IMAGING IN ORBIT

IMAGING TECHNIQUES

• X-RAY

• ULTRASONOGRPHY

• CT SCAN

• MRI

• MRA

X RAY

• Not commonly used now a days because

• A three-dimensional structure is seen in two dimensional plane, giving rise to disturbing superimposition.

• Moreover, its sensitivity to small differences in the attenuation is low

• , i.e., its contrast resolution is poor.

X-RAY

• WATERS VIEW

• CALDWELL’S VIEW

• LATERAL VIEW

• SUBMENTOVERTEX VIEW

• RHESE VIEW

WATERS VIEW: Waters projection is created by placing the chin of the patient on the x-ray cassette with the canthomeatal line (the line that connects the lateral

canthus and the external auditory meatus) at 37 degrees to 45 degrees

(a, frontal sinus; b, medial orbital wall; c, innominate line; d, inferior orbital rim;

e, orbital floor; f, maxillary antrum; g)superior orbital fissure; h, zygomatic-frontal suture; i, zygomatic arch) 

CALDWELL’S VIEW: The patient is positioned with both the nose and forehead against the x-ray cassette while the x-ray beam is directed downward

15 degrees to 23 degrees to the canthomeatal line.

(a, frontal sinus; b, innominate line; c, inferior orbital rim; d, posterior orbital floor; e, superior orbital fissure; f, greater wing of sphenoid;g, ethmoid sinus; h, medial orbital

wall; i, petrous ridge; j, zygomatic-frontal suture; k, foramen rotundum) 

LATERAL VIEW: lateral projection (Fig. 4) is created by placing the patient's head against the x-ray cassette and centering the cassette on the lateral canthus. The x-ray

beam is directed perpendicularly to the midpoint of the cassette and enters the patient's head at the lateral canthus remote from the cassette

Radiograph of a lateral projection. (a, orbital roof; b, frontal sinus; c, ethmoid sinus; d, anterior clinoid process; e, sella turcica; f, planum

sphenoidale)

SUBMENTOVERTEX VIEW :this projection is obtained with the patient's neck extended either in the supine or upright position. The top of the head is placed so that the infraorbitomeatal line is parallel with the x-ray cassette. The x-ray

beam is directed at right angles to the infraorbitomeatal line

(a, zygomatic arch; b, orbit; c, lateral orbital wall; d, posterior wall of maxillary sinus; e, pterygoid plate; f,

sphenoid sinus

RHESE VIEW: The zygoma, nose, and chin should touch the cassette. The x-ray beam is directed posterior-

anteriorly at 40 degrees to the midsagittal plane

 Radiograph of an oblique apical projection. (a, right optic canal; b, optic strut; c, superior orbital

fissure; d, ethmoid sinus; e, planum sphenoidale; f, greater wing of sphenoid) 

PROJECTION STRUCTURE PATHOLOGYWATERS VIEW ORBITAL FLOOR

ANT 2/3BLOW OUT#

CALDWELL’S VIEW

INNOMINATE LINE,ORBITAL FLOOR POST.1/3

MEDIAL, LATERAL WALL#

LATERAL VIEW ORBITAL ROOF ORBITAL ROOF #

SUBMENTO VERTEX

LATERAL WALL OF ORBIT

LATERAL WALL#

RHESE VIEW OPTIC CANAL OPTIC NERVE TUMORS

X-RAY SIGNS OF ORBITAL DISEASES

• SIZE OF ORBIT• CHANGE IN BONE DENSITY• CHANGE IN ORBITAL SHAPE• DEHISCENCE OF ORBITAL BONES• INTRAORBITAL CALCIFICATION• ENLARGEMENT OF SUP. ORBITAL

FISSURE• CHANGE IN OPTIC CANAL

SIZE OF THE ORBIT

• SYMMETRICAL ENLARGMENT observed in intraconal lesions

e.g ; optic nerve glioma,hemangioma

ASYMETRICAL ENLARGEMENTobserved in extraconal lesionse.g; rhabdomyosarcoma, dermoid cyst

CHANGE IN BONE DENSITY

• Localised decreased density/indentation of the orbital wall. Benign tumors like,

dermoid,mixed cell lacrimal gland tumor

• Diffuse bony destruction malignant tumors like,

lacrimal gland carcinoma

SUP.WALL DESTRUCTION IN RHABDOMYOSARCOMA

CHANGE IN ORBITAL SHAPE

• As a result of local expansion of the orbital wall

Orbital dermoids

Encapsulated lacrimal gland tumors

Intraorbital calcification

• Retinoblastoma

• Orbital varix

• Optic nerve sheath meningioma

• Phthisical eye

Enlargement of Sup.Orbital fissure

• Infraclinod carotid aneurysm

• Extraseller extension of pitutary tumors

Changes in Optic Canal

• Normal dimensions:

Vertical 6mm

Horizontal 5mm

• Abnormal when ,

Asymmetry greater than 1mm,

Vertical dimension greater than 6.5mm

Optic canal enlargement

• Seen in,

• Regular enlargement

• Optic nerve glioma

• Aneurysm of ophthalmic artery

• Irregular enlargement

• Retinoblastoma

• Optic nerve sheath meningioma

OPTIC CANAL ENLARGEMENTIN OPTIC NERVE GLIOMA

Optic canal compression

• Seen in

• Fibrous dysplasia

• Paget’s disease

• Hyperostosis secondary to meningioma

• Microphthalmos

OPTIC CANAL COMPRESSION IN FIBROUS DYSPLASIA

X-RAY IN ORBITAL WALL/RIM FRACTRURES

• TRIPOD FRACTURE

• BLOW OUT FRACTURE

TRIPOD FRACTURE

ORBITAL FLOOR FRACTURE

Intraorbital foreign body

Intra ocular foreign body

CT SCAN OF ORBIT

• ADVANTAGE:• BONY DETAILS /CALCIFICATION• SPACE OCCUPYING LESION CAN BE VISUALISED IN

THREE DIMENSIONS BY COBINATION OF CCT AND CAT

• STRUCTURES LIKE GLOBE ,EOM, OPTIC NERVE CAN BE VISUALISED

• IN ORBITAL TRAUMA FOR DETECTING SMALL ORBITAL WALL #

IOFB

HERNIATION OF EOM

DISADVANTAGE

• INABILITY TO DISTINGUISH BETWEEN PATHOLOGICAL SOFT TISSUE MASS WHICH ARE RADIOLOGICALLY ISODENSE

• RADIATION INDUCED CATARACT

CT scan is most informative,

• when the ophthalmologist seeks active participation of the radiologist in the diagnostic work-up.

• The clinical information supplied by the referring ophthalmologist is used by the radiologist .

Major consideration while requesting a CT Scan

• Slice thickness

• Imaging plane

• Tissue window

• Contrast enhancement

• Modification of CT procedure

• Orbit with brain CT

Slice thickness• Spatial resolution of a CT depends on

slice thickness.

• The thinner the slice, the higher the resolution.

• Usually, 2mm cuts are optimal for the eye and orbit.

• In special situations (like evaluation of the orbital apex), thinner slices of 1mm can be more informative.

Imaging plane• Routine CT scan involves axial& coronal

views .

• Saggital view: along the axis of the inferior rectus muscle is important in evaluation of orbital floor blow-out fractures.

• A spiral CT is Preferable when reformatted sagittal cuts are required.

• The plane inclined at 30° to the orbito-meatal line  best depicts the optic canal and the entire anterior visual pathway.

Tissue window• Each tissue window has a specific window

width and window level.

• Soft-tissue window  is best for evaluating orbital soft tissue lesions,

• Fractures and bony details are better seen with bone window settings .

Contrast enhancement

• Evaluation of optic chiasma, perisellar region and extra-orbital extensions of orbital tumours.

• Helps to define vascular and cystic lesions as well as optic nerve lesions, particularly meningioma and glioma.

Modification of CT procedure

• Certain cases may require special modifications during the scanning procedure to aid diagnosis.

• In a case of orbital venous varix, it is important to request for special scans (with contrast) while the patient performs a Valsalva maneuver.

Simultaneous brain CT • Suspected neurocysticercosis with orbital

involvement.

• Head injury with orbital trauma

• Optic nerve meningiomas

Components of CT scan

• Patient dataThis includes the name, age, gender of the patient as well as the date of the CT scan .

• Type of CT scan• Plain CT scan• Contrast enhancement• It will be printed next to each image whether

the scan is plain or contrast enhanced.

Laterality

• The best way to confirm laterality is to look for the "R" or "L" mark which represents right or left respectively .

Axial scan orientation

• Each axial slice is always displayed with the anterior (ventral) end facing up.

• As we move from inferior to superior, the prominence of the nose flattens out anteriorly, and increasingly more brain parenchyma appears posteriorly.

Coronal scan orientation

• Maximum globe diameter roughly represents the equator of the eyeball.

• The cross-sectional size of the orbital cavity reduces as we move to the posterior. 

Systemic evaluation of ocular and orbital structures on CT scan

• Orbital dimensions:

• Vertical and horizontal should be measured on coronal scans

• Medial ,lateral wall, sup.orbital fissure, optic canal evaluated on axial scan.

• Orbital roof and floor on coronal scan.

The eyeball• The sclera, choroid and retina together

form a well defined ring that enhances with contrast.

• The lens appears white, and the vitreous black.

Extraocular muscles

On axial cuts only the horizontal recti are seen. 

• The superior rectus and the levator palpebrae superioris are seen as a single soft tissue shadow on high axial scans  and coronal scans .

• The superior oblique is best seen in the coronal view lying supero-medial to the superior rectus .

• The inferior oblique is the least defined muscle on CT scan.

Size•  There is an excellent symmetry between

the extra-ocular muscles of both the orbits, and they are thus comparable in all respects.

• enlargement

• maximum : tumors,cysts

• moderate : thyroid ophthalmopathy, vascular lesions, and myositis. ,

• decreased muscle diameter suggests atrophy from denervation or myopathy.

Shape:

•  Diffuse enlargement inflammation, venous congestion or infiltration,

• focal enlargement

neoplasm or cyst.

• Tendon involvement suggests myositis.

Muscle margin

• Healthy extra-ocular muscles have sharp margins.

• Uniform configuration with distinct margins is seen in Graves' myopathy and vascular engorgement.

• Irregular enlargement with indistinct borders :diffuse infiltration by metastatic disease .

Contrast enhancement•  Normal muscles have moderate contrast

enhancement,

• Marked enhancement is seen in thyroid ophthalmopathy or myositis.

• Variable in arterio-venous fistulas and neoplasms.

Extraconal tissues• The lids, conjunctiva, and the orbital septum

which on axial scans is seen to extend from the pre-equatorial part of the globe to the lateral and medial orbital margins 

• The lacrimal gland lies within its fossa supero-temporally, and can be seen on high-axial as well as anterior coronal scans .

Intrconal tissue

• The two most important structures optic nerve and the superior ophthalmic vein (SOV).

• CT evaluation of optic nerve lesions is facilitated by 1.5 mm axial scans.

Gliomas• have fusiform enlargement with sharp

delineation from the surrounding tissue .

• They are isodense with the optic nerve, and

• show variable enhancement with contrast.

Optic nerve meningioma

• They tend to be hyperdense to the optic nerve,

• More consistent contrast enhancement.

• Calcification within the optic nerve shadow

Optic nerve meningioma

Orbital diseases and CT presentation

• Vascular disorders

• orbital venous varices,

• arteriovenous malformations,

• carotid cavernous fistulas, and

• aneurysms.

Orbital varix • Fusiform and globular density

• It has smooth, well-defined margins, and shows bright contrast enhancement.

• Increase in size during Valsalva maneuvre almost always confirms the diagnosis.

• carotid cavernous fistulas

  ipsilateral enlargement of the cavernous sinus, superior ophthalmic vein and extraocular muscles, causing proptosis.

• Arterio-venous malformations : Irregular tortuosities with marked contrast enhancement, and intracranial component

Orbital neoplasia• Assessment of proptosis: Hilal &Trokel.

•  Using a mid-orbital axial scan, a straight line is drawn between the anterior margins of the zygomatic processes.

• Normally it intersects the globe at or behind the equator.

• The distance between the anterior cornea and the inter-zygomatic line is normally 21mm or less.

• Asymmetry >2mm or value > 21mm indicates proptosis.

• Size of the tumour:  Measured with the geometric protractor at its widest dimensions

Circumscription of the tumour: Whether well delineated or diffuse. Shape of the tumour: Whether it conforms to the shape of adjacent structures.

• Shape of the tumour, and whether it conforms to the shape of adjacent structures.Margin of the tumour: whether smooth (benign lesion), or irregular (malignant lesion).Effect on surrounding structures: displacement (benign lesion) or infiltration (malignant neoplasm).Internal consistency: homogenous (benign lesion) or heterogenous (malignant lesion).

.

• Surrounding bone: fossa formation (benign lesion), erosion (malignant lesion), or hyperostosis

• Exact location:extrconal/intraconal

• Relationship with the adjacent vital structures such as the optic nerve, extra ocular muscles, proximity to superior orbital fissure and optic foramen, and its posterior extent helps to plan the surgical approach.

• Extraorbital extension of the tumour.

Vascular tumours• Cavernous haemangioma:

well demarcated contrast enhancing intraconal mass.

• Lymphangiomas : poorly defined masses with heterogeneous tumour density. irregular margins, little or no contrast enhancement.

• Capillary haemangioma: well demarcated, homogenous, contrast enhancing, extraconal mass .

Pleomorphic adenomas

• Nodular well delineated lesions with moderate contrast enhancement.

• smooth and well defined margins,

• local bony fossa formation is common.

Malignant neoplasm of lacrimal gland

• Mass with poorly defined margins and

• Intralesional calcification,

• Surrounding bone destruction

• Neoplastic lesions generally tend to extend posteriorly, and may cross the vertical midline of the orbital cavity.

Dermoid cysts 

• Well delineated may show calcification of the cyst rim.

• Lucent internal consistency

Orbital inflammatory diseases 

•  Orbital cellulitis• Small stippled densities appear within the

orbital fat • Secondary thickening of extra-ocular

muscles, especially the medial rectus• A frank orbital subperiosteal abscess 

shows a typical ring enhancement on contrast study.

Orbital pseudotumour

• Wide range of CT findings.

• A well-defined mass, or mimic a malignancy.

• May show an enlarged lacrimal gland.

• Thickening of the posterior scleral rim, with surrounding soft tissue involvement.

• Muscle thickening.

Myositis• Usually involves a diffuse (occasionally

irregular) enlargement of one or more muscles

• There are usually no bony changes, and involvement of tendinous insertionis common

Graves' ophthalmopathy• Graves ophthalmopathy typically shows

unilateral or bilateral involvement of single or multiple muscles.

• CT shows fusiform muscle enlargement with smooth muscle borders, especially posteriorly.

• The tendons are usually not involved and orbital fat is normal, but pre-septal oedema may be seen.

Orbital trauma

• Evaluation of fractures: their number, location, degree and direction of fracture fragment displacement, and demonstration of detached bony fragments in the orbital or intracranial cavity.

Evaluation of soft tissue injury: Muscle entrapment, haematoma, emphysema, etc.

CT in retained foreign body

 • determines its location (extraocular or

intraocular), and its relationship to the surrounding ocular structures.

• Metal foreign bodies up to 0.5 mm can be detected,

• stone, plastic or wood less than 1.5 mm size are usually not visualised.

Orbital floor fractures

• Bony discontinuity, and displacement of fragments into the maxillary sinus

• Prolapse of orbital fat or inferior rectus, as well as opacification of maxillary sinus with or without fluid level may be seen.

• In medial wall fractures, orbital emphysema & bony discontinuity.

Ocular lesions• A retinoblastoma is seen as a well-defined

high density mass with calcification.• To differentiate between extrascleral

extension of the tumour and orbital cellulitis secondary to tumour necrosis.

• The former shows a well-defined soft tissue density in continuity with the globe, and the latter shows a diffuse orbital haze.

•MAGNETIC RESONANCE IMAGING

BASIC IMAGE SEQUENCES• T1- weighted (T1W) images - Tissues

with shorter T1-relaxation times like fat appear brighter than those with longer T1-relaxation like water/vitreous/CSF.

• T2- weighted (T2W)mages -

Tissues with longer T2-relaxation like water/vitreous/CSF, appear brighter than tissues with shorter T2-relaxation like blood products.

Fluid attenuation inversion recovery (FLAIR)

• Signal from fluid can be suppressed using the FLAIR sequence.

• FLAIR is especially useful in demyelinating conditions where the white matter hyperintensities on T2W images are better appreciated when the bright signal from the adjacent CSF in the ventricles is nulled.

Postcontrast images

• Gadolinium CAUSES shortening of T1-relaxation times, which results in brighter areas on T1W images. Therefore postcontrast images are always obtained with T1 weighting.

• The optic nerve does not normally enhance.

Fat-suppressed images

 

• Bright signal from intraorbital fat can mask the signal and enhancement of pathology.

• This problem can be overcome by suppressing the signal of fat by special fat suppression sequences.  

Heavily T2W images• This sequence helps in better visualization

and tracing the course of the cisternal portions of the cranial nerves (useful in cases of suspected 3 rd nerve palsy).

Magnetic resonance angiography (MRA)

• the intracranial vessels and aneurysms alone can be demonstrated after subtracting the images of the brain parenchyma with or without injecting GADOLINIUM

Magnetic resonanace venography (MRV):

• Similar to MRA, images of the dural venous sinuses can be obtained with or without injecting gadolinium.

 Imaging Protocol

•  Routine imaging of the orbit should include:Thin section (3 mm or less) axial and coronal T2W images of the orbit.

• Thin section fat saturated pre and postgadolinium axial and coronal images.

• The cavernous sinuses should be included in all the sequences

• Advantages of MRI Excellent soft tissue details

• Entire course of optic nerve well studied

• No exposure to radiation

• Disadvantages:

• Less sensitive for detecting bony abn. And calcification.

• Fat saturation artifacts can mimic pathology, C/I in metallic IOFB,longer time

Contraindication Of MRI

• Suspected metallic intraocular foreign bodies:

• Cardiac pacemaker and implanted cardiac defibrillator:

• MRI incompatible aneurysm clip.• Implants: Cochlear, otologic, or ear implant. • Lid gold implants  and metallic orbital floor

implants .

Imaging plane

T2W Axial section with fat supression through mid orbit

T2W axial scan through sup.orbit

T2W axial scan through inf. orbit

T2W coronal section through ant. orbit

T2w coronal section through globe

T2W coronal section post to globe

MRI in retinoblastoma &cavernous hemangioma

MRI in orbital varix in supine position and prone position

Ultrasonography

• Non invasive

• Well tolerated

• Safe technique

USG

• D/D is based on

• Patterns of sound reflectivity at the surface of the mass.

• Transmission characteristics of the sound wave as it passes through the lesions.

Normal echo pattern

• Scan through the plane of the optic nerve

• Normal echo pattern appers as W shaped acoustially opaque area.

Echo pattern in mass lesions

• Cystic swellings:

• mucocele ,dermoid cyst

• Shrpely defined round border,good sound transmission

Solid tumors

• Like, optic nerve glioma

• Well outlined border

• Poor sound transmission

Spongy lesions of orbit

• Like, Hemangioma

• Irregular shape ,good sound transmission, strong internal echoes

Infiltrating orbital lesion

• Like, pseudotumors, lymphangioma, metastatic carcinoma

• Variable shape,

• Poor sound transmission

USG in grave’s ophthalmopathy

• Thickening of extra ocular muscle

• MR is the first muscle to enlarge

• Accentuation of retrobulbar fat

• Perineural inflammation of optic nerve

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