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CT
Head and NeckDemonstration data

CT Orbits

CT of the orbits provides rapid, high-resolution assessment of the bony orbit, globe, extraocular muscles, optic nerve and retrobulbar fat. It is the first-line modality for orbital trauma and is also used for proptosis, infection and mass evaluation, with contrast reserved for inflammatory and neoplastic indications.

Indications

  • Orbital trauma with suspected fracture, globe injury or retrobulbar haemorrhage
  • Suspected metallic or radiodense intraorbital foreign body
  • Proptosis and orbital mass characterisation
  • Orbital or preseptal cellulitis and suspected subperiosteal or orbital abscess
  • Suspected optic nerve or extraocular muscle pathology (e.g. thyroid eye disease)

Contraindications & Cautions

  • Standard iodinated contrast contraindications for enhanced protocols
  • MRI preferred for optic nerve, intracranial extension and detailed soft-tissue characterisation
  • Weigh radiation dose to the lens, particularly in children and repeated imaging

Patient Preparation

  • Remove metallic eyewear, jewellery and facial hardware where possible
  • Instruct the patient to keep the eyes still or gently closed during acquisition
  • Screen for iodinated contrast allergy and renal function if enhancement planned
  • Clarify mechanism of trauma or clinical concern to tailor windows and contrast use

Technique & Parameters

  • Thin-section axial acquisition (≤1 mm collimation) covering the orbital rims to orbital apex
  • Direct or reformatted coronal images, essential for orbital floor and roof assessment
  • Sagittal reformats to profile the orbital floor and herniated contents
  • Bone and soft-tissue window review; avoid gantry angulation through the lenses where feasible
  • Intravenous contrast for suspected infection, inflammation or neoplasm

Systematic Review

  • Inspect all four orbital walls (floor, medial, roof, lateral) for fracture
  • Assess extraocular muscles for entrapment, enlargement or displacement
  • Evaluate the globe for contour, hyphaema, lens dislocation and open-globe signs
  • Review the retrobulbar fat and optic nerve for haemorrhage, mass or tenting
  • Check paranasal sinuses and intracranial structures for associated injury or extension

Key Findings & Significance

  • Orbital floor (blowout) fracture with herniation of fat/inferior rectus and the trapdoor pattern in children
  • Medial wall (lamina papyracea) fracture with orbital emphysema
  • Extraocular muscle entrapment causing restricted motility
  • Retrobulbar haemorrhage with proptosis and posterior globe tenting (compartment syndrome)
  • Subperiosteal or orbital abscess with rim enhancement adjacent to sinus disease

Differential Considerations

  • Blowout fracture versus congenital orbital wall dehiscence
  • Orbital cellulitis versus preseptal cellulitis (relationship to orbital septum)
  • Thyroid eye disease (fusiform muscle enlargement sparing tendons) versus orbital myositis
  • Cavernous venous malformation versus optic nerve sheath meningioma versus schwannoma
  • Retrobulbar haemorrhage versus orbital mass or vascular lesion

Pearls & Pitfalls

  • Paediatric trapdoor fractures may show minimal bony displacement but entrap muscle (white-eyed blowout)
  • Posterior globe tenting and a taut optic nerve indicate sight-threatening orbital compartment syndrome
  • Coronal reformats are indispensable for orbital floor and roof fractures
  • Distinguishing preseptal from postseptal (orbital) infection is critical for management and drainage decisions

Structured Report

  • Specify fractured wall(s), degree of displacement and any herniated contents
  • State presence or absence of extraocular muscle entrapment
  • Report globe integrity, lens position, hyphaema and signs of open globe
  • Describe retrobulbar haemorrhage, proptosis and optic nerve tenting if present
  • For infection, localise abscess relative to the orbital septum and note sinus source

References

  • ACR-ASNR-SPR Practice Parameter for the Performance of CT of the Extracranial Head and Neck
  • Radiographics: Winegar BA et al. Spectrum of Critical Imaging Findings in Orbital Trauma
  • ACR Appropriateness Criteria: Orbits, Vision and Visual Loss
  • Radiographics: LeBedis CA, Sakai O. Nontraumatic Orbital Conditions

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.