Cortical superficial siderosis

Cortical superficial siderosis (cSS) refers to deposition of hemosiderin along the leptomeninges and subpial surfaces, localized to the cortical sulci, as a sequela of convexal subarachnoid hemorrhage.

Terminology

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

Clinical presentation

Cortical superficial siderosis is often asymptomatic, but if is present over regions of eloquent cortex can result in transient focal neurological episodes or symptoms, which are often referred to as “amyloid spells” when occurring in the setting of cerebral amyloid angiopathy ^1-4. Please see the article on cerebral amyloid angiopathy for a further discussion of this clinical presentation.

Pathology

Cortical superficial siderosis can be the chronic sequela of any cause of convexal subarachnoid hemorrhage, however, in an older demographic the most common cause is cerebral amyloid angiopathy ^1-3. In patients with cerebral amyloid angiopathy, presence of cortical superficial siderosis is a marker of increased risk of intracerebral hemorrhage ⁵.

Etiology

Causes of isolated cortical superficial siderosis are those that cause convexal subarachnoid hemorrhage, including having a past history of ^1-3,6:

• cerebral amyloid angiopathy

• amyloid related imaging abnormalities (ARIA)

• trauma or post-operative changes

• reversible cerebral vasoconstriction syndrome (RCVS)

• posterior reversible encephalopathy syndrome (PRES)

• dural venous sinus thrombosis or cortical vein thrombosis

• central nervous system vasculitis

• mycotic aneurysm

• moyamoya disease or syndrome

• vascular malformations

  • arteriovenous malformation

  • dural arteriovenous fistula

• severe internal carotid artery stenosis or intracranial atherosclerotic disease

Additionally, extensive superficial siderosis of the central nervous system can also result in radiographic appearances of cortical superficial siderosis ¹.

Radiographic features

CT

Cortical superficial siderosis is not appreciable on CT brain ².

MRI

MRI brain is the modality of choice for assessment of cortical superficial siderosis ^1-3. There are characteristically asymmetric bi-curvilinear regions of low signal (blooming artifact) seen on susceptibility-sensitive sequences (e.g. GRE, SWI) following the contour of cortical gyri, often resembling 'tram tracks' ^1-3. There is no accompanying hyperintensity in the convexal subarachnoid space on FLAIR, differentiating it from acute convexal subarachnoid hemorrhage.

The severity of cortical superficial siderosis can be quantified ³:

• focal: if 1-3 sulci have cortical superficial siderosis

• diffuse: if >3 sulci have cortical superficial siderosis

MRI brain may also provide demonstrate features of the underlying cause of cortical superficial siderosis, for example, the concurrent presence of lobar cerebral microhemorrhages may suggest underlying cerebral amyloid angiopathy ^1,2.

Treatment and prognosis

Management of the underlying condition is paramount, if possible. In patients who are symptomatic with transient focal neurological episodes or symptoms, antiseizure medications and migraine prophylactics (e.g. levetiracetam, sodium valproate) have been anecdotally trialed with varying benefits ⁴.

Differential diagnosis

• acute convexal subarachnoid hemorrhage

• superficial siderosis of the central nervous system ^1-3

• calcification (e.g. Sturge-Weber syndrome) ²

• thrombosed cortical vein ²

• cluster of lobar cerebral microhemorrhages ²