The newly discovered fourth meningeal layer.
A new study has revealed an interesting novel structure in the brain – a fourth meningeal layer. The Subarachnoid Lymphatic-like Membrane (SLYM) is located in the subarachnoid space and divides it into an outer, superficial compartment and an inner, deeper area surrounding the brain. SLYM is immunophenotypically distinct from the other meningeal layers in the human and mouse brain, and it acts as a barrier to particles with a molecular weight greater than 3kDa. SLYM encases blood vessels and harbours immune cells (mainly a large population of myeloid cells, the number of which increases in response to inflammation and ageing).…