Neuroscience I - Meninges

Subdural hematoma

(See image on slide 10 of Meninges PowerPoint for diagram). Dura is still attached to skull at the periosteal layer. VENOUS blood is filling what was the potential subdural space between the meningeal layer and the arachnoid layer. The brain is compressed.

Epidural hematoma - what has happened?

(See image on slide 10 of Meninges PowerPoint for diagram). Skull is fractured. Middle meningeal artery is ruptured, ARTERIAL blood has filled epidural potential space. The dura has been peeled off of the skull and the brain is compressed.

Infections in the CNS: Routes of entry

1. Hematogenous spread (via arterial blood supply) 2. Local extension from ongoing infection in skull or spine 3. Direct implantation arising from a penetrating trauma 4. Congenital malformations 5. Iatrogenic (rare)

Arachnoid mater

Arachnoid mater is attached to inner surface of the dura Arachnoid space is filled with CSF. Contains subarachnoid cisterns, the areas where the arachnoid has to bridge over large surfaces.

Aseptic meningitis

Aseptic meningitis, or viral meningitis, is the clinical term for illness comprising of meningeal irritation, fever, and alterations in consciousness. Aseptic meningitis has an acute onset with spontaneous recovery, is less fulminant than bacterial meningitis and is characterized by an increased number of lymphocytes with little changes in gross pathology of the brain. Vascular dilation, congestion, and edema are seen in aseptic meningitis.

Epidural space

Between skull and periosteal layer of the dura mater. Blood that flows into the epidural space ends up forming a clot called an epidural hematoma, which is associated with skull fracture.

Chemical meningitis

Chemical meningitis occurs in response to nonbacterial irritant introduced into subarachnoid space

What are meninges?

Connective tissue with 3 distinct layers - 1) Dura mater - the dura mater layer is the thickest, outermost layer. 2) Arachnoid mater - this layer has a weblike appearance. 3) Pia mater - this is the innermost layer and is very thin at only one cell thick.

Dura Mater: in the brain vs. in the spinal cord

Distinct differences between dura mater of the brain and of the spinal cord are: Dura mater brain = potential space that exists, but it shouldn't SC = dura mater is not adherent to vertebrae; there are no potential spaces, there are real spaces

Innervation of the Dura Mater

Dura is innervated by 2 different nerves: 1) trigeminal nerve 2) vagus nerve Physical stimulation of these nerves results in pain (headache). Trigeminal nerves are primary nerves that innervate dura. Vagal nerve does too, but in posterior portion.

Tentorium cerebelli

Forms a tent over the cerebellum. Separates cerebellum and brain stem from occipital and temporal lobes Forms 2 compartments: 1) supratentorial compartment = everything that lies above tentorum cerebellum 2) infratentorial compartment = everything that lies below tentorum cerebellum Function of tentorial cerebellum = prevents components from moving down or up, compartmentalizing them and anchoring them in place

Clinical manifestations of meningeal irritation

Headache Nuchal rigidity (stiff neck) Alteration in consciousness

Meningitis

Inflammation of the leptomeninges within the subarachnoid space Types: 1) Chemical meningitis 2) Acute pyogenic meningitis 3) Aseptic meningitis

Treatment of Meningitis

Lumbar puncture Antibiotics via IV

Middle Meningeal Artery

Meningeal artery travels in the periosteal layer of the dura and its main function is supplying bones of the skull Middle meningeal artery penetrates the dura and supplies blood to the dura If there is injury to middle mieningeal artery, you will see space, blood formed, etc.

What is potential space, in terms of the brain?

Potential space is space that doesn't exist normally. However, in the occurance of some pathological event, the space in brain opens up. Periosteal layer *should be adherent to the bones of the skull, but in in case of hematoma or blood clot, it can be separated so blood can flow between the layer and the skull. Similarly, can form space between meningal layer and arachnoid mater. Fluid can run through this subdural space (at this point, it will no longer be "potential space" and it becomes real space.)

Acute pyogenic meningitis

Predisposing factors to acute pyogenic meningitis: immunodeficiency chronic diseases infection open head or spine trauma 70% of cases occur in children. 2/3 of adults present with the classic triad: 1) fever 2) neck stiffness 3) headache or altered mental status

Subarachnoid Cisterns (4)

Quadrigeminal cistern Prepontine cistern Interpeduncular cistern Cerebellomedullary cistern

List (in order) the layers between the skin and the cerebral cortex, starting with the skin of the scalp.

Skin of scalp Periosteum Bone of the skull Dura mater (made up of first the 1) periosteal layer, and then 2) the meningeal layer) *The subdural space between the dura mater and the arachnoid mater is POTENTIAL SPACE, meaning it is only there and 'real' when a pathology is present.* Arachnoid mater Subarachnoid space Pia mater Cerebral cortex

Spinal Pia Mater

Spinal Pia Mater gives rise to 2 structures: 1) Denticulate ligaments - anchor spinal cord with vertebral column and anchors it to the dura so that the spinal cord won't move around 2) Filum terminale - anchors spinal cord to coccyx to give stability to spinal cord

Function of the meninges

Stabilize the position of the brain Stabilize the shape of the brain (Taking away the meninges would cause the brain to lose its shape. Meninges establish and maintain structure and function of neurons.)

Bridging Veins

Structures associated with subdural hematomas. Bridging veins empty into superior sagittal sinus, and drain the blood from the vein down into the sinus.

What are the 2 layers that make up the dura mater?

The 2 layers that makeup the dura mater are 1) Periosteal layer and 2) Meningeal layer

Meningeal Layer of Dura: Dural Reflections (Dural Septum)

The dural reflections are the infolding of the meningeal layer. The falx cerebri is where it comes together in the medial longitudinal fissure, separating the L/R cerebral hemispheres.

Dura Mater

The first layer of the dura mater is the periosteal layer, which is adherent to bones of the skull The layers of the dura mater are the only place that has 2 layers for connective tissue; they are also 'potential spaces' in the brain Function = to stabilize the brain within the skull

Subarachnoid Space: Lumbar Cistern

There are still subarachnoid spaces at the level of the spinal cord where the dura does not adhere to the vertebrae

Prevention of Meningitis

Vaccines

Where is potential space found within the brain?

Within the dura mater; Epidural and subdural spaces are potential spaces (Potential space is found between the periosteal layer and skull, or the epidural space, as well as between the meningeal layer and arachnoid mater, the subdural space.)

Characteristics and CS&S of epidural hematoma

Younger population, up until 30s Usually from some sort of trauma (car accident, fall, contact sports) CS&S: manifestations are quick (5-30 min), act unusual. Not make sense when speaking. Movement problems, odd sensations. Quickly progress to deterioration.

Meninges (spinal cord)

all 3 meninges are present at level of spinal cord

Pia Mater

last layer of connective tissue 1 cell thick Virchow Robin space