Anatomy of the orbit Prof. Pia C Sundgren MD, PhD Department of Diagnostic Radiology, Clinical Sciences, Lund University, Sweden Lay-out brief overview of the basic anatomy of the orbit and its structures the orbit is a complicated structure due to its embryological composition high number of entities, and diseases due to its composition of ectoderm, surface ectoderm and mesoderm Recommend you to read for more details 3 x 3 3 layers: - neuroectoderm (retina, iris, optic nerve) - surface ectoderm (lens) - mesoderm (vascular structures, sclera, choroid) 3 spaces: - pre-septal extraconal - post-septal intraconal 3 motor nerves: - occulomotor (III) - trochlear (IV) - abducens (VI) Imaging technique CT and / or MR IOM plane thin slices axial and coronal projections CT: soft tissue and bone windows MR: T1 pre and post, T2, STIR, fat suppression, DWI (?)
Superior orbital fissure cranial nerves (CN) III, IV, and VI lacrimal nerve frontal nerve nasociliary nerve orbital branch of middle meningeal artery recurrent branch of lacrimal artery superior orbital vein superior ophthalmic vein Roof frontal bone lesser wing of the sphenoid bone Floor maxilla zygomatic bone Medial wall ethmoid bone (lamina papyracea) lacrimal bone maxilla Lateral wall greater wing of the sphenoid bone zygomatic bone Mnemonic of the order in which the nerves passing through the Sup. orbital fissure Lazy French tarts sit naked in anticipation Lacrimal nerve (branch of CN V1) Frontal nerve (branch of CN V1) Trochlear nerve (CN IV) Superior division of the oculomotor nerve (CN III) Nascociliary nerve (branch of the CN V1) Inferior division of the oculomotor nerve (CN III) Abducens nerve ( CN VI) Courtesy Dr C Romanovski Orbital fissures and optic canal Superior orbital fissure: lesser and greater wing of the sphenoid bone Inferior orbital fissure: greater wing of sphenoid the maxilla and palatine bone Optic canal: at the apex of the orbit in the sphenoid bone Inferior orbital fissure infraorbital nerve zygomatic nerve parasympathetics to lacrimal gland infraorbital artery infraorbital vein inferior ophthalmic vein branch to pterygoid plexus
Infraorbital sulcus and foramen The infraorbital sulcus (SIO) crosses the floor of the orbit and carries infraorbital artery infraorbital vein infraorbital nerve from the inferior orbital fissure to the infraorbital foramen NOTE this is a route of spread for infection or maxillary tumors to the orbit and the skull base Optic canal Annulus of Zinn optic nerve ophthalmic artery central retinal vein dural sheath Calcifications of optic nerve www.clinicalgate.com Courtesy Dr A.I Ranchod, SA Optic nerve cranial nerve II transmits visual information from the retina to the brain composed of retinal ganglion cell axons and support cells optic n. glioma optic n. meningioma
septum - preseptal - postseptal intraconal extraconal preseptal soft tissue/edema Septum - med.palpebral lig. retrobulbar space - clinical term Courtesy M Annertz/Lund Mnemonic intraconal lesions of the orbita Mel met Rita mending hems on poor Charlies grave Melanoma Meningeoma pseudotumor Chemosis of the eye swelling of the tissue that lines the eyelids and surface of the eye (conjunctiva) Episcleral infiltration Metastasis Hemangioma cellulitis Retinoblastoma Optic glioma Graves disease Preseptal infiltration Courtesy Dr P Maly, Malmoe Postseptal extraconal Postseptal intraconal
Scleritis chronic, painful, inflammatory disease characterized by edema and cellular infiltration of the scleral and episcleral tissues (outermost coat of the eye) Buphthalmos and coloboma Buphthalmos enlargement of the globe due to increased intraocular pressure choroid lens anterior chamber secondary to obstruction of the Schlemm canal isolated / associated - Sturge Weber -NF type 1 - cobblestone lissencephaly sclera retina Cryptophthalmos A rare congenital anomaly in which the skin is continuous over the eyeball, with absence of eyelids. Eye might be normal or abnormal. Courtesy Dr A.I Ranchod, SA Retinal detachment occurs when the intraretinal space persists Courtesy Dr. S Andronikou, SA
Buphthalmos and coloboma Coloboma congenital fissures in the globe due to incomplete closure of the embryonic optic fissure 0.5 to 0.7 per 10,000 births iris coloboma: defect in anterior portion of the embryonic fissure cleft in the iris pigment epithelium retinochoroidal coloboma: arise from the wall of the globe optic nerve coloboma: insertion of the optic disc Retinoblastoma Clinical findings leukoaria (white pupillary reflex) cat eye reflex due to replacement of vitreous humor by a white mass www.retinoblastoma.com reduced vision, eye pain, strabismus Courtesy Dr A Rossi, IT Staphyloma Persistent hyperplastic primary vitreous protrusion of the uveal tissue through a thinning of the sclera - weak point in the eyeball severe axial myopia, more common posteriorly anteriorly more common after infection or trauma M Tsatsos and T Eke Eye (2007) 21, 857 858 Courtesy Dr A.I Ranchod, SA
Bulb laceration Action of the extra-ocular muscles Muscle Action Cranial Nerve Inf. rectus depresses, turns medially III Inf. oblique elevates turns laterally III Sup. obligue depresses, turns laterally IV (n. trochlearis) Extra ocular muscles develop in situ input from respective cranial nerve (III, IV,VI) 1 month gestation fully developed at 6 months gestation www.pinterest.com Annulus of Zinn a fibrous ring formed by the common origin of the 4 rectus muscles Thyroid ophthalmopathy m. rectus inferior > med >sup > lat Action of the extra-ocular muscles The major nerves Cranial nerves motor III oculomotor n IV trochlear n VI abducens n II optic nerve Muscle Action Cranial Nerve Lat. rectus moves eye laterally VI ( n.abducens) Med. rectus moves eye medially III (n. oculomotorius) Sup. rectus elevate, turns it medially III Cranial - sensory nerves V trigeminal n ophthalmic n V 1 (the upper eyelid, the conjunctiva and cornea of the eye) and its branches
The ophthalmic artery http://www.retinareference.com/anatomy/ first branch of the a. int car. The ophthalmic artery enters the orbit on the inferolateral side of the optic nerve and gives off the central retinal artery and posterior ciliary arteries near the orbital apex Involvement of the ophthalmic artery in giant cell arteritis Copyright 2016 British Society for Rheumatology Ophthalmic nerve The orbital veins branches nasociliary nerve frontal nerve lacrimal nerve NOTE the superior ophthalmic vein is a communication between facial vein and cavernous sinus Danger Zone Kumar JB et al EyeNet Magazine May 2015
Thank you T1 weighted, without fat suppression, showing bilateral enlarged superior ophthalmic veins in carotid cavernous stula Ophthamology.standford.edu Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology PC / ECNR Sundgren, Dubrovnik Spine / Oct 2018 Infect ASSR 12 Orbital phlebograhy showing left-sided venous fistula Courtesy Dr. P Maly, Malmoe Take home message complicated anatomy and embryology high number of possible diseases For correct diagnosis important to differentiate between the preseptal and postseptal space important to differentiate between extraconal and intraconal