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

 

 

 

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