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There have been 87 cases of superficial siderosis of the CNS reported in the world literature and 63 cases had developed the clinical syndrome with sufficient details to be reviewed. It is a distinct clinical syndrome characterized by sensorineural deafness (95%), cerebellar ataxia (88%) and pyramidal signs (76%). Other features include dementia (24%), bladder disturbance (24%), anosmia (at least 17%), aniscoria (at least 10%) and sensory signs (13%). Less frequent features are extra-ocular motor palsies, neck or backache, bilateral sciatica and lower motor neuron signs (5-10% each). Males are more often affected than females (3:1). The age of onset ranged from 14 to 77 years, age at death from 29 to 78 years and duration until death from 1 to 38 years excluding premature death due to the underlying cause or as a result of surgery. Up to 27% become bed bound at 1-37 years from the first symptom due to either cerebellar ataxia, a myelopathic syndrome or both. Symptomatic subarachnoid haemorrhage occurred in 37% and the CSF was haemorrhagic and/or xanthochromic in 75%. It is now accepted that superficial siderosis is due to chronic subarachnoid haemorrhage and a source of bleeding has been reported in 54% of cases; it was either due to dural pathology (47%) including a CSF cavity lesion or cervical root lesion, a vascular tumour (35%) or a vascular abnormality (18%). Arguments are presented that the remaining cases were also due to chronic haemorrhage and that there is no evidence for a non-haemorrhagic form of superficial siderosis. There have been 14 incidental cases diagnosed by MRI or at post-mortem with no symptoms attributable to superficial siderosis during life, supporting the notion of a pre-symptomatic phase to the illness. In 22 patients who had developed the syndrome, the duration of this pre-symptomatic phase could be calculated and ranged from 4 months to 30 years with an average of 15 years. At present the most promising treatment for superficial siderosis is surgical ablation of the bleeding sources.