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

 

 

 

 

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 might be enlarged in the presence of optic nerve glioma; 1 mm of asymmetry between right and left is abnormal