Day 1 (3): Radiology in Orbital Diseases Flashcards
How to describe findings in the different radiographic modalities of the orbit?
A. PLAIN RADIOGRAPH
- image formed is dependent on different tissue densities
- Density: very bright
- Radio-opaque/Opacity: bright
- blocks X-rays from passing due to tissue density - Radiolucent/Lucency: dark/black
- allows X-rays to pass through
B. CT SCAN
- image formed is dependent on different tissue densities
- Hyperdense/High Attenuation: bright
- Isodense: similar to surrounding tissue
- Hypodense/Low Attenuation: dark/black
C. ULTRASOUND
- image formed when sound waves are reflected back to the probe
- Hyperechoic/Echogenic
- bright (a lot of waves reflected back) - Isoechoic
- similar to surrounding tissue - Hypoechoic
- gray (few waves reflected back) - Anechoic
- black (no waves reflected back)
D. MRI
- Hyperintense/High Signal: bright
- Isointense: similar to surrounding tissues
- Hypointense/Low Signal: dark
Indication of radiographs of the orbit
- Bony details of the orbit and face
- Moderate soft tissue changes
Conventional reference point of the skull in orbital radiographs
Canthomeatal Line
- lateral canthus to the midpoint of the external auditory meatus
What are the standard orbital radiograph views?
Water’s Projection: chin up to sip water
Caldwell Projection: chin down to look at well
Lateral Projection: lateral skull to plate
Basal Projection
Describe the Water’s Projection
Occipitomental view (path of x-ray beam)
- 45 degree angle between cassette and CML
- 45 degree angle between beam and CML
- 90 degree angle between beam and cassette
- Eliminates overlapping shadow of the petrous ridge of the temporal bone
- Evaluate orbital floor blow-out fractures: (+) soft tissue density or opacification in the roof of the maxillary sinus (Teardrop Sign)
- Best view for:
1. Orbital roof: lucency superior to inferior orbital rim
2. Orbital floor/maxillary sinus: shadow/lucency inferior to inferior orbital rim
3. Ethmoid sinus: lucencies between orbital roof shadows
Describe the Caldwell Projection
Coronal view
- X-ray cassette and CML are perpendicular
- Face and nose are against the cassette
- 25 degree angle between downward x-ray beam and CML
- 65 degree angle between x-ray beam and cassette
- Best view for:
1. Frontal sinus
2. Medial wall: ethmoidal sinus
3. Lateral wall: lacrimal gland fossa, greater wing of Sphenoid
4. Posterior third of orbital floor: near apex and lesser wing of Sphenoid
- minimized superimposition of the sphenoid bone on paranasal sinuses
A depression on the temporal surface of the greater wing of the Sphenoid where it forms the medial wall of the temporal fossa and lateral wall of the orbit.
Innominate Line
- Fracture of lateral orbital wall - discontinuity
- Neurofibromatosis Type 1 - absent
What is the bare orbit sign and where is it seen?
- Innominate line is absent or destroyed
- Classic radiograph sign of:
1. NF-1: Sphenoid Wing Dysplasia
2. Sphenoid Wing Meningioma
3. Neuroblastoma
Features:
1. Egg-shaped enlargement of anterior orbit rim
2. Posterior orbit defect
3. AP enlargement of the middle cranial fossa
Best views for the walls of the orbit
Medial and Lateral: Caldwell
Roof: Water’s, Lateral
Floor: Water’s, Lateral
Sphenoid Sinus: Basal
Ethmoid Sinus: Water’s
Maxillary Sinus: Water’s, Lateral
Frontal Sinus: Caldwell, Lateral
Describe the Lateral Projection.
Sagittal view
- Side of the head is against the cassette
- Similar to Caldwell but instead of face and nose against the cassette, the ears are against it.
- X-ray beam and cassette are perpendicular
- X-ray beam passes from one side of the head to the other
- Check for air-fluid levels in trauma
- Best view for:
1. Orbital roof
2. Frontal sinus
3. Pituitary and sella tursica
What is the infraorbitomeatal line?
Imaginary line from the external auditory meatus passing along the orbital floor and the inferior orbital rim
Describe the Basal Projection.
Submentovertex view
- Neck is hyperextended
- Contraindication: NECK INJURY
- X-ray beam is perpendicular to cassette
- X-ray beam travels from below the chin (submento-) to the top of the head (-vertex)
- Cassette is parallel to the infraorbitomeatal line
- Best view for:
1. Sphenoid sinus
2. Ethmoid sinus
3. Lateral wall
4. Zygomatic arch
Axial VS Coronal VS Sagittal Views
Axial/Transverse View
1. Plane along the horizontal (X) axis
2. Divides body into superior and inferior portion
3. Looking up from below
Coronal/Frontal View
1. Plane along Z axis
2. Divides body into anterior and posterior portion
3. Looking at the back from in front
Sagittal View
1. Plane along Y-axis
2. Divides body into left and right portion
3. Looking from the side
Two views commonly utilized in CT and MRI studies
- Axial/Transverse View
- Coronal/Frontal View
Additional views:
1. Sagittal: course of ON
2. 3D Reconstruction: surgical planning in the surgery of congenital and post-traumatic facial-orbital deformities
Components of an adequate CT and MRI study of the orbit?
- Entire globe
- Brain and cavernous sinus
- Paranasal sinuses and facial soft tissues
Adequate slice thickness of CT and MRI studies of the orbit?
Sagittal (ON): < / = 1.5 mm
Axial: < / = 3 mm
Coronal: < / = 5 mm
Indications for Orbital CT scan
- Trauma (bony structure of face)
- Foreign body
- Calcifications
- Osseous, cartilaginous and fibro-osseous lesions
- Soft tissue lesions WITH bony erosions
- If with contraindications to MRI:
- ferromagnetic foreign bodies & vascular clips
- prosthetic materials
- electronic devices (pacemakers)
Indications for Orbital MRI
- Acute proptosis (hemorrhage, abscess, malignancy)
- Complex ON sheath lesions
- Intraocular tumor with extraocular extension
- Wood FB (won’t show up in CT scan)
- Pregnant
Differentiate T1 Weighted VS T2 Weighted VS FLAIR MRI studies
ALL: Fat is WHITE, Bone is DARK, Gray matter is GRAY
Look at CSF (WW2: Water is White in T2)
If bright - T2
If dark - T1 vs FLAIR
T1: White matter is BRIGHT
FLAIR: White matter is DARK
In summary:
T1: CSF is DARK, White matter is BRIGHT
T2: CSF is BRIGHT, White matter is DARK
FLAIR: CSF is DARK, White matter is DARK
Intraocular and intraorbital structures that appear bright (high signal/hyperintense on MRI?
- Choroid
- Orbital Fat
- Lens - T1 bright, T2 dark
- Vitreous (fluid) - T1 dark, T2 bright
RETINA: not detected
Compare CT scan and MRI
CT
1. Good for most orbital diseases (esp. trauma, fractures, hemorrhage)
2. Bone and calcifications
3. Less motion artifact
4. Quicker
5. Less claustrophobic
6. CI for pregnant: (+) ionizing radiation
7. Metallic foreign bodies
8. Cheaper
MRI
1. Soft tissue lesion delineation
2. Surgical planning
3. Good view of orbital apex: less bony artifact
4. More motion artifact: pt need to stay still
5. Longer to do
6. CI for claustrophobics and with metallic foreign bodies
7. Wood foreign bodies
8. Expensive
What to evaluate in cases of orbital trauma and fractures.
CABGS
Cranium - and intracranial structures
Adnexa - and soft tissue contents
Bones
Globe
Sinuses
Most common location of orbital fractures
- Medial wall (lacrimal bone)
- Orbital floor (medial to the infraorbital groove)
Screening test for orbital fractures
Medial wall: Caldwell
Floor: Water’s
Definitive study for orbital fractures
CT Scan in 2 views (Axial and Coronal): SSLs
- Size
- Shape
- Location
- Soft tissue injuries
MRI: not recommended; poor study for bony details
- (+) prolapsed fat
Appearance of blood on CT scan
Bright white
Mechanism of Orbital Floor Blowout Fracture
- BLUNT trauma
- by a NON-penetrating object
- causing POSTERIOR decompression of orbital contents toward the apex
- leading to a sudden increase in intra-orbital pressure
- and fracturing of the orbit at its weakest points
- Also, compressive force at the orbital rim leads to buckling of floor
Sequelae of orbital floor fracture
Prolapse of IO, IR and soft tissue at the maxillary sinus causing entrapment –> limitation in upgaze and downgaze
Differentiate Orbital floor BLOW-OUT fracture vs Orbital floor fracture
Orbital Floor Blow-out Fracture: only orbital floor is involved
Orbital Floor Fracture: orbital floor + inferior orbital rim
BUT FINDINGS AND MANAGEMENT ARE SIMILAR
OFBOF findings on radiograph, CT scan and MRI:
X-ray (Water’s): Tear drop sign (herniated intraorbital fat +/- IR/IO protruding through a fracture in the orbital floor into the maxillary sinus); opacity in the roof of the maxillary sinus
CT Scan: discontinuity along the bony outline of the orbital floor +/- prolapsed intraorbital fat
MRI: prolapsed intraorbital fat
Thinnest wall of the orbit
Medial wall (Lacrimal Bone)
Describe medial orbital wall fractures
- Subtle
- Rarely isolated; usually with orbital floor fractures
- (+) Orbital hemorrhage and epistaxis: ethmoidal vessels
- Findings and management similar if with OF fractures
Le Fort Fractures are complex fractures involving the midface and orbit. Describe the 3 types of LFF.
1: Palate/Maxilla
- “Speak no evil”
- floating palate
2: Palate/Maxilla + Nose/Central Midface
- “See no evil”
- floating maxilla
3: Entire face
- “Hear no evil”
- floating face
Describe Le Fort Fracture Type 1
Maxillary fracture
- above the teeth (involves palate only)
- NO orbital involvement
Involves:
1. Anterior nasal septum
2. Lateral nasal walls
3. Pterygoid plates
4. Anterior and lateral walls of Maxillary Sinus
Describe Le Fort Fracture Type 2
Pyramidal fracture:
- Apex: Nasofrontal suture
- Sides: Medial wall, orbital floor and infraorbital rim up to the inferior border of lateral wall
- Central midface and maxilla are separated from the face and cranium
Involves:
1. Nasofrontal suture
2. Nasal and lacrimal bones
3. Infraorbital rim up to zygomaticomaxillary suture
4. Maxilla
5. Pterygoid plates
Describe Le Fort Fracture Type 3
Craniofacial dysjunction
- Face separated from cranium and suspended only by soft tissues
- Almost horizontal fracture at the level of nasofrontal suture up to the lateral portion of the superior orbital rim
Involves:
1. Nasal bridge
2. Entire orbit
3. Frontozygomatic Suture
Describe the Tripod Fracture/Zygomatico-Maxillary-Orbital Fracture
- Second most common facial bone fracture after nasal bone injuries
- Involves the zygomatic bone and it’s attachments to other bones,
- Prone to fractures due to it’s prominent position in the face
Involves:
1. Zygomaticofrontal suture + Zygomaticosphenoid suture (lateral orbital wall)
2. Zygomatic arch
3. Zygomaticomaxillary suture
4. Lateral orbital floor near infraorbital canal
A segment of bone which adjoins the anterior clinoid process (a bony projection of the lesser wing of the Sphenoid) with the body of the Sphenoid bone.
Optic Strut
- forms the inferolateral wall of the optic canal
- separate the optic canal from the superior orbital fissure
Describe the orbital apex fracture.
Involves the optic canal and superior orbital fissure
Findings:
1. Decreased VA/blurring of vision: compression of the ON in the canal
2. CSF leak: ON surrounded by subarachnoid space and LW of Sphenoid is part of orbital roof
3. Carotid-cavernous fistula
Optic canal is located in what bone?
Lesser wing of the Sphenoid bone
Superior orbital fissure is located in what bone?
Sphenoid bone: separates greater wing from lesser wing
What are the different types of orbital foreign bodies?
- Organic: poorly-tolerated; significant inflammatory and foreign body reaction
- vegetable
- wood - Inorganic: well-tolerated; inert thus minimal inflammation
- glass
- metal: radio-opaque (bright) on radiographs - Mixed
Diagnostic exams for orbital foreign bodies.
Radiographs
- screening test
CT Scan
- determine size, location and extent of damage
- metallic FB
MRI
- wooden FB; avoid if suspecting metallic FB
Best diagnostic test to order in patients reporting proptosis?
Orbital CT Scan
What to look for in Orbital CT Scans of patients presenting with proptosis?
- Size and position of globe: is the globe enlarged or not? is the equator of the globe anterior to the orbital rim?
- Enlargement of EOMs: pattern and specific muscle involvement
- Straightening and crowding of ON
- Ancillary findings: (+) masses, hemorrhage, abscess
Different patterns of enlargement of EOMs
THYROID EYE DISEASE
Fusiform: smooth enlargement of muscle belly with SPARING of the tendon
- Coca-cola bottle sign
- IR > MR > SR > LR (I Mo So Laki)
MYOSITIS
Diffuse: irregular and generalized enlargement of both belly and tendon
- SR, LPS, MR
BOTH: may involve one or more EOMs, unilateral or bilateral
How does EOM enlargement cause compressive optic neuropathy?
All recti muscles become so enlarged, obliterating the intraconal space previously filled by fat and causing compression of the ON.
Clue on CT scan: crowding of the ON
Can happen to both fusiform and diffuse patterns of enlargement
What is the Tram-Track sign and in what condition is it seen?
Optic Nerve Meningioma
- Hyperdensity of the sheath with a central hypodensity/lucency (ON)
- parallel thickening and enhancement around the ON
- distinguishes dural diseases from glioma
Differentiate ON enlargement with ON gliomas vs meningiomas
Glioma: glial cells; FUSIFORM enlargement
Meningioma: meninges; DIFFUSE enlargement
ON Meningioma classification according to extent of lesion.
I: Intraorbital
- A: flat around ON
- B: bulbiform around ON
- C: exophytic on ON
II: Orbital apex extension
- A: optic canal
- B: SOF
III: Intracranial extension
- A: optic chiasm
- B: contralateral ON
What radiographic features should be noted for orbital masses?
C3E2DI ay may intraorbital mass.
- Consistency: solid/cystic
- Contouring or molding: (+) contouring = soft, (-) molding = solid
- Calcification: (+) = malignant, (-) = benign
- Enhancement with contrast: (+) = vascular
- Erosion of bone: (+) = usually malignant
- Delineation: well-delineated border (benign) or poorly-delineated (malignant)
- Indentation of globe: (+) = solid
Pt presenting with gradually progressive unilateral proptosis since birth with no other associated s/sx.
CT: extraconal hypodense solid mass with a hyperdense wall and well-delineated smooth margins located in the superotemporal orbit
Benign Lacrimal Gland Tumor
Common differentials for medial orbital lesions
- Orbital cyst: well-delineated cystic hypodense cavity
- Nasoethmoidal meningoencephalocoele: sac of CSF, brain tissue and meninges prolapsing through a cranial floor defect
Examples of well-delineated/encapsulated vs poorly-delineated/diffuse lesions.
Well-delineated/Encapsulated = usually benign
- Cavernous hemangioma
- Fibrous histiocytoma
- Neurilemomma
- Benign lacrimal gland tumor
- Dermoid/epidermoid cyst
Poorly-delineated/Diffuse = usually malignant
- Lymphangioma
- Plexiform neurofibroma
- Histiocytosis
- Pseudotumor
- Lymphoid tumor
- Metastatic CA
Most common cystic orbital mass
Dermoid Cyst
- HETEROgenous, EXTRAconal mass with smooth margins
- contains solid and cystic components
- enhancing wall with non-enhancing lumen
- calcifications may be present
- NO indentation of the globe (if cystic)
- (+) contouring (if cystic)
Most common solid orbital mass
Epithelial (Benign) Lacrimal Gland Tumor
- homogenous or heterogenous well-circumscribed, solid, ovoid mass
- EXTRAconal at the superotemporal orbit
- WITHOUT CALCIFICATION
- (+) indentation of the globe
- NO contouring
- (+) bone REMODELLING and hyperostosis due to chronicity
Most common vascular orbital tumor in adults
Cavernous Hemangioma
- large dilated veins presenting as a well-delineated retrobulbar mass
- WITH contrast enhancement
- WITHOUT indentation of globe
- usually INTRAconal
- may present with BOV if with ON compression
- usually with no other associated s/sx
DDX:
Neurilemmoma/Schwannoma
- solid mass composed of proliferation of Schwann cells that are well-encapsulated by perineurium
- WITHOUT contrast enhancement
- WITH indentation of globe
Lymphoproliferative disorder of Lacrimal Gland vs Epithelial (Benign) Lacrimal Gland Tumor.
LPD: contouring/molding around globe
ELGT: indentation of the globe
Palpable, solid, mobile, smooth, well-delineated, non-tender mass in the superotemporal aspect of the upper lid presenting with proptosis
CT: homogenous, isodense, well-delineated, non-enhancing, ovoid mass in the superotemporal orbit with no calcifications
Lacrimal gland tumor probably benign
Rule of 50% in lacrimal gland tumors
50% lymphoid
50% epithelial
- 50% benign
- 50% malignant
Most common benign lacrimal gland tumor
Pleomorphic adenoma/Benign Mixed Cell Tumor
- well-circumscribed, solid, ovoid mass with smooth borders
- EXTRAconal at the superotemporal orbit
- WITHOUT CALCIFICATION
- (+) indentation of the globe
- NO contouring
- (+) bone REMODELLING and hyperostosis due to chronicity
Most common malignant lacrimal gland tumor
Adenoid Cystic Carcinoma
- poorly-delineated, heterogenous mass with irregular borders
- usually EXTRAconal
- WITH CALCIFICATION
- (+) bone EROSION
