Superficial siderosis of the central nervous system is a rare condition caused by hemosiderin deposits in the subpial layers of the brain and spinal cord. The hemosiderin deposition results from recurrent bleeding into the subarachnoid space. Patients often present in adulthood with hearing loss and slowly progressive gait ataxia. A remote history of injury or intradural surgery is common, but many cases are idiopathic, with no source of bleeding evident.
It has been noted by Mayo Clinic neurologists, neurosurgeons and neuroradiologists that an intraspinal fluid-filled collection accompanies some cases of superficial siderosis. Intraspinal fluid-filled collections have also been seen in patients with craniospinal hypovolemia and dural defects.
"We have had some patients with superficial siderosis and intraspinal fluid collection in whom repairing the defect has resulted in resolution of the fluid collection, resolution of red blood cells in the cerebrospinal fluid and clinical stability," says Neeraj Kumar, M.D., a consultant in the Department of Neurology at Mayo Clinic in Rochester, Minnesota.
Before MRI, superficial siderosis was generally diagnosed only postmortem. The condition progresses slowly over the course of decades and remains rare. Clinical presentation can include orthostatic headache and cognitive difficulties. "Superficial siderosis can also present as a myelopathy. Not infrequently, I have seen patients who are misdiagnosed as having a degenerative cerebellar condition," Dr. Kumar says.
MRI of the head is key to diagnosis. "There are MRI sequences, such as gradient-echo sequencing, that allow the iron pigment to be detected in the brain. But these sequences are not routine," says David G. Piepgras, M.D., a consultant in the Department of Neurologic Surgery at Mayo Clinic's campus in Minnesota.
Further, neuroradiologists may view hundreds of images on a CT myelogram from a patient to see the single image showing contrast leakage from a dural defect. "The MRI findings are striking but somewhat subtle," Dr. Kumar says. "The abnormality is very confluent, and it sort of coats the surface of the brain."
Improvement or arrest?
A dural defect can usually be repaired with surgery. The procedure is especially complex if the defect is located in front of the spinal cord. "However, for surgeons experienced in the condition and repair, it's not a great technical challenge," Dr. Piepgras says.
Anecdotal evidence from patients treated at Mayo Clinic suggests clinical stability after surgery. However, in the absence of longitudinal studies of this slowly progressing condition, it isn't clear whether repairing the dural defect improves symptoms or merely arrests neurological deficit. "There has already been significant iron deposition in the central nervous system of these patients, which could have future toxic effects even if the mechanism is arrested," Dr. Piepgras says.
For more information
Kumar N. Beyond superficial siderosis: Introducing "duropathies." Neurology. 2012;78:1992