Abnormal meningeal morphology Superficial CNS hemosiderin deposition 2025-05-03T09:32:30Z An anomaly that can be ascertained by iron-specific magnetic resonance imaging (MRI) sequences such as gradient-echo (GRE) and susceptibility-weighted imaging (SWI). Superficial siderosis of the central nervous system is a chronic condition due to persistent or repeated long-term bleeding into the subarachnoid space, leading to subpial hemosiderin deposition. Hemosiderin deposition on MRI is seen as a T2 hypointensity and preferentially outlines the cerebellum and brainstem surface. Superficial siderosis Superficial CNS hemosiderin deposition is a manifestation of superficial siderosis (SS) of the central nervous system (CNS), which is typically due to chronic low-grade extravasation of blood into the subarachnoid space. Hemoglobin in red blood cells in the cerebrospinal fluid (CSF) breaks down into globin and neurotoxic heme. In response to the presence of neurotoxic heme, neuroglial cells release hemoxygenase and apoferritin. Hemoxygenase breaks heme into free iron and biliverdin, and apoferritin binds free iron to form ferritin and subsequently hemosiderin. This process is likely neuroprotective and prevents free iron mediated neuronal injury. Persistence of blood in the subarachnoid space eventually overwhelms the ferritin production capacity and unbound iron results in free-radical mediated neuronal injury. Hemosiderin deposits in regions of the brain or spinal cord adjacent to CSF. This confluent subpial hemosiderin deposition results in a characteristic marginal and confluent T2-hypointensity on magnetic resonance imaging that is referred to as SS and it is best appreciated on iron-sensitive sequences.