anatomical variations associated with the vertebral column Flashcards
Sclerotome parts of the somites formed from what?
mesodermfrom the vertebrae.
during week 4 what happens to the sclerotome?
the sclerotome migrate around the neural tube and notochord descending cranial to caudal.
The sclerotome undergoes what?
resegmentation which is when the caudal half fuses with the cephalic half of the subadjacent sclerotome.
mesenchymal cells do what?
Mesenchymal cells fill the space between the sclerotomes but they do not proliferate and they contribute to the intervertebral discs.
The notochord remains as what?
The notochord remains as the nucleus pulposus but is not present in vertebral bodies.
Myotomes bridge what?
Myotomes bridge the intervertebral discs and this allows movement of the vertebral column.
Chondrification centres where and when?
form within the sclerotome mesenchyme at week 6 and cartilage replaces it.
During week 8 what occurs?
cartilage is replaced by bone with 3 primary ossification centres. One centre in the endochondral centrum which will become the vertebral body and the other perichondral centres in each half of the neural arch.
what is the last region to ossify?
spinous process
Regional differences caused by what
expression of the HOX gene.
is congenital absence of the posterior arch of the atlas rare?
yes
do congenital absence of the posterior arch have symptoms?
asymptomatic mostly
what are some of the symptoms of congenital absence of the posterior arch?
from mild neck pain to neurological deficits after traumatic injury.
what can congenital absence of the posterior arch be associated with?
occipitalisation of the atlas or block vertebra.
what is type a of congenital absence of the posterior arch?
failure of posterior midline fusion
what is type B of congenital absence of the posterior arch?
unilateral defect
what is type C of congenital absence of the posterior arch?
bilateral defect
what is type D of congenital absence of the posterior arch?
absence of posterior arch with preservation of posterior tubercle
what is type E of congenital absence of the posterior arch?
absence of posterior arch including tubercle
what is the Arcuate foramen?
is an extra bony feature present on the posterior arch of the atlas.
what results in the Arcuate foramen?
A result of ossification of the lateral edge of the posterior atlanto-occipital membrane.
what can the arcuate foramen cause?
May lead to compression of the vertebral artery.
what are the ways to classify the arcuate foramen?
Partial or complete ossification
Bilateral or unilateral
what is common for the arcuate foramen to co-exist with?
Common to co-exist with stretching of the vertebral artery on rotation at C1-2 level.
The artery passing through the arcuate foramen on the opposite side to the direction of head turn becomes what?
becomes elongated and narrowed compressing against the lateral mass of the atlas – impairing blood flow
implications of arcuate foramen compression of neurvascular structures?
Barre Lieou syndrome Vertebrobasilar ischemia Vertigo Headaches Neck pain Vertebral artery strokes Vision disturbance Hearing loss Neuralgia Loss of consciousness Thrombus Dissection
The ventromedial portion of the somite forms what?
sclerotome which surrounds the notochord and develops
into the vertebral body.
The dorsal portion surrounds what?
the neural tube and develops into the posterior
vertebral arch
The caudal half of each sclerotome combines with what?
with the cranial half of the sclerotome
below it.
The cranial half of the first cervical sclerotome combines with what to form what?
with the caudal half of the last
occipital sclerotome to form the base of the skull,
the caudal half of the first cervical sclerotome
combines with what?
with the cranial half of the second cervical sclerotome to form the first cervical vertebra, the
pattern continues in this fashion to form the rest of vertebrae.
The body, posterior arch and transverse processes of second cervical vertebra (axis) is derived from what?
from second cervical sclerotome
what is Occipitalisation of Atlas?
Congenital fusion of the atlas and the occiput
how often does Occipitalisation of Atlas occur?
0.08%-3%
what are the causes of Occipitalisation of Atlas?
Failure of segmentation - Possibly to do with inactivation of HOX D-3
what are the fusion types of Occipitalisation of Atlas?
- Complete fusion: anterior arch, lateral masses and posterior arch
- partial fusion: osseous discontinuity between occiput and part of the atlas
what are the classifications of Occipitalisation of Atlas?
Zone 1: anterior arch
Zone 2: lateral processes Zone 3: posterior arch
Combinations of zones
what is Neurological compression syndrome due to?
due to the proximity to the spinomedullary region – narrows the foramen magnum which may compress the brain stem, vertebral artery and cranial nerves
what are some of the associated cranial nerve problems?
tinnitus, visual disturbances lower cranial nerve palsies leading to dysphagia and dysarthria
what is Subluxation?
ligamentous laxity and instability with ageing
how common is spina bifida of the atlas?
3% of normal adults
is the Accessory Ossicle of the Anterior Arch of the Atlas rare or very common ?
rare
is Accessory Ossicle of the Anterior Arch of the Atlas pathological?
no, normal anatomical variant
what are the implications of Accessory Ossicle of the Anterior Arch of the Atlas
- Interference with rotatory movements
- Degenerative changes
- Neck pain
what is the most common type of accessory rib?
lumbar rib
development of costal processes usually on seen where?
thoracic region
lumbar rib is usually symptomatic or asymptomatic?
asymptomatic
lumbar rib is associated with what?
lumbarisation
variations of the cervical rib is how common?
0.5% of population with 10% symptomatic
is cervical rib variations more common in females or males?
females
what percentage of cervical rib variations is bilateral?
50-80%
symptoms for cervical rib variation is usually what?
neurological but sometimes arterial
what usually occurs to the cervical rib in variations?
C7 costal element which is usually a small part of the transverse process becomes abnormally large
the extra rib or fibrous connection extends where\?
extends to the thoracic rib and may put pressure on the superior thoracic aperture leading to thoracic outlet syndrome
thoracic outlet syndrome is caused by what?
Caused by compression of the neurovascular bundle extending from the upper thorax to the axilla
the compression in relation to the thoracic outlet syndrome can be caused by what?
caused by the cervical rib, bony tubercles, thoracic rib or soft tissuestructures
what is the most common lumbosacral transitional anomalies?
sacralisation of L5
lumbrosacral junction in relation to sacralisation of L5 is where?
L4-S1
what is present in relation to lumborisation of S1?
S1 displays a lumbar vertebrae configuration
lumbrosacral junction in relation to lumborisation of S1 is where?
L6-S1