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Ophthalmology > Day 1 (3): Radiology in Orbital Diseases > Flashcards

Day 1 (3): Radiology in Orbital Diseases Flashcards

1
Q

How to describe findings in the different radiographic modalities of the orbit?

A

A. PLAIN RADIOGRAPH
- image formed is dependent on different tissue densities

  1. Density: very bright
  2. Radio-opaque/Opacity: bright
    - blocks X-rays from passing due to tissue density
  3. Radiolucent/Lucency: dark/black
    - allows X-rays to pass through

B. CT SCAN
- image formed is dependent on different tissue densities

  1. Hyperdense/High Attenuation: bright
  2. Isodense: similar to surrounding tissue
  3. Hypodense/Low Attenuation: dark/black

C. ULTRASOUND
- image formed when sound waves are reflected back to the probe

  1. Hyperechoic/Echogenic
    - bright (a lot of waves reflected back)
  2. Isoechoic
    - similar to surrounding tissue
  3. Hypoechoic
    - gray (few waves reflected back)
  4. Anechoic
    - black (no waves reflected back)

D. MRI

  1. Hyperintense/High Signal: bright
  2. Isointense: similar to surrounding tissues
  3. Hypointense/Low Signal: dark
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2
Q

Indication of radiographs of the orbit

A
  • Bony details of the orbit and face
  • Moderate soft tissue changes
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3
Q

Conventional reference point of the skull in orbital radiographs

A

Canthomeatal Line
- lateral canthus to the midpoint of the external auditory meatus

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4
Q

What are the standard orbital radiograph views?

A

Water’s Projection: chin up to sip water
Caldwell Projection: chin down to look at well
Lateral Projection: lateral skull to plate
Basal Projection

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5
Q

Describe the Water’s Projection

A

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

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6
Q

Describe the Caldwell Projection

A

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

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7
Q

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.

A

Innominate Line

  1. Fracture of lateral orbital wall - discontinuity
  2. Neurofibromatosis Type 1 - absent
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8
Q

What is the bare orbit sign and where is it seen?

A
  • 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

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9
Q

Best views for the walls of the orbit

A

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

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10
Q

Describe the Lateral Projection.

A

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

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11
Q

What is the infraorbitomeatal line?

A

Imaginary line from the external auditory meatus passing along the orbital floor and the inferior orbital rim

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12
Q

Describe the Basal Projection.

A

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

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13
Q

Axial VS Coronal VS Sagittal Views

A

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

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14
Q

Two views commonly utilized in CT and MRI studies

A
  1. Axial/Transverse View
  2. 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

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15
Q

Components of an adequate CT and MRI study of the orbit?

A
  1. Entire globe
  2. Brain and cavernous sinus
  3. Paranasal sinuses and facial soft tissues
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16
Q

Adequate slice thickness of CT and MRI studies of the orbit?

A

Sagittal (ON): < / = 1.5 mm
Axial: < / = 3 mm
Coronal: < / = 5 mm

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17
Q

Indications for Orbital CT scan

A
  1. Trauma (bony structure of face)
  2. Foreign body
  3. Calcifications
  4. Osseous, cartilaginous and fibro-osseous lesions
  5. Soft tissue lesions WITH bony erosions
  6. If with contraindications to MRI:
    - ferromagnetic foreign bodies & vascular clips
    - prosthetic materials
    - electronic devices (pacemakers)
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18
Q

Indications for Orbital MRI

A
  1. Acute proptosis (hemorrhage, abscess, malignancy)
  2. Complex ON sheath lesions
  3. Intraocular tumor with extraocular extension
  4. Wood FB (won’t show up in CT scan)
  5. Pregnant
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19
Q

Differentiate T1 Weighted VS T2 Weighted VS FLAIR MRI studies

A

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

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20
Q

Intraocular and intraorbital structures that appear bright (high signal/hyperintense on MRI?

A
  1. Choroid
  2. Orbital Fat
  3. Lens - T1 bright, T2 dark
  4. Vitreous (fluid) - T1 dark, T2 bright

RETINA: not detected

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21
Q

Compare CT scan and MRI

A

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

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22
Q

What to evaluate in cases of orbital trauma and fractures.

A

CABGS

Cranium - and intracranial structures
Adnexa - and soft tissue contents
Bones
Globe
Sinuses

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23
Q

Most common location of orbital fractures

A
  1. Medial wall (lacrimal bone)
  2. Orbital floor (medial to the infraorbital groove)
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24
Q

Screening test for orbital fractures

A

Medial wall: Caldwell
Floor: Water’s

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25
Q

Definitive study for orbital fractures

A

CT Scan in 2 views (Axial and Coronal): SSLs

  1. Size
  2. Shape
  3. Location
  4. Soft tissue injuries

MRI: not recommended; poor study for bony details
- (+) prolapsed fat

26
Q

Appearance of blood on CT scan

A

Bright white

27
Q

Mechanism of Orbital Floor Blowout Fracture

A
  1. BLUNT trauma
  2. by a NON-penetrating object
  3. causing POSTERIOR decompression of orbital contents toward the apex
  4. leading to a sudden increase in intra-orbital pressure
  5. and fracturing of the orbit at its weakest points
  6. Also, compressive force at the orbital rim leads to buckling of floor
28
Q

Sequelae of orbital floor fracture

A

Prolapse of IO, IR and soft tissue at the maxillary sinus causing entrapment –> limitation in upgaze and downgaze

29
Q

Differentiate Orbital floor BLOW-OUT fracture vs Orbital floor fracture

A

Orbital Floor Blow-out Fracture: only orbital floor is involved

Orbital Floor Fracture: orbital floor + inferior orbital rim

BUT FINDINGS AND MANAGEMENT ARE SIMILAR

30
Q

OFBOF findings on radiograph, CT scan and MRI:

A

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

31
Q

Thinnest wall of the orbit

A

Medial wall (Lacrimal Bone)

32
Q

Describe medial orbital wall fractures

A
  1. Subtle
  2. Rarely isolated; usually with orbital floor fractures
  3. (+) Orbital hemorrhage and epistaxis: ethmoidal vessels
  4. Findings and management similar if with OF fractures
33
Q

Le Fort Fractures are complex fractures involving the midface and orbit. Describe the 3 types of LFF.

A

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

34
Q

Describe Le Fort Fracture Type 1

A

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

35
Q

Describe Le Fort Fracture Type 2

A

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

36
Q

Describe Le Fort Fracture Type 3

A

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

37
Q

Describe the Tripod Fracture/Zygomatico-Maxillary-Orbital Fracture

A
  • 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

38
Q

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.

A

Optic Strut
- forms the inferolateral wall of the optic canal
- separate the optic canal from the superior orbital fissure

39
Q

Describe the orbital apex fracture.

A

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

40
Q

Optic canal is located in what bone?

A

Lesser wing of the Sphenoid bone

41
Q

Superior orbital fissure is located in what bone?

A

Sphenoid bone: separates greater wing from lesser wing

42
Q

What are the different types of orbital foreign bodies?

A
  1. Organic: poorly-tolerated; significant inflammatory and foreign body reaction
    - vegetable
    - wood
  2. Inorganic: well-tolerated; inert thus minimal inflammation
    - glass
    - metal: radio-opaque (bright) on radiographs
  3. Mixed
43
Q

Diagnostic exams for orbital foreign bodies.

A

Radiographs
- screening test

CT Scan
- determine size, location and extent of damage
- metallic FB

MRI
- wooden FB; avoid if suspecting metallic FB

44
Q

Best diagnostic test to order in patients reporting proptosis?

A

Orbital CT Scan

45
Q

What to look for in Orbital CT Scans of patients presenting with proptosis?

A
  1. Size and position of globe: is the globe enlarged or not? is the equator of the globe anterior to the orbital rim?
  2. Enlargement of EOMs: pattern and specific muscle involvement
  3. Straightening and crowding of ON
  4. Ancillary findings: (+) masses, hemorrhage, abscess
46
Q

Different patterns of enlargement of EOMs

A

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

47
Q

How does EOM enlargement cause compressive optic neuropathy?

A

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

48
Q

What is the Tram-Track sign and in what condition is it seen?

A

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
49
Q

Differentiate ON enlargement with ON gliomas vs meningiomas

A

Glioma: glial cells; FUSIFORM enlargement

Meningioma: meninges; DIFFUSE enlargement

50
Q

ON Meningioma classification according to extent of lesion.

A

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

51
Q

What radiographic features should be noted for orbital masses?

A

C3E2DI ay may intraorbital mass.

  1. Consistency: solid/cystic
  2. Contouring or molding: (+) contouring = soft, (-) molding = solid
  3. Calcification: (+) = malignant, (-) = benign
  4. Enhancement with contrast: (+) = vascular
  5. Erosion of bone: (+) = usually malignant
  6. Delineation: well-delineated border (benign) or poorly-delineated (malignant)
  7. Indentation of globe: (+) = solid
52
Q

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

A

Benign Lacrimal Gland Tumor

53
Q

Common differentials for medial orbital lesions

A
  1. Orbital cyst: well-delineated cystic hypodense cavity
  2. Nasoethmoidal meningoencephalocoele: sac of CSF, brain tissue and meninges prolapsing through a cranial floor defect
54
Q

Examples of well-delineated/encapsulated vs poorly-delineated/diffuse lesions.

A

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

55
Q

Most common cystic orbital mass

A

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)

56
Q

Most common solid orbital mass

A

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

57
Q

Most common vascular orbital tumor in adults

A

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

58
Q

Lymphoproliferative disorder of Lacrimal Gland vs Epithelial (Benign) Lacrimal Gland Tumor.

A

LPD: contouring/molding around globe
ELGT: indentation of the globe

59
Q

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

A

Lacrimal gland tumor probably benign

60
Q

Rule of 50% in lacrimal gland tumors

A

50% lymphoid
50% epithelial
- 50% benign
- 50% malignant

61
Q

Most common benign lacrimal gland tumor

A

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

62
Q

Most common malignant lacrimal gland tumor

A

Adenoid Cystic Carcinoma
- poorly-delineated, heterogenous mass with irregular borders
- usually EXTRAconal
- WITH CALCIFICATION
- (+) bone EROSION

Ophthalmology (44 decks)

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