ICL 12.3: Imaging Skull Based Pathologies Flashcards
what is an olfactory neuroblastoma?
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
what is a sinonasal undifferentiated carcinoma?
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
what is an olfactory groove meningioma?
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
which tumors effect CN 1?
- olfactory neuroblastoma (malignant)
- sinonasal undifferentiated carcinoma (malignant)
- olfactory groove meningioma (benign)
what is the most common type of tumor to effect CN II?
optic nerve glioma
usually in children
what condition are optic nerve gliomas highly associated with?
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
which visual field would be effected by something compressing the optic chiasm?
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)
what is Tolosa-Hunt syndrome?
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!
what is a pituitary macroadenoma?
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
what is the most common clinical presentation of a pituitary macroadenoma?
bitemporal hemianopsia is most common presentation because you’re compressing on the optic chiasm
so both eyes will have poor peripheral vision
what happens if a pituitary macro adenoma is hormone-secreting?
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
which tumors can effect CN II?
- optic nerve glioma1
- Tolosa-Hunt syndrome
- pituitary macroadenoma
what’s important about the location of CN 3?
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!
what does a CN 3 palsy present as clinically?
eyes will be down and out because SO and LR which are innervated by CN 4 and CN 6, respectively, will be left unopposed
which CN can get a schwanoma?
all of them except CN 1 and 2 because they’re myelinated by oligodendrocytes!
which tumors can effect CN 3?
- internal carotid artery cavernous aneurysm
- oculomotor schwanoma
- 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)
why is a PE so important to do before you order imaging?
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
what is vascular nerve compression and which CN does it usually effect?
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
which CN run in the cavernous sinus?
3, 4 and 6 run inside
V1 and V2 run on the wall of the cavernous sinus
what injury often effects V2?
orbital blowout fracture
when you get punched in the face and break the bottom of your orbit, you effect V2
what injury often effects V3?
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
what types of tumors most often effect CN 7 and 8?
- meningioma (most common)
- schwannoma - can be of the facial, vestibular or cochlear nerves
- 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
which nerves exit the skull through the jugular foramen?
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!
what tumor is most likely to effect the jugular formate?
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
what conditions could cause isolated CN 10 injury?
- thyroidectomy
- carotid endarterectomy
- 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
what is the foramen lacerum predominantly made of? what kind of tumor can you get there?
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
how do you know if there is a CN 12 schwanoma?
their tongue sticks out towards the side of injury!
muscle will also atrophy and the tongue becomes fatty
