Surgery for Superior Semicircular Canal Dehiscence
Superior Semi-circular Canal Dehiscence Syndrome is a rare condition where the superior semicircular canal (SSC) of the inner ear is exposed to the intracranial cavity. This results in characteristic hearing and balance symptoms. There two surgical approaches available to correct this condition.
Middle Fossa Craniotomy
This is a surgical approach through the side of the skull, above the ear. A hole, about 2 inches square, is made in the skull, the dura (lining) of the brain is gently retracted off of the skull base, the Superior Semicircular Canal is identified, and the defect is either plugged or resurfaced. Plugging is associated with a more stable repair but potentially with a higher risk of mild to moderate hearing loss. Although resurfacing has not yet been shown to be associated with hearing loss, there is a higher incidence of recurrence.
The other advantage to a middle fossa craniotomy is the exposure that is obtained during the surgery. Often, the skull base surrounding the SCC is also very thin, or even dehiscent (like Swiss-cheese) - and requires a repair using a thin slab of bone harvested from the same bone flap that is raised during the initial craniotomy. This ensures that the entire skull base is repaired, not just the SCC. Why is this important? Holes in the skull base can lead to other problems, like a small portion of the brain (with the lining called the dura) to push through and fill the middle ear or mastoid. This is called a meningoencephalocele.
This is an approach behind the ear, through the mastoid to expose the superior canal and plug it. The actual SCC defect is never visualized directly and new holes are made in the canal to plug it. Ideally, the transmastoid approach may be useful for a patient that has SCC and a skull base or tegmen that is NOT low-lying and has no other associated holes or brain herniating into the ear. The transmastoid approach is a safe approach and small studies have shown that this is a reasonable alternative surgical technique, provided that the skull base / tegmen is not too low and that there is no evidence for large defects / holes in the skull base or brain sagging into the ear.