Lecture 13: Anatomy of the Cavernous Sinus, Orbit, and Eye Flashcards
What 5 things passes through the Superior Orbital Fissure?
1) Oculomotor n. (CN III)
2) Trochlear n. (CN IV)
3) Opthalmic division of Trigeminal n. (CN V1)
4) Abducens (CN VI)
5) Opthalmic veins
What 2 things pass through the optic canal?
1) Optic n. (CN II)
2) Opthalmic a.
What innervates the Oricularis Oculi and what are actions of its 2 parts?
- Innervated by CN VII (Temporal and Zygomatic branches)
Palpebral part: gentle closing of lid
Lacrimal part: increased lid contact to eye, dilates lacrimal sac
What muscle acts as a direct antagonist of the Orbicularis Oculi and what nerve innervates it?
- Levator Palpebrae Superioris (LPS)
- Innervated by CN III (Oculomotor n.)
Destruction of the oculomotor nerve (CN III) or one of its branches to the Levator Palpebrae Superioris m., may lead to what?
- COMPLETE ptosis (eyelid completely shut)
- Pupils will be down and out
- Loss of pupillary constriction reflex so pupils will be dilated
- Seen in Oculomotor (CN III) palsy
What is special about the Tarsal Muscle (of Muller)?
- Smooth muscle that inserts on the tarsal plate of the upper lid
- Innervated by postganglionic sympathetics originating from T1
- Horner’s syndrome usually involved paralysis of this muscle
What are the 4 major signs of Horner’s syndrome and what muscle involved?
- Slight ptosis (paralysis of the Tarsal muscle)
- Miosis (pupillary constriction due to paralysis of dilator pupillae muscle)
- Enopthalamos (paralysis of the orbitalis muscle of Muller which has slight protrusion function
- Anhidrosis and blushing
What is the tear drainage pathway from the orbit into the nose? (the flow chart!)
Lacrimal gland —> Lacrimal Canaliculi —> Lacrimal Sac —–(Nasolacrimal duct) —-> Inferior Concha
What 2 nerves form the Vidian n and what are their sources, where do these nerves synapse and how do we get to the Lacrimal gland?
- Greater Superficial Petrosal N. from Superior Salivatory nucleus (preganglionic parasympathetic) + Deep Petrosal N. from SCG (postganglionic sympathetic) = Vidian N.
- Vidian N. synapses on Sphenopalatine Ganglion.
- Postganglionic fibers travel to the lacrimal gland via: Maxillary N., Zygomatic N. (V2), and Lacrimal N (V1).
What are the 3 branches of V1 seen during the superior orbit dissection?
1) Nasociliary
2) Frontal
3) Lacrimal
*NFL*
What is a Le Forte fracture?
Fractures of the Maxillary region of the skull
What is a Le forte fracture type I?
- Above the alveolar processes. Avoids the orbit.
- Lower lip swelling/ecchymosis, damaged teeth
What is a Le Forte fracture type II?
- Pyramidal- shaped fracture. Involves medial portion of orbit
- Periorbital edema, CSF rhinorrhea, nasal disfigurement
What is a Le Forte fracture type III?
- Transverse fracture across both orbits and nasofrontal sutures
- Leads to separation from base of skull
- Craniofacial Dysjunction
- Panda facies, complete mobility of facial skeleton, antimongoloid slant
Which muscle and sinus is commonly affected with a blow-out fracture of the orbit?
- Floor of orbit displaced or a depressed fracture of the zygomatic bone may cause:
- Entrapment of Lateral rectus m. causes Diplopia (downward gaze)
- Displacement of structures into Maxillary sinus
What are the contents of the Cavernous Sinus (Mnemonic)?
OTOM CAT
- Oculomotor (CN III)
- Trochlear (CN IV)
- Opthalmic (CN V1)
- Maxillary (CN V2)
- ICA
- Abducens (CN VI)
Where do the Opthalmic veins drain?
- The Cavernous Sinus —> Petrosal Sinus —–> IJV
- Infections of the orbit have chance to spread to the brain!
What are the clinical signs of Cavernous Sinus Thrombosis (CST); which nerve at risk for impingement?
- Acute onset of unilateral periorbital edema and proptosis (displacement of eye)
- Headache
- Photophobia
- Impingement syndrome (CN VI)
What is Papilledema; why is it clinically significant?
- Swelling of the optic disc due to increases in CSF
- CSF increase could be due to: venous obstruction, mass effect secondary to tumor, edema (vasogenic, infection)
What is the input and output for the Corneal Reflex?
Input: Cornea —-> Nasociliary n./Long Ciliary (CN V1)
Output: Facial n. –> Orbicularis Oculi m. (CN VII)
What controls the ipsilateral and contralateral pupillary constriction when shining light in someones eye; what is the connecting point; what nucleus is utilized for the response?
- Direct light stimulus sensed by retina and info sent to brainstem via CN II
- Information sent from Superior Colliculus to Pretectum
- Posterior Commisure is the connecting point and causes a response in the contralateral eye as well
- Edinger-Westphal Nucleus delivers the motor response (CN III) to the Ciliary Ganglion and finally the Sphincter Pupillae
*IN BY 2 OUT BY 3*
What portion of the ANS control pupillary constriction (miosis) versus dilation (mydriasis)?
- Constriction = parasympathetics (remember your pupils don’t need to be huge when resting/digesting)
- Dilation = sympathetics (want to be able to see far when running from the dianosaur!)
What is accomodation of the eye; what type of response; and what 3 things happen?
-
Cortically mediated reflex to focus on structures/objects that are close (near vision)
1) Convergence (pupils ADduct)
2) Pupillary constriction
3) Lens Thickening (nearsightedness)
What is the chief artery of the orbit?
- Opthalmic artery, the first branch off the ICA
What branches off the Opthalmic artery supply the optic nerve?
- Posterior ciliary artery
- Central artery of the retina
Which branches off the Opthalmic arteries supply the eyelid and scalp?
- Supraorbital artery
- Supratrochlear artery
Which branch off the opthalmic artery supplies the nasal cavity and external nose?
Anterior ethmoidal artery
What is the key player that allows for the consensual light reflex?
Posterior Commisure
What is Argyll-Robertson Pupil?
- Also known as the Prostitue sign
- Eyes are accomodating, but unreactive to light.
- You will get slight pupil constriction upon accomodation, but pupils will NOT be reactive to light
- Tertiary Neurosyphylis = Lesion of the Pretectum!
What’s Holmes-Adie Pupil?
- A benign situation with a tonic pupil that slowly constricts on covergence
- Parasympathomimetic drugs will constrict the tonic pupil, but have no effect on the normal pupil
Explain the paraympathetic innervation of the lacrimal gland?
- Superior salivatory nucleus sends preganglionic fibers via the Facial (VII), Greater superficial petrosal, and Vidian nerve to sphenopalatine ganglion
- Postganglionic fibers course to the lacrimal gland via the Maxillary, Zygomatic and Lacrimal nerves
Explain the sympathetic innervation of the lacrimal gland?
- The deep petrosal nerve arises from the internal carotid plexus and fuses with the greater superficial petrosal nerve to form the Vidian n.
- Postganglionic fibers course through sphenopalatine ganglion without synapsing and distribute to the lacrimal gland via the maxillary-zygomatic-lacrimal nerve route
Increased intracranial pressure may compress which nerve to the eye; what’s the effect?
- Compress the abducens nerve and result in paralysis of the lateral rectus muscle
- Inability to aBduct the affected eye
What is the main sensory (GSA) nerve to the orbit (eyeball)?
Nasociliary nerve
What is commonly seen with Trochlear nerve palsy?
- Superior Oblique muscle is denervated so patient cannot adduct and depress the affected eye
- Patient tends to compensate with head tilt and tucking chin
- CN IV dysfunction
