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Vertebral Column > Anatomical Variation in the Vertebral Column > Flashcards

Anatomical Variation in the Vertebral Column Flashcards

1
Q

What are the complete anatomical features of ocipitalisation of the atlas?

A

Fusion of the anterior arch, posterior arch and lateral masses

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2
Q

What are the partial anatomical features of the occipitilisation of the atlas?

A

Discontinuity between any part of the axis and occiput

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3
Q

What is occipitilisation of the atlas?

A

Congenital fusion of the atlas to the base of the occiput.

Associated with abnormalities which lead to narrowing of the space available for the spinal cord or brainstem.

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4
Q

Describe the morphologic classification of occipitilisation by Ghlove et al. (2007)

A

4 patterns according to the anatomic site of occipitilisation (zones 1, 2 and 3).

  • Zone 1 - fused anterior arch
  • Zone 2 - fused lateral masses
  • Zone 3 - fused posterior arch
  • 4th pattern - combination of these fused zones
    *
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5
Q

Describe the effects of occipitilisation found by Ghlove et al. (2007)

A
  • 57% had atlantoaxial instability
  • 27% had associated C2-C3 fusion
  • 37% had spinal canal encroachment
    • Highest prevalence of spinal canal encroachment (63%) was noted in patients with occipitilisation in zone 2.
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6
Q

How does occipitilisation occur in embryological development?

A
  • Resegmentation of sclerotome into caudal and cephalic parts
  • Sclerotome fails to differentiate into cranial and caudal parts
  • Cranial part of C1 does not sgement from caudal part of O4
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7
Q

What are the implications of occipitilisation of the atlas?

A
  • Anomalous vertebral arteries
  • Torticollis
  • Neck pain and stifness
  • Myelopathy
  • Atrophy of rectus capitis posterior major
  • Inadequate attachment for obliquus capitis muscles
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8
Q

Describe anterior congenital absence of C1

A
  • 0.1% prevalence
  • Unfused anterior synchondrosis
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9
Q

Describe posterior congenital absence of C1

A
  • 4-5% prevalence
  • Type A - 2 hemiarches (90%)
  • Type B - Unilateral cleft
  • Type C - Bilateral cleft
  • Type D - Absence of arch with tubercle
  • Type E - Absence of arch and tubercle
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10
Q

What are the implications of anterior congenital absence of C1?

A
  • Instability
  • Torticollis due to asymmetrical lateral masses
  • No articulation site for the dens
  • Absence of the transverse atlantal ligament
  • Lack of attachment site for:
    • Longus colli and anterior longitudinal ligament (anterior tubercle)
    • Atlanto-occipital membrane and anterior atlanto-axial ligament (superior and inferior borders).
  • Subluxation and cord compression - quadriparesis
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11
Q

What are the implications of posterior congenital absence of C1?

A
  • Usually stable
  • Generally asymptomatic
  • Spinal canal stenosis
  • Myelopathy
  • Neck pain
  • Pathogenesis unknown
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12
Q

What are the anatomical features of atlantoaxial subluxation?

A
  • Anterior sliding of C1
  • 15-20% occurrence with Down’s Syndrome
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13
Q

Describe the variant: arcuate foramen of the atlas

A
  • Prevalence = 16-17%
  • No difference between sexes
  • Develops due to genetic or environmental factors
  • Pathogenesis:
    • ​Calcification of posterior atlanto-occipital membrane
    • Ossified primitive ligaments
    • Bony feature that forms a bridge over the vertebral artery
    • Accessory transverse foramen of atlas
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14
Q

What are possible reasons for anatomical variation of the atlas (arcuate foramen, occipitalisation and defect of the posterior arch)?

A
  • Some suggest that these ponticles may be remnants of the proatlas (occipital vertebra).
  • Others have suggested that they represent ossified primitive ligaments or parts of the posterior atlanto-occipital ligament.
    • But, ossification of ligaments resulting in the formation of the foramen arcuale is unlikely because ossification centres have not been observed in these structures
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15
Q

Describe the posterior atlanto-occipital membrane

A
  • From the posterior portion of the superior articular process to the posterior arch of the atlas
  • Encloses V3 portion of the vertebral artery
  • Variants:
    • Complete / incomplete
    • Bilateral / unilateral
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16
Q

What are the anatomical features of odontoid dysgenesis?

A
  • Hypoplasia
    • Short dens height
  • Os odontoideum
    • Failed fusion of the dens to the centrum
  • Os terminale persistens
    • Failed fusion of ossiculum terminale to the body of the dens
  • Bifid dens
    • Failed or partial fusion of 2 parts of the body of the dens
    • Bifurcation of os terminale (dens bicornis)
  • Agenesis
    • Dens fails to develop
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17
Q

What are the implications of odontoid dysgenesis?

A
  • Neck pain
  • Torticollis
  • Quadraparesis
  • Neuropathies
  • Brain stem strokes
  • Atlantoaxial instability
  • Atlantoaxial subluxation
  • No anchorage to transverse atlantal ligament
  • Hypermobile dens causing spinal cord or brain stem compression
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18
Q

What are the anatomical features of pseudosubluxation of C2?

A
  • Anterior sliding of C2 on C3
  • Juvenile skeleton:
    • Hypermobility
    • Lax ligaments
    • Large head in relation to weak neck muscles
    • Shallow, angled facet joints
    • Incomplete ossification of odontoid
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19
Q

What are the implications of pseudosubluxation of C2?

A
  • Juvenile skeleton:
    • None
  • Adult skeleton:
    • C2 dislocation
    • Possible hangman’s fracture
  • Associated with:
    • Down’s syndrome
    • Moquio’s syndrome
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20
Q

What is Klippel-Feil syndrome?

A

Abnormal congenital fusion of two or more cervical vertebrae.

Carries a risk of injury to the cervical spinal cord.

21
Q

Describe the epidemiology of Klippel-Feil syndrome

A
  • 0.71% prevalence
  • Female predominance
22
Q

Describe the aetiology of Klippel-Feil syndrome

A
  • Genetic: autosomal recessive or autosomal dominant
  • Environmental: alcohol use
23
Q

Describe the pathogenesis of Klippel-Feil syndrome

A

Caused by improper segmentation of cervical vertebrae during weeks 3-8 of gestation.

24
Q

Describe type 1 Klippel-Feil syndrome

A

Cervical spine fusion in which elements of many vertebrae are incorporated into a single block.

25
Q

Describe type 2 Klippel-Feil syndrome

A

Cervical spine fusion in which there is a failure of complete segmentation at only one or two cervical levels and may include an occipito-atlantal fusion.

26
Q

Describe type 3 Klippel-Feil syndrome

A

Type 1 or type 2 KFS with co-existing segmentation errors in the lower dorsal or lumbar spine.

27
Q

What is the most commonly fused spinal level?

A
  • C2 and C3
  • Cho et al. (2014) case study:
    • Complete fusion on anterior and posterior aspects
    • Foramen transversarium present on both vertebrae
    • No IV disc
28
Q

List the implications of Klippel-Feil Syndrome

A
  • Functional:
    • Reduced range of motion
  • Degenerative changes / pathology:
    • Acquired cervical stenosis → Myelopathy
    • Osteoarthritis → Radiculopathy
    • Dens fracture
  • Abnormal curvature
    • Scoliosis in 53.3% of young KFS patients
29
Q

What causes neural arch variations?

What are the usual symptoms?

A

Changes in the ossification process.

Often asymptomatic.

30
Q

List the neural arch variations

A
  • Retrosomatic clefts - vertical defects in the pedicle (thickening/thinning).
  • Retroisthmic clefts (rare) - dorsal lamina inferior articular process.
  • Spinal dysraphism - failure of fusion of the neural arch.
  • Articular processes non-existent.
  • Failure of posterior midline fusion (atlas) - unilateral or bilateral.
  • Primary spondylosis of the axis - clefts through the C2 pedicles.
31
Q

What is spinal canal stenosis?

In which regions does it occur?

A

Narrowing of the spinal canal.

Occurs most commonly in the lumbar or cervical region.

32
Q

What are the symptoms of cervical spinal canal stenosis?

A
  • Gait disturbance resulting in partial paralysis of the lower limbs.
    • This can also limit flexion of the neck
33
Q

What does stenosis of the spinal canal in the lumbar region lead to?

A

Compression

34
Q

What is spina bifida?

A

A congenital condition where the vertebral column in open posteriorly.

35
Q

What is the epidemiology of spina bifida?

A

0.5-0.8 live births

36
Q

Describe the pathogenesis of spina bifida

A
  • Failed closure of the neural tube in the 4th week post-fertilisation.
  • Vertebral arch of the spinal column is either incompletely formed or absent.
37
Q

Describe spina bifida occulta

A
  • Absence of spinous process
  • Variable amount of lamina
38
Q

Describe meningiocele

A

Meningeal tissue and CSF herniation

39
Q

Describe myelomeningiocele

A

Herniation of meningeal tissue, CSF and CNS tissue

40
Q

What are the clinical signs of spina bifida occulta?

A

None

41
Q

What are the clinical signs of meningiocele?

A

Usually asymptomatic

42
Q

What are the symptoms of myelomeningiocele?

A
  • Sensory deficit
  • Motor deficit
  • Urinary incontinence
  • Faecal incontinence
  • 65-85% associated with hydrocephalus
43
Q

How common is spina bifida occulta?

A

Found in 10-15% of the general population - usually an incidental finding.

44
Q

Describe the pathogenesis of myelomeningiocele

A
  • Primary pathogenesis:
    • ​Failed neural tube closure in the embryonic spinal region.
    • Leads to prologned exposure of the open neural tube to the amniotic fluid environment.
    • Remarkably, the bifid neuroepithelium initially undergoes relatively normal neuronal differentiation, with the development of spinal motor and sensory function even below the lesion level.
    • As gestation progresses however, the exposed spinal cord becomes haemorrhagic and neurons die as a result of toxicity of the amniotic fluid.
45
Q

Describe butterfly vertebra

A
  • Rare, only a few cases reported
  • Considered asymptomatic
  • Occurs between 3-6 weeks gestation
  • Symmetric fusion defect - ‘split’ vertebra
  • Both chondrification centres fail to develop
  • May be confused with a compression fracture if there is trapezoidal or cuneiform anterior wedging.
46
Q

List the associations of butterfly vertebra

A
  • Pfeiffer syndrome
  • JarchoLevins syndrome
  • Crouzon syndrome
  • Alagille syndrome
  • Other spinal anomalies such as kyphoscoliosis, hemivertebrae or spina bifida
47
Q

Describe hemivertebrae

A
  • Occurs during 4-6 weeks development
  • One chondrification centre fails to develop, producing a wedge of bone (half a vertebral body, a single pedicle and a hemilamina).
  • In anterior ossification fails, posterior hemivertebrae results.
  • Occurs in the thoracic and lumbar regions.
  • Results in congenital scoliosis.
48
Q

What are the 4 classifications of hemivertebra?

A
  • Fully segmented - no attachment to any other vertebrae. The most concerning type.
  • Semi segmented - half fused with vertebra. No IV disc.
  • Incarcerated - joined by the pedicles. Less concerning.
  • Non segmented - connected to others. Less concerning.
49
Q

List the associations of hemivertebrae

A
  • VATER syndrome
  • VACTERL syndrome
  • Jarcho-Levin syndrome
  • Klippel-Feil syndrome

Vertebral Column (13 decks)

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