New: Viva Hot Seat, now 100 stations Today's spot-the-diagnosis case → Free mock tests


Neuro-Imaging for Ophthalmologists: CT, MRI, MRV and Angiography

Home Ophthalmology Blog Neuro-ophthalmology Neuro-Imaging for Ophthalmologists: CT, MRI, MRV and Angiography

Neuro-Imaging for Ophthalmologists: CT, MRI, MRV and Angiography

Last updated: November 2026

Ordering the right scan, with the right request, is half the diagnosis. The radiologist needs the clinical question and the area to image; a "routine brain CT" will miss an optic nerve lesion or a venous sinus thrombosis.

CT or MRI?

Choose CT forChoose MRI for
Trauma: orbital fractures, bony detailOptic nerve and chiasm lesions
Metallic or suspected intraocular foreign body (MRI is unsafe)Demyelination (optic neuritis, MS)
Acute haemorrhage, emergency head injuryPosterior fossa and brainstem (cranial nerve palsies, nystagmus)
Orbital cellulitis and abscess (with contrast), sinus diseaseOrbital apex, cavernous sinus, perineural spread
Calcification (though for retinoblastoma use MRI to avoid radiation)Pituitary and parasellar lesions
When MRI is contraindicated or unavailableSoft tissue tumours of the orbit

Which sequence or study for which question

Clinical questionRequest
Optic neuritisMRI brain and orbits with gadolinium and fat suppression (look for nerve enhancement and white-matter lesions)
Papilloedema / IIHMRI brain with MR venography (exclude venous sinus thrombosis and mass)
Pupil-involving III nerve palsyUrgent CT or MR angiography (posterior communicating artery aneurysm)
Bitemporal hemianopiaMRI pituitary with contrast
Homonymous hemianopiaMRI brain; diffusion-weighted imaging for acute stroke
Thyroid eye diseaseCT or MRI orbits (muscle enlargement with tendon sparing; apical crowding)
Carotid-cavernous fistulaCT or MR angiography, then catheter angiography
Horner syndrome (acute, painful)Urgent CT or MR angiography of head and neck (carotid dissection)

Safety

  • MRI contraindications: metallic intraocular or orbital foreign bodies, some pacemakers and cochlear implants, older aneurysm clips. Check every patient.
  • Gadolinium: caution in severe kidney disease; iodinated CT contrast: check allergy and kidney function.
  • Pregnancy: MRI without gadolinium is generally preferred over CT.

Writing a good request

State the clinical findings, the question ("exclude compressive lesion of the left optic nerve"), the region (orbits, chiasm, brain, venous sinuses), and whether contrast or angiography is needed. Speak to the radiologist for urgent cases.

Where residents slip

  • Ordering a plain CT head for a suspected optic nerve lesion.
  • Forgetting MRV in suspected IIH.
  • Sending a patient with a metallic foreign body for MRI.
  • Not requesting angiography for a pupil-involving III palsy.

Test yourself: flip cards

Related: Approach to Diplopia: Monocular vs Binocular and the Three-Step Test, Papilledema vs Pseudopapilledema, Hereditary and Compressive Optic Neuropathies: LHON, DOA and Chiasmal Lesions.

Key sources

  • Lee AG, Brazis PW. Clinical Pathways in Neuro-Ophthalmology. 3rd ed. Thieme
  • American College of Radiology. ACR Appropriateness Criteria: Orbits, Vision and Visual Loss (current)

📘 Want more exam-ready material? See Most Commons in Ophthalmology on Kindle, or browse all my books.

Written by Dr. Dhaval Patel, MD (Ophthalmology, AIIMS New Delhi)

Consultant, Cataract & Refractive Surgery — among a small number of AIIMS-trained ophthalmologists practicing in Gujarat. Read full credentials & experience or view his 28 publications on ResearchGate.

📚 Also the author of OKAT Decoded and other high-yield ophthalmology exam-prep books used by residents and PG aspirants.

Looking for an eye specialist in Ahmedabad? Learn about our Eye Department or book a consultation with Dr. Dhaval Patel.

Related Posts