SGW - cranial nerves

Question 1

where do the branches of the trigeminal nerve exit the skull?

Answer 1

V1: ophthalmic - SOF into orbit (sensory to cornea)
V2: maxillary - foramen rotundum into ptergopalatine fossa (sensory to soft palate)
V3: mandibular - foramen ovale into infratemporal fossa (sensory + motor)

Question 2

which cranial nerves pass into orbit?

Answer 2

CN II (optic canal), III, IV, Va, VI (SOF)
(cavernous sinus has Vb as well)

Question 3

where is the pituitary gland found?

Answer 3

within hypophyseal fossa (deepest part of sella turcica within middle cranial fossa)

Question 4

which anatomical structures lies in close proximity to the pituitary gland?

Answer 4

superior: hypothalamus
anterosuperior: optic chiasm (of optic nerve) just above pituitary gland, in front of infundibulum (pituitary stalk)

Question 5

what is the optic chiasm?

Answer 5

area where a proportion of the optic nerves from either retina cross over to contralateral (opposite) side before continuing posteriorly as the optic tracts
optic nerve –> optic chiasm –> optic tract

Question 6

what can pathology affecting the pituitary gland cause? example?

Answer 6

e.g. pituitary adenoma

can cause visual symptoms due to close anatomical relationship with optic chiasm

Question 7

what is the cavernous sinus?

Answer 7

a type of dural venous sinus

Question 8

what is a dural venous sinus?

Answer 8

a ‘space’ created when the INNER most layer of the dura (meningeal layer) leaves the periosteal layer (adhered to bone) of the dura
creating a endothelial lined channel between the 2

Question 9

what are the walls of cavernous sinus?

Answer 9

folds of dura

Question 10

how many cavernous sinuses are there?

Answer 10

2: one on either side of the sella turcica

Question 11

what forms the floor of the cavernous sinuses?

Answer 11

sphenoid and part of temporal bone

Question 12

where is the pituitary gland in relation to the cavernous sinus?

Answer 12

hangs between the 2 cavernous sinus by its stalk

Question 13

what is the space within cavernous sinus split up by? what does it contain?

Answer 13

multiple fibrous sepa

containing a large plexus of veins

Question 14

where does the venous plexus of cavernous sinus receive its veinous drainage from?

Answer 14

anteriorly: superior and inferior orbital veins
posterior: receives some minor venous sinuses draining the brain

Question 15

what are the 2 cavernous sinuses joined by?

Answer 15

joined around and beneath the pituitary gland via intercavernous sinuses

Question 16

what do dural venous sinuses e.g. cavernous sinus contain?

Answer 16

a venous plexus, internal carotid artery and cranial nerves

between meningeal and periosteal layers of dura, periosteal remains adhered to the skull

Question 17

where is the cavernous sinus in relation to other structures?

Answer 17

overlying foramen lacerum (cartilage)
lateral to sella turcica (both sides)
medial to foramen rotundum, ovale and spinosum (MMA from ECA –> maxillary)

Question 18

where does the cavernous sinus extend?

Answer 18

anteriorly: SOF
posterior: apex of petrous bone

Question 19

which structures / CN passes through cavernous sinus?

Answer 19

middle of sinus:
ICA (and associated sympathetic plexus - ciliary + pterygopalatine)
abducens (CN VI) - close to ICA

lateral wall of sinus: CN III, IV, V1, V2

Question 20

where does mandibular branch of the trigeminal run?

Answer 20

foramen ovale
angle of mandible
along body of mandible (innervating mandible teeth and gums on the ipsilateral side), gives off mental nerve (sensory to lower lip, chin)

Question 21

what is cavernous sinus thrombosis?

Answer 21

venous blood clot within cavernous sinus

Question 22

when can cavernous sinus thrombosis occur? what can it affect?

Answer 22

be a late complication of an infection - affecting:
central part of the face (danger triangle)
orbits
paranasal sinuses
maxillary teeth

Question 23

what can infection in the affected areas from cavernous sinus thrombosis cause?

Answer 23

septic emboli
which can travel to cavernous sinus due to its many anastomotic links with veins draining these areas
e.g. veins draining face + orbit (facial vein, superior and inferior ophthalmic veins)

Question 24

where can blood flow from cavernous sinus?

Answer 24

either directions (without valves), so depends on pressure gradients

Question 25

what is cavernous sinus thrombosis associated with?

Answer 25

high morbidity and mortality

Question 26

what will venous blockage within cavernous sinus (e.g. from septic emboli / thrombosis) result in?

Answer 26

impede venous drainage from the orbit, eye and central face | causing VENOUS CONGESTION

Question 27

what can venous congestion secondary to venous blockage within cavernous sinus lead to?

Answer 27

tissue oedema around the orbit, conjunctiva and central face | also in the tissues behind the eyeball, causing exophthalmos

Question 28

what can increased pressure within cavernous sinus lead to (from venous congestion secondary to venous blockage e.g. facial / superior + inferior ophthalmic veins)?

Answer 28

space (cavernous sinus) is relatively fixed | any increased pressure within cavernous sinus will start to compress structures that travel within the cavernous sinus

Question 29

what are the structures at risk of being compressed in increased pressure within cavernous sinus?

Answer 29

``` oculomotor (CN III) - runs in lateral wall of cavernous sinus parasympathetic fibres (ciliary ganglion) - running on outside of oculomotor nerve - leading to compression of autonomic fibres BEFORE nerve --> unreactive, dilated pupils (loss of tone to sphincter pupillae muscle) ```

Question 30

if a patient presented with unilateral cavernous sinus thrombosis, why might the patient still develop signs on both sides of their face and orbit?

Answer 30

the 2 cavernous sinuses are linked via the intercavernous sinus and there are rick anastomoses between the veins

Question 31

what are pathologies which may increase pressure within cavernous sinus?

Answer 31

e.g. internal carotid aneurysm tumour metastases

Question 32

what are signs of horner's syndrome?

Answer 32

loss of sympathetic tone: partial ptosis (superior tarsal muscle) anhydrosis on ipsilateral side (decreased sweating from glands of face) Miosis: constricted pupil (dilator pupillae not innervated, so unopposed action of sphincter pupillae) Enophthalmos: sinking of eyeball (can be from ptosis - squashing eyeball, but only mild)

Question 33

what is special about CN I + II?

Answer 33

paired extensions of the CNS (forebrain) | contains meninges and CSF

Question 34

what is special about the (spinal) accessory nerve?

Answer 34

has a spinal and cranial root | (arise C1-C6 --> foramen magnum to enter skull) - vertebral arteries also through foramen magnum

Question 35

how do you test the accessory nerve?

Answer 35

ask patient to shrug shoulders testing actions of SCM and trapezius innervated by SPINAL accessory nerve - only testing spinal part, not accessory

Question 36

where do the 12 cranial nerves arise?

Answer 36

``` 2,2,4,4, 1,2: forebrain 3,4: midbrain 5,6,7,8: pons 9,10,12: medulla 11: C1-C6 ```

Question 37

where do the CN exit the skull?

Answer 37

olfactory: cribriform plate (ethmoidal bone) optic: optic canal 3,4,5a,6: SOF 5b: foramen rotundum 5c: foramen ovale 7,8: IAM 9,10,11: jugular foramen 11: FORAMEN MAGNUM (enters skull)--> jugular foramen (exits skull) 12: hypoglossal canal