rad anatomy

1. RADIOLOGIC ANATOMY
OF ORBIT
BY DAGNE KIESSA (R1)
MODERATOR -DR FITHAEGEST (MD, SCR)
1

2.  Introduction
 Bony orbit
 Orbital foraminas
 Lacrimal apparatus
 extra ocular muscles
 Globe
 Orbital spaces
 Optic nerve sheath complex
 Visual pathway
 Blood supply
 Imaging modalities
 references
2

3.  orbits are bilateral structures in the
upper half of the face
 below the anterior cranial fossa and
anterior to the middle cranial fossa
that
 orbit has a volume of approximately 30
mL
 pyramidal bony cavities with the apex
lying posteriorly and the base anteriorly
 The orbit is a feature of the face and
contains
3
INTRODUCTION
ORBIT

4. Orbit…..
Anterior view Lateral viewSuperior view

5. contents
1. contain the eyeball
2. the optic nerve
3. the extra-ocular
muscles
4. the lacrimal
apparatus
5. adipose tissue
6. Fascia
7. the nerves and
vessels that supply
these structures.
5

6. Orbit…
 The long axes of the orbits
are divergent by
approximately 45° and the
medial walls are roughly
parallel.
 The fragile medial (lamina
papyracea) and inferior walls
are vulnerable to blowout
fractures in blunt trauma
 Paranasal sinus pathology
may involve the orbits by
direct extension.
6

7. Bony orbit
 Seven bones contribute to
the framework of each orbit
 They are
 the maxilla
 zygomatic
 frontal
 ethmoid,
 Lacrimal
 sphenoid
 palatine bones.
7
Fig.Bones of the orbit.

8. Anatomic relations
 Superior:
anterior cranial fossa
and frontal sinus
 Medial:
nasal cavity, ethmoid
and sphenoid sinus
 Inferior:
maxillary sinus
 Posterolateral:
temporal fossa and
middle cranial fossa
8

9. Osseous anatomy of the orbital walls
 Roof: frontal bone
(predominantly), lesser wing of
sphenoid posteriorly
 Medial: (anterior to posterior)
 frontal process of maxilla,
lacrimal bone, ethmoid bone,
small sphenoid contribution at
apex
 Floor: (medial to lateral)
 orbital plate of maxilla and
zygomatic bone, orbital
process of the palatine bone
posteriorly
 Lateral: zygomatic bone and
frontal bone
9

10. 10
A-Frontal view
B-apex view

11. A-lateral wall internal
view
B- medial wall-
internal view
11

12. 12
Floor internal view

13. 13
Boundaries of orbit
summary

14. 14

15. Important anterior structures
 Skin and connective
tissues
 Eye lids
 Orbicularis occuli
muscle
 Orbital septum
 Tarsus
 levator palpebrae
superioris
 Conjactiva
 glands
15

16. 16

17. Orbital septum
 Deep to the palpebral part of the
orbicularis oculi
 It is an extension of periosteum into
both the upper and lower eyelids from
the margin of the orbit
 extends downward into the upper eyelid
and
 upward into the lower eyelid
 is continuous with the periosteum
outside and inside the orbit.
 The orbital septum attaches to the
tendon of the levator palpebrae
superioris muscle in the upper eyelid
 attaches to the tarsus in the lower
eyelid.
17
Fig. Orbital septum.

18. TENON’S CAPSULE
 Also known as Fascia bulbi or bulbar
sheath.
 Dense, elastic and vascular
connective tissue that surrounds the
globe (except over the cornea).
 Begins anteriorly at the perilimbal
sclera, extends around the globe to
the optic nerve, and fuses with the
dural sheath and the sclera.
 Separated from the sclera by
subtenon’s space/ periscleral space,
which is in continuation with
subdural and subarachnoid spaces.
18

19. Lacrimal apparatus
 The lacrimal apparatus is
involved in the production,
movement, and drainage of fluid
from the surface of the eyeball.
 It is made up of the
 lacrimal gland and its ducts,
 the lacrimal canaliculi,
 the lacrimal sac, and
 the nasolacrimal duct.
 The lacrimal gland is anterior in
the superolateral region of the
orbit
 and is divided into two parts by
the levator palpebrae superioris
19

20. 20

21. Fissures and
foramina
 Numerous structures
enter and leave the
orbit through a variety
of openings
21

22. Optic canal
 round opening at the
apex at anterolateral
position,
 opens into the middle
cranial fossa
 bounded
 medially by the body of
the sphenoid
 laterally by the lesser
wing of the sphenoid.
 Passing through the
optic canal are
 the optic nerve and the
 ophthalmic artery
22

23. Superior orbital fissure
 Just lateral to the optic canal is a
triangular-shaped gap between the roof
and lateral wall of the bony orbit.
 This is the superior orbital fisure and
allows structures to pass between the
orbit and the middle cranial fossa
 Passing through the superior orbital fisure
are
 the superior and inferior branches of the
oculomotor nerve [III],
 the trochlear nerve [IV],
 the abducent nerve [VI],
 the lacrimal, frontal, and nasociliary branches
of the ophthalmic nerve [V1], and
 the superior ophthalmic vein
23

24. 24

25. Inferior orbital fissure
 Its borders are the greater
wing of the sphenoid and the
maxilla, palatine, and
zygomatic bones.
 This long fissure allows
communication between:
 the orbit and the pterygopalatine fossa
posteriorly,
 the orbit and the infratemporal fossa in the
middle, and
 the orbit and the temporal fossa
posterolaterally.
25

26. Infra-orbital foramen
Contents…
 The infra-orbital nerve,
 part of the maxillary nerve
[V2],
 and vessels pass through this
structure as they exit onto the
face.
26

27. Fissures and foramina summary

27

28. MUSCLES 28

29. Muscles…..
 extrinsic muscles of
eyeball (extra-ocular
muscles)
 involved in movements of
the eyeball or raising
upper eyelids, and
 intrinsic muscles within
the eyeball,
 which control the shape
of the lens and size of the
pupil.
29

30. 30

31. 31

32. 32

33. The extra-ocular
muscles….
 The oblique muscles are
necessary to assist in direct
upward and downward globe
movements.
 The extraconal levator
palpebrae superioris elevates
the upper eyelid.
33

34. EOM…
 Normal measurements of extra-ocular
muscles (with max ø = 5 mm)
 Morphology is at least as important a
marker of pathology as muscle size.
 Measurements also vary with age, sex and
interzygomatic distance
 The eye position (appreciated from the
lens or optic nerve) should be accounted
for when assessing relative sizes of the
muscles.
 Divergence of the eyes may be normal in
the sleeping patient
34

35. 35

36. GLOBE
 The globes or simply, the eyes
are paired spherical sensory
organs, located anteriorly on the
face within the orbits, which
house the visual apparatus.
 Anterior to posteior
 cornea
 the anterior chamber,
 the iris and pupil,
 the posterior chamber,
 the lens,
 the postremal (vitreous)
chamber, and
 the retina.
36

37.  The globe is divided into anterior and
posterior segments.
 The anterior segment, containing
 aqueous humour, is anterior to the lens and
its supporting circumferential ciliary body,
 which is attached to the lens by zonule fibres,
the contraction of which allows
accommodation.
 The anterior segment is further divided by the
iris into:
 the anterior chamber – the major chamber
between cornea and iris
 the posterior chamber – a potential space
between iris and lens ligament complex.
37

38. Anterior and posterior chambers
 The anterior chamber
 is the area directly posterior to the
cornea and anterior to the colored
part of the eye (iris).
 The central opening in the iris is
the pupil.
 Posterior to the iris and anterior to
the lens is the smaller posterior
chamber.
38

39.  The anterior and posterior chambers are
continuous with each other through the
pupillary opening.
 They are filed with a fluid (aqueous
humor),
 which is secreted into the posterior
chamber,
 flows into the anterior chamber through
the pupil, and
 is absorbed into the scleral venous
sinus (the canal of Schlemm),
 which is a circular venous channel at the
junction between the cornea and the iris
39

40. 40

41. 41

42. The globe..
 The lens (due to its low
water content) and ciliary
bodies are demonstrated as
dense structures distinct
from the fluid of the
anterior chamber and
vitreous on CT
 The normal aqueous and
vitreous humours are of
similar attenuation to
CSF, although streak
artefact from the bone may
produce areas of apparent
high density.
42

43. Walls of the eyeball
 Surrounding the internal components of
the eyeball are the walls of the eyeball.
 They consist of three layers:
 An outer fbirous layer,
 a middle vascular layer, and
 an inner retinal layer
 The outer fibrous layer consists of the
sclera posteriorly and the cornea
anteriorly.
 The middle vascular layer consists of the
choroid posteriorly and is continuous
with the ciliary body and iris anteriorly.
 The inner layer consists of the optic part
of the retina posteriorly and the
nonvisual retina that covers the internal
surface of the ciliary body and iris
anteriorly.
43

44. The orbital compartments 44

45. Orbital spaces….. 45

46. Space… 46

47. The optic nerve
 The optic nerve is an
evagination of cerebral
white matter and
 is therefore surrounded
by all of the normal
meningeal layers.
 The ‘optic nerve-sheath
complex’ is formed by
 the optic nerve
 the dural
 leptomeningeal
coverings.
47

48.  The dura blends with the sclera anteriorly and is tightly adherent to the
bone of the optic canal posteriorly.
 Intracranial pressure changes are transmitted to the optic nerve-sheath
complex, resulting in papilloedema.
 The individual components of the complex are not separated on CT
 but on MRI the optic nerve, the dura and the CSF-containing
subarachnoid space can be identified separately,
 particularly with high-resolution T2-weighted and gadolinium-enhanced
T1-weighted images
 Unenhanced T1-weighted images do not resolve the components of the
normal optic nerve-sheath complex.
48

49. 49

50. 50

51. The segments of the
optic nerve a…
1. Intra ocular
2. Intra-orbital
3. Intra-canalicular
4. intracranial
51
Axial T2WI illustrating the normal optic nerve anatomy and its 4
segments with length

52. The optic tracts
 the optic tracts run posterolaterally between the crus cerebri and uncus (inferior to the anterior
perforated substance).
 They merge with brain substance as they course posteriorly to the lateral geniculate nucleus (LGN),
an elevated region of grey matter on the posterior aspect of the thalamus, lateral to the pulvinar.
 Fibres from the LGN and visual cortex project to the superior colliculi, which are involved in the
control of eye movements ( Fig. 2.7a ).
52

53. The optic radiation
 Two groups of fibers run to the primary visual cortex.
 The inferior visual field fibers pass directly to the occipital cortex, lateral to the occipital horn of the lateral ventricle.
 These parallel, compact, myelinated fibres can be identified on axial T2-weighted MRI.
 The superior visual field fibres sweep inferiorly around the temporal horn, forming Meyer’s loop.
 These fibres are not readily apparent on MRI.
53

54. The visual cortex (primary)
 The visual cortex is located along the
superior and inferior margins of the
calcarine fissure on the medial aspect
of the occipital lobe.
 The inferior contralateral visual field
lies on the superior aspect of the
 fissure, the superior contralateral
visual field on its inferior aspect.
54

55. 55

56. Vascular anatomy 56
Arteries

57. Vein drainage 57

58. nerve
58

59. Vascular anatomy….
 The orbit
 Arterial supply
 The ophthalmic artery is the first
angiographically visible branch of
the intradural internal carotid
artery.
 It runs through the optic canal in the
dural sheath, inferolateral to the
nerve at the orbital apex and then
crosses (usually superiorly) to the
medial aspect of the nerve.
 Its major branch,
 the central retinal artery, pierces the
nerve inferomedially, 10 mm
posterior to the globe, and runs
centrally inside the nerve to the
globe.
59

60.  Other branches include
 the long and short posterior
ciliary,
 lacrimal,
 posterior and anterior
ethmoidal,
 supraorbital and palpebral
arteries.
 There are extensive anastomoses with the
external carotid artery (ECA),
 notably the middle meningeal and internal
maxillary branches,
 which can put the ophthalmic artery at risk
during particulate embolization of lesions
supplied by the ECA.
60

61. Venous drainage
 The superior ophthalmic vein
intraconal, coursing inferior to the
superior rectus muscle.
 It provides venous drainage from
the face via the angular and
supraorbital veins.
 The SOV is routinely visualized on
CT and MRI.
 Its diameter is variable
(approximately 2 mm is usual) and
minor asymmetry is not
uncommon.
61

62.  The inferior ophthalmic vein (IOV) drains into the SOV or directly to the cavernous
sinus.
 It communicates with the pterygoid venous plexus via the IOF and is not consistently
demonstrated on cross-sectional imaging.
 The central retinal vein drains to the SOV, another orbital vein or directly to the
cavernous sinus.
 There is no functionally signif cant collateralization within the bulb, hence glaucoma
and haemorrhage may occur as a result of its occlusion
62

63. The visual pathways –blood supply
 Arterial supply
 Optic chiasm: internal carotid A,
anterior cerebral branches
 Optic tract: posterior communicating
A and anterior choroidal A
 Lateral geniculate nucleus: anterior
choroidal and posterior cerebral A
 Optic radiations: anterior choroidal,
middle cerebral and posterior cerebral
 Visual cortex: posterior cerebral A
(with a variable contribution from the
middle cerebral A)
63

64. Imaging approach
 Plain f lm
 Plain film radiography is no longer used routinely for the evaluation of orbital
pathology,
 but familiarity with normal anatomy remains important when reviewing
emergency department trauma radiographs
 The orbital margins may be assessed by plain radiography
 The floor of the orbit is undulating and not well defined
 Lateral radiography of the anterior part of the eye may be performed on small dental
films using a low exposure, and demonstrates the cornea and eyelids
 CT has replaced radiography and may be required to assess the f loor of the orbit for
trauma
64

65. 65

66. views 66

67. 67

68. 68

69. 69

70. 70

71. Ultrasound
 Ultrasound of the eye using high-frequency transducers (5 – 20 MHz) can demonstrate its internal
anatomy
 The higher-frequency transducer visualizes the anterior segment and the lower-frequency
transducers (5 – 10 MHz) image the posterior segment
 Scans may be performed in any plane, but are usually obtained in
 transverse (axial) and longitudinal (sagittal) planes
 The aqueous and vitreous chambers are anechoic spaces
 The cornea and lens are echogenic and easily defined
 The inner walls of the eye – the choroid, retina and sclera – are not distinguishable from each other
and are seen as a line of low-amplitude echoes
 The retrobulbar fat is also echogenic, and the extraocular muscles and optic nerve appear as echo-
free structures within it

72. Ultrasound…...
 ROLE OF ULTRASOUND
 Ultrasound is used primarily to assess
internal structures of the
globe,
 particularly when direct visualization is
obscured by cataracts or hemorrhage.
 Assessment of intraocular masses &
measurement of tumour thickness for
staging.
 Differentiating between choroidal or
retinal detachments.
 Some retro-occular applications.
Relationship of normal anatomy and
pathology to each other
72

73. Ultrasound……. 73

75. 75

76. Computed tomography
 CT is an excellent modality for demonstrating the extraocular
contents of the orbit
 The lacrimal gland, extraocular muscles, globe, optic nerve and
superior ophthalmic vein are routinely seen
 The lens has a low water content and is dense on CT
 The bony walls of the orbit are demonstrated, and the foramina
of the orbit and related anatomy are readily assessed Coronal
images are best for assessment of the orbital floor, especially
in trauma

77. CT…..
 CT demonstrates orbital anatomy
well due to the substantial
differences in attenuation of
 bone, air in adjacent paranasal
sinuses, orbital fat and soft tissues.
 In particular, helical CT with
multiplanar reconstructions
provides excellent bony anatomical
detail.
 Coronal reformatted images are
important for the bony anatomy at
the orbital apex, the orbital floor
and roof
77

78. 78

80. 80

81. MRI
 MRI atomy and is unhindered by
artefacts from surrounding bone.
 Imaging protocols usually include
axial and coronal sequences,
including thin-section coronal T2-
weighted scans with fat suppression.
 Intravenous gadolinium-enhanced
T1-weighted imaging is also
combined with fat suppression so
that enhancing structures are not
obscured by the intrinsic high-T1
signal of normal orbital fat.
 Acquisition times should be short to
minimize the ef ects of eye
movement.
 MRI is the preferred technique for
demonstration of the intracranial
optic nerves, optic chiasm and tracts.
81

82. 82
MRI……

84. Sagittal T1-weighted HR-MR image. The minute anatomical structures of the eyelids,
globe and orbital connective tissue system are depicted

85. Radiology of the lacrimal gland
 Dacryocystography
 The canaliculi may be cannulated and injected with radioopaque
contrast to outline the drainage system of the lacrimal apparatus
 Patency of the duct can also be established by nuclear
dacryocystography without cannulation of the duct
 Drops containing radionuclide are dropped on to the
conjunctiva and the path of the duct is imaged by gamma camera

87. CT and MRI
 These imaging techniques may be used to study the lacrimal gland and
orbital contents
 The bony canal of the nasolacrimal duct may be identified on axial and
coronal CT images

89. References
1. American academy of ophthalmology, basic science coarse
2. Sectional anatomy for imaging professionals
3. Applied radiologic anatomy, 2nd edition
4. DI Anatomy Brain-Head-Neck-Spine
5. Anatomy for diagnostic imagining 3rd edition
6. Practical radiological anatomy
7. Diagnostic imaging head and neck
8. Grant’s atlas of anatomy
9. Thieme atlas of anatomy
10. Radiopaedia.org
11. Internet source
12. Gray ‘s surface ultrasound anatomy
13. Atlas of imaging in opthalmology
89

90.  Thank you for your patience
90