Video: Superior and inferior orbital fissures
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As you know, our bodies are made up of vast amounts of blood vessels and nerves that wind their way through our bodies to supply their target organs. Much like a train going through a tunnel to get... Read more
As you know, our bodies are made up of vast amounts of blood vessels and nerves that wind their way through our bodies to supply their target organs. Much like a train going through a tunnel to get to the other side of a mountain, our neurovasculature often needs a way to pass through bony obstructions to reach its destination. It does this by passing through canals, foramina, and fissures, and that's exactly what happens in today's structures of interest which are the superior and inferior orbital fissures. So what do you say? Shall we get started?
Before we get into the good stuff, here's a quick overview of what we'll look at today. We'll start by defining the superior and inferior orbital fissures then we'll quickly review the bones of the orbit. Next, we'll look at the superior orbital fissure and the structures that pass through it followed by the inferior orbital fissure and its structures. Then we'll move on to the contents of the optic canal, and lastly, we'll conclude our tutorial with some clinical notes.
As I mentioned in our introduction, fissures allow neurovascular structures to reach their destination, but what exactly are the superior and inferior orbital fissures? We can figure out a lot based on the names of these structures alone. Let's start with the words they have in common.
Firstly, the word orbital tells us where in the body we should be looking for these structures – the orbit. The orbits are sockets within the skull in which the eyeballs are accommodated in addition to their associated musculature, vessels, and nerves. A fissure, on the other hand, is just another term used to describe a groove or a cleft. In this case, they are open and serve as passageways for other structures. In this image, we've zoomed in for a closer look at the right orbit. At its posterior aspect are two open elongated clefts – the superior orbital fissure and the inferior orbital fissure.
Okay, now it's time to review the bones that make up the orbit and contribute to these fissures. This is going to be a speedy tour of the orbit but if you're hungry for more, check out our video on the bones of the orbit.
The orbit has a roof, a floor, a lateral wall, a medial wall, and a posterior wall. Let's quickly remind ourselves which bones form these structures. The roof of the orbit is made up of the orbital surface of the frontal bone, and in turn, the floor of the orbit is formed by the orbital surface of the maxilla. Within the maxilla, we can see the infraorbital groove which transmits the infraorbital vessels and nerve.
The lateral wall of the orbit is made up of the orbital surface of the zygomatic bone while the medial wall of the orbit is composed of two bones – the lacrimal bone and the orbital plate of the ethmoid bone. Within the medial wall are two foramina – the anterior ethmoidal foramen and the posterior ethmoidal foramen. These foramina are found between the ethmoid bone and the frontal bone and allow for the passage of neurovascular structures between the orbit and the nasal cavity.
Finally, we have the posterior wall of the orbit which is the part of the eye socket we're most interested in. The majority of the posterior wall is formed by the sphenoid bone. Specifically, it is made up of the orbital surface of the greater wing of the sphenoid bone and the orbital surface of the lesser wing of the sphenoid bone. Within the lesser wing is an opening called the optic canal which we'll look at in more detail later on. The final bone that contributes to the posterior wall is the orbital process of the palatine bone.
Okay, to bring this all together, let's talk about how these bones form the superior and inferior orbital fissures. The superior orbital fissure is found between the greater and lesser wings of the sphenoid bone whereas the inferior orbital fissure is found inferior to the greater wing. It is also bordered by the zygomatic, maxilla. and palatine bones. Medial to both fissures is the ethmoid bone.
Alright, now that we're up to speed with the osteology of the orbit, let's take a look at some neurovascular structures that travel within the superior orbital fissure.
Beginning at the lateral end of the superior orbital fissure, the first structure that we can see is the lacrimal nerve. In the image on the right, we're looking into the right orbit from a superior view and the lacrimal nerve is highlighted in green. We can see it branching from this larger nerve. This is the ophthalmic nerve which is the first division of the trigeminal nerve – cranial nerve 5. We can see from this image that all branches of the ophthalmic nerve travel through the superior orbital fissure and we'll be getting to those soon.
The lacrimal nerve provides sensory innervation to the lacrimal gland and the conjunctiva and the skin of the lateral part of the upper eyelid. Within the orbit, it also receives some parasympathetic fibers from the pterygopalatine ganglion that innervates the lacrimal gland stimulating fluid secretion.
Next up is the frontal nerve. The frontal nerve is the second and largest branch of the ophthalmic division of the trigeminal nerve. Within the orbit, the frontal nerve gives off two branches – the supraorbital nerve and the supratrochlear nerve. Both of these nerves exit the orbit anteriorly to provide sensory innervation to the skin of the forehead and scalp and the conjunctiva and skin of the upper eyelid.
Moving medially, we can see the trochlear nerve – cranial nerve 4. In this image, we're looking at the left orbit from a lateral view. The trochlear nerve, highlighted in green, travels through the superior orbital fissure and passes medially to innervate the superior oblique muscle of the eye. Also traveling through the superior orbital fissure with the three nerves we've just identified is a vein called the superior ophthalmic vein. We can see its full course in this lateral view of the left orbit. Anteriorly, it communicates with the veins of the face, and posteriorly, it drains into the cavernous sinus.
Moving in for medially, we find a little bundle of nerves traveling through a structure called the common tendinous ring, which you can see here highlighted in green. The common tendinous ring is a structure formed by the four rectus muscles’ tendons. You can learn more about these muscles by watching our videos on extraocular muscles.
The first in this bundle is the oculomotor nerve or cranial nerve 3 which divides into two branches – a superior branch and an inferior branch. In our next illustration, we can see the superior and inferior branches of the oculomotor nerve within the orbit.
If we change our view to show the left eye from a lateral perspective, we can see that the superior branch provides motor innervation to the superior rectus muscle of the eye and the levator palpebrae superioris muscle of the eyelid. The inferior branch provides motor innervation to the medial rectus muscle, the inferior rectus muscle, and the inferior oblique. The oculomotor nerve also carries parasympathetic fibers to the constrictor pupillae and ciliary muscles within the eyeball.
Another nerve in this medial bundle is the nasociliary nerve. This is the third and final branch of the ophthalmic nerve. In this image, we can see the nasociliary nerve branching from the ophthalmic nerve and running along the medial wall of the orbit. As it does so, it gives off several branches of the anterior and posterior ethmoidal nerves which travel through the anterior and posterior ethmoidal foramina that we identified earlier and the long ciliary nerves which travel into the eyeball itself. Anteriorly, the nasociliary nerve becomes the infratrochlear nerve which leaves the orbit below the trochlea.
All of these branches originally from cranial nerve 5 are providing sensory innervation to the nasal cavity, ethmoidal and sphenoid sinuses, iris and cornea, and skin and conjunctiva onto the medial side of the eye and bridge of the nose.
The final nerve traveling through the superior orbital fissure is the abducens nerve or cranial nerve 6. Don't forget that this structure also travels through the common tendinous ring. This nerve only innervates one muscle – the lateral rectus muscle – which abducts the eyeball and is where the name abducens comes from. We can see the abducens nerve entering the medial aspect of this muscle here.
The final structure traveling through the superior orbital fissure is the inferior ophthalmic vein. In the example pictured here, this vein is not contained in the common tendinous ring but it can also pass through the superior orbital fissure within the ring. The inferior ophthalmic vein receives tributaries from the eyeball, the eyelid, the nasolacrimal sac, and from two muscles which control the eye movements – the inferior rectus and the inferior oblique muscles. As it courses along the floor of the orbit, the inferior ophthalmic vein divides into two branches – a superior branch and an inferior branch – which drain into different places. Of the two branches, it's the superior branch that travels through the superior orbital fissure. Similar to the superior ophthalmic vein, it drains into the cavernous sinus.
If you're struggling with the structures of the superior orbital fissure, don't worry. We've got a mnemonic for you to help you remember all of these structures. So we have F for the frontal nerve, I for the inferior division of the oculomotor nerve, N for the nasociliary nerve, A for the abducens nerve, L for the lacrimal nerve, I for the inferior ophthalmic vein, S for the superior ophthalmic vein, T for the trochlear nerve, and S for the superior division of the oculomotor nerve. And what does it spell? FINALISTS.
Alright, finally done with the superior orbital fissure. Time to tackle the inferior orbital fissure. And don't worry, there are fewer structures that travel through this space, and first up is the inferior branch of the inferior ophthalmic vein which passes through the inferior orbital fissure. We can see the inferior branch of the inferior ophthalmic vein better from a lateral perspective. This vessel drains into this plexus here called the pterygoid venous plexus.
Next, we have the infraorbital nerve which is a branch of the maxillary division of the trigeminal nerve. This nerve travels anteriorly along the floor of the orbit within the infraorbital groove. It then exits the orbit via the infraorbital foramen to provide sensory innervation to the lower eyelids and conjunctiva. Lateral to the infraorbital nerve is the infraorbital artery which is a branch of the maxillary artery. This artery follows the same course as the infraorbital nerve traveling along the infraorbital groove and through the infraorbital foramen. Within the orbit, it gives off branches to supply the inferior rectus and the inferior oblique muscles.
Traveling with the infraorbital artery, you also have a corresponding infraorbital vein. This vein travels along the floor of the orbit and may communicate with the inferior ophthalmic and facial veins. It then travels through the inferior orbital fissure and drains into the pterygoid venous plexus.
Next we're looking at the zygomatic nerve, which is a branch of the maxillary division of the trigeminal nerve. Soon after entering the orbit, this nerve divides into two branches – the zygomaticotemporal nerve and the zygomaticofacial nerve. These nerves provide sensory innervation to the skin of the temple and to the skin of the cheeks, respectively.
The last structure, or rather structures, traveling through the inferior orbital fissure are the orbital branches of the pterygopalatine ganglion. The pterygopalatine ganglion is the largest of the peripheral parasympathetic ganglia and is housed within the similarly named pterygopalatine fossa. The orbital branches carry sensory innervation from the ethmoidal air cells in the ethmoid sinus.
Since we have a mnemonic for the structures of the superior orbital fissure, it only makes sense to have one for those found within the inferior orbital fissure, right? The memory aid here is ZOI3 which I know might seem more like a mathematical equation instead of an anatomy mnemonic. So we have Z for zygomatic nerve, O for orbital branches of the pterygopalatine ganglion and then triple I for the inferior branch of the inferior ophthalmic vein, the infraorbital artery and vein, and finally, the infraorbital nerve.
Alright, the orbital fissures are done. Since we're in the same area, let's now take a quick look at the structures that pass through the optic canal. Although the optic canal is not a part of the orbital fissures, it is located immediately adjacent to it which provides a good excuse to talk about it. We're starting with the optic nerve or cranial nerve 2, which is this large nerve traveling through the optic canal.
The optic nerve carries visual information from our eyes to our brain. Traveling with the optic nerve is the ophthalmic artery which arises from the C6 segment of the internal carotid artery. From this lateral view, we can see the ophthalmic artery arising from the internal carotid and traveling along the superior aspect of the orbit. It is the main blood supply to the structures of the orbit giving off several branches along its course.
As the optic nerve travels away from the brain, the meninges surrounding the brain also extend into the optic nerve and ophthalmic artery all the way to the eyeball. This covering is known as the dural sheath and we can see it here highlighted in green.
Alright, we're done with identifying anatomical structures, let's get clinical.
Today's clinical note section is full of big complicated words – craniomaxillofacial, ophthalmoplegia, ptosis, proptosis. What unites these words? The traumatic superior orbital fissure syndrome, which in itself, is quite a mouthful so we'll refer to it as SOFS to keep it simple. This condition is caused by craniomaxillofacial trauma which refers to a wide range of injuries to the soft tissues and the underlying bones of the head and the face as well as inflammation and tumors. The occurrence of the traumatic superior orbital fissure syndrome is rare – only present in about one percent of these traumas. The structures of the superior orbital fissure can be severed or compressed by bone fragments displaced by trauma.
The diagnosis relies on the range of present symptoms. Ophthalmoplegia is a weakness or paralysis of the extraocular muscles caused by damage to the oculomotor, trochlear, and abducens nerves. Proptosis is the anterior protrusion of the eyeball caused by the decreased tension of the extraocular muscles again suggesting damage to the same three nerves. Ptosis refers to the drooping of the upper eyelid which is controlled by the levator palpebrae superioris muscle. And which structure passing through the superior orbital fissure innervates it? That's right, it's the superior branch of the oculomotor nerve, so ptosis indicates damage to this specific nerve.
A fixed dilated pupil is also a result of damage to the oculomotor nerve as we have parasympathetic fibers to the pupil coursing with the oculomotor nerve. Loss of sensation on the upper eyelid and forehead indicates damage to the lacrimal and frontal nerves while loss of sensation on the bridge of the nose and the cornea tells us the nasociliary nerve has been damaged. And that's the remainder of our terms cleared up.
The treatment may involve conservative treatment, a sort of wait-and-see approach; steroid administration, or surgical intervention.
Alright, we're just about done. Before I let you go, here's a quick review of what we covered today.
Once we figured out what the superior and inferior orbital fissures were, we reviewed the bones of the orbit. We saw that the roof is made up of the orbital surface of the frontal bone and the floor is formed by the orbital surface of the maxilla which is where we found the infraorbital groove. Laterally, we found the orbital surface of the zygomatic bone, and medially, we saw the lacrimal bone and the orbital plate of the ethmoid bone. We also saw the anterior and posterior ethmoidal foramina contained within the medial wall. Posteriorly, we identified the orbital surface of the greater and lesser wings of the sphenoid bone, the optic canal, and the orbital process of the palatine bone.
Next, we looked at the neurovascular structures that travel through the superior orbital fissure. From lateral to medial, we found the lacrimal nerve which is a branch of the ophthalmic division of the trigeminal nerve, the frontal nerve which is also a branch of the ophthalmic nerve, the trochlear nerve or cranial nerve 4, and the superior ophthalmic vein and superior branch of the inferior ophthalmic vein. Also in the superior orbital fissure, that traveling through the common tendinous ring, we found the superior branch of the oculomotor nerve, the nasociliary nerve which is the final branch of the ophthalmic nerve, the abducens nerve or cranial nerve 6, and the inferior branch of the oculomotor nerve.
Next up, we identified the structures traveling through the inferior orbital fissure. We saw the inferior branch of the inferior ophthalmic vein; the infraorbital nerve which is a branch of the maxillary division of the trigeminal nerve; the infraorbital artery, a branch of the maxillary artery; the infraorbital vein draining into the pterygoid venous plexus; the zygomatic nerve which is also a branch of the maxillary nerve; and the orbital branches of the pterygopalatine ganglion.
The last space we looked at was the optic canal and the structures travelling through it – the optic nerve or cranial nerve 2, the ophthalmic artery which is a branch of the internal carotid artery, and the dural sheath enclosing both of these structures.
In our clinical notes, we looked at traumatic superior orbital fissure syndrome which is a condition caused by craniomaxillofacial trauma.
And that's it! Now you're an expert on the superior and inferior orbital fissures.
I hope you enjoyed this tutorial and thanks for joining me.