ICL 12.3: Imaging Skull Based Pathologies

Question 1

what is an olfactory neuroblastoma?

Answer 1

formerly known as esthesioneuroblastoma

it’s a soft tissue mass in the superior olfactory recess and middle ethmoid air cells that extends through the cribriform plate and effects CN I

it arises from epithelium in the superior recess of the nasal cavity and is a really aggressive tumor so it starts to grow through the bone and involves the anterior fossa, then grows through the cribriform plate into the nasal cavity and perinatal sinuses –> it destroys and erodes the cribriform plate and then sits in the nasal cavity (can even grow into the orbital cavity)

bimodal age distribution = 2nd decade and 5-6th decade

Question 2

what is a sinonasal undifferentiated carcinoma?

Answer 2

a tumor that arises from mucosa of paranasal sinuses and effects CN I – most commonly from ethmoid sinuses and superior nasal cavity

aggressive

nearly impossible to differentiate by imaging from the olfactory neuroblastoma because it starts in the nasal cavity and then grows up through the cribriform plate and erodes it

Question 3

what is an olfactory groove meningioma?

Answer 3

an enhancing tumor along the dura in the olfactory grooves bilaterally that effects CN I–> meningioma grows out of the dura in the olfactory groove and then they expand up

WHO grade I so their benign! the worst they can do is cause a mass effect which could cause seizures but you can just take them out and they usually DON’T invade the bone (sometimes they can though)

patients frequently present with anosmia because they grow where CN I is

Question 4

which tumors effect CN 1?

Answer 4

1. olfactory neuroblastoma (malignant)
2. sinonasal undifferentiated carcinoma (malignant)
3. olfactory groove meningioma (benign)

Question 5

what is the most common type of tumor to effect CN II?

Answer 5

optic nerve glioma

usually in children

Question 6

what condition are optic nerve gliomas highly associated with?

Answer 6

neurofibromatosis type 1

so if someone has an optic nerve glioma you need to check if there’s other tumors that could be caused from NF1 and also do genetic testing to see if they have NF1

Question 7

which visual field would be effected by something compressing the optic chiasm?

Answer 7

temporal visual fields of each eye!

that’s because the medial retinal fibers cross over through the chiasm which the temporal retinal fibers do not (the medial retina is responsible for temporal field of vision and vice versa with the medial retina)

Question 8

what is Tolosa-Hunt syndrome?

Answer 8

infiltration of lymphocytes and plasma cells, with thickening of the dura mater within the cavernous sinus that effects CN II

since it’s inflammatory you treat it with steroids and then it’ll usually go away

patients will present with painful opthalmoplegia

can present with cranial nerve symptoms other than CN II due to involvement of the cavernous sinus –> CN 3, 4, 5 and 6 all go through the cavernous sinus!

Question 9

what is a pituitary macroadenoma?

Answer 9

a tumor of the pituitary gland that arises in the sella turcica

it then grows through the diaphragmata sellae and pushes on the optic chiasm

they’re commonly benign and non-hormone secreting

Question 10

what is the most common clinical presentation of a pituitary macroadenoma?

Answer 10

bitemporal hemianopsia is most common presentation because you’re compressing on the optic chiasm

so both eyes will have poor peripheral vision

Question 11

what happens if a pituitary macro adenoma is hormone-secreting?

Answer 11

acromegaly aka you’re giant because the pituitary will secrete a lot of growth hormone

your bones increase in size, including those of your hands, feet and face with dysmorphic facial features

can cause heart problems and diabetes

Question 12

which tumors can effect CN II?

Answer 12

1. optic nerve glioma1
2. Tolosa-Hunt syndrome
3. pituitary macroadenoma

Question 13

what’s important about the location of CN 3?

Answer 13

it’s in the cavernous sinus right next to the internal carotid artery

the ICA passes medial to CN 3, 6, 4 and 5 but the closes things to it are CN 3 and 6 so an ICA aneurysm that projects into the cavernous sinus will really hurt CN 3 and 6 (if it gets really big, it can effect the other nerves too)

so if you see isolated CN 3 pathology, your differential isn’t complete till you include an ICA aneurysm!

Question 14

what does a CN 3 palsy present as clinically?

Answer 14

eyes will be down and out because SO and LR which are innervated by CN 4 and CN 6, respectively, will be left unopposed

Question 15

which CN can get a schwanoma?

Answer 15

all of them except CN 1 and 2 because they’re myelinated by oligodendrocytes!

Question 16

which tumors can effect CN 3?

Answer 16

1. internal carotid artery cavernous aneurysm
2. oculomotor schwanoma
3. pituitary macroadenoma

even though these effect CN 2 first, they can invade through bony structures to the cavernous sinus where they cause CN 3, 4, 5 and 6 too (CN 3 and 6 effected first)

Question 17

why is a PE so important to do before you order imaging?

Answer 17

because that way the radiologist can look specifically at certain parts of the brain and they don’t waste their time someone else!

also sometimes there’s special imaging they can do that will get specific stuff to show up

Question 18

what is vascular nerve compression and which CN does it usually effect?

Answer 18

CN 5 –> compression of the trigeminal nerve by the basilar artery or the SCA/AICA at the root entry zone = the transition between central and peripheral myelin

compression can cause focal demyelination of CN 5 which causes trigeminal neuralgia

the superior cerebellar artery frequently passes too close to the trigeminal nerve as it exits the brainstem and causes compression – patients present with pain in the trigeminal nerve sensory distribution over the ipsilateral face

surgeons can go in and put a cotton pad between the blood vessel and CN 5 so that when the vessel pulses it doesn’t compress CN 5 so much

Question 19

which CN run in the cavernous sinus?

Answer 19

3, 4 and 6 run inside

V1 and V2 run on the wall of the cavernous sinus

Question 20

what injury often effects V2?

Answer 20

orbital blowout fracture

when you get punched in the face and break the bottom of your orbit, you effect V2

Question 21

what injury often effects V3?

Answer 21

jaw fractures

V3 (inferior alveolar nerve specifically) travels through mandibular canal

you can also have lingual nerve damage from squamous cell carcinomas of the mouth which love to grow along the nerves and use it infiltrate other parts of the body like the skull or the internal auditory canal via the greater superficial petrosal nerve

Question 22

what types of tumors most often effect CN 7 and 8?

Answer 22

1. meningioma (most common)
2. schwannoma - can be of the facial, vestibular or cochlear nerves
3. intracranial spread of head and neck cancer (involves mostly CN 7; especially squamous cell carcinomas that can either directly grow on CN 7 or they can hop of CN 5 and cross over via the greater petrosal nerve over to CN 7

Question 23

which nerves exit the skull through the jugular foramen?

Answer 23

CN 9, 10 and 11

they run together along the jugular vein

so any lesion in the jugular foramen or along the jugular vein will effect all 3 of these nerves!

Question 24

what tumor is most likely to effect the jugular formate?

Answer 24

paraganglioma; specifically a glomus jugular –> grows right in the jugular foramen until it fills up

so it will effect CN 9, 10, and 11 which all pass through it!

if it happens lower down then it’s called a glomus vagale because it most often grows off CN 10 inside the carotid space but they can get really big and still effect all 3 nerves

Question 25

what conditions could cause isolated CN 10 injury?

Answer 25

1. thyroidectomy
2. carotid endarterectomy
3. anterior spinal fusion because you have to go past carotid sheath

check all the way down to the aortic arch where the recurrent laryngeal nerve passes! especially if they have a hoarse voice

Question 26

what is the foramen lacerum predominantly made of? what kind of tumor can you get there?

Answer 26

it’s mostly made of cartilage!!!

so you can get a chondrosarcoma there! it can then invade and destroy the skull base and destroys the other CN that pass through the skull base in order of proximity to the foramen lacerum

Question 27

how do you know if there is a CN 12 schwanoma?

Answer 27

their tongue sticks out towards the side of injury!

muscle will also atrophy and the tongue becomes fatty