This is an on-demand teaching session for medical professionals that focuses on the different foramina at the base of the skull and in relation to the cranial nerve exits and internal arteries that pass through them. Participant will learn about the locations, structures, and clinical relevance of the internal acoustic canal, the optic canal, foramen rotund, foramen ovale, foramen spinosum, lacerated foramen, and jugular foramen. This session provides an in depth survey of these foramina and will help medical professionals identify, understand, and share clinical knowledge related to them.
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In this video, we focus on describing all skull base openings from the superior view.

Hosted by Dr. Doris George Yohannan

An Assistant Professor of Anatomy at Trivandrum Medical College, Dr. Doris George Yohannan is a highly qualified and awarded educator in the field. With an MBBS and an MD in Anatomy, Dr. Yohannan is passionate about clinically oriented and imaging anatomy. He brings a wealth of experience and accolades, including the best poster award at the 2013 state conference of the Kerala chapter of Anatomical Society of India, and the Dr. Saramma Joseph memorial award in 2014, and is actively involved in leveraging technology for medical education.

Learn more about Air Anatomy on our youtube channel here!

Learning objectives

Learning Objectives: 1. Explain the function and key structures of four foramina in the base of the skull: the Kippel's fissure, superior orbital fissure, foramen rotundum, and foramen ovale. 2. Recall the mnemonic Ma Le Ma for remembering the structures passing through the foramen ovale. 3. Describe the significant of the middle meningeal artery that passes through the foramen spinosum. 4. Recognize the foramen lacerum's role as a dried skull artifact. 5. Identify the structures passing through the internal acoustic meatus, jugular foramen, and petrous foramina.
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Computer generated transcript

The following transcript was generated automatically from the content and has not been checked or corrected manually.

Hello. In this video, we are going to survey through all the foramina present in the base of the skull or in the skull base or in the cranial fossa in the anterior cranial fossa. The a very important foramen that you see here. These are, these are the cripple form plate. The K cripple form plate contains a lot of minor foramina, almost 20 to 25 foramina and they will be transmitting the cranial nerve. Number one, cranial nerve, number one. Uh the next uh foramen that you see here, that is the optic canal. It is not a foramen. Technically, it is a canal because it is a tunnel. This allows the passage of cranial nerve. Number two, that is the optic nerve along with that ophthalmic artery, ophthalmic artery is an important branch of the internal carotid artery. Now, uh the next foramen that you need to know as as actually not technically a foramen again. Uh so to understand that we are going to slightly tilt this model and you can see uh this long uh deficiency and that is the superior orbital fissure. This is called the superior uh orbital fissure. This one, the superior orbital fissure allows the passage of cranial nerves. Number three, that is oculomotor for that is trochlea and six. All these three nerves are concerned with eye movements with Craner. Number three, having an additional function of pupillary constriction and accommodation. That means parasympathetic function. Ok. That is also a, a function of Craner. Number three along with 34 and six, you also have V one. What do you mean by V one V trigeminal nerve? V one, it means the first division of trigeminal nerve, trigeminal nerve as you know, has three divisions, ophthalmic maxillary and mandibular. So the ophthalmic nerve also runs along the superior orbital fissure. It's not the ophthalmic nerve that is running through it. They are the branches of the ophthalmic nerve for the time being. I'll just name those branches. They are the lacrimal frontal and nasociliary. So all these are running through the superior artificial. There are a lot of nerves 346 and the V one, ophthalmic ophthalmic branches that is a lacrimal frontal and nasociliary and uh superior ori fissure is transmitting superior fissure. And uh the optic canal is actually uh communications into the orbit. OK. There are communications into the orbit. I'm just turning and you can see the super orbital fissure here. You can see the optic canal here. OK. So both of these are basically communications of the cranial fossa to the orbit. OK. The next uh opening that you need to know is this, this is the foramen rot, foramen rot lodges. The cranial nerve V two V is trigeminal, the second division of trigeminal that is, is the maxillary. Now to see the forum more clearly, we'll just tilt it. And you can understand that the for is almost having a, an orientation that goes forward. Now where is foramen rotten reaching? We when whenever we learn this foramina, it is good if you know where this is going to reach. Ok. Uh I I didn't mention about the plate if we uh run through this small for you are going to reach the roof of the nasal cavity. OK. It's very obvious this is the nasal cavity, the roof of the nasal cavity, you have the deficiencies of the uh of the cripple form plate. OK. So it is, it is basically as you know, these are the olfactory nerves that are running through it. So the sense of smell from the nasal cavity pierces, the cripple form plate to reach the uh the olfactory tract that is olfactory bulb and olfactory tract that is running in the Antero fossa. So uh like that the optic canal and the superior artificial is to the orbit just like that. The foramen rotten them is allowing the passage into the pterygopalatine fossa, rigo palatine foss is a, a little bit uh tricky uh you know, uh a crevice within the uh brain, OK. This region where my cursor now is that is the ter palatine fossa. So just know that for Andum is allowing the passage of maxillary. No cranial, no number V two from the middle cranial fossa into ter palatine fossa. Now, the next very important note that is very commonly asked in many of the examinations, including practical or your MC examinations. Is this, this is the foramen o veil. As you can see, it is an oval foramen unlike this, which is a round foramen. This is an oval foramen. Now, what are the structures that runs through the foramen ove? There is a very famous mnemonic Ma Le ma Lem stands for mandibular or cranial nerve V. Three A is accessory meningeal artery. L stands for very, very important, L stands for lesser petrosal nerves. There are a number of petrosal nerves that we learn later, but this stands for lesser petrosal nerve and E stands for a miss vein amis vein. OK. This is a very common pneumonic and very commonly asked in many of your examinations. What is male? OK. And now where is the foramen or ove going into foramen? Ove will allow access to the infra temporal fossa. Now, if I put a probe, if I put a probe through the foramen o veil from the cranial fossa, if I put a thread down, it is going to reach this place. This is the uh infra or infra temporal fossa. I'll just uh you know, uh kind of uh navigate through the foramen veil to make that clear. OK. Through the foramen o veil, I'm going to reach the infra fossa. OK. This is the infra fossa. I'm now zooming out infra temporal fossa. This is the infra temporal foss inal fossa is over here. OK. So that is where this will reach now, the next foramen that you find here, that is the foramen spinosa, foramen spinosa allows the passage of the middle meningeal artery, middle meningeal artery is very important. Middle meningeal artery is not an artery that is going to supply the brain, but it is an artery that is going to lie between the inner table or the skull, inner table, skull and the dura between this, you have the uh middle mening artery, middle mening artery will be located over here, ok, between the inner table and the dura. So the point is that it is not supplying the brain, it is outside the dura. It is not at all supplying the brain. But the point point that all of you should remember is that the middle meningeal artery is extremely for an injury. If you have a fracture of the skull, especially on the lateral aspect of the skull, a fracture can cause a tear of the middle mening artery and that can cause an extra dural hemorrhage, an extra dural hem hemorrhage that will have an appearance of a biconvex lens. Ok? Because the dura will be stripped off and uh the will have convex collection. A convex surface will be seen uh towards the brain and this can compress on the brain. So that is the middle meningeal artery and that artery is ascending up through the foramen spinosa. Uh This is important and you can even see a grooves of the middle meningeal artery on the inner part of the skull. You can see these are all grooves that are seen of the middle meningeal artery. Ok. They are all, If you, if you see get an actual skull, you can trace it to the foramen spinosa to get oriented, the foramen that we learn till. Now, you please note that there are a crescent of foramen over here, the superior orbital fissure, the foramen rotund, the foramen ove and the foramen spinosa is creating a crescent at the root of the greater wing of sp this is the greater wing of sphenoid, the greater wing of the sphenoid root, you have this crescent of uh foramina. You can remember it like sof and o veil and spinal, some ross sof and R OS. Now, with that, we are going into more uh larger and more posterior foramina. Uh This foramen that you find here, it's a very, very interesting foramen. This foramen is called the lacerated foramen, also called the foramen la serum. Now, uh there are slight difference of opinions. Uh when uh people ask about what passes through the foramen la serum, the point that you need to know is that Foramen LA serum is actually a dried sky artifact. You see Foramen LA serum, as you see in this model, only in a dried sky. Ok? In an actual live person, this will be usually closed by fibrocartilage uh tissues uh and only the upper part of the foramen LA serum allows the passage of the internal car. Ok. This point is important uh because the internal carotid artery is going to run like this. Ok? Run like this. I'll, I'll just highlight it like this. It is going to emerge out like this or the upper part of the Foramen Las Serra. OK. Nothing passes through and through the Foramen laser, but only through the upper part, you have the passage of the internal carotid. OK. So that is about the Foramen LA here, you also have very minor foramina over here. This is the Foramen for the greater petrosal nerve. This is the Foramen for the lesser Pitro. Now, I hope you remember lesser Pitro now because lesser Pitocin now was just mentioned in the Foramen of weight. OK. Now, here, if you look carefully at this uh uh model, you can see that the greater Pitro no groove is directed towards the Foramen LA serum and the lesser petrosal no groove is directed towards the foramen O. These all have very important significance when we learn about these Pitro nos. But for the time being, I'm going to leave that. Now, I'm going to more important Phe Aena on the posterior aspect on the posterior cranial fossa. This is the posterior cranial fossa as you know, poster cranial fossa. This is the piru temporal bone in the middle of the, almost in the middle of the puts temple bone. You have a large foramen. This foramen is the internal acoustic canal or the internal acoustic meatus, internal acoustic meatus allows for the passage of cranial nerve. Number seven and the cranial nerve number eight, OK, seven is facial nerve and eight is vestibulocochlear. You should not call it as auditory nerve, you should call it as vestibulocochlear. So vestibulocochlear and the facial nerve, uh if you uh read textbooks, you will also learn that you also have the nervous intermediate, ok, nervous intermedius is basically the sensory root of the facial nerve. Ok. So uh nervous intermediate, facial nerve and the vestibular cochlea runs through the internal along with an artery and that artery is a labyrinth artery. All the are uh in its core towards structures within the terus temporal bone. It can be uh the inner or it can run through the temporal bone and exit out. For example, the facial nerve, facial nerve is going to run through the temporal bone and it is going to exit out. Next, we are going to learn a very important foramen. And that foramen is this, this is the jugular foramen. The jugular foramen is formed by a peculiar arrangement of the temporal bone here. And the occipital bone here. OK. This is the occipital bone and this is the temporal bone. Both of them together going to create the uh jugular foramen. Jugular foramen is not an opening in a single bone. Unlike all these, this is seen in the temporal, this is seen in the sphenoid. OK. Unlike that the jugular foramen is found between the temporal and the occipital bone. OK. What passes through the jugular foramen? A lot of structures are going through the jugular foramen. The uh the cranial nerves that are running through the jugular foramen are cranial nerve. Number nine, cranny ner number 10 and cranial nerve number 11, that is glossopharyngeal vagus and accessory nerves are going to go out through the jugular foramen. In spite of that, in addition to that, you also have the inferior petrosal sinus because this is a petros bone. So this is the inferior petrosal sinus that is going to drain down and drain out through the jugular foramen. Also, you have this large groove, this large groove is the sigmoid groove through which the sigmoid sinus is going to drain down. And that is also going to drain out through the jugular foramen as the internal jugular vein. So you can see two communications. One is the inferior petrosal sinus and next is the sigmoid sinus along with 9, 10 and 11 renal ners very, very important. These are running through the jugular foramen. Next, we have a very important foramen. Again, this uh Foramen is not a foramen, it is a canal but this canal is notorious to be hiding around here. Ok. It is, it is hiding over here. This is the canal and this is the hypoglossal canal. You can see it is not a single foramen. It is, it is a short canal and this is the hypoglossal canal. Please note that the hypoglossal canal is uh somewhat related inferior to the jugular foramen. So please note this relation. You have uh the internal A sig here you have the jugular foramen here. And this is the uh hypoglossal canal. Hypoglossal canal is almost inferior that hypoglossal canal inferior to the hypoglossal canal. You have the occipital condyle. This is the occipital condyle. I'm now looking from the inferior aspect. This is the occipital condyles uh uh which articulates with the C one atlas vertebra. So just about the uh occipital condyle, you have the uh hypoglossal canal through which the hypoglossal nerve. That is the cranial nerve. Uh Number 12, cranial nerve, number 12 is going to exit cranial nerve. Number 12 is going to exit through the hypoglossal canal anteriorly. OK. So these are the main foramina that you see that are very commonly asked in examinations and obviously the greatest foramen you should not miss and that is the Foramen magnum that you are seeing here. This is the Foramen magnum. Now, we are going to learn about Foramen magnum foramen magnum uh is can be uh divided the cons of the foramen magnum can be divided into an oo ligament over here, which contains mainly uh ligaments and uh fibrous tissues. OK. That structures that passes through the here can be remembered by the mnemonic AC T A is the epic ligament of dens AIC ligament of DS C is the vertical band of the cruciate ligament and uh T is membrana uria membrane uria is the continuation of the posterior longitudinal ligament of the spinal column. At you can remember by the mnemonic A CT, the posterior part is more nervous. Ok. Nervous structures are going to run through the posterior aspect. What are the nervous structures running through the posterial aspect? The middle oblong is going to continue as the spinal cord, the vertebral arteries are going to ascend up the vertebral arteries. The V four segment of the vertebral artery are going to ascend up onto the me through the posterior aspect. The accessory nerve. Now this can be confusing for students accessory nerve is going to ascend up the spinal root of the accessory nerve is going to ascend up. Now, you already learned that the jugular foramen contains accessory. So can how can here also accessory come? You should remember that accessory nerve is unique accessory nerve is arising from the upper segments of the spinal cord, from the upper five segments of the spinal cord and it is going to ascend up into cranium and then it is going to live through the jugular foramen. OK. So that is the course of the accessory. Now, so you have vertebral artery here, you have accessory nerve, you have the anterior spinal arteries which has uh branches of the vertebral artery and also the posterior spinal artery. These are also running through this, running through the Foramen magnum. You also have the meninges surrounding the uh middle uh uh spinal cord. Uh that is the pia arachnoid and the dura matter will also be uh running through the Foramen magnum. OK. Uh Some uh textbooks also say uh the tonsils of the cerebellum. Now, that is technically incorrect, tonsil of the cerebellum cannot pass through the Foramen magnum. Uh tonsil passing through the Foramen magnum or descending down through the Foramen Magnum. Uh It's uh it's a feature of chiari malformation and it is also seen in tonsilla herniation, which are, which is a uh a grave condition which is a herniation syndrome. When an intracranial pressure is uh increased in a normal anatomy. The cerebellar tonsil is not a of the Foramen magnum. So these are the main phe that you need to learn. Uh when you uh learn about the cranial fossa. Thank you.