Discussion Author: Ozgur Kilickesmez
Superficial siderosis(SS) is a rare condition characterized by deposition of hemosiderin in the leptomeninges and on the surface of the inferior cerebral hemispheres, cerebellum, brain stem, cranial nerves and spinal cord. Symptoms include sensorineural hearing loss, cerebellar ataxia, dementia, and pyramidal signs. It is caused by chronic, sometimes intermittent, subarachnoid hemorrhage, often resulting in progressive mental deterioration. Pathologically, there is deposition of hemosiderin in those parts of the central nervous system that are in close proximity to cerebrospinal fluid. This deposition of hemosiderin is associated with gliosis, neuronal loss, and demyelination. It is thought that the cochlear nerve and the cerebellar cortex are particularly vulnerable owing to their accelerated ferritin synthesis.
The common sources of subarachnoidal bleeding causing SS are dural abnormalities, vascular lesions, and tumors, as well as posttraumatic or postsurgical lesions. Routine laboratory studies are typically unremarkable. CSF examination reveals hemorrhage and xanthochromia in roughly half of cases. The diagnosis should be especially considered in patients who present with slowly developing hearing loss and ataxia many years after surgery. Increased numbers of red blood cells, an increased level of siderophages, xanthochromia, and high concentrations of proteins in the CSF support the diagnosis, however MRI appears superior to confirm the diagnosis.
The hypointense rim typically seen on T2W images and coating the cerebellum, brainstem, cranial nerves, cerebral hemispheres and/or spinal cord is produced by the strong magnetic susceptibility effect of iron. This effect is more pronounced at T2*W sequences.The regions of low signal on T2W images correspond to the yellow-brown staining due to hemosiderin deposition that is seen post mortem. CT scanning of the head can occasionally identify atrophy of the cerebellar vermis or a hyperdense rim over the brain surface, corresponding to hemosiderin deposition.
The optimum treatment would be an ablation of the bleeding source, but no source is detected in most cases.
Differential Diagnosis:
None : this is a pathognomonic appearance. The only differential issue is the etiology of the siderosis.
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