Superficial Siderosis

Definition and epidemiology

Superficial siderosis is a progressive neurodegenerative disease in which haemosiderin, a breakdown product of blood, is deposited on the pial surface of the brain, cerebellum, spinal cord and cranial nerves as a result of slow, low-volume, recurrent or continuous bleeding into the subarachnoid space (Kessler et al., 2018; Kharytaniuk et al., 2022). There are two main subtypes: classical infratentorial superficial siderosis affects the brainstem, cerebellum and spinal cord and sometimes extends to supratentorial regions, while cortical superficial siderosis affects only the surface of the cerebral cortex and is a different clinical entity (Kharytaniuk et al., 2022). This article focuses on the classical infratentorial form.

Wilson et al. (2017) divided infratentorial siderosis into two types. In type 1 (classical) there is no intracranial haemorrhage to explain the deposition; 83% of their 48 patients had hearing loss, ataxia or myelopathy. In type 2 (secondary) there is a known spontaneous or traumatic haemorrhage, and none of these 17 patients had these clinical features. The condition has long been considered rare, but recognition is increasing as sensitive MRI sequences become more widely used. In a UK study of brain MRI in 10,305 people, infratentorial siderosis was found in five, giving a prevalence of 48.5 per 100,000 (95% CI 20.7-113.5) (Kharytaniuk et al., 2025).

Symptoms and signs

Hearing loss is almost always present and is often the first symptom (Kharytaniuk et al., 2022). In a series of 49 patients, 92% reported hearing loss and 67% a balance disorder; the hearing loss was progressive, sloping towards the high frequencies, often asymmetric and worse than expected for age (Sydlowski et al., 2011). Relative sparing of the low and mid frequencies early on can make the audiogram look like presbycusis, but the loss starts at a younger age and spreads to the low frequencies over time. It may range from mild-to-moderate to profound (Kharytaniuk et al., 2022). Tinnitus may also occur.

The second prominent feature is gait ataxia: the gait is broad-based and worse in the dark, and in severe cases truncal ataxia develops so that the person cannot sit or walk unaided. Imbalance arises from both cerebellar involvement and peripheral vestibular impairment. Myelopathy from spinal cord involvement causes gait disturbance, leg stiffness, reduced dexterity and radicular pain, and bladder and bowel dysfunction may appear in advanced disease. Loss of smell is common but is often not volunteered. In one centre, half of the patients had marked cognitive impairment, mainly in executive function (Kharytaniuk et al., 2022). Symptoms progress slowly over years.

Causes and risk factors

The classical form is usually caused by slow, low-volume bleeding into the subarachnoid space from a defect in the dura. The defect is most often spinal, sometimes in the posterior fossa, and typically follows trauma or brain or spinal surgery years and often decades before diagnosis (Kharytaniuk et al., 2022). In the series of Wilson et al. (2017), 83% of type 1 patients had a potentially causal cranial or spinal dural abnormality, 11% had another cause and in 6% no cause was found.

Red cells that reach the subarachnoid space break down and release haem. Microglia release haem oxygenase, and Bergmann glia in the cerebellum produce apoferritin; free iron is bound into ferritin and deposited as haemosiderin. When ferritin production is overwhelmed, free iron causes lipid peroxidation, gliosis, demyelination and axonal damage (Kharytaniuk et al., 2022). The vestibulocochlear nerve is particularly vulnerable because of its long glial segment running from the brainstem into the internal auditory canal, and demyelination is most marked in this nerve and the cerebellum (Kharytaniuk et al., 2022; Sydlowski et al., 2011).

Audiological and clinical assessment

The diagnosis is made on MRI. T2* gradient-echo and susceptibility-weighted imaging (SWI) are more sensitive to haemosiderin than standard T2 imaging and show a hypointense (dark) rim outlining the brainstem, cerebellum and spinal cord. Diagnostic criteria require symmetrical haemosiderin deposition in at least two infratentorial regions (cerebellum, brainstem, craniocervical junction or spinal cord), and the superior cerebellar vermis is always involved (Kharytaniuk et al., 2022). Spotting this rim on an internal auditory canal MRI requested for asymmetric hearing loss can lead to the diagnosis, so it is important not to overlook siderosis while investigating for vestibular schwannoma.

• Pure-tone audiometry: bilateral, often asymmetric sensorineural loss sloping towards the high frequencies, with progression on follow-up (Kharytaniuk et al., 2022; Sydlowski et al., 2011).
• Speech audiometry: word recognition may be poorer than the thresholds predict (Sydlowski et al., 2011); this disproportion suggests retrocochlear involvement. Speech-in-noise tests better reflect everyday difficulty.
• OAEs: reduced or absent as cochlear involvement progresses; OAEs that are better preserved than the thresholds suggest point to a retrocochlear contribution.
• ABR: progressive changes in wave latencies and morphology have been reported on follow-up (Kharytaniuk et al., 2022); with retrocochlear involvement, the I-V interpeak latency may be prolonged or waves may be absent.
• Acoustic reflexes: as in other retrocochlear lesions, elevated or absent reflexes may be expected; the finding should be interpreted alongside the hearing thresholds.
• Vestibular tests: involvement has both central (cerebellar) and peripheral features. Caloric testing and VEMPs can be used; vHIT should not be performed after recent brain or spinal surgery, with a shunt, abnormal intracranial pressure or restricted neck movement (Kharytaniuk et al., 2022). Oculomotor testing looks for central signs.

Once the diagnosis is made, the bleeding source is sought. MRI of the brain and whole spine, ideally with iron-sensitive sequences, is required; dynamic CT myelography and digital subtraction myelography are the most successful methods for localising a dural leak. Cerebrospinal fluid may contain hundreds or thousands of red cells and a raised ferritin, whereas angiography is generally unhelpful (Kharytaniuk et al., 2022; Wilson et al., 2017). With this systematic approach a potential cause, most often a dural abnormality, is found in nearly every patient (Wilson et al., 2017). The differential diagnosis includes presbycusis, noise-induced loss and autoimmune inner ear disease, as well as other neurological causes of ataxia and of central vertigo; on MRI, mimics such as cerebral amyloid angiopathy and dural fistula have to be distinguished.

Treatment and audiological rehabilitation

The main aim of treatment is to stop the bleeding. If a dural defect is found, surgical repair is planned; there are no randomised trials, but most series suggest that repair may halt deterioration (Kharytaniuk et al., 2022). Treatment decisions rest with the neurology and neurosurgical team.

Deferiprone, an iron chelator that crosses the blood-brain barrier, has been used to slow progression, but the evidence is limited. In a systematic review of 11 studies and 69 patients, imaging improved in 28.9% of those with repeat MRI; the drug kept the disease stable in some patients and occasionally led to improvement. Neutropenia occurred in 8.7% and agranulocytosis in 5.8%, and 17.4% stopped treatment (Flores Martin et al., 2021). In a two-year observational study, 63% of the 30 evaluable patients showed no progression or some improvement in at least one neurological domain, and about 40% reported stable hearing; the authors stressed that efficacy needs to be shown in a placebo-controlled trial (Kessler et al., 2018). In a consecutive series of 10 patients, 40% stopped the drug because of side effects, three of them because of neutropenic sepsis (Sammaraiee et al., 2020). Its use and blood count monitoring must therefore be closely supervised by the doctor.

Hearing rehabilitation should start early. Conventional hearing aids are the first option (Kharytaniuk et al., 2022), but when word recognition is poor, amplification may not give the expected benefit (Sydlowski et al., 2011). Remote microphone systems and communication strategies should be added. A cochlear implant (CI) can be considered for profound loss, but outcomes vary. In a systematic review of 19 studies covering 38 patients and 44 implants, 72.7% of implants gave benefit at some point, 52.3% still had a good hearing outcome at last follow-up, 20.5% showed initial benefit that later declined and 27.3% gave no benefit; all the evidence came from case reports and uncontrolled series (Chaudhry et al., 2020). Because the cochlear nerve is progressively involved, thorough preoperative assessment and counselling that benefit may be limited or temporary are essential. Vestibular rehabilitation and falls prevention address the balance problem, and hearing should be monitored at regular intervals, with word recognition recorded at every visit.

Impact on quality of life and advice

Because superficial siderosis affects several functions at once, including hearing, balance, walking and sometimes cognition, it can markedly reduce quality of life. The combination of hearing loss and imbalance may lead people to withdraw from crowded places and social activities, and reliance on visual cues and lipreading increases. Difficulty walking in the dark raises the risk of falls. Loss of smell can make it harder to notice spoiled food or a gas leak. The rarity of the condition and diagnostic delay can add to anxiety and uncertainty.

Practical advice: wear your hearing aids consistently and describe to your audiologist the situations in which you struggle to follow speech; ask about assistive technology such as remote microphone systems. Use night lights at home, remove trip hazards such as rugs and cables, and fit grab rails in the bathroom. Use gas and smoke detectors. Keep to your scheduled hearing and balance tests, and if you notice a rapid decline in hearing, seek review without waiting for the next appointment. If you take deferiprone, contact your doctor immediately if you develop fever, sore throat or other signs of infection.