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The subarachnoid lymphatic-like membrane (SLYM) is a possible fourth meningeal layer that was proposed in 2023 in the brain of humans and mice. [10] The SLYM is located in the subarachnoid space, the space between the middle reticular meninges and the innermost tender meninges that lie close to the brain. [10]
In bacterial meningitis, bacteria reach the meninges by one of two main routes: through the bloodstream (hematogenous spread) or through direct contact between the meninges and either the nasal cavity or the skin. In most cases, meningitis follows invasion of the bloodstream by organisms that live on mucosal surfaces such as the nasal cavity ...
The arachnoid mater is interposed between the two other meninges, the more superficial (closer to the surface) and much thicker dura mater and the deeper pia mater, from which it is separated by the subarachnoid space. The delicate arachnoid layer is not attached to the inside of the dura but against it, and surrounds the brain and spinal cord.
In the skull, the periosteal layer of the dura mater adheres to the inner surface of the skull bones while the meningeal layer lays over the arachnoid mater. Between them is the epidural space . The two layers of the dura mater separate at several places, with the meningeal layer projecting deeper into the brain parenchyma forming fibrous septa ...
The latter is the thickest and outermost of the three membrane layers; it contains the most collagen, and it is derived from the mesoderm - the middle germ layer or the primary layer of the cells formed in embryogenic development via epigenetic effects induced by developmental cues, in the early embryo. Also there are the two parietal bones and ...
MRI of the brain with contrast may show enhancement of the meninges and the subarachnoid space however MRI may also be normal. [ 6 ] [ 2 ] MRI is the preferred neuroimaging test to diagnose chronic meningitis, being more sensitive than CT of the brain, however, MRI scanners are not available in many resource-limited settings where chronic ...
The dura mater covering the spinal cord is known as the dural sac or thecal sac, and only has one layer (the meningeal layer) unlike cranial dura mater. The potential space between these two layers is known as the epidural space , [ 5 ] which can accumulate blood in the case of traumatic laceration to the meningeal arteries .
The membrane in this area is much thicker than the cranial pia mater, due to the two-layer composition of the pia membrane. The outer layer, which is made up of mostly connective tissue, is responsible for this thickness. Between the two layers are spaces which exchange information with the subarachnoid cavity as well as blood vessels.