hello everybody and welcome back to another radiology tutorial today we're going to be discussing the skull base foramina now i know this is a topic that many people find confusing and difficult to understand so i'm going to go through each foramen systematically one by one showing you exactly what they look like on a ct scan how you yourself can identify them on the scan as well as mention some of the structures that pass through these foramina now the way i want to do it today is by following the cranial nerve starting your cranial nerve one working our way down to cranial nerve 12 and then discussing some of the other foramina that don't have cranial nerves passing through them so let's start with cranial nerve one our olfactory nerve we can see here on this axial bone windowed ct we're at the level of the skull base and cranial nerve one is further up and that's superior to that so we want to scroll superiorly let's start by looking at the frontal bone here with our frontal sinus and then work our way slowly inferiorly until we see this bony protuberance which is the crystal galley of the ethmoid bone we can see it here that's where our folk cerebri comes down and attaches that crystal galley is just superior to the cribriform plate of the ethmoid bones the cribriform plate is that superior portion of the ethmoid bone on top of that lies our olfactory bulb which then sends no fibers down into the nasal passages and we can see these nerve fibers go through these little olfactory foramina of the cribriform plate here and then retrieve sensory information which give us our sense of smell so that's our first foramen that we're going across our olfactory foramina in the cribriform plate now let's move on to cranial nerve number two which is our optic nerve it's easy to find the optic nerve if we have a look here at the globe of the eye we can see the optic nerve coming out centrally let's scroll down so we cut that optic nerve in the transverse plane we can see if we follow that optic nerve closely it juts in medially like this coming through the optic canal now there's many ways we can describe holes in the skull we've got foramina which are small holes widths are equal to their breasts then we've got longer tubes which we call canals here we can see that this is a tube within the bone and then we have irregular shapes that normally formed by two bones coming together making a space between the two of them and we call those irregular shapes fishes we've got foramina canals and fishes so here we have our optic canal which our optic nerve runs through and laterally to that and running superiorly is our superior orbital fissure because of its irregular shape and the way it runs superiorly as we scroll up we will see the fissure here coming out laterally all the way up to the top so we can follow that fissure all the way down so we've done cranial nerve one and two the superior orbital fissure has cranial nerve three four a part of cranial nerve five and cranial nerve six so three the oculomotor nerve for the trochlea and six the abducent nerve come through the superior orbital fissure and then the superior portion of our trigeminal nerve our fifth cranial nerve comes through this fissure as well so our fifth cranial nerve the trigeminal nerve has three branches the first of which our ophthalmic division comes through the superior orbital fissure and our other two divisions will go through two separate fissures which we'll now try and find here so now we need to scroll down slightly inferiorly we can see our cella tursica here our ethmoidal uh sinuses anterior to that we scroll down scroll down we can now see the sphenoidal sinus here and as we scroll down we can see here another foramen forming on either side of the sphenoid sinus and this is what's known as the foramen rotundum that's our second division of our trigeminal nerve our maxillary division so we've got the first division going through the superior orbital fissure the second division going through our foramen rotundum now what can be confusing with this is if we scroll down further we can see another canal forming here which you can often confuse with the foramen rotundum the best way to differentiate these is to carry on scrolling down until you can see the pterygoid plates we can see our medial and lateral pterygoid plates and in between the pterygoid and this maxillary bone here is a space here and this is something i hadn't heard of in medical school but it clinically is so so important because it connects so many different structures in the face and this is what's called our terrigo palatine fossa and that is a fossa that runs along the vertical plane in the face so as we come now superiorly we can see our terrigo palatine fossa getting bigger it's like an upside down pyramid as we go higher the fossa gets bigger we keep scrolling up we can see it gives away this first canal this is what's called alvidian canal and we'll look at later our carotid coming through here and sending the vidian artery through that canal now that's not our foramen rotundum there's no nerve passing through that we need to scroll more superiorly and we can see the next defect in the bone here that small circular structure coming through the bone there's our foramen rotundum and you'll see when we look at some coronal slices just now that that foramen actually runs from anterior to posterior it's not like a most of our foramina which are running from superior to inferior so that's got our second division our maxillary division of our trigeminal nerve now let's scroll down further and we will see another foramen forming posteriorly and laterally to that foramen rotundum and this is what's known as our foramen ovale or foramen ovale it's quite an easy structure to identify you can see it's nice and big there and that is the one that's got our last division our mandibular division of our trigeminal nerve so there's three foramina the superior orbital fissure the foramen rotundum and the foramen ovale they have our three divisions of our trigeminal nerve posterior to that and lateral to it is a very small foramen and it's very easy to identify because it's quite distinctive it's a small foramen in the posterior and lateral portions of our sphenoid here and this is known as the foramen spinosum the frame of spinosum has no nerves passing through it it has a vessel called the middle meningeal artery coming up into the brain so about external carotid artery that gives off a maxillary artery that maxillary artery then gives off our middle meningeal artery that comes on the interior surface of our temporal bone supplying blood to the meninges that's one of the vessels that if we have a fracture on the side of the skull can rupture and give us an extra dural hematoma so in our sphenoid bone we've got many foramina we've got our superior orbital fissure our foramen rotundum our vidian canal our foramina valley and our foramen spinosum i just want to show you how you can see that on coronal section as well these structures are quite complex the bone itself the sphenoid bone itself is a complex bone it's quite nice on coronal images let me now scroll through this coronal image so you can kind of get your bearings i'm going to go now to the anterior portion of the patient we can see the globes here as i now head posteriorly we can see our superior middle and inferior turbinates of our nasal passages here i'm going to keep scrolling posteriorly and what you'll begin to notice this is our phenoid sinus we can see here we've cut our foramen rotundum in the coronal plane if i come anterior to that we can see this is our terragopalator palatine fossa that gives off our foramen rotundum and slightly inferior to that we can see our vidian canal coming backwards that's the one that if i scroll further back you will see joins with our carotid canal coming back there okay alvidian canal then the foramen ovale is quite easy to see on these because it forms a large defect here in the sphenoid bone there it is on the left hand side of the patient a large defect like that it's very easy that's our foramen ovale our third division of our trigeminal nerve and as we scroll backwards we can see that small hollow structure having our middle meningeal artery coming in here that's our foramen spinosum okay we're making our way through this we've covered the sphenoid bone let's now go back into the temporal bone i'm gonna be back into this thin slice bone window axial ct just let it load up here you can see our foramen rotundum coming back foramen evol spinosum now posterior to that we can see here our carotid canal in the petrus portion here of the temporal bone as we follow that carotid canal superiorly we can see why it's called a canal that carotid runs horizontally through the petrous bone and this whole section here is what's known as the carotid canal it runs anterior medially and then terminates in what looks like a really oddly shaped space here and this is what's known as our foramen less serum it's filled with cartilage the karate doesn't actually run through the foramen it runs superior to the frame and less serum here and we will if we follow that up we'll see the carotid runs up superiorly before diving anteriorly past our or through our cavernous sinus before heading up into the brain into the forming the circle of willis so here's our carotid canal no cranial nerve running through there so we've covered cranial nerves one two three four five and six let's look at cranial nerve seven and eight our vestibular cochlear nerve and our facial nerve facial nerve number seven vestibular cochlear number eight now the way to find this is if we scroll inferiorly find our petrous bone here now as we come up we look at this petrous bone we can see our external auditory canal tympanic membrane what we want to do is find this internal acoustic canal we can see it running really clearly here anteriorly you see this little cloverleaf leaf shaped structure that's our cochlea and our vestibular system posteriorly so anteriorly and superiorly we have our facial nerve inferior to that we've got our cochlear section of our vestibular cochlear nerve and then posterior to that we have our vestibular section of our vestibulocochlear nerve so our vestibular cochlea terminates here but our facial nerve runs a bit of a long course you know our facial nerve is ending up in our parotid so how does it get there well let's look at this we've got our internal acoustic canal what we can do is if we scroll through here we'll see there's a small gap between our cochlea and our vestibular system and what our facial nerve does is it goes through that gap and then it goes posterior and inferior dives its way down through the mastoid here so let's try and follow that down it comes round we can see the facial nerve is coming in this gap here it's difficult to see on these slices what it does is as we go down down down we can follow it here follow it here it will come out here between our mastoid and our styloid this is our stylomastoid foramen now the facial nerve comes through there and then dives down to the parotid gland so you can actually follow that facial nerve all the way and then we can follow it back up come in [Music] we've lost it there come in and we should then bring it through between the cochlea and the vestibular system great so we've done seven and eight let's go nine ten eleven find our karate canal posterior to carotid canal is our jugular foramen so here we go this carotid coming here in the vertical plane behind that is our jugular foramen which has our jugular vein coming down our sigmoid sinus draining blood away from the brain will then contribute blood into this jugular foramen and we've got three cranial nerves running down there we've got glossopharyngeal cranial nerve 9 our vagus nerve cranial nerve 10 and then we've got our spinal accessory nerve cranial nerve 11. you might be wondering how the spinal accessory nerve gets there it's going out the brain but we know that the spinal accessory has got cervical components it's got components in the medulla and so what happens is that uh spinal accessory nerve actually comes up through the foramen magnum before heading across and down the jugular foramen so it's the only nerve that enters the skull comes in and then exits the skull again okay and then moving on to our last cranial nerve cranial nerve 12 our hypoglossal nerve people can also find this quite difficult and the way that i uh go about finding the hypoglossal canal is first by looking at the dense so we're going to scroll all our way down we can see our adontoid process here so we know the bones surrounding that is our atlas our c1 now atlas then communicates with our occipital condyles that's how our skull rests on the cervical spine is our atlas and occipital condyles coming together so if we scroll superiorly we know that these two processes here are our occipital condyles and our hypoglossal canal actually runs through those occipital condyles so we can see if we scroll scroll scroll there's a foramen coming through or a canal a hypoglossal canal running through and down so a hypoglossal nerve goes through that hypoglossal canal it's just inferior to those occipital condyles and i'll show you now in our coronal plane how we can go about detecting that it's a really um distinctive looking image as we come through our occipital canals so let me let this image load here we've actually got a ct scan of our cervical spine so you can see here we've got our odontoid process here is our atlas our c1 and these communicating with the atlas is our occipital condyles and we can see what looks like an eagle here we've got the beak the head wings coming out and this proud chest coming here and this canal that we can follow coming through here that is our hypoglossal canal perfect so we've got one more the one that everyone remembers one that i probably don't need to teach you about let's go back to our axial ct windows and that's the big hole at the back of the skull which is our foramen magnum so i've already told you what comes through this foramen magnum now this is a really thin slice ct scan so we're not getting the full ring of the frame in magnum but we can see here's our occipital condyles as we scroll upwards here we can see the back of the foramen magnum so everyone no one forgets the medulla oblongata the spinal cord going through the foramen magnum we have our cerebellar tonsils just peeking through that foramen magnum our vertebral arteries coming off and i've already told you that our spinal accessory nerve will come up through that foramen magnum before passing anteriorly and going down the jugular foramen so there we have it we've got a whistle-stop tour from the front of the skull all the way posteriorly following those cranial nerves and if you're human being for a second why don't we start at the top and quickly label all of those show you that it's actually not that difficult to remember them the way to do this is to just repetition going over it and over it scanning through yourself looking at these structures yourself so we've got our olfactory foramina we scroll down our optic canal our superior orbital fissure here then we come back we've got our foramen rotundum keep going sorry our frame and rotundum here keep going down we've got our foramen ovale foramen spinosum our carotid canal foramen less serum come down we've got our jugular foramen here we can see our internal acoustic canal you can see our cochlea and vestibular system here we get it we can follow that facial nerve all the way down like we did the facial nerve will come between the mastoid and the styloid there again we can work our way down see our hypoglossal canal coming through there and lastly our foramen magnum so i hope that's helped it's a really quick tour and what you can do is on these images i've listed below me here the radiopaedia links to these scans themselves and i highly encourage you type in that rid the radiopaedia id it's a five digit number load up the scan yourself and go through the scan follow the foramina yourself it's going to really cement that knowledge so i hope that's helped i hope you've learned something here today i'll see you all in the next video i'd love to hear your comments about what anatomy structures you would like to hear about next until next time goodbye everybody