Superficial Siderosis

Superficial siderosis is chronic haemosiderin deposition on the surfaces of the brain, brainstem, cerebellum and spinal cord, caused by repeated or persistent bleeding into the subarachnoid space. The central nervous system form is the classic disease, and cortical (convexity) siderosis is a related pattern.

It is rare, found mostly in adults over 40 years. Presentation is often delayed for years, because the source of bleeding may be small.

Causes. Dural defects from previous surgery, nerve root avulsion or trauma (often decades earlier), spinal or posterior fossa tumours (ependymoma, schwannoma), vascular malformations, cerebral amyloid angiopathy (cortical form), and spinal cerebrospinal fluid leak with a ventral dural tear. Many cases have no source found.

Pathophysiology. Free haemoglobin in cerebrospinal fluid is converted by microglia and Bergmann glia to haem oxygenase products and haemosiderin, which deposits on pial surfaces. Iron toxicity damages cranial nerve VIII, the cerebellum and the spinal cord.

The classic triad is progressive sensorineural hearing loss (most often), cerebellar ataxia and myelopathy. Others are anosmia, dementia, anisocoria, headache, bladder disturbance and neck or back pain. Evolution is slow over years.

MRI with T2*-weighted gradient echo or susceptibility weighted imaging shows a hypointense rim on the surface of the cerebellum, brainstem and cranial nerves. Whole spine MRI, including T2-weighted heavily fluid sensitive sequences, looks for a dural defect, fluid collection or tumour. CT myelography (including dynamic or digital subtraction) and angiography help localise a leak or vascular lesion. CSF may show xanthochromia, raised ferritin and red cells. Audiometry measures hearing loss.

Differential diagnosis.

• Other causes of ataxia, myelopathy and hearing loss (multiple system atrophy, spinocerebellar ataxia, mitochondrial disease).
• Cortical siderosis from cerebral amyloid angiopathy, and post-traumatic haemorrhage.
• Haemorrhagic tumour and cavernous malformation.

Finding and treating the source of bleeding is the priority.

Source control. Surgical repair of a dural defect or removal of a tumour or vascular lesion, which can stop progression. Repair of ventral dural tears (spinal cerebrospinal fluid leaks) is done by specialist spinal surgeons.

Chelation. Deferiprone has been studied: about 30 mg/kg daily in two or three divided doses, with weekly neutrophil counts for the first 6 months, then every 2 weeks while treated. Stop if neutrophils fall under 1.5 x 10^9/L. Risks are agranulocytosis, joint pain and liver enzyme rise. Evidence of benefit is limited, with partial reduction of iron on imaging and some stabilisation.

Hearing. Hearing aids and cochlear implantation (best response in early disease).

Avoid anticoagulants and antiplatelet drugs where possible.

Rehabilitation. Physiotherapy, occupational therapy, balance training and falls prevention.

Monitoring. MRI every 1 to 2 years, audiometry, neurological examination and blood counts on chelation.

Referral and escalation. Refer to neurology and neurosurgery. Refer urgently for rapid progression or new neurological deficits.

Special groups. Avoid deferiprone in pregnancy, in neutropenia and in people unable to attend regular blood tests.