Cranium, Ventricles and Meninges

Question 1

Cranial Vault

Answer 1

• brain encased in protective layers that cushion it from trauma
• SCALP: Skin, subcutaneous Connective tissue, galea Aponeurotica, Loose areolar connective tissue, Pericardium (periosteum)

Question 2

Fossae

Answer 2

• ridges of bone separate base of cranial cavity into compartments
• anterior fossa: frontal lobe, lesser wing of sphenoid separates from middle fossa
• middle fossa: temporal lobe, petrous ridge of temporal bone
• posterior fossa: cerebellum and brainstem

Question 3

Potential Spaces of Meninges

Answer 3

• epidural space: dura-skull interface
• subdural space: dura-arachnoid interface
• sub-arachnoid space: arachnoid-pia interface, contains CSF (protects brain, circulates throughout brain and spinal cord, helps maintain ICP) space extends to 2nd sacral segment
• spaces: layers are touching each other and should fluid get in a space will form

Question 4

Dura Mater

Answer 4

• tough, fibrous membrane
• periosteal layer: inner surface of skull (outer layer)
• meningeal layer (inner layer-divides in between hemispheres to become –> falx cerebri-interhemispheric fissure; tentorium cerebelli-horizontal shelf between inferior portion of posterior cerebrum and dorsal portion of cerebellum, midbrain passes through tentorial notch=tent over cerebellum and separates it from occipital lobe
• structures above tentorial notch=supratentorial (occipital lobe)
• structures below tentorial notch=infratentorial (cerebellum)

Question 5

Arachnoid Mater

Answer 5

• soft,translucent membrane
• separated from dura by narrow subdural space
• CSF percolates over surface of brain

Question 6

Pia Mater

Answer 6

• microscopically thin, delicate and highly vascular membrane
• adheres closely to surface of brain and into sulci and over gyri

Question 7

Epidural Space

Answer 7

• potential space between skull inner surface and dura

- middle meningeal artery enters foramen spinosum and runs in epidural space: branch of external carotid, supplies dura

Question 8

Epidural Hematomas

Answer 8

• tearing of middle meningeal artery
• causes increased ICP
• requires neurological intervention
• usually caused by head trauma or fracture to temporal bone
• lots of bleeding that’s typically faster
• biconvex shape-bleed into space that tends to stop at sutures
• usually no symptoms right away until pressure builds up –> increased volume –> increased ICP –> compression/herniation –> death

Question 9

Subdural Space

Answer 9

• between inner layer of dura and loosely adherent arachnoid
• bridging veins in here: drain cerebral hemispheres and pass blood thru dural venous sinuses, sigmoid sinuses, internal jugular veins

Question 10

Subdural Hematoma

Answer 10

• tearing of veins in subdural space as they pass from brain to venous sinus
• may be rapid or slow developing
• venous so makes it a slower bleed
• often looks like a crescent shape on CT but not as bright
• Tx: shunts

Question 11

Subarachnoid Space

Answer 11

• CSF filled space between arachnoid and pia
• major arteries of brain travel within this space (ACA, MCA, PCA)
• actual space

Question 12

Subarachnoid Hematoma

Answer 12

• sub-arachnoid hemorrhage into space often due to saccular (berry) aneurysms…sub-arachnoid HA
• most common in circle of willis (ant communicating and posterior communicating branches)
• diffuse bleeding thinner and ruptures over larger area because it’s an actual space

Question 13

Intracerebral Hematoma

Answer 13

-bleeding in brain as a result of trauma, contusion, and/or tearing

Question 14

Meningitis

Answer 14

• viral or bacterial
• viral=normally mild
• bacterial=more serious, may lead to damage of brain and cranial nerves
• headache, photophobia, and vomiting
• febrile, purulent
• neck stiffness
• may cause death due to increased ICP and brain displacement

Question 15

Ventricular System

Answer 15

• neural tube forms cavities within brain called ventricles
• contain CSF which is produced by choroid plexus inside the ventricles
• brain=elaborate interconnecting ventricular system
• lateral ventricles (one inside each hemisphere)
• 3rd ventricle (diencephalon)
• 4th ventricle (surrounded by pons, medulla, and cerebellum)
• spinal cord-central canal
• brain folds around neural tube when developing and space left behind becomes the ventricles

Question 16

Lateral Ventricles

Answer 16

• also called 1st and 2nd
• have extensions or horns that extend in direction where they’re located
• interventricularforamen of monro
• large, C-shaped, located within cerebrum: anterior horn (frontal) begin anterior to foramen of monro, body, posterior horn (occipital), inferior horn (temporal)
• extends into each of the lobes

Question 17

3rd Ventricle

Answer 17

• diencephalon (thalamus and hypothalamus form walls)
• interventricular foramen (foramen of monro)
• cerebral aqueduct-communicates to 4th ventricle and travels through midbrain

Question 18

4th ventricle

Answer 18

• dorsal surface of brain stem just anterior to cerebellum
• roof of 4th formed by cerebellum and floor by pons and medulla
• cerebral aqueduct (junction to 4th ventricle)
• drained by medial opening=foramen of magendie and laterally there are two foramen of luschka
• these then drain into subarachnoid space
• lateral canal of spinal cord is open in embryos but is close din adults

Question 19

CSF

Answer 19

• produced by choroid plexus: located in lateral, 3rd and 4th ventricles
• colorless fluid with little protein or cells
• 150 cc (produced continuously, enough to fill ventricles several times a day
• about 500 cc/day is produced

Question 20

Circulation of CSF

Answer 20

• lateral ventricles then through interventricular foramen to 3rd ventricle
• 3rd ventricle then through cerebral aqueduct to 4th ventricle
• 4th ventricle to subarachnoid space
• CSF leaves ventricular system through foramina in 4th ventricle
• percolates around brain
• reabsorbed by arachnoid granulations
• into dural sinuses
• back to bloodstream

Question 21

CSF Examination

Answer 21

• usually obtained from lumbar subarachnoid space via spinal tap
• usually L34 or L45 interspaces
• indications…
• suspected infection
• diagnosis of subarachnoid hemorrhage
• chemical and immunologic profiles to aid in diagnosis of disorders
• cytologic examination when carcinomatous meningitis is suspected
• manometric pressure

Question 22

Hydrocephalus

Answer 22

• buildup of fluid in cavities (ventricles) deep within brain
• excess fluid increases size of ventricles and puts pressure on brain
• can occur at any age but is common among infants and older adults
• surgical treatment can restore and maintain normal CSF levels in brain
• variety of interventions often required to manage symptoms or functional impairments resulting from hydrocephalus

Question 23

Blood Brain Barrier

Answer 23

• capillary walls of endothelial cells in most of body separated by fenestrations allowing free passage of fluids and molecules
• in brain the capillary endothelial cells linked by tight junctions
• substances leaving or entering brain must travel through endothelial cells via cellular transport
• protects brain from chemical fluctuations in body
• barbiturates can enter; HTN can also cause junctions to be looser and less effective

Question 24

Blood-CSF Barrier

Answer 24

• similar to blood brain barrier
• between choroid plexus and CSF
• capillaries of choroid plexus are permeable but choroid epithelial cells form a barrier between blood and CSF

Question 25

Disruptions to Blood Brain Barrier

Answer 25

• brain tumors
• infections
• trauma
• HTN
• can allow fluids into interstitial space
• in certain brain regions called circumventricular organs, BBB is disrupted to allow brain to respond to changes in chemistry and secrete modulatory neuropeptides into bloodstream

Question 26

Elevated ICP

Answer 26

• contents of intercranial space are confined: blood, brain, CSF
• when there is a space-occupying mass, something must leave skull to accommodate
• smaller lesions can be accommodated but larger ones will cause ICP to rise leading to herniation and death of tissues

Question 27

Symptoms of Elevated ICF

Answer 27

• headache
• altered mental status
• nausea and vomiting
• papilledema (engorgement and elevation of optic disc)
• visual loss
• diplopia
• cushing’s triad: HTN, bradycardia, and irregular respirations –> pressing on brainstem

Question 28

Brain Herniations

Answer 28

-mass effect severe enough to push structures from one area to another

Question 29

Head Trauma

Answer 29

• concussion-reversible impairment of neurologic function for a period of hours or minutes following head injury
• CT and MRI are normal
• clinical features…
• LOC
• “seeing stars”
• headache
• dizziness
• nausea
• vomiting
• can lead to increased ICP

Question 30

Corticomedullary Junction

Answer 30

• where spinal cord meats brainstem at medulla

- happens at the foramen magnum of skull

Question 31

Meningioma

Answer 31

• tumor in meninges or space between meninges

- compressesnervous tissues and may cause a shift in them toward midline

Question 32

CSF Cistern in Subarachnoid Space

Answer 32

• CSF collection sites
• where arachnoid space widens to hold CSF
• Prepontine cistern: in front of pons
• cisterna magna: largest and below cerebellum
• lumbar cistern: where cauda equina is; lumbar punctures happen here

Question 33

Circumventricular Organs

Answer 33

• organum vasculosum: keeps fluid balance
• neurohypophysis: maintains blood and releases hormones
• pineal: use of melatonin for sleep
• area postrema: vomiting center-detects toxins and expels them