A proposed mechanism of superficial siderosis supported by surgical and neuroimaging findings.

Superficial siderosis is a rare disease with a low incidence of known etiologies and successful management in clinical practice. The presence of a fluid collection secondary to a dural tear has been reported in patients and is considered to be related to superficial siderosis. We report on a patient with superficial siderosis who had a multi-lobulated arachnoid cyst incarcerating the inner dural layer and showing rhythmic pulsations indicating the free connection with cerebrospinal fluid (CSF) circulation. Surgical removal of the arachnoid cyst and leakage repair halted the progression of clinical impairment and reduced epidural fluid collection shown by post-operative magnetic resonance myelogram. Based on the surgical and neuroimaging findings, especially the heavily T2-weighted MR myelogram, we propose a hypothesis, increased epidural pressure microtraumatizing the fragile internal venous plexus leading to recurrent microbleeding, to explain the formation of the superficial siderosis.