Main page/Anterior skull base/Superior orbital fissure

Superior orbital fissure

General

  • The triangular superior orbital fissure is bounded medially by the body of the sphenoid, above by the lesser wing, and below by the greater wing and is completed laterally by the frontal bone as the greater and lesser wings converge.
  • The optic canal and the superior orbital fissure together form the orbital apex.

Location

  • The SOF provides communication between the orbit and the middle cranial fossa.
  • The cavernous sinus is located immediately behind and fills the posterior margin of the fissure, while the orbital fat and contents fill its anterior margin.

Osseous Borders

  • The SOF is situated entirely within the sphenoid bone, primarily between the lesser and greater sphenoid wings and the sphenoid body.
  • Superior Wall:
    • Formed by the
      • Lower surface of the lesser sphenoid wing
      • Anterior clinoid process
      • Adjacent part of the optic strut.
    • The upper edge of the fissure is located below the medial half of the sphenoid ridge.
  • Inferior Wall:
    • Formed by the greater sphenoid wing.
  • Medial Wall:
    • Formed by the body of the sphenoid bone.
    • The optic strut forms the upper medial border, which also forms the lateral edge of the optic foramen.
  • Lateral Apex:
    • The greater and lesser wings approach, but often do not meet, leaving a small portion of the lateral apical margin to be formed by the frontal bone.

Shape and Orientation:

  • The SOF has a somewhat triangular shape, with a wide base medially on the sphenoid body and a narrow apex laterally between the sphenoid wings.
  • The fissure is directed forward, with the lateral apex located slightly forward of the medial margin.

Relations to Adjacent Structures:

  • Optic Canal:
    • The SOF is separated from the optic canal (optic foramen) by the optic strut
      • A bridge of bone (posterior root of the lesser wing) extending from the base of the anterior clinoid process to the sphenoid body.
  • Foramen Rotundum: The lower edge of the SOF is separated from the foramen rotundum by the maxillary strut, a narrow bridge of bone.
  • Sphenoid Sinus: The medial aspect of the SOF produces a bulge/prominence in the lateral wall of the sphenoid sinus, located between the optic and maxillary struts.

Contents and Divisions

  • The SOF is divided into three sectors—lateral, central, and inferior—by the annular tendon (tendinous ring of Zinn)
  • The annular tendon surrounds the orbital end of the optic foramen and the adjacent upper-medial part of the SOF, where it attaches to a bony prominence on the lateral margin of the fissure.
Sector
Structures Transmitted
Annular Tendon Relation
Lateral Sector
Trochlear nerve (CN IV),
Frontal nerve (V1 branch),
Lacrimal nerve (V1 branch),
Superior ophthalmic vein.
These structures pass outside (lateral to) the annular tendon. The superior ophthalmic vein passes through this narrow sector, along the lower side of the lacrimal and frontal nerves, to reach the cavernous sinus.
Central Sector (Oculomotor Foramen)
Oculomotor nerve (CN III) (superior and inferior divisions),
Nasociliary nerve (V1 branch),
Abducens nerve (CN VI), and the sensory and sympathetic roots of the ciliary ganglion.
These structures pass through (inside) the annular tendon.
Inferior Sector
Inferior ophthalmic vein
Orbital fat/smooth muscle.
Situated below the annular tendon.
  • Ophthalmic nerve most lateral in the Cavernous Sinus
notion image
notion image
  • Coronal histological sections of the right cavernous orbital region.
    • Froelich et al 2007
    • FN, Frontal nerve; GSW, Greater sphenoid wing; IRM, Inferior rectus muscle; LN, Lacrimal nerve; LRM, Lateral rectus muscle; LSW, Lesser sphenoid wing; MRM, Medial rectus muscle; NeN, Nasociliary nerve; OA, Ophthalmic artery; SRM, Superior rectus muscle; SS, Sphenoid sinus.
      • Clinoidal segment C5 of the ICA
      Clinoidal segment C5 of the ICA
      The optic strut
      The optic strut
      The lateral narrow part of the SOF
      The lateral narrow part of the SOF

Neurovascular Relationships

Nerves Passing Through

  • The SOF transmits the following:
  • The oculomotor nerve (CN III) splits into superior and inferior divisions as it approaches the fissure. CN III enters the orbit through the central sector, medial to CN IV and the nasociliary nerve.
  • The trochlear nerve (CN IV) passes above and outside the superomedial edge of the annular tendon (lateral sector).
  • The ophthalmic nerve (V1) flattens in the cavernous sinus wall and splits into its three terminal branches (lacrimal, frontal, and nasociliary nerves) as it approaches the fissure.
  • The abducens nerve (CN VI) courses medial to the ophthalmic nerve in the cavernous sinus, but passes below the ophthalmic nerve in the SOF to enter the medial surface of the lateral rectus muscle (central sector).

Vessels Passing Through

  • Ophthalmic Veins
    • The superior and inferior ophthalmic veins exit the orbit by passing through the SOF and usually join to form a common trunk that enters the anterior part of the cavernous sinus.
    • The superior ophthalmic vein usually passes through the narrow lateral sector (outside the annular tendon).
  • Arterial Supply
    • The SOF transmits
      • Recurrent meningeal branch of the ophthalmic artery.
      • Deep recurrent ophthalmic artery, a branch of the inferolateral trunk of the cavernous carotid, supplies the cavernous sinus dura around the SOF.
        • Arterial branches may course through the SOF to anastomose with branches of the middle meningeal artery (MMA).

Surgical Relevance

  • Surgical Landmark:
    • The SOF defines the anterior limit of the cavernous sinus and is an important reference point for surgical approaches to the orbital apex, middle cranial fossa, and sellar region.
  • Vulnerability:
    • The nerves passing through the SOF are protected by the inner dural layer of the lateral cavernous sinus wall, meaning the outer dural layer can often be peeled away to expose CNs III, IV, and V1 without entering the main venous spaces.
  • Orbital Access:
    • Surgical approaches (e.g., orbitozygomatic craniotomy) often involve removing the bony margins of the SOF and adjacent structures to access lesions in the orbital apex, cavernous sinus, or middle fossa.
  • SOF Triangles (Middle Fossa):
    • The anteromedial middle fossa triangle is situated between the lower margin of the ophthalmic nerve (V1) and the upper margin of the maxillary nerve (V2), and its third edge connects where V1 exits the SOF and V2 exits the foramen rotundum.
    • Removing bone here opens into the sphenoid sinus.