30 Orbital Surgery Flashcards
Describe the important bony anatomy of the orbit.
Describe the important bony anatomy of the orbit.
The orbit is a pyramidal shaped space that is made up of seven bones: frontal, zygomatic, ethmoid, lacrimal, maxillary, sphenoid, and palatine (Figure 30-1). The medial walls of each orbit lie parallel to each other and the lateral walls lie 45 degrees to the ipsilateral medial wall and 90 degrees to the contralateral lateral wall. The orbital walls are lined by periosteum referred to as periorbita.
What bones make up each wall of the orbit?
What bones make up each wall of the orbit?
The roof of the orbit is made up of the frontal bone and lesser wing of the sphenoid. The floor of the orbit is made up of the maxillary, palatine, and zygomatic bones. The medial wall of the orbit is made up of the ethmoid, lacrimal, maxillary, and sphenoid bones. The lateral wall of the orbit is made up of the zygomatic bone and greater wing of the sphenoid.
What are the dimensions of the orbit in adults?
What are the dimensions of the orbit in adults?
The pyramidal shaped orbit has a typical volume of 30 mL. The entrance height is 35 mm and the entrance width is 40 mm. The width of the orbit is greatest 1 cm posterior to the entrance of the orbit which corresponds to the equator of the globe. The medial wall length is 45 mm.
What are the orbital foramina and what structures are contained within them?
What are the orbital foramina and what structures are contained within them?
The optic foramen passes through the lesser wing of the sphenoid extending from the middle cranial fossa to the orbital apex and contains the optic nerve, ophthalmic artery, and sympathetic fibers from the carotid plexus. The supraorbital foramen is located at the medial third of the superior margin of the orbital rim and contains the supraorbital nerve, artery, and vein. The anterior ethmoidal foramen is located at the frontoethmoidal suture 24-mm posterior to the orbital rim and contains the anterior ethmoidal vessels and nerve. The posterior ethmoidal foramen is located 12 mm posterior to the anterior ethmoidal foramen at the junction of the medial wall and orbital roof and contains the posterior ethmoidal vessels and nerve. The 24/12/6 rule is a nice reference to help remember foramina locations in the orbit, which stands for anterior ethmoid artery (24 mm), posterior ethmoid artery (12 mm), and optic nerve (6 mm) in sequential measurements from the posterior lacrimal crest. The zygomaticotemporal and zygomaticofacial foramina are located within the lateral wall of the orbit and transmit branches of the zygomatic nerve and artery.
What are the orbital fissures and what structures are contained within them?
What are the orbital fissures and what structures are contained within them?
The superior orbital fissure is 22 mm in length and lies inferior and lateral to the optic foramen. It is formed by the greater and lesser wing of the sphenoid and is divided into superior and inferior parts by the lateral rectus. The superior part contains the frontal and lacrimal branches of cranial nerve V1 and cranial nerve IV. The inferior part contains the superior and inferior divisions of cranial nerve III, the nasociliary branch of V1, cranial nerve VI, the superior ophthalmic vein, and the sympathetic nerve plexus. The inferior orbital fissure lies between the lateral wall and orbital floor (runs deep to the orbital floor) and contains branches of cranial nerve V2 and the inferior ophthalmic vein (Figure 30-2).
What are the extraocular muscles and where are they located?
What are the extraocular muscles and where are they located?
There are six extraocular muscles (Figure 30-3) within each orbit that control movement of the globe: medial rectus, lateral rectus, inferior rectus, superior rectus, superior oblique, and inferior oblique. With the inferior oblique as the exception, all extraocular muscles originate at the orbital apex. The four rectus muscles originate from the annulus of Zinn (a tendinous ring that encircles the inferior portion of the superior orbital fissure and optic foramen) and insert onto the anterior portion of the globe. The superior oblique travels from the orbital apex to the trochlea and makes a sharp turn (54 degrees) to insert on the globe. The inferior oblique travels from a shallow depression in the orbital plate of the maxillary bone, inferior to the lacrimal fossa, posteriorly laterally and superiorly to insert on the globe.
Describe the innervation of the extraocular muscles.
Describe the innervation of the extraocular muscles.
The medial rectus, superior rectus, inferior rectus, and inferior oblique muscles are innervated by cranial nerve III. The superior oblique muscle is innervated by cranial nerve IV. The lateral rectus muscle is innervated by cranial nerve VI. The blood supply to the extraocular muscles is provided by the inferior and superior muscular branches of the ophthalmic artery, lacrimal artery, and infraorbital artery.
Describe the vasculature to the orbit.
Describe the vasculature to the orbit.
The arterial supply to the orbit is from the internal carotid artery via the ophthalmic branch with contributions from the external carotid artery system (superficial facial artery). The branches of the ophthalmic artery include the central retinal, the lateral and medial posterior ciliary, the lacrimal, muscular, supraorbital, anterior and posterior ethmoidals, supratrochlear, nasofrontal, and dorsonasal arteries. The lacrimal artery forms an anastomosis with the external carotid system via the transverse facial and superficial temporal arteries. Medially, the dorsonasal arteries anastomose with the external carotid system via the angular arteries. The maxillary artery contributes via its infraorbital branch.
The venous drainage of the orbit is from the superior and inferior ophthalmic veins. The inferior ophthalmic vein originates from a plexus of vessels in the inferior orbit, joins the pterygoid plexus, and terminates at the superior ophthalmic vein to enter the cavernous sinus. The superior ophthalmic vein originates at the superior medial orbit and crosses midorbit below the superior rectus muscle. The lacrimal vein joins the superior ophthalmic vein prior to exiting the orbit to enter the cavernous sinus.
Describe the anatomy of the lacrimal system.
Describe the anatomy of the lacrimal system.
The lacrimal gland, which is responsible for reflex tearing, is found within the lacrimal fossa in the orbital portion of the frontal bone. The gland is divided into the palpebral lobe and the orbital lobe by the lateral horn of the levator aponeurosis. Eight to twelve lacrimal gland ductules empty into the superior lateral conjunctival fornix. The accessory lacrimal glands (glands of Wolfring and Krause), which are responsible for basal tearing, are located in the eyelid. The lacrimal papillae are located medially on the posterior edge of the upper and lower eyelids and lead to the lacrimal canaliculi. The lacrimal canaliculi (superior and inferior) lead to the lacrimal sac within the lacrimal fossa, most often (>90%) forming a single common canaliculus prior to entering the sac. The valve of Rosenmuller is located at the medial end of the common canaliculus and prevents tear reflux. The nasolacrimal duct forms (exits) at the inferior portion of the lacrimal sac and lies within the bony nasolacrimal canal. The nasolacrimal duct drains into the inferior meatus of the nose beneath the inferior turbinate through the valve of Hasner.
What is a dacryocystorhinostomy (DCR)?
What is a dacryocystorhinostomy (DCR)?
DCR is a surgical procedure involving fistulization of the lacrimal sac into the nasal cavity. The procedure can be performed through an external incision or endoscopically through the nose.
What are the advantages of endoscopic DCR?
What are the advantages of endoscopic DCR?
With the advances in endoscopic visualization and the development of improved instrumentation, endoscopic DCR has shown success rates (80% to 100%) that are similar to traditional external techniques. The advantages of endoscopic approaches include the absence of external skin incision and resultant scar, the preservation of the orbicularis oris pump mechanism, decreased disruption of the medial canthal anatomy, decreased intraoperative bleeding, and the abilty to address contributing nasal cavity or paranasal sinus abnormalities.
What are the indications of endoscopic DCR?
What are the indications of endoscopic DCR?
Excess tearing (epiphora) can result from hypersecretion (lacrimation) or failure of drainage. Bothersome epiphora due to nasolacrimal duct obstruction is the primary indication for DCR. Other causes include recurrent dacryocystitis, dacryolithiasis, tumors of the lacrimal system, nasal pathology, or anatomic abnormalities that obstruct the drainage pathway. Nasolacrimal duct obstruction often presents with epiphora or infection and can be confirmed via several diagnostic tests including the dye disappearance test, lacrimal system irrigation or probing, scintigraphy, and contrast dacryocystography.
How does one perform an endoscopic DCR?
How does one perform an endoscopic DCR?
The surgical approach is similar to performing endoscopic sinus surgery. Important landmarks include: the maxillary line (corresponds to the suture line between the frontal process of the maxilla and the lacrimal bone), which serves as a landmark for the lacrimal sac, the uncinate process, and the superior attachment of the middle turbinate. A sickle knife is used to create a mucosal flap on the lateral nasal wall over the lacrimal sac, which may be debulked or trimmed. The lacrimal bone and frontal process of the maxilla are removed to expose the medial portion of the lacrimal sac. The sac is incised and marsupialized into the nasal cavity, and silicone lacrimal intubation stents may be placed.
What is the leading cause of proptosis in adults?
What is the leading cause of proptosis in adults?
Thyroid eye disease (TED or Graves’ opthalmopathy) is the most common extrathyroidal manifestation of Graves’ disease and is the leading cause of proptosis in adults. It is considered an autoimmune process with thyroid stimulating hormone (TSH) receptor as the likely autoantigen in both the thyroid gland and orbit. Fibroblasts and adipocytes act as effector cells, inducing a complex cytokine-mediated immunologic response marked by tissue inflammation and hypertrophy.
What is the typical presentation of thyroid eye disease?
What is the typical presentation of thyroid eye disease?
Patients will often complain of blurry vision, foreign body sensation, photophobia, tearing, diplopia, dull pain, and discomfort. Clinical features include eyelid retraction (90% of patients), periorbital soft tissue swelling, lid lag, lagophthalmos, conjunctival injection, exposure keratopathy, restrictive myopathy, exophthalmos, and optic neuropathy. Imaging usually reveals fusiform enlargement of the extraocular muscles. MRI is more sensitive than CT for showing optic nerve compression at the orbital apex. Approximately 5% of patients will experience severe orbital inflammation and congestion resulting in compressive optic neuropathy, requiring urgent treatment.
