Blood cells are not native to the cerebrospinal fluid, and their presence there is problematic. Once they eventually break down, they release the heme containing protein hemoglobin. Hemoglobin breaks down and releases iron-containing heme into the cerebrospinal fluid. In response to this upsurge in heme levels, Bergmann glia and microglia produce heme oxygenase 1. Heme oxygenase 1 breaks down free heme into biliverdin, carbon monoxide, and iron. It is this breakdown of heme that is the source of iron deposition that ultimately causes<unk> . The excess free iron is circulated in the cerebrospinal fluid and deposited in neuronal tissues, where it catalyzes the formation of reactive oxygen species which can damage DNA, lipids and proteins, and is otherwise toxic to the cells. Iron deposition is prevalent in siderotic brain tissues, with iron concentrations of 1.79 to 8.26 times normal levels. Ferritin, an iron storage protein, is over-produced in response to excess heme by glial cells in order to sequester iron, with production ranging from 20.1 to 27.4 times normal levels. Excess iron, ferritin, and red blood cells may result in xanthochromia of the cerebrospinal fluid. Amongst neuronal cells types, iron deposition appears to be preferential for oligodendroglial cells, which is supported by the belief that they can act as iron sinks in the central nervous system. Schwann cells are also frequently damaged, contributing to demyelination. Iron deposition is most prevalent in the inferior temporal lobes, the brainstem, the cerebellum, peri-ventricular structures, the spinal cord, and cranial nerve VIII. Iron deposition is also present in cranial nerves I & II, but this damage less frequently presents symptoms when compared to cranial nerve VIII, which can be explained by cranial nerve VIII’s notable segment of glial cells, which are preferentially affected by iron deposition. The presence of ‘foamy’, ‘spheroid’, or ‘cytoid’ bodies in affected neuronal tissues has been noted but what they are and their origin remains somewhat unclear. They are believed to be swollen axonal bodies, but some evidence exists that they may be astrocytic in origin.
Superficial siderosis
Geographic atrophy
Neurofibrillary tangle
Polymicrogyria
Posterior cortical atrophy
Amyloid plaques
Hippocampal sclerosis
Hemosiderin hyperpigmentation