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Topic

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Orbital cavity

The orbital cavity (orbit) is a paired, pyramidal bony cavity of the skull that houses and protects the globe (eyeball) along with its associated muscles, nerves, vessels, lacrimal apparatus, and connective tissues. It forms a critical interface between the cranial cavity, nasal cavity, paranasal sinuses, and face.

The orbit is of major importance in anatomy, ophthalmology, radiology, maxillofacial surgery, and neurosurgery due to its complex structure and dense concentration of vital neurovascular elements.

Synonyms

  • Orbit

  • Orbital cavity of the skull

Location

  • Situated on either side of the midline of the face

  • Inferior to the anterior cranial fossa

  • Lateral to the nasal cavity

  • Superior to the maxillary sinus

  • Anterior to the middle cranial fossa

  • Opens anteriorly to the face and posteriorly toward the cranial cavity

Shape and orientation

  • Pyramidal in shape

  • Base: Anterior orbital rim

  • Apex: Posteromedial, directed toward the optic canal

  • Medial walls: Nearly parallel

  • Lateral walls: Diverge posteriorly at approximately 45°

Bony walls

  • Roof:

    • Frontal bone (orbital plate)

    • Lesser wing of sphenoid

  • Floor:

    • Maxilla (orbital surface)

    • Zygomatic bone

    • Palatine bone (small contribution)

  • Medial wall:

    • Ethmoid (lamina papyracea)

    • Lacrimal bone

    • Maxilla

    • Body of sphenoid

  • Lateral wall:

    • Zygomatic bone

    • Greater wing of sphenoid

Openings and communications

  • Optic canal:

    • Transmits optic nerve (CN II) and ophthalmic artery

  • Superior orbital fissure:

    • Communicates with middle cranial fossa

  • Inferior orbital fissure:

    • Communicates with pterygopalatine and infratemporal fossae

  • Nasolacrimal canal:

    • Drains into the inferior meatus of the nasal cavity

Contents

  • Globe (eyeball)

  • Extraocular muscles:

    • Superior, inferior, medial, and lateral recti

    • Superior and inferior oblique muscles

  • Nerves:

    • Optic nerve (CN II)

    • Oculomotor (CN III)

    • Trochlear (CN IV)

    • Abducens (CN VI)

    • Ophthalmic division of trigeminal nerve (V1)

  • Vessels:

    • Ophthalmic artery

    • Superior and inferior ophthalmic veins

  • Lacrimal gland and apparatus

  • Orbital fat and connective tissue

Relations

Superiorly:

  • Anterior cranial fossa

  • Frontal lobe of the brain

Inferiorly:

  • Maxillary sinus

Medially:

  • Ethmoid air cells

  • Nasal cavity

Laterally:

  • Temporal fossa

Posteriorly:

  • Cavernous sinus and middle cranial fossa

X-ray appearance

Orbital radiographs (Caldwell / Waters views):

  • Orbital rims: Smooth, well-defined bony margins

  • Roof and floor: Thin radiopaque lines

  • Medial wall: Often indistinct due to thin lamina papyracea

  • Symmetry: Orbits appear symmetric in size and shape

CT appearance

Non-contrast CT:

  • Modality of choice for bony anatomy

  • Orbital walls: Clearly visualized cortical bone

  • Extraocular muscles: Soft-tissue density structures

  • Orbital fat: Low attenuation

  • Optic canal and fissures: Well delineated

Post-contrast CT:

  • Ophthalmic vessels: Enhance

  • Extraocular muscles and lacrimal gland: Mild enhancement

  • Orbital apex: Well assessed for vascular and soft-tissue detail

3D CT VRT appearance

Volume-rendered technique (VRT):

  • Orbital rims: Clearly visualized three-dimensional contours

  • Wall integrity: Excellent depiction of fractures or deformities

  • Symmetry: Allows comparison between right and left orbits

  • Clinical utility: Preoperative planning and trauma assessment

MRI appearance

T1-weighted images:

  • Orbital fat: High signal intensity

  • Extraocular muscles: Intermediate signal

  • Optic nerve: Intermediate signal with surrounding CSF sheath

  • Globe: Intermediate-to-low signal vitreous

T2-weighted images:

  • Vitreous humor: High signal

  • Extraocular muscles: Intermediate-to-low signal

  • Optic nerve sheath CSF: High signal

CT VRT 3D image

Orbital cavity 3d

X Ray image

Orbital cavity