The anatomy of the craniovertebral junction and its relation to the blood vessels and nerves and ligaments

1. Craniovertebral Junction CVJ
-Anatomy-
Mohamed Elsayed Elsebaey
Neurosurgery Registrar
Egypt, Ismailia
Ministry of Health
Seba3y700025@gmail.com
Mohamed E Elsebaey

2. Embryology
• During the 3rd week,
The notochord is formed between the ectoderm
and endoderm

3. Ectoderm overlying the notochord (cephalic end)
Thicken and differentiate
Neural ectoderm
Neural plate
Neural groove
Neural folds on each side

4. In the same time
• Collection of mesenchymal cells begins to
coalese in 3 regions
• The most medial :
1. Solid mass
2. Paraxial mesoderm
3. Just lateral to the notochord
4. Precursor of bone, skeletal Ms, skin

5. Bony cranial base
• Process called Endochondral Ossification
1. Cartiliginous framework is first developed,
2. further deposition of bone,
3. Presence of other distorting forces like brain, eye,
suture growth,
4. Clivus is elongated,
5. further sutural growth along the lateral portion of
base

6. Bjork described
• 2 sutural growth sites:
1. Petro-occipital junction
2. Sphenopetrosal junction
Result in the marked lowering of the occiput and FM

7. • Most of the skull & facial bones developed by
intramembranous ossification
Mandible
Maxilla
Paramaxilla
Zygoma
Frontal
Parietal
Vomer
Palatine
Nasal bones

8. 4th week
42 Somites are formed
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8 – 10 coccogeal

9. Somite
Differentiate into:
1. Outer dermatome
2. Inner myotome
3. Medial sclerotome

10. Sclerotome
Ventromedial in location
Sclerotome  Vertebral body
The bilateral venteromedial cells migrate to the
midline and surround the notochord
each sclerotome develops central cleft, called:
Von Ebner fissure  loose collection of cells
Become precursors of the intervertebral disk

11. • Usually the superior ½ of one sclerotome
unites with lower ½ of neighbor sclerotome ,
forms the early start of vertebral body
But
The first 4 Sclerotomes:
1. Do not follow this course
2. Fuse to form the occipital bone post. Portion
of FM

12. In the same time
• Differentiation of cranial bones is simultaneous with
differentiation of the nervous system
• At the 3th and 4th week:
Neural fold  neural tube
Occurs in the region of the future atlanto-
occipital junction
Corresponds to the 4th somite

13. Neural tube
Proceeds in the same time rostral and caudal
Both ends remain opening
6th week roof of 4th ventricle thins, midline
forms magendie, laterally forms luschka
7th week  connection between 4th ventricle
and subarachanoid space is establishe d

14. Occipital Sclerotomes (4)
• 1st two occipital sclerotomes develop basiocciput
• 3rd sclerotome develops the jugular tubercles
• 4th sclerotome is called the ProAtlas
ProAtlas is the key of understanding the CVJ

16. ProAtlas
• Hypocentrum  ant. Tubercle of clivus
• Centrum  Apical cap of dens & apical Lig.
• Neural arch: divides into
1. Ventral portion  ant. Margin of FM, occipital
condyles & midline 3rd occipital condyle
2. Caudal portion  lateral atlantal masses of C1,
superior portion of post. arch of C1
3. Lateral portion  cruciate ligament & alar ligs.

17. So what about Atlas??
• Formed by the 1st spinal sclerotome
• Also this sclerotome has
• Centrum is separated from atlas and fuse with
Axis body, forming the odontoid process

18. 2nd sclerotome
• Hypocentrum  disappears
• Centrum  body of Axis
• Neural arch  facets & post. Arch of axis

19. • At birth,
odontoid process is separated from body of axis by a cartilaginous
band (vestigial disk)
Tip of odontoid process is still not ossified yet, so, not appear on
lateral radiograph
• At age 3y, it is represented by separate
ossification centre
• At age 12y, fuses with the reminder of the
dens

22. Anatomy of FM
• Osseous relationships
• Ligamentous & articular relationships
• Neural relationships:
Cranial Ns, spinal nerve roots
• Arterial relationships
• Venous relationships

23. Osseous
• Foraminal opening
• Occipital bone: squamous part, basal part &
paired condylar parts lateral to FM
• Hypoglossal canal, transmit hypoglossal N.
• Condylar fossa
• Atlas
• Axis

25. Atlas
• Ring shaped
• No body
• No spinous process
• 2 thick lateral masses  contribute with
occipital condyles
• Short ant. Arch, transverse process and
foramen transversarium
• Long curved post. Arch

26. Atlas C1

27. Axis C2

29. Ligamentous & articular
• Occiput
• Atlas
• Axis
show 4 synovial joints:
2 median ( anterior & posterior)
2 lateral (on the lateral facets)

31. Occiput/Atlas
• Articular capsules
• Anterior atlanto occipital membrane
• Posterior atlanto occipital membrane
The lateral border of the posterior
atlantooccipital membrane arches behind the
vertebral A. & C1 root, and may be ossified
where it arches behind the vertebral A.

32. Atlas/Axis
United by:
1. Cruciate ligament, Consists of transverse and
longitudinal ligs.
2. Anterior longitudinal ligament (ALL)
3. Posterior longitudinal ligament (PLL)
4. Anterior capsules

33. Occiput/Axis
4 fibrous bands:
1. Tectorial membrane
2. Apical ligament
3. 2 Alar ligs.

34. Tectorial membrane
• Cephalic extension of PLL
• Covers the dens & cruciate ligament
• Attaches above to upper surface of occipital
bone infront of FM & below to posterior
surface of body of axis

35. Apical ligament
Extend from tip of dens to anterior margin of FM

36. Alar ligament
• Arises from side of dens
• Attaches to medial side of occipital condyle

39. Neural elements
• Caudal part of brainstem
• Cerebellum
• 4th ventricle
• Rostral part of spinal cord
• Lower cranial nerves (9th , 10th , 11th & 12th Cr.Ns)
• upper spinal nerves (C1 & C2)

40. • It is believed that the limit between the medulla
and spinal cord is the C1 root
• It is easy to differentiate the limiting level from
the ventral aspect than the dorsal aspect, why??
As the ventral rootlets are always present but the
dorsal rootlets are usually absent , & , in cases
where the C1 dorsal rootlets are present, they
contribute in spinal part of spinal accessory N.

41. Dentate ligament
• White fibrous sheet, that attached to spinal
cord medially and dura laterally
• Medial border: continuous linear attachment
to spinal cord, midway between the ventral &
dorsal rootlets
• Lateral border: attached to the dura at
intervals by fibrous triangular processes

42. • The most rostral triagle of dentate lig. Is
attached to dura at the level of FM
• The 2nd triangle, is attached to the intradural
segment of the vertebral A (posterolaterally)

43. Arterial
• Vertebral A.
• PICA
• Anterior meningeal artery, br. Of vertebral A.
• Posterior meningeal artery, br. Of ascending
pharyngeal artery
• Anterior spinal artery, combination or
continuation of the paired anteroventral spinal
arteries
• Posterior spinal arteries

44. Venous
Consists of 3 groups:
1. Extradural veins
2. Intradural veins
3. Dural venous plexus
The 3 groups are interconnected by emissary
veins

45. Extradural veins
Consists of:
• Extraspinal:
vertebral venous plexus which is formed by
veins draining the deep muscles and upper
cervical vertebrae
• Intraspinal:
Epidural venous plexus that courses the epidural
space