Timothy C. Hain, MD. Hearing Page Page last modified: July 15, 2017
Superficial siderosis (SS) is a very uncommon type of deafness that is caused by iron deposition in the brain. Most individuals have a source of bleeding around their auditory nerves, or in other words, in the posterior fossa, but the bleeding may also be remote, such as from a cervical meningocele (Lekgabe et al, 2012), cerebral amyloid angiopathy(Profice et al, 2011), or dural tear (Egawa et al, 2013). Over years, iron accumulates in the brain and hearing and the sense of smell is gradually lost.
With the common use of brain MRI scanning, SS is more commonly diagnosed, as there is a characteristic low signal seen on both T1 and T2. Ordinary fluid is black on T1 and white on T2. Iron, is black on both.
Recent studies of patients in dementia clinics suggest that superficial siderosis is found in about 3%, associated with microbleeds. There is also an association with cerebral white matter lesions. (Shams et al, 2016). This suggests that superficial siderosis might be a contributer to the common age dependent hearing loss. As SS causes nerve damage, this type of hearing loss might not be amenable to developing treatments to regenerate hair cells.
Unless the source of bleeding can be stopped, only supportive treatment, such as cochlear implant (Sugimoto et al, 2012), is available at this date for SS. The logic of a cochlear implant is difficult to follow, given that SS damages the auditory nerve.
|Audiogram when patient first presented with hearing loss, when patient was in early 20's, about 10 years after her surgery. Hearing is worse on the side of the tumor.||Hearing after 11 years, is worse on side of tumor. There has been considerable deterioration.|
A woman in her 20's complained of progressive hearing loss over the last year. In addition she has tinnitus, and trouble understanding. 10 years prior, a cerebellar astrocytoma was removed from her right cerebellar hemisphere. Several MRI scans done subsequently noted not an area of damage to the R cerebellar hemisphere but also hemosiderin accumulation was noted by one radiologist. Another attributed the same findings to cerebellar atrophy.
An extremely thorough set of tests were done for alternative causes of hearing loss including autoimmune tests. Balance was normal, Reflexes were normal, and the general neurological exam was entirely normal including the cerebellar examination.
She was seen again about 10 years later, with similar findings. Again, hearing was profoundly diminished, cerebellar examination was normal, and a current MRI scan still was still very abnormal due to low signal seen on T2 imaging. Detailed vestibular testing (rotatory chair, VEMP) was normal -- thus in spite of severe hearing loss, vestibular function was entirely unaffected. This suggests that the site of damage is specific to the cochlea or cochlear nucleus. This is against the report of Miwa et al (2013) who found VEMPs to be reduced in 3 patients with SS.
The obvious question in superficial siderosis is where is the lesion ? Is it in the cochlea, 8th nerve, brainstem ?
Our patient also had no OAE response at all, suggesting a cochlear origin to her hearing loss. There have been only a few other cases of superficial siderosis where OAE’s were done. Kim(Kim, Song, Park, Kim, & Koo, 2006), reported a young man with SS and no OAE’s. Takahashi(Takasaki et al., 2000) reported another case with no OAE, and a “remarkable elevation of the detection threshold for the cochlear microphonic”. In other words, again saying that at least part of the hearing problem was in the cochlea, as the cochlear microphonic is generated from the hair cells and does not require an 8th nerve.
|T2 image of superficial siderosis. Note the low signal in the folia of the cerebellum, although on T2, fluid images as high signal.||Flair image. Again, note low signal in the folia of the cerebellum.|
Ryan (Ryan, Piplica, & Zhang, 2014) stated that only 15 cases of SS had been implanted world-wide. Their particular new case had only marginal improvement with CI.
Tyler(Tyler, Martin, & Baguley, 2012) reviewed the world literature at the time, and stated that about half of implant recipients, had “clear sustained benefit”, while 6 showed limited/no benefit, and 2 had temporary improvement that was not sustained. They suggested that when there is “stable” disease, implants are helpful, but when there is progression, implants are not a good idea.
Overall then, it appears that cochlear implants are presently only reasonable when hearing is stable (i.e. not deteriorating).
Electroaudiometry should be done prior to committing to a cochlear implant in patients with superficial siderosis. Electroaudiometry is a method of determining if the 8th nerve is still working, by bypassing sound and using electricity to stimulate the 8th nerve.