Cranial Cavity, Dura Matter and Dural Sinuses

Question 1

The floor of the cranial cavity is divisible into three descending ‘steps’ by two sharp bony ridges on each side, which are __________________________ and __________________________.

Answer 1

the posterior free border of the lesser wing of the sphenoid (sphenoidal ridge) in front, and the sharp superior border of the petrous temporal bone (petrous ridge) behind

Question 2

These three ‘steps’ in question 1 are cranial fossae. Name them.

Answer 2

Anterior cranial fossa
Middle cranial fossa
Posterior cranial fossa

Question 3

Which bones (and their parts) comprise the floor of the anterior cranial fossa? (5)

Answer 3

• orbital plate of the frontal bone
• cribriform plate of ethmoid bone
• crista galli of ethmoid bone
• lesser wing of sphenoid bone
• anterior part of body of sphenoid bone

Question 4

REVIEW QUESTION: What passes through the foramina of cribriform plate?

Answer 4

Olfactory nerves (they are surrounded by leptomeninges i.e. pia and arachnoid matter) from the nasal mucosa to the olfactory bulb of the brain

Question 5

What bony landmark marks the junction between the anterior and middle cranial fossae?

Answer 5

Anterior clinoid process of sphenoid bone

Question 6

What bony landmarks are there in the anterior cranial fossa? (Appreciate these features with an atlas and on an actual cranial base, superior view)

Answer 6

• orbital plate of frontal bone
• frontal crest
• fronto-ethmoidal suture
• foramen cecum
• cribriform plate
• crista galli
• anterior part of the body of the sphenoid bone (jugum sphenoidale)
• sulcus chiasmaticus
• anterior clinoid process
• middle clinoid processes
• lesser wings of sphenoid bone

Question 7

QUICK REVIEW: What structure passes through foramen cecum?

Answer 7

The emissary vein from the nasal mucosa to the superior sagittal sinus

Question 8

What traverses the:
I) anterior ethmoidal foramen
II) posterior ethmoidal foramen

Answer 8

I) anterior ethmoidal neurovasculature
II) posterior ethmoidal neurovasculature

Some notes:
Anterior and posterior ethmoidal nerves are branches of the nasociliary nerve, which is in turn a branch of the ophthalmic nerve.
Anterior and posterior ethmoidal arteries are branches of ophthalmic artery.
Anterior and posterior ethmoidal veins are tributaries of ophthalmic vein.

Question 9

What is the clinical relevance of the foramen cecum?

Answer 9

Foramen cecum may transmit an emissary vein from the nasal cavity to the superior sagittal sinus and hence serve as a potential route for nasal infections to spread to the meninges of the cranial cavity.

Question 10

What is the embryonic origin of the meninges?

Answer 10

1. dura mater - mesoderm
2. arachnoid and pia mater - neural crest cells

Question 11

a) Name the two layers of the dura matter.
b) Name three meningeal spaces and where they are located.

Answer 11

1. (outer) endosteal dura and (inner) meningeal dura
2. epidural/extradural space - between skull and dura mater, subdural space - between dura mater and arachnoid mater, subarachnoid space - between arachnoid matter and pia mater

Question 12

Name four dural folds and their locations.

Answer 12

1. falx cerebri - in the median longitudinal fissure of the cerebrum
2. falx cerebelli - in the posterior cerebellar notch
3. tentorium cerebelli - in the transverse fissure
4. diaphragma sellae - it bridges the interpeduncular fossa

Notes:
- falx cerebri: between the two cerebral hemispheres
- falx cerebelli: between the two cerebellar hemispheres
- tentorium cerebelli: between cerebrum and cerebellum
- tentorium cerebelli separates the cerebellum and brainstem from the occipital lobes of the cerebrum.

Question 13

What are the functions of the dural folds?

Answer 13

1. they protect the brain
2. they limit rotational displacement of the brain
3. they minimize the effect of vibrations

Question 14

Name the bones which unite at the pterion and indicate its clinical significance.

Answer 14

1. parietal bone, squamous part of temporal bone, greater wing of sphenoid bone, frontal bone
2. It is the weakest part of the skull. The anterior division of the middle meningeal artery runs underneath the pterion. Consequently, a traumatic blow to the pterion may rupture the artery, causing an epidural hematoma. [The pterion may also be fractured indirectly by blows to the top or back of the head that place sufficient force on the skull to fracture the pterion.]

Question 15

Describe the innervation of the dura mater.

Answer 15

The supratentorial dura is supplied by the ophthalmic nerve.

The infratentorial dura is supplied by three different nerves in the three cranial fossae:
a) anterior cranial fossa: anterior and posterior ethmoidal nerves [and receives some twigs from the maxillary nerve]
b) middle cranial fossa: by the meningeal branch of the maxillary nerve (medially) and the meningeal branch of the mandibular nerve (nervus spinosus) (laterally)
c) posterior cranial fossa: meningeal branches of the vagus and hypoglossal nerves; (and) anterior rami of C1, C2 and C3 nerves [Actually, as you move down the medulla, you find that vagus nerve feeds into C1 nerve]

Dura mater around foramen magnum is directly supplied by the C2 and C3 cervical nerves - this is part of the posterior cranial fossa dura mater

Notes:
The meningeal branch of the mandibular nerve is called nervus spinosus because it passes through foramen spinosum.

Question 16

Clinical relevance of innervation of dura mater?

Answer 16

• The brain is insensitive to pain, but the cerebral dura is very sensitive, especially around the venous sinuses.
• Many headaches are of dural and/or vascular origin.
• One of the commonest presentations of meningitis is severe headache and neck stiffness.
• Irritation of C1-C2 in meningitis causes posterior neck muscles to contract causing the stiffness.

Question 17

All the venous sinuses, except the ____(a)____ and ____(b)____ sinuses, lie between the meningeal and endosteal layers of the dura mater. The sinuses have thin walls and are lined by endothelium which is continuous with that of veins. They drain blood from the brain and skull bones. The blood from dural venous sinuses is ultimately drained into ____(c)____ veins. Several of the sinuses communicate with the veins outside the skull, through ____(d)____.

Answer 17

a) inferior sagittal [and] b) straight
c) internal jugular
d) emissary veins

Question 18

What are some features of dural venous sinuses?

Answer 18

1. they lie between the layers of the dura mater
2. they have no muscle in their walls
3. lined by endothelium only (muscular coat is absent)
4. are devoid of valves in their lumen
5. receive venous blood and CSF
6. receive valveless emissary veins which regulate the blood flow and maintain the equilibrium of venous pressure within and outside the skull
7. drain blood from the brain and cranial bones

Question 19

Name the seven paired sinuses.

Answer 19

cavernous, superior petrosal, inferior petrosal, transverse, sigmoid, sphenoparietal and petrosquamous

NB: The sigmoid and transverse sinuses together are often termed lateral sinus by clinicians.

Question 20

Name the seven unpaired sinuses.

Answer 20

superior sagittal sinus, inferior sagittal, straight, occipital, anterior intercavernous, posterior intercavernous, basilar venous plexus

Question 21

Describe the blood supply of the dura mater. [Hint: It’s different in the three cranial fossae.]

Answer 21

a) anterior cranial fossa: meningeal branches of ophthalmic artery
b) middle cranial fossa: middle meningeal artery, accessory meningeal arteries
c) posterior cranial fossa: branch of occipital artery and meningeal branch of ascending pharyngeal artery, vertebral arteries

Question 22

Cavernous sinus
1. location?
2. extent?
3. structures in its lateral wall?
4. structures passing through?

Relations, communications and tributaries of the cavernous sinus have been covered in separate flashcards.

Answer 22

1. it is situated on either side of the body of the sphenoid and sella turcica in the middle cranial fossa
2. it extends from the medial end of the superior orbital fissure to the apex of the petrous temporal bone
3. (superiorly to inferiorly) oculomotor nerve, trochlear nerve, ophthalmic nerve, maxillary nerve (OTOM) [Diagram]
4. internal carotid artery surrounded by the sympathetic plexus of nerves, abducens nerve

Question 23

What are the tributaries of the cavernous sinus?

Answer 23

a) From the orbit: superior and inferior ophthalmic veins, central vein of retina (sometimes)
b) From meninges: sphenoparietal sinus, anterior trunk of middle meningeal vein
c) From brain: superficial middle cerebral vein, few inferior cerebral veins

Notes:
The central retinal vein is a vein that drains the retina of the eye. It travels backwards through the centre of the optic nerve accompanied by the central retinal artery before exiting the optic nerve together with the central retinal artery to drain into either thesuperior ophthalmic vein or thecavernous sinus.

Question 24

What are the communications of the cavernous sinus?

Answer 24

Cavernous sinus communicates with:
1. Transverse sinus via superior petrosal sinus
2. Internal jugular vein via inferior petrosal sinus
3. Pterygoid venous plexus via emissary veins which pass through foramen ovale, foramen lacerum, and emissary sphenoidal foramen
4. Facial vein via two routes:
(a) superior ophthalmic vein —> angular vein —> facial vein
(b) emissary veins —> pterygoid venous plexus —> deep facial vein —> facial vein
5. opposite cavernous sinuses via anterior and posterior intercavernous sinuses
6. superior sagittal sinus via superficial middle cerebral vein and superior anastomotic vein
7. internal vertebral venous plexus, via basilar venous plexus

Question 25

State the distributaries and bidirectional flow of the cavernous sinus.

Answer 25

DISTRIBUTARIES:
- superior petrosal sinus
- inferior petrosal sinus

BIDIRECTIONAL FLOW:
- intercavernous sinus
- emissary vein to pterygoid plexus

Question 26

What are the relations of the cavernous sinus?

Answer 26

a) superiorly: optic chiasma, optic tract, internal carotid artery, anterior perforated substance
b) inferiorly: foramen lacerum, junction of body and greater wing of sphenoid
c) anteriorly: superior orbital fissure, apex of orbit
d) posteriorly: apex of petrous temporal bone, crus cerebri of midbrain
e) laterally: temporal lobe of brain, cavum trigeminale containing trigeminal ganglion
f) medially: pituitary gland, sphenoidal air sinus

Question 27

Discuss cavernous sinus thrombosis. (Hint: cause and 3 symptoms)

Answer 27

Cause
CST involves the formation of a blood clot within the cavernous sinus. The commonest cause of thrombosis is the passage of septic emboli from the dangerous area of the face through the facial vein —> deep facial vein —> pterygoid venous plexus —> emissary vein [check Atlas!].

Symptoms
1. Severe pain in the eye and forehead due to involvement of the ophthalmic nerve
2. Ophthalmoplegia (paralysis of ocular muscles) due to involvement of the 3rd, 4th and 6th cranial nerves
3. Marked edema of eyelids with exophthalmos, due to obstruction of ophthalmic veins

Notes:
- A septic embolus is a blood clot containing bacteria that has become dislodged and travelled through the bloodstream.
- There is also aseptic cavernous sinus thrombosis, usually associated with trauma, dehydration, anemia, and other disorders.
- Exophthalmos: protrusion of the eye(s) anteriorly out of the orbit

Question 28

Discuss arteriovenous communication with respect to the cavernous sinuses (carotid-cavernous fistula). (Hint: cause and 4 symptoms)

Answer 28

Cause
If the internal carotid artery is ruptured in a fracture of the base of the skull, an arteriovenous communication/fistula is established between the artery and the cavernous sinus. Consequently, arterial blood rushes into the cavernous sinus, enlarging it and forcing blood into the connecting veins.

Symptoms
1. Pulsating exophthalmos; the eyeball protrudes and pulsates with each heartbeat
2. A loud bruit (loud systolic murmur) is easily heard over the eye
3. Ophthalmoplegia (paralysis of ocular muscles) due to involvement of the 3rd, 4th and 6th cranial nerves
4. Marked orbital and conjunctival edema due to raised venous pressure in the cavernous sinus [conjunctival edema is also called chemosis]

Notes:
Fistulas are abnormal connections between epithelial walls (between organs).

Question 29

All the dural venous sinuses lie between the meningeal and endosteal layers of the dura mater except the ________ and ________ sinuses.

Answer 29

inferior sagittal
straight

Question 30

State the location of the pituitary gland/hypophysis cerebri.

Answer 30

It is located in the hypophyseal fossa in the midline of the sphenoid body. It is found in the middle cranial fossa at the base of the skull. It is covered by diaphragma sellae.

Question 31

Which two structures drain into the straight sinus?

Answer 31

inferior sagittal sinus
Great cerebral vein of Galen
[Diagram]

Question 32

State the relations of the pituitary gland.

Answer 32

Superior
Tuber cinereum of hypothalamus, infundibulum, optic chiasma, diaphragma sellae

Inferior
sphenoidal air sinuses with thin bony plate of the hypophyseal fossa intervening

Lateral
Cavernous sinus on each side

NOTES:
optic chiasm: the part of the brain where the optic nerves cross

Question 33

Discuss arterial supply and venous drainage of the pituitary gland.

Answer 33

Arterial supply [branches of internal carotid artery]
1. Superior hypophyseal artery
2. Inferior hypophyseal artery

Venous drainage
Short veins from the pituitary gland drain into neighboring dural venous sinuses (cavernous and intercavernous sinuses)

FURTHER NOTES:
1. The pituitary gland has two subdivisions, anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis).
2. The hormones pass out of the gland through venous blood to the target sites.

Question 34

QUICK REVIEW: What are the parts of the sella turcica from anterior to posterior?

Answer 34

(1) Tuberculum sellae
(2) Hypophyseal fossa
(3) Dorsum sellae, medial to (4) Posterior clinoid process

Question 35

Which of the following is not true about the pituitary gland?
A. The gland is oval in shape
B. It is situated in the hypophyseal fossa
C. It measures 8 mm anteroposteriorly and 19 mm transversely
D. It weighs about 500 mg

Answer 35

C. It measures 8 mm anteroposteriorly and 12 mm transversely [not 19 mm transversely].

Question 36

QUICK QUESTIONS
1. Largest bony cavity in the body?
2. Deepest cranial fossa?
3. Most common site of fracture of the base of skull?
4. Longest dural venous sinus?
5. Chief source of blood supply to the skull bone?
6. Commonest tumors of the pituitary gland?
7. Rathke’s pouch?
8. Commonest cause of extradural hematoma?
9. What is Meckel’s cave?
10. Largest diploic vein?

Answer 36

1. Cranial cavity
2. Posterior
3. Middle cranial fossa
4. Superior sagittal sinus
5. Meningeal vessels
6. Adenoma arising from its chromophobe cells
7. Ectodermal diverticulum from roof of stomodeum giving rise to adenohypophysis
8. Tear of the anterior trunk of middle meningeal vein and anterior branch of middle meningeal artery
9. Pouch of the inner layer of the dura mater over trigeminal impression on the anterior surface of the petrous temporal bone containing the trigeminal ganglion
10. Occipital diploic vein

Notes:
diploic veins: these are veins located in the diploe, between the inner and outer tables of the bone of the calvarium

Question 37

What is a subdural hematoma?

Answer 37

This refers to accumulation of blood in the subdural space [the space between the dura mater and the arachnoid mater] due to injury of bridging veins as a result of head trauma.

[Bridging veins drain blood from the cerebral cortex into the dural venous sinuses.]

Question 38

What is an epidural/extradural hematoma?

Answer 38

This refers to the accumulation of blood in the epidural space [the space between inner surface of the skull and the outer layer of the dura mater] due to injury of the middle meningeal artery as a result of head trauma.

Question 39

What is subarachnoid hematoma?

Answer 39

This refers to accumulation of blood in the subarachnoid space due to injury of arteries within this space.

Question 40

What is hydrocephalus?

Answer 40

• accumulation of cerebrospinal fluid in the subarachnoid space and consequent enlargement of the head
• accumulation is usually caused by some kind of obstruction to the flow of CSF, in which case it is referred to as obstructive hydrocephalus
• common sites of obstruction: cerebral aqueduct or one of the interventricular foramina
• common causes of obstruction: tumor [pressing and hence reducing passage], cellular debris [resulting from interventricular hemorrhages and infections of the central nervous system]

Question 41

What is trigeminal cave/cavum trigeminale/Meckel’s cave? (Location to be understood too)

Answer 41

It is a pouch of dura mater containing cerebrospinal fluid.
The trigeminal cave is formed by the two layers of dura mater (endosteal and meningeal) which are part of an evagination of the cerebellar tentorium near the apex of the petrous part of the temporal bone. It envelops the trigeminal ganglion. It is bounded by the dura overlying four structures:
- cerebellar tentorium superolaterally
- lateral wall of the cavernous sinus superomedially
- clivus medially
- posterior petrous face inferolaterally

Note: The trigeminal ganglion is the sensory ganglion of each trigeminal nerve.

Question 42

List symptoms of fractures of the anterior cranial fossa. (5)

Answer 42

1. Epistaxis (bleeding from the nose)
2. CSF rhinorrhea (leakage of CSF from the nose)
3. Anosmia (partial or complete loss of the sense of smell)
4. Black eye (aka. raccoon eyes)
5. Caroticocavernous fistula

Further notes:
~ When the base of the skull is fractured, disruption of the dura can allow cerebrospinal fluid and blood to leak into the sinuses or foramina that are close to the injury. This can result in bruising around the eyes, giving the appearance of a black eye.

Question 43

List symptoms of fractures of the middle cranial fossa.

Answer 43

1. Battle’s sign (bruising or ecchymosis over the mastoid process in the line of the posterior auricular artery)
2. CSF otorrhea (leakage of CSF from subarachnoid space from the ear)
3. Hemotympanum (presence of blood in the middle ear)
4. Ossicular disruption and conductive deafness
5. CN VII and VIII nerve palsy

Notes:
ecchymosis: discoloration of the skin resulting from bleeding underneath, typically caused by bruising

Question 44

List symptoms of fractures of the posterior cranial fossa.

Answer 44

1. Leakage of blood and CSF through the mouth
2. Accumulation of blood over the nape of the neck

Notes:
Halo/double-ring sign: blood from head injury patients may mix with CSF and mask the leaking site. If the mixture is placed on filter paper there will be a central area of blood with an outer ring of halo.

Question 45

Regarding meningeal spaces, which one is normal?
A. A visible cranial epidural space on radiograph
B. Fat within the spinal epidural space
C. A true subdural space
D. Blood within the subarachnoid space
E. None of the above

Answer 45

Choice B. The spinal epidural space normally contains fat and other structures such as veins, arteries, and spinal nerve roots. This fat helps absorb shock, protecting the other contents in the area, as well as the dura mater.

Epidural and subdural spaces are potential spaces.

Question 46

Which sinus interconnects the inferior petrosal sinuses?

Answer 46

The basilar venous plexus
[Diagram]