98796-Anatomy of the Orbit

Home , Annulus of Zinn, Bone, Canal (anatomy), Choroid, Frontal bone, Globe (human eye)

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 Imaging technique

3 layers: - neuroectoderm (retina, iris, optic nerve) - surface ectoderm (lens) • CT and / or MR - mesoderm (vascular structures, sclera, choroid) •IOM plane 3 spaces: - pre-septal •thin slices extraconal - post-septal • axial and coronal projections intraconal • CT: soft tissue and bone windows

3 motor nerves: - occulomotor (III) • MR: T1 pre and post, T2, STIR, fat suppression, DWI (?) - trochlear (IV) - abducens (VI)

• 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 Mnemonic of the order in which the nerves frontal bone lesser wing of the sphenoid bone passing through the Sup. orbital fissure

Floor ”Lazy French tarts sit naked in anticipation” maxilla zygomatic bone Lacrimal nerve (branch of CN V1) Medial wall Frontal nerve (branch of CN V1) ethmoid bone (lamina papyracea) Trochlear nerve (CN IV) lacrimal bone Superior division of the oculomotor nerve (CN III) maxilla Nascociliary nerve (branch of the CN V1) Lateral wall Inferior division of the oculomotor nerve (CN III) greater wing of the sphenoid bone Abducens nerve ( CN VI) zygomatic bone Courtesy Dr C Romanovski

Orbital fissures and optic canal Inferior orbital fissure

Superior orbital fissure: • infraorbital nerve lesser and greater wing of the sphenoid bone • zygomatic nerve • parasympathetics to Inferior orbital fissure: lacrimal gland greater wing of sphenoid • infraorbital artery the maxilla and palatine bone • infraorbital vein Optic canal: • inferior ophthalmic vein at the apex of the orbit branch to pterygoid plexus in the sphenoid bone

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 optic n. glioma • composed of retinal ganglion cell axons and support cells

optic n. meningioma

Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 - preseptal “septum” - postseptal intraconal preseptal ”Septum” extraconal soft tissue/edema - med.palpebral lig.

“retrobulbar space” - clinical term Courtesy M Annertz/Lund

Mnemonic intraconal lesions of the orbita Chemosis of the eye

”Mel met Rita mending hems on poor Charlies grave” swelling of the tissue that lines the eyelids and surface of the eye (conjunctiva)

Melanoma Meningeoma pseudotumor Episcleral infiltration Metastasis Hemangioma cellulitis Retinoblastoma Optic glioma Graves disease

Preseptal infiltration

Courtesy Dr P Maly, Malmoe

Postseptal extraconal

Postseptal intraconal

Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 Scleritis Buphthalmos and coloboma chronic, painful, inflammatory disease characterized by edema and cellular infiltration of the scleral and episcleral Buphthalmos enlargement of the globe due to tissues (outermost coat of the eye) 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 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018

Retinal detachment

occurs when the intraretinal space persists

Courtesy Dr. S Andronikou, SA

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 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018 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

Thyroid ophthalmopathy www.pinterest.com

Annulus of Zinn m. rectus inferior > med >sup > lat a fibrous ring formed by the common origin of the 4 rectus muscles

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 Cranial - sensory nerves Lat. rectus moves eye laterally VI ( n.abducens) V trigeminal n – ophthalmic n V1 (the upper eyelid, the conjunctiva and cornea of the eye) and its branches Med. rectus moves eye medially III (n. oculomotorius) Sup. rectus elevate, turns it medially III

first branch of the a. int car. http://www.retinareference.com/anatomy/ 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

The orbital veins Ophthalmic nerve

nasociliary nerve NOTE the superior ophthalmic vein is a communication frontal nerve branches between facial vein and cavernous sinus “Danger Zone” lacrimal nerve Kumar JB et al EyeNet Magazine May 2015

T1 weighted, without fat suppression, showing bilateral enlarged superior ophthalmic veins in carotid cavernous stula

Ophthamology.standford.edu

Orbital phlebograhy

showing left-sided venous fistula

Courtesy Dr. P Maly, Malmoe

Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018

Take home message

¾ complicated anatomy and embryology

¾ high number of possible diseases

For correct diagnosis

¾ important to differentiate between the preseptal and postseptal space

¾ important to differentiate between extraconal and intraconal

Lund University / Faculty of Medicine / Inst. Clinical Sciences / Radiology / ECNR Dubrovnik / Oct 2018