Superficial siderosis of the central nervous system

Superficial siderosis of the central nervous system refers to a condition resulting from deposition of hemosiderin along the leptomeninges and subpial surfaces, particularly infratentorially, with eventual neurological dysfunction, presumably due to a source of slow and chronic/recurrent subarachnoid bleeding.

Terminology

Superficial siderosis of the central nervous system is a largely infratentorial pathology, and should not be confused with cortical superficial siderosis, which is a supratentorial pathology and has a different aetiopathogenesis with different clinicoradiological stigmata.

Epidemiology

As there are many causes of recurrent or extensive subarachnoid hemorrhage, the demographics are ill-defined and represent those of the underlying cause ^1,2. Cases have been reported in patients from a wide range of age groups, including from adolescence to older adults ¹³. Overall, there is a male predilection (M:F 3:1) ¹³.

Clinical presentation

The most common clinical features are ^1-3:

• sensorineural hearing loss

  • progressive and bilateral

• cerebellar ataxia

  • often prominent gait ataxia

• pyramidal and other long-tract signs

Less common clinical features include ^1-3:

• myelopathy (e.g. neurogenic bladder)

• cognitive impairment

• hyposmia or anosmia

• seizures

• clinical features of spontaneous intracranial hypotension may also be present depending on the cause ^4,5

If cerebrospinal fluid samples are taken via lumbar puncture, red blood cells and/or xanthochromia is commonly present ².

Pathology

Superficial siderosis of the central nervous system is thought to result from recurrent occult subarachnoid bleeds from spinal dural pathologies, although the source of bleeding is not usually identified on imaging ^1,2. Although it is common to see a small amount of hemosiderin deposition at the margins of a previous hemorrhage or surgical resection margin, a single episode of subarachnoid hemorrhage (e.g. berry aneurysm rupture) is usually not sufficient to result in this condition ^1,2.

Most patients will have a history of either spinal trauma (especially with ventral dural tears) or previous intradural neurosurgical intervention, and it is thought that these result in friable vessels prone to causing chronic or recurrent subarachnoid bleeding ². Rarely, patients will have tumors or vascular malformations as the cause for superficial siderosis of the central nervous system ^1,2.

The result of this subarachnoid bleeding, regardless of etiology, is accumulation of iron and its degradation products in the leptomeninges and subpial structures ^1,2. Given these products are neurotoxic, there is subsequent neuronal loss and eventual atrophy of affected regions of the central nervous system ¹. The prominent involvement of the vestibulocochlear nerve (CN VIII), which results in sensorineural hearing loss, is believed to be due to the combination of a long cisternal course (thus with ample exposure to the subarachnoid space) and the susceptibility of microglial cells (which have a role in myelination) to be damaged by iron compounds ⁶.

Etiology

There are many etiologies ^1-9,14:

• idiopathic

• spinal dural defects

  • traumatic cervical nerve root avulsion

  • dural defect with spinal CSF collections/spinal cyst

  • CSF-venous fistula

  • postoperative pseudomeningocoele

• vascular abnormalities

  • arteriovenous malformation (AVM)

  • aneurysm

  • cerebral cavernous venous malformation

  • fragile capillary regrowth after neurosurgery

  • friable vessels due to dural ectasia

• intracranial neoplasms

  • occult small ependymoma

  • oligodendroglioma

  • astrocytoma

Radiographic features

CT

CT brain is often normal, but in some cases, there may be a hyperdense ring appreciated around the brainstem ².

Angiography (DSA)

Usually unrewarding and will usually not demonstrate a point of bleeding ².

MRI

Brain

MRI brain is the modality of choice for assessment and diagnosis of superficial siderosis of the central nervous system ^1,2. The findings are characteristic, with all pial and ependymal surfaces coated symmetrically with T2/T2* low signal hemosiderin, particularly those of the brainstem and cerebellum (the cerebellar vermis and folia are classic locations for identifying subtle deposits), but can be more extensive to involve the Sylvian fissure and even sulcal convexities ^1,2. In long-standing cases, cerebellar atrophy will inevitably develop, particularly affecting the superior vermis ².

• T1: low signal

• T2: low signal

• GRE/SWI: low signal with blooming

Spinal cord

As part of the workup for superficial siderosis, if no lesion is identified in the intracranial compartment, then imaging of the entire spinal canal should be performed (e.g. superficial siderosis due to myxopapillary ependymoma). In the spinal cord, like in the brain, the pial surfaces are again typically coated with T2/T2* low signal hemosiderin ^1,2.

Treatment and prognosis

Workup and management is focused on identifying the causative lesion, although often even this is not possible. Regardless of cause, iron chelating agents may have benefit ¹⁰.

When no correctable cause is identified, signs and symptoms are slowly progressive.

History and etymology

Superficial siderosis of the central nervous system was first described by Ralph C Hamill (1877-1961), American neurologist and psychiatrist, in 1908 ¹¹.

Differential diagnosis

• cortical superficial siderosis

  • notably cerebral amyloid angiopathy can also result in cerebellar superficial siderosis ¹²

• remote cerebellar hemorrhage

  • cerebellar ​bleeding following craniectomy, spinal surgery or lumbar puncture