Management Options in SCDS
Patients with hearing loss and fullness or autophony as their only complaints should be observed. A hearing aid can be helpful if a low to mid frequency conductive hearing loss is seen.
There is a real risk of hearing loss following SCD repair (12% if performed for the first time, via a middle fossa approach and using a plugging technique) and surgery should only be offered to a patient with confirmed SCD if:
- Dizziness with symptoms referable to the ear that has the SCD seen on high resolution CT scans of the temporal bone, reformatted to the planes parallel and perpendicular to the superior canals.
- Compelling clinical history (ear fullness, autophony, oscillopsia and sound and pressure sensitivity)
- Signs of symptomatic SCD are present on exam (nystagmus to pressure or sound, tuning forks lateralize to ear that has "normal" hearing, etc.)
- VEMP testing shows low thresholds in the involved ear
- High resolution CT scans reformatted to examine the superior canals in the Poschel and Stenver planes
Surgical approaches include either a middle fossa craniotomy approach performed by a neurotologic surgeon (and sometimes with a neurosurgeon) or a transmastoid approach.
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 SCD 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 surround the SCD 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 SCD. 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.
TRANSMASTOID REPAIR (Case #4) - this is an approach behind the ear, through the mastoid to expose the superior canal and plug it. The actually SCD defect is never visualized directly and new holes are made in the canal to plug it. There is a potential of greater risk of hearing loss using this surgical approach compared with SCD plugging using a middle fossa craniotomy approach based on an older small study of two patients but a recent study with three patients and our experience at the Massachusetts Eye and Ear Infirmary has shown that this is a safe approach that preserves hearing and improves dizziness.
Ideally, the transmastoid approach may be useful for a patient that has SCD and a skull base or tegmen that is NOT low-lying and has no other associated holes or brain herniating into the ear. In some cases, the SCD may be located along the SIDE of the canal (Case #4) and not on the TOP, as seen in most classic cases of SCDS. If the defect is located on the side of the canal away from the surgeon (posterior-medial), the SCD may be more difficult to visualize using a craniotomy approach.
The transmastoid approach is a safe approach and small studies have shown that this is a reasonable alternative surgical technique for SCDS, 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.