Orbital Tumors - Bone Anatomy

Orbital Anatomy

The orbits are conical or four-sided pyramidal cavities, which open into {the} midline of {the} face and point back into {the} head. Each consists of a base, an apex and four walls. They protect {the} eye from mechanical injury

The base, which opens in {the} face, has four borders. The following bones take part in their formation:

  1. Superior margin: frontal bone
  2. Inferior margin: maxilla and zygomatic
  3. Medial margin: frontal, lacrimal and maxilla
  4. Lateral margin: zygomatic and frontal

 

Orbital volume and dimensions: = 30 cc, 35(Height) x 45(Width) x 45 mm(medial wall depth), globe 25 x 25 mm

Bones: (F)rontal, (M)axillary,(Z)ygomatic, (L)acrimal, (E)thmoid, (P)alatine, (S)phenoid

 

 
WALL BONES CONTENTS Clinical Correlation  
Roof

Frontal
Lesser wing of sphenoid

lacrimal gland fossa
trochlea 4mm posterior to margin for superior oblique tendon

Supraorbital notch/foramen

subperisteal abscess

 
Medial Wall

Maxillary
Lacrimal

Ethmoid - thinnest

Sphenoid

lacrimal sac fossa
cribiform plate is medial to anterior orbit at {the} level of fronto-ethmoidal suture

Nasoclacrimal duct obstructions./tumors/DCRs
Medial wall fractures

subperisteal abscess

Orbital cellulitis/proptosis from ethmodial extension

 
Floor

Maxillary- second thinnest, thins posteriorly
Palatine

Zygoma

infraorbital foramen
inferior oblique origin

slopes 20 degrees down

suspensory ligament of eyeball

subperiosteal abscess
blow-out fractures

 
Lateral Wall

Zygomatic bone
Greater wing of sphenoid

lateral orbital tubercle is 11mm below F-Z suture
serves as attachment of check ligament of lateral rectus

Tripod fractures
Ruptured globes

Lateral tarsal strips

adjacent to middle cranial fossa, temporal fossa, and pterygopalatine fossa

 

 

 

  • Clinical Correlations
 
  • The medial orbital walls are nearly parallel and are 25 mm apart
  • The orbit is widest not at its entrance, but 1 cm from {the} orbital rim
    1. Yellow: fontal bone
    2. Purple: maxilla
    3. Blue: zygomatic bone
    4. Green: lacrimal bone
    5. Gray-green: nasal bone (not part of orbit)
    6. Pink: sphenoid bone
    7. Brown: ethmoid bone
    8. Light blue: palatine bone

    This is a file from {the} Wikimedia Commons. The description on its description page there is shown below. Commons is a freely licensed media file repository

  • Fissures
  • Superior orbital fissure (SOF):
    • 22 mm long
    • separates greater wing of sphenoid from lesser wing of sphenoid
    • transmits third, fourth, sixth and V1 AND SYMPATHETIC FIBERS
    • lateral rectus origin separates into superior and inferior divisions
      • Superior division transmits lacrimal, frontal and trochlear nerves
      • Inferior division transmits superior and inferior divisions of CN III, nasociliary branch of CN V, CN IV, superior ophthalmic vein, and sympathetic nerve plexus
      • Venous system: superior ophthalmic vein
  • Inferior orbital fissure (IOF)
    • Located between lateral orbital wall and {the} orbital floor
    • Transmits V2 ( maxillary) , pterygoid nerves nerve arising from pterygopalatine ganglion
    • infraorbital nerve (a branch of V2) enters {the} infraobital groove and infraorbital canal for sensation to lower eyelid, cheek, upper lid, upper teeth
    • Venous system inferior ophthalmic vein

Holes/Notches/Canals

 

 

Nasolacrimal canal Nasolacrimal canal
  • lacrimal sac fossa to {the} inferior meatus
  • separates greater wing of sphenoid from lesser wing of sphenoid
  • transmits third, fourth, sixth and V1 AND SYMPATHETIC FIBERS
  • lateral rectus origin separates into superior and inferior divisions
    • Superior division transmits lacrimal, frontal and trochlear nerves
    • Inferior division transmits superior and inferior divisions of CN III, nasociliary branch of CN V, CN IV, superior ophthalmic vein, and sympathetic nerve plexus
    • Venous system: superior ophthalmic vein
  • Supraorbital foramen/notch
    • transmits blood vessels
    • supraorbital nerve
    • Anterior/posterior ethmoidal foramen: transmits ethmoidal blood vessels and nerve
    • Zygomatic foramen: transmits zygomaticofrontal and zygomaticotemporal nerves, zygomatic artery
    • Nasolacrimal duct (NLD): exits into inferior meatus
    • Infraorbital canal: transmits infraorbital nerve (V2)
  • Ethmoidal foramina
    • anterior ethmoidal artery
    • posterior ethmoidal artery
    • allows infections and neoplasms to enter to orbit from {the} sinuses
  • Optic Canal
    • 8-10 mm long
    • located within {the} less wing of sphenoid
    • separated from SOF by OPTIC STRUT
    • Transmits. Ophthalmic nerve, ophthalmic artery, sympathetic nerves
    • Optic foramen is 6.5 mm wide: it may possibly be enlarged in {the} presence of optic nerve glioma; 1 mm of asymmetry between right and left is abnormal
 
Procedures
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