and constant, disabling dizziness that worsened with physical activity.

Audiometric testing revealed conductive hyperacusis in the right ear, normal tympanometry and intact acoustic reflexes. Cervical and ocular VEMP testing demonstrated low threshold and large amplitude responses in the right ear.

High resolution temporal bone CT scans (Fig. 1) revealed NO evidence of a tegmen defect or a low-lying tegmen and intact arcuate eminence. However, a prominent right-sided superior canal dehiscence is clearly seen in the posterior-medial aspect of the most cephalic portion of the superior canal of the right ear.

She underwent a transmastoid plugging (using a minimally invasive post-auricular surgical approach) to repair the SCDS (Fig. 2). A prominent superior petrosal sinus was seen through the sinodural angle in the mastoid cavity when transilluminating under the surgical microscope. After exposure and delineation of the right superior semicircular canal (SSC), two labyrinthotomies were created using a high-speed surgical drill and diamond burr on EITHER side of the dehiscence (the ascending and descending limbs). Bone wax was used to plug both of these labyrinthotomies. She was discharged the following morning and has enjoyed normal hearing and resolution of her dizziness.




Figure 1. High resolution temporal bone CT, right ear, from Case #4. A, Coronal view demonstrating a right superior canal dehiscence in the region of the superior petrosal sinus (white arrow) of the right middle fossa. Note that the tegment is NOT low-lying and otherwise intact. B, Poeschl view demonstrating a right superior canal dehiscence in the region of the superior petrosal sinus (white arrow). Note that the top of the SCC is intact (called the arcuate eminence)(arrowhead).

Figure 2. Intraoperative images from Case #4, right ear, transmastoid approach. A, right mastoidectomy, canal wall up with the superior semicircular canal exposed (SSC). HSC - horizontal semicircular canal, PSC, posterior semicircular canal, EAC, external auditory canal. B, High magnification view showing the right SSC and the bluish hue defining the prominent superior petrosal sinus in the middle fossa. C, Careful drilling using a low speed setting and a diamond burr to gently perform a labyrinthotomy, or hole, of the right SCC behind the dehiscence. A second labyrinthotomy is also performed (not shown) in front of the dehiscence. D, The exposed membraneous labyrinth is exposed following labyrinthotomy of the right SCC. E and F, plugging of the labyrinthotomy created in the SSC.