Superficial Siderosis

Excerpt

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. It is a slowly progressive neurodegenerative condition that can significantly impact a patient’s quality of life. A clinical history of subarachnoid hemorrhage is usually not present, but prior trauma and intradural surgery increase the risk of superficial siderosis.

Superficial siderosis can be classified by the brain regions affected, with 2 distinct forms: cortical or infratentorial. Several underlying conditions can lead to superficial siderosis, and etiologies vary depending on the classification. Cortical superficial siderosis most commonly occurs due to iron deposits in the superficial cortical layers following bleeding from leptomeningeal vessels, most often from cerebral amyloid angiopathy (CAA) in patients aged 55 or older. The most common etiology for classic or primary infratentorial superficial siderosis (iSS) is spinal dural defects, often dural tears. Typically, the source of bleeding is fragile, leaky bridging veins with trabeculae around dural tears. Secondary iSS may result from trauma, craniospinal surgery, tumors, or vascular lesions. Almost 35% of cases of superficial siderosis are idiopathic.

Patients with superficial siderosis can be asymptomatic but commonly present with gait ataxia, myelopathy, or hearing impairment in varying combinations. Cerebellar signs are obligatory, whereas signs of cranial nerve dysfunction and myeloradiculopathy are facultative. Diagnosis is made when characteristic hemosiderin deposition is seen on iron-specific magnetic resonance imaging (MRI) sequences like gradient-echo (GRE) and susceptibility-weighted imaging (SWI).