CSF-venous fistulae—An underrecognized cause of superficial siderosis

Superficial siderosis (SS) of the central nervous system is a rare chronic neurological disorder characterized by hemosiderin deposition over the subpial surface of the brain, cranial nerves, and spinal cord. This deposition can result from acute subarachnoid hemorrhage or from chronic or repeated hemorrhage, most often due to cerebral amyloid angiopathy and less commonly to cerebrospinal fluid (CSF) leaks, usually from ventral dural tears. Chronic microhemorrhages associated with spinal CSF leaks without ventral epidural CSF collections or meningoceles are exceedingly rare. Herewith, we describe a case of symptomatic SS as the sole clinical manifestation of a CSF-venous fistula (CSF-VF) of the thoracic spine. A male patient in his 60s presented with long-standing intermittent right-sided headache, anosmia, bilateral tinnitus, and gait instability. Neuraxis imaging revealed extensive SS involving the basal supratentorial brain, infratentorial brain, and spinal cord. A small intraforaminal thoracic nerve root dural ectasia was identified. There were no clear imaging signs of intracranial hypotension. Computed tomography myelography demonstrated a clear CSF-VF of the thoracic spine, which was subsequently closed by transvenous embolization. Postprocedure, the patient experienced progressive symptomatic improvement. This case highlights the importance of considering CSF-VF in the differential diagnosis of SS, especially when dural tears and epidural collections are absent on imaging.