Cranial Meninges

Question 1

Pia Mater

Answer 1

areolar C.t. directly applied to the surface ofthe brain

follows contours of brain and invests its vessels; not dissectible

Question 2

Arachnoid mater

Answer 2

Somewhat more dense c.t. layer than pia (increase in elastic and collagen fibers)

Trebeculated on deep surface between arachnoid and pia; forms SUBARACHNOID SPACE (contains CSF and cerebral arteries & veins)

Covers brain but does not dip into sulci (except for longitudinal fissure)

Spans space between contours of brain to form cisterns (areas of accumulated CSF)

NOTE: CSF is formed by choroid plexus (modified capillary tuft located in ventricles of the brain) and circulates through ventricular channels to the fourth ventricle where openings communicate with the sub-arachnoid space. CSF is reabsorbed superiorly into the superior sagittal sinus via the ARACHNOID GRANULATIONS

Question 3

Dura Mater

Answer 3

Dense fibrous c.t. layer enclosing brain; continuous with spinal dura at foramen magnum.

Periosteal layer- periosteum of cranial vault adherent to meningeal dura

Meningeal layer- duplications of dura which are prolonged between major portions of the brain; form dural reflections

Prolonged along cranial nerves (will eventually fuse with neural sheaths)

Question 4

Dural reflections

Answer 4

Falx cerebri
Tentorium cerebelli
Falx cerebelli
Diaphragma sellae

Question 5

Falx cerebri

Answer 5

midline sickle-shaped extension of dura between cerebral hemispheres

Atttached anteriorly to crista galli of ethmoid bone

Follows conour of sagittal suture posteriorly to the internal occipital protuberance to becomem continuous with the TENTORIUM CEREBELLI

Superior sagittal sinus lies within its convex attachment (superior margin); inferior sagittal sinus lies within its concave free border (inferior margin)

Question 6

Tentorium cerebelli

Answer 6

forms a tent over the posterior cranial fossa; separates cerebellum from posterior portions of cerebral hemispheres

Attached along its periphery to the occipital bone at grooves for the transverse sinus (which it encloses) and to the petrous ridge where it encloses the SUPERIOR PETROSAL SINUS

Attached anteriorly to anterior and posterior clinoid processes of the sphenoid bone.

Tentorial notch- free anterior concave margin of tentorium which wraps around the midbrain

NOTE- the tentorial notch can transect the midbrain during rapid deceleration.

Site of fusion of falx cerebri to tentorium; contains straight sinus.

Question 7

Falx cerebelli

Answer 7

extension of dura between cerebellar hemispheres
extends from the tentorium above to the occipital crest below
contains the occipital sinus

Question 8

Diaphragma sellae

Answer 8

specialized portion of dura which forms a roof over the hypohphyseal fossa

Question 9

Dural Venous Sinuses

Answer 9

Endothelial lined spaces between opposed layers of dura.
Collect blood and CSF
system has NO valves
Flow of all sinuses is ultimately to the INTERNAL JUGULAR VEIN

Question 10

Dural venous sinuses drain blood from where?

Answer 10

Brain via bridging veins
Meninges
diploe (highly vascular layer between inner and outer tables of the calvaria)
Vertebral column (vertebral venous plexus)
emissary veins (veins which communicate between the dural sinuses and the veins of the scalp or diploe) which receive blood directly from the:
- face
- orbit
- nasal cavity
- parietal
- mastoid
- occiput

Question 11

Clinical note re: bridging veins

Answer 11

Shaking a baby ruptures the veins that bridge the gap between the cerebral hemisphere and dural venous sinuses filling the subarachnoid space resulting in death (Shaken Baby syndrome)

Question 12

Superior Sagittal Sinus

Answer 12

located in the superior margin of the falx cerebri

Begins anteriorly at the foramen cecum (transmits emissary vein from the nasal cavity; variable and not always patent)

Ends at confluens of sinuses.

In its course, receives emissary veins, cerebral veins, meningeal veins, diploic veins, and CSF via arachnoid granulations which protrude into the venus at venous lacunae

Question 13

Inferior Sagittal Sinus

Answer 13

located in the inferior concave margin of the falx cerebri

Receives cerebral and meningeal veins

Ends at the straight sinus

Question 14

Straight sinus

Answer 14

located at the junction of the falx cerebri and the tentorium cerebelli

receives the inferior sagittal sinus and great cerebral vein (GALEN) - drains the core of the cerebrum

Opens posteriorly at the confluence of sinuses when present (30-40%)

Question 15

Transverse Sinus

Answer 15

Bilateral continuations of the superior sagittal and straight sinuses; normally, the superior sagittal sinus forms the right transverse sinus while the straight sinus forms the left transverse sinus

occupies the perimeter of the tentorium to a point just short of the petrous portion of the temporal bone

Continuous with the sigoid sinus

Question 16

Sigmoid sinus

Answer 16

Named for its S shape; located on teh internal surface of the temporal bone posterior to the petrous ridge

becomes confluent with the jugular bulb at the jugular foramen

receives the superior petrosal sinus at its juncture with the transverse sinus

receives the inferior petrosal sinus at its juncture with the jugular bulb

Question 17

Occipital sinus

Answer 17

located in falx cerebelli

Surrounds foramen magnum as the marginal sinus to communicate with teh basilar sinus

Opens superiorly at confluens

Question 18

Confluens of sinuses

Answer 18

exists approximately 30-40%; point of juncture of superior sagittal, straight, transverse and occipital sinuses

Question 19

Sphenoparietal Sinus

Answer 19

Located bilaterally between opposed layers of dura along the posterior edge of the lesser wing of the sphenoid bone

drains dura to the cavernous sinus