BASICS

What is CT or Computed Tomography..?

• It employs X rays which pass through body and reach a detector , image is reconstructed using computer.

Where to use CT..?

• At present main use of CT is in• Suspected trauma.• Foreign body.• Evaluation of orbital infections/

abscesses.• Evaluation of extraocular muscles.• Not so useful in optic nerve

disease / demyelinations.

How to read CT…?

CT scan is bascially a densitometer. Fluid filled structures like globe , fat are dark , dense structures like bone are dense

Any thing to be cautious while asking for CT..

• CT is associated with radiation. There is a small increased risk of cancer with CT examination.

• A CT head delivers 2-3 mSv of radiation dose.• Repeated CTs are also associated with rising

incidence of cataract.

What is MRI ..?

• MRI employs a powerful magnet , radio waves and movement of protons inside our body to produce images.

• High soft tissue resolution.• MRI is used in• In particular useful in optic nerve pathology ,

demyelination and cranial nerve assessment.• Less useful in trauma. Fractures not well depicted.

Caution about MRI

• MRI should not be done in a patient suspected of metallic foreign body without doing CT. if a ferromagnetic particle is present , it can have missile effect and damage orbital structures.

• Should be cautious while doing MRI in patients with pacemakers , protruding metallic objects.

I hear so many terms like T1,T2 in MRI what are they..?

• MRI is an unique diagnostic technique in the sense that one can see pathology in many colors. We label these as T1,T2 and other names.

Another commonly done sequence is called STIR sequence , this sequence suppresses fat to highlight

pathology.

ANATOMY CORONAL

Anatomy in Axial

Showing vessels

Anatomy of foramina

Cases..

Case 1

• Loss of vision right eye…

STIR sequence shows enlarged right optic nerve with hyperintensity.

Coronal images showing periventricular hyperintensity.

Diagnosis -

• Demyelination with optic neuritis• MRI is the best imaging modality to diagnose

optic neuritis and brain demyelination.• STIR sequence in MRI is useful in diagnosing

optic neuritis.

Case 2

• Proptosis for evaluation

Enlarged superior ophthalmic vein right side.

Dynamic angio

Dynamic angio

Visualization of cavernous sinus on arterial phase

Enlarged sup oph vein

DSA showing carotico cavernous fistula

Enlarged Superior ophthalmic vein

Contrast filling of cavernous sinus on arterial phase.

Carotid-cavernous fistula

• CCF (carotid-cavernous fistula )represents high flow communication between cavernous internal carotid artery and cavernous sinus.

• Remember that on MRI , only sign may be enlargement of Superior ophthalmic vein , hence easily missed.

• Type A CCF- direct communication between internal carotid artery and cavernous sinus.

• Type B-D – various types of indirect communication between ICA and cavernous sinus.

• Endovascular management of CCF is the preferred treatment.

• Treated by appropriately placing detachable balloons or detachable coils.

• Covered Stent placement is a new technique.

CCF pre procedure

CCF post procedure

PROPTOSIS DEFINITION

• A line connects bony lateral margins.

• Distance form this line to anterior surface of cornea is measured.

• Normal less than 18-20 mm.• Difference of more than 2

mm between two eyes is abnormal.

Case 3

• 2 year old child with eyelid swelling

T2 axial

T1 coronalCoronal STIR

Parasitic cyst in eyelid

• Parasites like Dirofilaria preferentially involve eye.

• In differential diagnosis of cystic lesions in orbit , this needs to be given.

• High resolution USG is characteristic , it can show live larva.

Smitha M, Rajendran VR, Devarajan E, Anitha PM. Case report: Orbital dirofilariasis. Indian J Radiol Imaging 2008;18:60-2

Case 4

• History of trauma to face left side.

2

2

Fluid level in left maxillary sinus and soft tissue tear drop caused

by blow out fracture

Case 5

• 12 year old boy hit by a tree while travelling.

Plain CTContrast CT

T2

Contrast MRI

Lucent areas seen within left orbit.Remember that wood also can cause similar appearance.

Enhancement suggests orbital cellulitis.

Final diagnosis

• Wood particles (foreign body) in orbit with granuloma.

Imaging in orbital trauma

• CT is modality of choice.• Take minimum 3 mm axial

sections with coronal reformations.

• Pay particular attention to fractures of optic canal / orbital apex fractures.

• Look for foreign body. Small FBs can be missed.

Right orbital apex fracture

Case 6..

• Severe periorbital pain right side and right 3rd nerve palsy

T2 images showing subtle mass at superior orbital fissure

Plain MRI Contrast MRI showing a mass at SOF region.

Diagnosis --Tolosa Hunt syndrome. It is an idiopathic inflammatory condition involving orbital apex and cavernous sinus.In active phase enhancing tissue is seen.

Case 7

• Pain and proptosis right orbit.

Enlarged lateral rectus muscle involvement of belly and tendinous insertion is seen which is classical of myositic form of pseudotumor.

Diagnosis– pseudotumor.It is an idiopathic inflammatory condition. Can involve many parts of orbit.Hence can be Myositic type.Involve lacrimal gland.Intraconal mass involving sclera.

Hence is one of common differential diagnosis.Difficult to separate from lymphoma.Follow up is advised always.

Thyroid associated ophthalmopathy is differential of pseudotumor. `` coke bottle `` appearance seen sparing anterior tendon.Pneumonic- IMSLOW

Case 8

A Spotter

Bilateral retinoblastoma.

Intraocular mass with calcifications.90% show calcifications.40% bilateral.

What`s new …

• With high resolution imaging , it is possible to see cranial nerves on MRI .

6th nerve

Arrows showing 3rd nerves

Arrows showing 5th nerve

What`s new ..?

• Functional MRI of visual pathway..• Newer MRI can map brain activity , by giving a

visual stimulus we can which areas of brain are getting activated.

Demonstration of visual cortex.

What`s new

• Fiber tracking of visual pathway using diffusion tensor imaging.

Common ocular lesionsRetinal detachmentRetinoblastomaChoroidal detachmentMelanomatrauma

Common intraconal lesionsOptic nerve gliomaOptic neuritisVascular malformations

Common conal lesionsPseudotumorThyroid ophthalmopathy

Common extraconal lesionsSubperiosteal abscess.Fibrous dysplasia.Lacrimal gland lesions

30 year old with headache and pain in left eye.? Caroticocavernous fistula/ vascular malformation

Case 9

Axial T2

Axial T1

STIR COR

Normal angiogram

T1 post contrast

Diagnosis

• ? Myositic pseudotumor• ? Vascular malformation

I said

Ophthalmologist said..Please see again , can not be pseudotumor

Before valsalva

Aftervalsalva

Diagnosis

• Orbital varix.

Rule out superior oblique pathology .History of trauma

CASE 10

Normal superior oblique

Question from ophthalmologist? Blow out fracture

A small blow out fracture was missed on initial look..

Commonly missed orbital lesions inmy experience on MRI and CT

• Blow out fracture if proper coronal not taken.• Carotico-cavernous fistula– due to dynamic

nature.• Worm granuloma- may need to high

resolution USG.• Small orbital varix- may need valsalva .

Thank you for viewing this presentation.Hope it was useful.