When is a CT (Computed Tomography) head and orbit recommended?

CT Head and Orbit Indications

CT of the head and orbits with IV contrast is most appropriate for evaluating orbital infections, suspected retinoblastoma, and metal foreign bodies in the eye, while MRI is preferred for nontraumatic vision loss and detailed assessment of intraocular masses. 1

Orbital Infections

• CT orbits with IV contrast is the most useful imaging for suspected orbital infections, helping differentiate preseptal from postseptal cellulitis and detecting orbital abscesses 1
• CT head with IV contrast should be added when intracranial complications of orbital cellulitis (such as subdural empyema or cavernous sinus thrombosis) are suspected 1
• Precontrast imaging is typically not necessary in these cases as it doesn't add significant diagnostic information 1
• MRI of orbits and head with contrast can complement CT when more detailed assessment of intraorbital spread of infection is needed or when intracranial complications are suspected 1

Leukocoria and Intraocular Masses

• CT head and orbits with IV contrast is helpful for differentiating various causes of leukocoria and evaluating the extension of retinoblastoma along optic nerves and intracranially 1
• MRI of head and orbits with and without IV contrast is the most useful imaging modality for evaluating malignant intraocular masses, particularly retinoblastoma 1
• MRI is superior for showing retrolaminar optic nerve infiltrations, orbital invasion, and possible intracranial spread of tumors 1
• CT is valuable for detecting calcifications, which helps differentiate retinoblastoma (calcified) from other conditions like PHPV and Coats disease (non-calcified) 1

Orbital Trauma and Foreign Bodies

• Non-contrast thin-section orbital CT with multiplanar reconstructions is recommended for suspected metal foreign bodies in the eye 2
• CT is superior to MRI for foreign body assessment, calcification detection, and osseous evaluation 1, 2
• MRI is contraindicated when metallic foreign bodies are suspected due to potential movement of the object caused by the magnetic field 2
• CT has 94.9% sensitivity for detection of intraorbital foreign bodies, especially metallic ones 2, 3

Nontraumatic Vision Loss

• MRI of the head and orbits with and without IV contrast is the most useful imaging modality for evaluating acute nontraumatic vision loss 1
• CT head without IV contrast may complement MRI when infarct or hemorrhage in the neurovisual pathway is suspected 1
• For patients with junctional scotoma or bitemporal visual defects, MRI of the brain with contrast is preferred to evaluate the pituitary gland and optic chiasm 1
• For homonymous hemianopia or quadrantanopia defects, MRI of the brain with contrast is the preferred imaging modality 1

Ophthalmoplegia or Diplopia

• CT is complementary to MRI in evaluating patients with ocular, orbital, and skull base neoplasms 1, 4
• CT provides additional information about adjacent bone involvement, including bone erosion, sclerosis, or periosteal reaction 1
• MRI is preferred for evaluating soft tissue abnormalities and intracranial extension 1, 5

Common Pitfalls and Caveats

• Wooden foreign bodies may appear hypoattenuating on CT and can be mistaken for air; MRI may be useful as a supplementary imaging modality in these specific cases 2
• CT head alone is only indicated when concurrent head trauma or intracranial abnormality is suspected 2
• Orbital or skull radiographs are insufficient to detect pathology in patients presenting with vision loss 1, 2
• The diagnostic yield is optimal when the ophthalmologist and radiologist collaborate in the radiodiagnostic workup 4