Cortical Superficial Siderosis

Cortical superficial siderosis (cSS) is hemosiderin deposition along the leptomeninges and/or subpial surfaces localized to cortical sulci, representing a chronic sequela of convexity subarachnoid hemorrhage.

It is a supratentorial process and should not be confused with superficial siderosis of the central nervous system, which is predominantly infratentorial and has a different etiopathogenesis and clinicoradiologic phenotype.

Clinical Presentation

cSS is often asymptomatic. When it overlies eloquent cortex, it may cause transient focal neurologic episodes or symptoms.

In cerebral amyloid angiopathy these are often called amyloid spells and may be recurrent, spreading, positive, or negative focal symptoms.

Pathology and Risk

cSS may follow any cause of convexity subarachnoid hemorrhage. In older adults, the most common cause is cerebral amyloid angiopathy (CAA).

In CAA, cortical superficial siderosis is a marker of increased future intracerebral hemorrhage risk.

Extensive classic CNS superficial siderosis can also produce a cortical superficial siderosis appearance.

Primary Etiologies

Cerebral amyloid angiopathy, sometimes with cerebellar siderosis
Inflammatory cerebral amyloid angiopathy
Amyloid-related imaging abnormalities (ARIA)
Trauma or postoperative change
Reversible cerebral vasoconstriction syndrome
Posterior reversible encephalopathy syndrome

Venous and Inflammatory Causes

Dural venous sinus thrombosis
Cortical vein thrombosis
Central nervous system vasculitis
Intracranial mycotic aneurysm

Clinical history and vascular imaging are important when the distribution or patient age is atypical for CAA.

Arterial and Vascular Causes

Moyamoya disease or syndrome
Arteriovenous malformation
Dural arteriovenous fistula
Severe internal carotid artery stenosis
Intracranial atherosclerotic disease

Radiographic Features

CT

Chronic cortical superficial siderosis is not appreciable on CT brain.

MRI

STRIVE-2 definition: Thin areas of hypointensity with blooming on susceptibility-sensitive sequences (GRE or SWI), within or overlying the superficial cortex.

Often bicurvilinear and follows gyral contours, producing a “tram-track” appearance.
Absence of associated convexity sulcal FLAIR hyperintensity helps distinguish chronic cSS from acute convexity subarachnoid hemorrhage.
Do not report superficial siderosis immediately adjacent to an intraparenchymal hemorrhage.
Concurrent lobar microbleeds support underlying CAA.

Severity

Focal: involvement of 1–3 sulci.
Diffuse: involvement of more than 3 sulci.

Treatment and Prognosis

Management of the underlying condition is paramount.

For symptomatic transient focal neurologic episodes, antiseizure medication or migraine prophylaxis—such as levetiracetam or sodium valproate—has been tried anecdotally with variable benefit.

Differential Diagnosis

Acute convexity subarachnoid hemorrhage
Classic superficial siderosis of the central nervous system
Cortical calcification, including Sturge-Weber syndrome
Thrombosed cortical vein
Cluster of lobar cerebral microbleeds
Recent (within approximately 3 months) parenteral superparamagnetic iron oxide, such as ferumoxytol