DR 3 - Orbit and Nasal Cavity DEMO COPY.docx

202 DR3: Orbital and Nasal Cavity Learning Outcomes: By the end of the module you should be able to: Identify the bones of the orbit Identify the extraocular muscles, their action and nerve supply from cranial nerves 3,4,6 Identify the ophthalmic artery and the venous drainage of the orbit Describe...

202 DR3: Orbital and Nasal Cavity Learning Outcomes: By the end of the module you should be able to: Identify the bones of the orbit Identify the extraocular muscles, their action and nerve supply from cranial nerves 3,4,6 Identify the ophthalmic artery and the venous drainage of the orbit Describe the nerve supply to the eye (cranial nerve 2) and lacrimal gland Identify the main bony and cartilaginous structures of the nose Locate the paranasal sinuses Apply clinical examples to anatomical principles In this practical session you will study the anatomy of the eye and nose. For this session, you will be examining a range of prosected specimens as well as the anatomical models available within the dissecting room. As with all your other practical sessions in the dissecting room make sure you work through this handout, answer the questions and complete the checklist. Workstation 1. Orbit In this workstation you will examine the bony orbit, the lacrimal gland and eyeball. Examination of the orbit Examine the bones that make up the orbit using the available skulls. The orbit is a pyramidal-shaped cavity in the facial skeleton, with the apex lying medio-posteriorly and the base of the pyramid (orbital aperture) lying anteriorly. Pay particular attention to the roof, floor and walls of the orbit and the differences in their thickness. Observe the foramina and fissures of the orbit (using a pipe cleaner may help you): optic canal - superior orbital fissure - inferior orbital fissure inferior orbital canal - supraorbital foramen The image above depicts the bones of the orbit. What structure passes through the notch in the frontal bone? Supraorbital nerve, artery and vein. Trigeminal Nerve The trigeminal nerve (CNV) has three branches that divide intracranially. The first branch is the ophthalmic nerve (V1). This nerve provides somatic sensory (touch, pain, temperature) innervation to the eye, lacrimal gland, orbit and the skin around the orbit and forehead. It enters the orbit via the superior orbital fissure and has three main branches – frontal, lacrimal and nasociliary. The first two of these can be found in the superficial dissection, the lobular fat has been carefully removed. The frontal nerve runs just under the roof of the orbit and is easily visible. This image depicts the superior aspect of the orbit showing the ophthalmic division of the trigeminal nerve. Locate the frontal nerve. Identify the frontal nerves two terminal branches. The larger more lateral branch is the supraorbital nerve that will exit the orbit through the supraorbital foramen. The other branch is the supratrochlear. What innervation do you think these branches provide? Sensory The lacrimal nerve is the smallest branch. In the orbit the lacrimal nerve runs along the superior aspect of the lateral rectus muscle and receives parasympathetic nerve fibres of origin from the facial nerve (CN7) that have travelled up the zygomatic nerve (a branch of V2) to then pass into the lacrimal nerve. Locate the lacrimal nerve. The third branch of the ophthalmic nerve is the nasociliary nerve. This supplies the structures of the eye itself (as well as the ethmoid sinus and the skin over the nose). The nasociliary nerve crosses the optic nerve and runs beneath the superior rectus muscle towards the medial wall of the orbit; carrying pain and touch sensation from the cornea via its long posterior ciliary branches. Its other branches are the anterior and posterior ethmoidal nerves that supply the mucous membranes of the paranasal sinuses and nasal cavity, and the terminal branch, the infratrochlear nerve, which supplies the medial portion of the eyelids and conjunctiva, as well as the skin of the nose. Locate on the deeper side of the prosection the nasociliary nerve. Locate the deeper optic nerve (CN2) The image above depicts the superior aspect of the orbit showing the ciliary ganglion. Lacrimal Gland The lacrimal gland is responsible for tear production. Tears are produced and then wash across the eye as you blink. They nourish and protect the front of the eye. As they wash across, tears are drained into the lacrimal sac in the infero-medial orbital margin, and then drain into the nasal cavity via the nasolacrimal duct (When you cry lots, you sniff lots). In most cases the contents of the orbit are embedded in lobular fat bounded by a connective tissue membrane, this fat has been removed for you see the lacrimal gland. This screenshot from Complete Anatomy shows the lacrimal gland in situ. Locate the lacrimal gland in the supero-lateral aspect of the orbital aperture. Carefully locate the lacrimal branch of the ophthalmic nerve as it runs from the apex of the orbit to this gland. The lacrimal nerve carries somatic sensory information from the lacrimal gland, lateral conjunctiva, and also from a small area of skin over the lateral portion of the eyelids. Parasympathetic nerve innervation to the lacrimal gland (for tear production) originates from the lacrimal nucleus which is part of the facial (CN7) nucleus in the brainstem, these fibres synapse in the sphenopalatine ganglion. The postganglionic fibres “hitch-hike” with branches from the maxillary nerve (CNV2) to reach the terminal part of the lacrimal nerve (branch of CNV1). Clinical Context Fractures of the orbit The orbit is relatively strong, however blows to the orbit can cause fracturs affecting the bones forming the margin of the orbit. Because the medial and inferior walls of the orbit are thin trauma to the orbit can cause these walls to fracture whilst the orbital margin remains intact. Indirect trauma that displaces the orbital wall is called a ‘blowout’ fracture. Orbital blowout fractures classically present with posterior displacement of the globe (eyeball), diplopia (double vision), ophthalmoplegia (incorrect eye movements) and hypoaesthesia (reduced sensation) in the maxillary nerve distribution (think about the course of the infra-orbital nerve). Some cases of orbital trauma can result in bleeding into the retrobulbar space (the potential space behind the globe, between the extra-ocular muscles). In these cases, intra-orbital pressure increases, causing reduced perfusion to the eyeball and the optic nerve resulting in potential loss of vision. Emergency lateral canthotomies can reduce this pressure. Case example: Orbital blowout and retro-orbital haematoma (Radiopaedia) Multiple facial fractures: fractures of the left zygomatic arch; medial, anterior and lateral walls of the left maxillary sinus; medial, lateral and inferior orbital margins and multiple nasal bridge fractures. The left maxillary sinus is filled with blood and soft tissue swelling with flecks of gas in the tissues can be seen. Corneal abrasions/ulcers An epithelial layer covers the outer-most surface of the globe (cornea), which is vulnerable to damage. Commonly mechanical trauma (foreign bodies, finger nails, contact lenses etc.) is the likely culprit. But be aware of “over-exposure” as a cause - consider the Bell’s palsy patient (CN 7) or the anaesthetised patient, who are unable to close their eye lids and risk corneal dryness and subsequent erosion. Wheater’s Functional Histology, 6th Edition: Figure 21-04. Eye, monkey H&E (LP) C cornea  CB ciliary body  Ch choroid  I iris  L lens  O optic nerve  Patients with corneal abrasions will usually present with a clear history of foreign body sensation in the affected eye. Conjunctival hyperaemia (red eye) and reduced visual acuity may also be present. The majority of corneal abrasions are of little clinical consequence; however, the exposed irregular epithelial surface is prone to bacterial infection and resultant ulceration. As such, prophylactic antibiotic eye drops are commonly prescribed. Workstation 2. Eye In this workstation you will examine the eye and the extraocular muscles. Eyeball The eyeball contains the optical apparatus for the visual system. Using the eye model and eye for part 1. Identify the outer fibrous layer- the sclera and cornea. Locate the vascular layer which includes the iris. Locate the inner retina The optic nerve (CN2) is 3-4mm diameter and joins the eyeball on the posterior surface. This carries nerve axons from the retina all the way to the thalamus of the brain. Now focus on where the optic nerve reaches the optic chiasm. This is where the nasal (medial) half of the axons cross over to the contralateral side. The temporal fibres stay on the lateral side. The pituitary gland sits directly below the optic chiasm in the midline. This crossing over means that posterior to the chiasm, the right side of the brain deals exclusively with your left field of vision (served by both eyes) and vice versa. Leaving the optic chiasm are the two optic tracts that are directed to the lateral geniculate nucleus of the thalamus. Here the axons derived from the retina synapse with the nerve fibres of the optic radiation. This large fan shaped projection spans much of the temporal lobe and the parietal lobe of the brain to reach the visual cortex in the occipital lobe. This is where visual stimuli are processed. Using the transverse slices of brains examine the optic tract. Total compression of the right optic nerve by an intraorbital tumour on the right side would cause what visual disturbance? Monocular blindness – blindness in one eye (right eye in this case). Rectus Muscles There are six muscles that act on the eye (in addition to the levator palpebrae superioris that lifts the upper eyelid). In particular, it is important to understand their innervation and function as this is the basis for identifying intracranial pathology as part of the neurological examination – which could be life-saving. The six muscles that act to move on the eye include the four recti: superior, inferior, medial and lateral rectus. And the two oblique muscles: superior and inferior oblique. Each of the rectus muscles arise from the apex of the orbit and insert in the anterior hemisphere of the eye. Identify each of these on the prosections. Observe how the rectus muscles are directed at an angle of about 20° antero-laterally. However, the visual axis is directed anteriorly in the primary gaze (looking straight ahead). The Oblique Muscles The superior oblique runs from the apex along the supero-medial aspect of the orbit to the trochlea, where it turns backwards and medially to insert on the postero-lateral aspect of the globe. The inferior oblique is the only muscle not to originate from the apex. It arises from the maxillary bone in the infero-medial orbital margin. The muscle passes under the eye to insert into the postero-lateral aspect of the globe. Examine the superior and inferior oblique muscles- you will need to look at different prosections to do so. This image depicts the superior aspect of the orbit showing the extraocular muscles. Can you identify them? Nerve supply to the extraocular muscles The oculomotor nerve (CN 3) carries motor innervation to the levator palpebrae superioris and inferior oblique as well as the superior, medial and inferior recti muscles. It also carries parasympathetic supply to the ciliary muscle to adjust the lens for near vision (accommodation) and to the sphincter pupillae for pupil constriction. The trochlear nerve (CN 4) supplies the superior oblique muscle. The abducent nerve (CN 6) supplies the lateral rectus muscle. Although you do not need to describe the precise course of these nerves, you should be aware that these nerves exit the brainstem in close proximity to a number of arterial branches, where they may be compressed by an aneurysm. Before entering the orbit through the superior orbital fissure, all three of these nerves pass through the cavernous sinus, along with the ophthalmic branch of the trigeminal nerve. Use the prosections to locate these nerves. The image above depicts the superior aspect of the orbit showing CN 3 and 6 and the lateral aspect of the orbit showing the extraocular muscles. Vasculature The main artery supplying the orbit is the ophthalmic artery, the first branch of the internal carotid artery. As it branches from the internal carotid, it travels through the optic canal along with the optic nerve. After entering the orbit, it gives a variety of branches that you should attempt to locate. These branches will supply the lacrimal gland, extraocular muscles, the ethmoid and sphenoid sinuses, eyelids, as well as the skin over the forehead and nose. Blood supply to the globe of the eye itself is two-fold: the central retinal artery and the ciliary arteries. The former is the first branch of the ophthalmic artery and enters the optic nerve sheath to supply this nerve as well as the retina. This artery and its 4 terminal branches are what can be visualised by ophthalmoscopy (see image below). The long and short posterior ciliary arteries enter the back of the eye along with the ciliary nerves to supply the other structures within the eye. Locate the ophthalmic artery. The orbit blood supply drains via the superior and inferior ophthalmic veins. You may have already come across the former. If not you should try to find it now. This vein passes through the superior orbital fissure into the cavernous sinus (part of the intracranial dural venous sinus network). The inferior vein may drain into the cavernous sinus or may pass through the inferior orbital fissure into the sphenopalatine fossa. Both of these have communications with veins of the face and sinuses, and so are important potential routes of entry for pathogens causing intracranial infections e.g. cavernous sinus thrombosis, meningitis, encephalitis. What would be the result of a blockage of the central retinal artery? (think back to your first-year notes from Module 102) Sudden loss of sight in affected eye Clinical Context To test the extraocular muscles clinically you need to isolate the muscle. To isolate the superior or inferior recti muscles you must first align the muscle directions with the visual axis i.e. ask the patient to look laterally, and then to look up or down. The medial and lateral rectus muscles will move the eyes in the medial and lateral direction as expected. To isolate the superior and inferior oblique muscles you must first align the muscle directions with the visual axis i.e. ask the patient to turn the eye in question medially first. Then, if they are asked to look up or down, the oblique muscles will work in isolation to elevate (inf. oblique) or depress (sup. oblique) the eye. The image above depicts the clinical testing of the extraocular muscles. It is important to note that all the extraocular muscles are continuously involved in the movement of the eye and as such actions made by individual muscles are not tested clinically. Ophthalmoplegia (incorrect eye movement) will usually present with diplopia (double vision). The action of which muscles of the left eye would you therefore be testing if you asked a patient to look up and to the right? Superior rectus Oculomotor nerve palsy and abducent nerve palsy Damage to the oculomotor nerve (CN 3) will classically result in a “down and out” pupil, an infero-lateral gaze. Lateral gaze occurs as the oculomotor nerve innervates the medial rectus muscle, whereas the lateral rectus muscle is innervated by the abducens nerve (CN 6). Paralysis of medial rectus (CN 3 palsy) will result in unopposed lateral rectus muscle tone, resulting in lateral gaze. Conversely, abducens nerve palsy will produce an inability to complete lateral gaze in the affected eye. An abducens nerve palsy is considered an ominous sign, due to its long and tortuous course along the base of the brain, usually being the first cranial nerve effected in raised intra-cranial pressure. The inferior (and some lateral) gaze of an oculomotor nerve (CN 3) palsy occurs due to the unopposed action of superior oblique (innervated by trochlear nerve CN 4) against the paralysed inferior oblique, superior rectus and inferior rectus (innervated by CN 3). However, patients will not only have a “down and out” pupil, they will also have ptosis (drooped eyelid) and mydriasis (dilated pupil). The levator palpebral superioris, also innervated by CN 3, is responsible for raising the eyelid, with paralysis resulting in ptosis. Damage to the parasympathetic fibers of the oculomotor nerve (CN III) that usually act to constrict the pupil, will result in mydriasis (pupil dilatation). Parasympathetic fibers run on the outside of the nerve and motor fibers on the inside. Therefore, external compression of the nerve will result in mydriasis before ophthalmoplegia or ptosis. The timing of these clinical presentations can help delineate the potential aetiologies. This image is an example of a patient with oculomotor nerve palsy. Note the visible characteristics of the condition on their right eye. Workstation 3. Nose In this workstation you will examine the nose, nasal cavity and paranasal sinuses. On the face examine the nose and nasal cavity. Using the skull locate the nasal bones and where the major alar cartilages would join. Next examine the vestibule of the nose immediately above the nostril. The vestibule leads posteriorly into the larger atrium of the nose. Posterior to the atrium are three longitudinally running bony shelves – the conchae or turbinate bones. Identify the superior, middle and inferior concha and the spaces that lie inferior to each one. These spaces or grooves are known as the superior meatus, middle meatus and inferior meatus, respectively. The image above depicts the sagittal section through the nasal cavity. Underlying the anterior lip of the inferior concha (anterior end of the inferior meatus) is the opening to the nasolacrimal duct, which drains lacrimal fluid from the conjunctival sac of the eye into the nasal cavity. Locate the nasolacrimal opening. Immediately inferior to the attachment of the middle concha the lateral wall elevates to form the dome-like ethmoidal bulla (see diagram). The ‘bulging’ of the underlying middle ethmoidal air cells creates the bulla. Inferior to the bulla is a curved groove known as the hiatus semilunaris, which forms a channel towards the frontal sinus and aids in mucus drainage. At the posterior end of the hiatus semilunaris you should identify the opening of the maxillary sinus. Identify the hiatus semilunaris and the opening of the maxillary sinus. The image above depicts a sagittal section through the nasal cavity with conchae removed. What purpose do the conchae serve? Humidify and warm inspired air and cause a turbulent flow of air through the cavity. The nose receives the olfactory nerves that emerge from the olfactory bulb. The olfactory bulb sits superior to the cribiform plate and has around 20 olfactory nerves feeding into it. The olfactory nerves pass through the tiny holes in the cribiform plate. Once inside the olfactory bulb the olfactory nerves synapse with mitral cells. The axons of these cells form the second order neurons that make up the olfactory tract. Each olfactory tract (one on the right one on the left) divide into medial and lateral striae. The lateral stria terminates in the piriform cortex of the temporal lobe whilst the medial stria projects through the anterior commissure to the contralateral piriform cortex. Examine the skull and locate the cribiform plate of the ethmoid bone. Examine the olfactory bulb on the prosected brain. Examine the paranasal sinuses. The paranasal sinuses are made up of the frontal, sphenoidal and maxillary sinuses and the ethmoidal air cells. Each sinus is lined by mucus secreting mucosa, has an opening into the nasal cavities and is innervated by branches of the trigeminal nerve. Firstly, identify the frontal sinus, which lies within the frontal bone and drains onto the lateral wall of the middle meatus via the frontonasal duct. Next examine the ethmoidal air cells, which are a cluster of small sinuses separated from each other and the orbit and nasal cavity by thin plates of bone. The individual chambers are divided into anterior, middle and posterior based on the aperture location. Locate the sphenoid sinus which lies within the body of the sphenoid bone with apertures on the anterior walls draining into the space above the superior concha. The image above depicts a sagittal section through the nasal cavity showing the paranasal sinuses. Based on their location, which branch(es) of trigeminal do you think innervates the various paranasal sinuses? Frontal – V1 ­/ Ophthalmic, frontal branch Ethmoidal - V1 ­/ Ophthalmic, ethmoidal nerve Sphenoid - V1 ­/ Ophthalmic & V2 / Maxillary Maxillary - V2 / Maxillary Clinical Context Imaging Because the maxillary sinus is not visible in the sagittal section use the image below to identify it and appreciate the close relation to the orbit. Also note the irregularity of the conchae. The image above depicts an MRI from the anterior aspect of the head. Using the MRI scan ensure you can locate: The frontal and sphenoidal sinus The nasal septum The image above depicts an MRI from the lateral aspect of the head. Epistaxis (Nosebleeds) Nosebleeds will arise either anteriorly or posteriorly. Anterior nosebleeds involve Little’s area or Kiesselbach’s plexus (different names for the same thing) - where branches of the maxillary, facial and ophthalmic artery converge at the antero-inferior nasal septum. Little’s area receives arterial supply from both the internal and external carotid arteries. Therefore, some conservative treatments of epistaxis can be targeted at inducing vasoconstriction of these arteries. Posterior nosebleeds can be more troublesome. These usually arise from the sphenopalatine artery (branch of maxillary artery) in the posterior nasal cavity. They may require direct tamponade of the culprit vessel in the form of a posterior nasal packing. Why might prolonged bleeding of posterior nosebleeds cause issues? Bleeding may travel posteriorly into pharynx – into respiratory or GI tract. Anosmia The inability to perceive odor (anosmia) can occur for a number of reasons. Naturally, as part of aging, smell declines but there are a range of other conditions which affect smell. Without gloves on check with your own nose that you have air moving in and out of each nostril. Work through the following flow chart to identify the other conditions which may affect smell. Patient details: Mr. Mike Healy is a 65-year-old male who has noticed his ability to smell has declined over several months and his wife reports changes in behaviour. Discuss each of the following and if this would form part of your diagnosis. What is an olfactory hallucination? Detection of smells which aren’t actually present. Workstation 4: Imaging Pathologies of the Orbit and Nasal Cavity Case 1 - Radiopaedia Presentation: 35-year-old rode their motorbike into a car door at low speed (10 km/hour). They were wearing a helmet, although there was significant facial injury. Axial bone window CT Coronal bone window CT Discuss the above case, considering the following: Signs and symptoms the patient may present with Facial pain, headache, rhinorrhoea, bleeding, swelling Which structures of the orbit and nasal cavity have been injured? Use a skull model to help appreciate the compact bony anatomy of the area Ethmoid, vomer This patient may present with rhinorrhoea (running nose) with a thin, transparent fluid. What could this fluid be? CSF Case 2 – Radiopaedia Patient age: 35 years old Presentation: Car accident Coronal CT Parasagittal CT Discuss the above case, considering the following: Signs and symptoms the patient may present with Visual disturbances, pain, swelling Which structures of the orbit have been injured? Sphenoid and frontal bones Which nerves could have been damaged in this injury? CN II, III, IV, V1 & 2, VI and their respective branches Case 3 – Complication of Orbital Fracture A 35-year-old was involved in a fight and sustained a punch to the right orbit. They came to the emergency department with double vision. The double vision was only in one plane. Examination of the orbits revealed that when the patient was asked to look upward the right eye was unable to move superiorly when adducted. There was some limitation in general eye movement. Assessment of the lateral rectus muscle (CNVI), superior oblique muscle (CNIV), and the rest of the eye muscles (CNIII) was otherwise unremarkable. The patient underwent a CT scan (right). Discuss the above case, considering the following: What plane was this CT scan taken in? Coronal Which structures of the orbit and nasal cavity can you identify on the image? Frontal bone, ethmoid, conchae, maxilla, zygoma Which muscles are involved in allowing and opposing superior movement of the eye? Allowing – Superior rectus, inferior oblique Opposing – Inferior rectus, superior oblique Can you see any evidence of bone fractures in the above CT scan? Floor of right orbit The above CT scan of the facial bones demonstrates a fracture through the floor of the orbit. A careful review of this CT scan demonstrated that the inferior oblique muscle had been pulled inferiorly with the fragment of bone in the fracture; this produced a tethering effect. How would this tethering effect restrict the movement of the patient’s eye? Restricted in “up and out” movement of the eye - Unable to look superolaterally Due to restricted action of inferior oblique Could also restrict all elevation of the eye due to the added tension of the tethered area What interventions would be undertaken to rectify this issue? Surgical intervention to release the tethered muscle. Checklist Review all the structures you have examined today and ensure that you are satisfied that you have completed the check list below before you leave the dissecting room: Identify the bones of the orbit Identify the extraocular muscles, their action and nerve supply from cranial nerves 3,4,6 Identify the ophthalmic artery and the venous drainage of the orbit Describe the nerve supply to the eye (cranial nerve 2) and lacrimal gland Identify the main bony and cartilaginous structures of the nose Locate the paranasal sinuses Apply clinical examples to anatomical principles