SUBARACHNOID HEMORRHAGE

Superficial siderosis

Created 06/04/2021, last revision 07/07/2023

  • cerebral superficial siderosis (SS) is characterized by deposits of hemoglobin breakdown products in the subarachnoid space (SA) on the surface of the brain and spinal cord (regardless of etiology)
  • occurs as a result of chronic or intermittent extravasation of blood into the SA space
    • early diagnosis and treatment of dural defects are essential to lower the risk of an irreversible neurologic injury
  • on MRI (particularly noted with GRE/SWI sequences), it appears as a low signal rim covering the surface of the brain and/or spinal cord
  • the idiopathic progressive infratentorial form of SS (iSS) is a sporadic disease

Classification

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Pathophysiology

  • cSS is most commonly caused by focal convexial subarachnoid hemorrhage
  • iSS results from low-volume but prolonged or rather repeated occult SA bleeding from damaged intradural or epidural vessels
    • a hemosiderin rim is often present at the edge of the hemorrhage or surgical resection; however, a single episode of bleeding rarely leads to significant symptoms – the condition requires repeated bleeding
  • hemoglobin from erythrocytes degrades in the CSF into globin and neurotoxic heme. In response to its presence, glia and microglia release heme oxygenase-1 and apoferritin. The breakdown of heme produces free iron, the excess of which leads to neuronal damage
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Topically non-specific or diffuse siderosis

Cortical superficial siderosis (cSS)

see chapter non-traumatic convexial SAH

Mainly infratentorial superficial siderosis (iSS)

  • source of bleeding often remains undetected (up to 50% of cases)
  • dural defects
    • spinal and/or cranial
    • sometimes associated with epidural fluid collection
    • post-operative pseudomeningocoele
  • dural ectasia (e.g., described in Marfan syndrome, neurofibromatosis type 1)
  • a consequence of craniospinal surgery
    • a most common consequence of posterior fossa surgery
    • spinal surgery may be complicated by dural tear with subsequent development of pseudomeningocoele and SS
    • development of SS has also been reported after a ventriculoperitoneal shunt implantation

Clinical presentation

  • the clinical presentation varies depending on the localization and extent of hemosiderin deposition
    • SS can be asymptomatic (incidental finding on MRI)
    • the degree of clinical impairment may not correlate with the extent of imaging abnormality
  • distinguish the symptoms of the underlying disease that led to SS (e.g., dementia caused by CAA)
  • infratentorial SS – symptoms often appear several years after the onset of siderosis; symptoms and their latency are probably related to the duration of bleeding and the amount of deposited hemosiderin
    • gait ataxia
    • myelopathy
    • sensorineural hearing impairment (in up to 95% of cases)
      • usually bilateral, asymmetric, progressive
      • may have both retrocochlear and cochlear components
      • tinnitus
      • impairment results from a long cisternal course (exposure to the subarachnoid space) and the susceptibility of microglial cells to be damaged by iron compounds   [Swartz, 2008]
    • dysphagia or cerebellar dysarthria may occur in advanced stages (can lead to misdiagnosis of degenerative cerebellar ataxia)
  • convexial SS
    • epileptic seizures (in < 5% of cases)
    • cognitive deterioration in extensively disseminated cSS
    • sensory deficits
    • cranial neuropathies
    • anosmia

Diagnostic evaluation

  • CT of the brain + CTA
    • rough exclusion of structural or vascular pathology
    • atrophy or post-traumatic changes in parenchyma or bones may be present
    • rarely a hyperdense rim around the brainstem is seen
  • MRI of the brain and spinal cord
    • the modality of choice to demonstrate hemosiderin deposition
      • T1 – hypointense rim
      • T2 – hypointense rim mainly on the surface of the cerebellum (vermis and folia), brainstem, and spinal cord, often also in the area of the Sylvian furrow or cerebral convexity (however, secondary gliosis can also lead to increased signal)
      • GRE/SWI – hypointense lesions with blooming artifacts in the same localization
      • often symmetrical and confluent hypointensity following the contours of the brain and spinal cord
      • iSS  typically affects the cerebellum and brainstem, most commonly the superior vermis or vestibulocochlear nerve (n.VIII)
    • in the classic iSS form, cerebellar atrophy is present, mainly in the superior vermis
    • exclude myxopapillary ependymoma among spinal cord lesions
  • CT or MR myelography
    • epidural fluid collection
    • dural defect
  • cerebrospinal fluid
    • there may be evidence of ongoing bleeding, like xanthochromia, and elevated protein levels
    • with a longer interval since the attack, the CSF may become normal
  • cerebral or spinal DSA
    • DSA rarely reveals an apparent source of bleeding not visible on CTA or MRA
  • in up to 50% of patients, no potential source of bleeding is found (history of trauma or CNS surgery is often present)
Superficial siderosis in patient with CAA
Infratentorial superficial siderosis
Superficial siderosis after repeated SAH
Cortical siderosis and chronic and late-subacute lobar hematoma in a patient with CAA

Management

Causal therapy

  • elimination of the source of bleeding, if detected
    • dural defects can be closed with sutures, patches, or a fibrin glue
    • even a successful surgical treatment does not always halt the clinical progression
    • the initiated secondary neurodegenerative process may be the reason for therapy failure
  • pharmacotherapy is most commonly not effective (corticosteroids, selegiline, vitamin C, and E)
  • promising results of a pilot study with deferiprone (an iron chelator) have been published; half of the patients experienced an improvement on MRI and stabilization of neurological deficit  Infratentorial superficial siderosis (Kessler)   [Kesseler, 2017]

Symptomatic therapy

  • most symptoms of infratentorial SS, such as ataxia or myelopathy, cannot be effectively treated
  • supportive therapy can help patients to adapt and minimize further neurological disabilities ⇒ order physical and occupational therapy
  • consider a cochlear implant for hearing loss

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Superficial siderosis
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