In approximately 95% of superficial siderosis patients, progressive hearing loss and Overview Tinnitus, often experienced as a soft indication of... More are frequently one of the initial symptoms. This condition primarily affects the eighth cranial nerve, a sensory nerve comprising two main components: the vestibular nerve, which governs balance, and the cochlear nerve, responsible for hearing. The accumulation of free iron, trapped by the ferritin protein and deposited as hemosiderin, attaches to the eighth cranial nerve, leading to a gradual loss of neural function. This process results in bilateral-asymmetric sloping sensorineural hearing loss.
The term ‘bilateral-asymmetric’ indicates that while both sides of your hearing will be affected, the loss will not be identical. ‘Sloping’ describes the pattern of hearing loss, where high-frequency hearing diminishes first, followed by a lower-frequency loss in the later stages as the disorder progresses.
In some cases, superficial siderosis related sensorineural hearing loss may be misdiagnosed as early-stage presbycusis. However, professional audiology journals are increasingly emphasizing the importance of identifying at-risk patients by correlating their current hearing loss symptoms with past trauma or surgical events from their medical history, aiding in early diagnosis.
Early Signs of Sensorineural Hearing Loss
- Muffled hearing
- Difficulty understanding speech
- Gradual loss of hearing
- A feeling of fullness or plugged in the ear
- Ringing in the ear (Tinnitus)
The damage to the specialized, impulse-conducting cells (neurons) leading to neuronal loss in the eighth cranial nerve and potential vascular structure compression from gliosis is considered permanent.
Plan of Care
- Annual audiogram testing is recommended to monitor the progression.
- Evaluation and fitting of specialized hearing aids to enhance word recognition.
- Use of assistive speech-to-text devices.
- Evaluation for surgical options, including cochlear implants.
Assistive Devices and Surgical Options
Specialized hearing aids and cochlear implants can significantly improve the quality of life for patients with superficial siderosis. These devices are designed to enhance word recognition and compensate for hearing loss. Some patients have reported excellent results after undergoing cochlear implant surgery. Pre-procedure determination of intact and functioning brainstem auditory conduction has been identified as a good predictor of cochlear implant success.
The eighth cranial nerve is particularly susceptible to damage from superficial siderosis, caused by the breakdown of slow or repeated episodes of subarachnoid hemorrhage into hemosiderin. This sensitivity is attributed to its long cisternal segment, exposing it to high concentrations of iron, and the transition from central to peripheral myelin occurring near the Internal Auditory Canal (IAC) in the eighth cranial nerve but relatively close to the brainstem in cranial nerves III–XII. The central myelin and the microglia that produce it are especially sensitive to siderosis. The high iron concentration lining the brain and cranial nerves causes local magnetic inhomogeneity and is most easily visualized on susceptibility-weighted or gradient-echo T2*-weighted images¹.
¹Neurologic/Head and Neck Imaging Intracranial Causes of Ophthalmoplegia: The Visual Reflex Pathways Seth T. Stalcup, August S. Tuan, John R. Hesselink Published Online: Aug 30, 2013, https://doi.org/10.1148/rg.335125142