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Findings: On these T2 weighted images there is a thin black coating of the entire brain stem as well as many of the cortical surfaces of the cerebral hemispheres, most prominently noted along the Sylvian fissure bilaterally.
Diagnosis: Superficial siderosis.
Discussion: Superficial siderosis is a rare condition consisting of deposition of hemosiderin on the leptomeninges, as well as on the surface of the brain, cerebellum, brainstem, and cranial nerves. The presenting clinical symptoms primarily consist of sensorineural hearing loss and ataxia and in more advanced cases myelopathy may develop. In addition, loss of the sense of smell has on occasion been reported. The clinical symptoms generally are slowly progressive leading to deafness and ataxia. The underlying cause of superficial siderosis is felt to most likely represent repeated chronic subarachnoid hemorrhages. These repeated hemorrhages leading to superficial siderosis have been reportedly secondary to tumors, vascular malformations, subdural hematoma, prior hemispherectomy, or idiopathic. Among the current theories proposed to explain the superficial siderosis in idiopathic cases include increased permeability of meningeal arteries with passage of red blood cells into the CSF. A second potential cause is bleeding from angiographically occult vascular malformations. The areas of the brain that are most severely affected include the superior vermis, brainstem, and cortex (especially around the Sylvian cisterns). In addition, involvement of the first, second and eighth cranial nerves has been described. The MRI findings consist of a thin rim of hypointensity on T2 weighted images on the surface of the central nervous system. Specifically, these findings are most commonly demonstrated along the vermis, brainstem, and interhemispheric sulci as well as the Sylvian fissure.
References:
Dracchi Maurizio. Superficial Siderosis of the CNS:
MR Diagnosis and Clinical Findings. AJR 1993;14:227-236.
Osborn Anne. Diagnostic Neuroradiology. Mosby, St. Louis;1994:184.
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