It’s not surprising, therefore, that for the past five years, Dr. Roland and his colleagues at UT Southwestern have been using MRI almost exclusively to assess candidates for CI surgery. That approach works, he said, even in cases that involve severe inner-ear deformities. “If there is something significantly aberrant going on in the inner ear,” he explained, “the MRI will make that very clear to you, based on the absence of various types of fluid and air signals. It has to be a fairly subtle, and thus not really clinically significant, abnormality to be missed completely by the MRI.”
Explore this issue:May 2012
But he acknowledged that what works at UT Southwestern may not play in other hospitals or clinics. “I am associated with a children’s hospital that does five to ten MRIs on one-year-olds a day,” he said. ‘These kids have to be put to sleep in a sometimes-hectic scanning environment, and for us, that is absolutely routine. But that is decidedly not the case in many hospitals in the U.S., where putting a one-year-old to sleep for an MRI scan becomes a complicated business that is very uncomfortable for everyone involved.”
In such cases, in children who have not had meningitis and have some residual hearing, indicating that a nerve connects the cochlear cavity to the brain, “they are a clear candidate for a relatively uncomplicated cochlear implant, and for them, I think a CT scan is just fine,” Dr. Roland said. “I certainly would not be dogmatic and impose our preference for MRI on such a case.”
CT Scans in Select Patients
Andrew Fishman, MD, an otologist/neurotologist and skull base surgeon at the Feinberg School of Medicine, Northwestern University, Chicago, said choosing the best scan for evaluating CI candidates is not, at its heart, all that complicated: The decision should be based on the question of whether there are any cochlear-vestibular anomalies that preclude implantation. Or, stated a bit more simply, “Is there an adequate cavity that the implant can be successfully put in; are there nerves that are stimulable by the implant?” he said.
For the “vast majority” of adult patients, he said, CT scans can answer that question without the need for an adjunctive MRI. That is the case, he explained, because in most adults, the hearing loss is progressive, with no history of severe infections (such as meningitis) that would lead to scar tissue that shows up better on MRIs. Moreover, it’s rare for such patients to have otosclerosis or some other disease process that can actually physically obstruct the cochlea and require MRI to guide surgery.