SGW - cranial nerves Flashcards
where do the branches of the trigeminal nerve exit the skull?
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)
which cranial nerves pass into orbit?
CN II (optic canal), III, IV, Va, VI (SOF) (cavernous sinus has Vb as well)
where is the pituitary gland found?
within hypophyseal fossa (deepest part of sella turcica within middle cranial fossa)
which anatomical structures lies in close proximity to the pituitary gland?
superior: hypothalamus
anterosuperior: optic chiasm (of optic nerve) just above pituitary gland, in front of infundibulum (pituitary stalk)
what is the optic chiasm?
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
what can pathology affecting the pituitary gland cause? example?
e.g. pituitary adenoma
can cause visual symptoms due to close anatomical relationship with optic chiasm
what is the cavernous sinus?
a type of dural venous sinus
what is a dural venous sinus?
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
what are the walls of cavernous sinus?
folds of dura
how many cavernous sinuses are there?
2: one on either side of the sella turcica
what forms the floor of the cavernous sinuses?
sphenoid and part of temporal bone
where is the pituitary gland in relation to the cavernous sinus?
hangs between the 2 cavernous sinus by its stalk
what is the space within cavernous sinus split up by? what does it contain?
multiple fibrous sepa
containing a large plexus of veins
where does the venous plexus of cavernous sinus receive its veinous drainage from?
anteriorly: superior and inferior orbital veins
posterior: receives some minor venous sinuses draining the brain
what are the 2 cavernous sinuses joined by?
joined around and beneath the pituitary gland via intercavernous sinuses
what do dural venous sinuses e.g. cavernous sinus contain?
a venous plexus, internal carotid artery and cranial nerves
between meningeal and periosteal layers of dura, periosteal remains adhered to the skull
where is the cavernous sinus in relation to other structures?
overlying foramen lacerum (cartilage)
lateral to sella turcica (both sides)
medial to foramen rotundum, ovale and spinosum (MMA from ECA –> maxillary)
where does the cavernous sinus extend?
anteriorly: SOF
posterior: apex of petrous bone
which structures / CN passes through cavernous sinus?
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
where does mandibular branch of the trigeminal run?
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)
what is cavernous sinus thrombosis?
venous blood clot within cavernous sinus
when can cavernous sinus thrombosis occur? what can it affect?
be a late complication of an infection - affecting:
central part of the face (danger triangle)
orbits
paranasal sinuses
maxillary teeth
what can infection in the affected areas from cavernous sinus thrombosis cause?
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)
where can blood flow from cavernous sinus?
either directions (without valves), so depends on pressure gradients
what is cavernous sinus thrombosis associated with?
high morbidity and mortality
what will venous blockage within cavernous sinus (e.g. from septic emboli / thrombosis) result in?
impede venous drainage from the orbit, eye and central face
causing VENOUS CONGESTION
what can venous congestion secondary to venous blockage within cavernous sinus lead to?
tissue oedema around the orbit, conjunctiva and central face
also in the tissues behind the eyeball, causing exophthalmos
what can increased pressure within cavernous sinus lead to (from venous congestion secondary to venous blockage e.g. facial / superior + inferior ophthalmic veins)?
space (cavernous sinus) is relatively fixed
any increased pressure within cavernous sinus will start to compress structures that travel within the cavernous sinus
what are the structures at risk of being compressed in increased pressure within cavernous sinus?
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)
if a patient presented with unilateral cavernous sinus thrombosis, why might the patient still develop signs on both sides of their face and orbit?
the 2 cavernous sinuses are linked via the intercavernous sinus and there are rick anastomoses between the veins
what are pathologies which may increase pressure within cavernous sinus?
e.g. internal carotid aneurysm
tumour
metastases
what are signs of horner’s syndrome?
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)
what is special about CN I + II?
paired extensions of the CNS (forebrain)
contains meninges and CSF
what is special about the (spinal) accessory nerve?
has a spinal and cranial root
(arise C1-C6 –> foramen magnum to enter skull) - vertebral arteries also through foramen magnum
how do you test the accessory nerve?
ask patient to shrug shoulders
testing actions of SCM and trapezius
innervated by SPINAL accessory nerve - only testing spinal part, not accessory
where do the 12 cranial nerves arise?
2,2,4,4, 1,2: forebrain 3,4: midbrain 5,6,7,8: pons 9,10,12: medulla 11: C1-C6
where do the CN exit the skull?
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
