SGW - cranial nerves Flashcards

1
Q

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

A

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)

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2
Q

which cranial nerves pass into orbit?

A
CN II (optic canal), III, IV, Va, VI (SOF)
(cavernous sinus has Vb as well)
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3
Q

where is the pituitary gland found?

A

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

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4
Q

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

A

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

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5
Q

what is the optic chiasm?

A

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

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6
Q

what can pathology affecting the pituitary gland cause? example?

A

e.g. pituitary adenoma

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

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7
Q

what is the cavernous sinus?

A

a type of dural venous sinus

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8
Q

what is a dural venous sinus?

A

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

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9
Q

what are the walls of cavernous sinus?

A

folds of dura

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10
Q

how many cavernous sinuses are there?

A

2: one on either side of the sella turcica

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11
Q

what forms the floor of the cavernous sinuses?

A

sphenoid and part of temporal bone

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12
Q

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

A

hangs between the 2 cavernous sinus by its stalk

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13
Q

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

A

multiple fibrous sepa

containing a large plexus of veins

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14
Q

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

A

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

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15
Q

what are the 2 cavernous sinuses joined by?

A

joined around and beneath the pituitary gland via intercavernous sinuses

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16
Q

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

A

a venous plexus, internal carotid artery and cranial nerves

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

17
Q

where is the cavernous sinus in relation to other structures?

A

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

18
Q

where does the cavernous sinus extend?

A

anteriorly: SOF
posterior: apex of petrous bone

19
Q

which structures / CN passes through cavernous sinus?

A

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

20
Q

where does mandibular branch of the trigeminal run?

A

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)

21
Q

what is cavernous sinus thrombosis?

A

venous blood clot within cavernous sinus

22
Q

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

A

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

23
Q

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

A

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)

24
Q

where can blood flow from cavernous sinus?

A

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

25
Q

what is cavernous sinus thrombosis associated with?

A

high morbidity and mortality

26
Q

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

A

impede venous drainage from the orbit, eye and central face

causing VENOUS CONGESTION

27
Q

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

A

tissue oedema around the orbit, conjunctiva and central face

also in the tissues behind the eyeball, causing exophthalmos

28
Q

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

A

space (cavernous sinus) is relatively fixed

any increased pressure within cavernous sinus will start to compress structures that travel within the cavernous sinus

29
Q

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

A
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)
30
Q

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

A

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

31
Q

what are pathologies which may increase pressure within cavernous sinus?

A

e.g. internal carotid aneurysm
tumour
metastases

32
Q

what are signs of horner’s syndrome?

A

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)

33
Q

what is special about CN I + II?

A

paired extensions of the CNS (forebrain)

contains meninges and CSF

34
Q

what is special about the (spinal) accessory nerve?

A

has a spinal and cranial root

(arise C1-C6 –> foramen magnum to enter skull) - vertebral arteries also through foramen magnum

35
Q

how do you test the accessory nerve?

A

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

36
Q

where do the 12 cranial nerves arise?

A
2,2,4,4,
1,2: forebrain
3,4: midbrain
5,6,7,8: pons
9,10,12: medulla
11: C1-C6
37
Q

where do the CN exit the skull?

A

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