Vasculature of the Vertebral Column Flashcards
Where does arterial supply to the cervical vertebral column arise from?
- Vertebral arteries
- Ascending cervical arteries
Where do the vertebral arteries arise from?
- From the subclavian arteries as the V1 (osteal) segment
- Upon entering the C6 transverse foramen, it is the V2 segment
Describe the V2 segment of the vertebral artery
- Arises from the C6 transverse foramen
- Runs anterior to cervical nerve roots
- Artery is covered by intertransverse muscles
- Accompanied by a sympathetic plexus from the inferior cervical sympathetic ganglion
- Surrounded by a venous plexus, which becomes the vertebral vein
Describe the anterior branches of the vertebral artery and what they supply
- Supply the ventral surface of the cervical vertebral bodies
- May also supply the uncovertebral joints of Luschka
- Most commonly present at C3, C4
- At C2, an anterior arterial ascending branch supplies the ventral aspect of the body of C2 and an arch around the odontoid process.
- Anterior branches directly penetrate the cortical bone.
Describe the posterior branches of the vertebral artery and what they supply
- Supply the dorsal surfaces of the cervical laminae and the spinous processes.
- Most commonly present at C4, C5
Describe the lateral branches of the vertebral artery and what they supply
- Mostly responsible for supply of deep neck musculature
- Osteoarticular branches supply the facet joints
Describe the medial branches of the vertebral artery and what they supply
- One branch passes deep to the posterior longitudinal ligament and anastomoses with the artery of the other side, forming an arterial plexus.
- Main blood supply to the vertebral body
- Enters via the dorsal surface of the vertebral body
- Single nutrient vessel enters at midline and penetrates to about 1/2 of vertebral body depth
- Another branch forms an arcuate pattern on the posterior spinal canal, supplying:
- Lamina
- Spinous processes
- Pedicle
- Facet joints
Describe the ascending cervical arteries
- Main origins:
- Inferior thyroid artery (72.3%)
- Thyrocervical trunk (10.7%)
- Sends off spinal branches through the intervertebral foraminae into the spinal canal
- Main function is to supply the spinal cord and meninges
- Can give some supply to the edges of the dorsal vertebral body and ventral laminae
- Spinal branches further branch into anterior and posterior segmental medullary arteries
Describe the anterior meningeal branch of the vertebral artery
- Arises from the medial surface of the vertebral artery above C3 transverse foramen.
- Osseous branches supply:
- Body of the odontoid process of C2
- Articular plate of the atlanto-occipital and atlanto-axial joints
Where do the posterior intercostal arteries which supply the thoracic vertebrae run?
- They cross the anterolateral aspects of the vertebral bodies.
- As they do this they give off:
- Periosteal branches
- Equatorial branches
Where does the blod supply to the thoracic vertebrae arise from?
Posterior intercostal arteries
What are the major banches given off by the posterior intercostal artery to supply the thoracic vertebral column?
- Spinal branch enters the spinal canal at the level of the costotransverse joint via the intervertebral foramen.
- This artery gives off:
- An anterior branch that will supply the dorsal aspect of the ventral vertebral body
- A posterior branch that will supply the ventral aspect of the laminae
Where does the blood supply to the lumbar vertebral column come from?
- The lumbar arteries
- Origin of the lumbar arteries: 4 pairs of arteries arising from the posterolateral aspect of the abdominal aorta
- A 5th pair arises from the middle sacral artery
Describe branches of the lumbar arteries supplying the lumbar vertebral column
- Gives spinal branches which enter the spinal canal via the intervertebral foraminae.
- A posterior spinal canal branch gives off well-defined branches to supply the epidural fat, dural sac, laminae and the base of each spinous process.
- The branch from each lamina bifurcates to supply superior and inferior articular processes.
Which arteries supply the sacrum?
- Iliolumbar arteries
- Lateral sacral arteries
- Median sacral arteries
Describe the iliolumbar arteries
- Usually branch from the posterior trunk of the internal iliac artery
- Run superolaterally in front of the sacroiliac joint
- A lumbar branch may anastomose with the 4th lumbar artery
- A small spinal branch enters the spinal canal via the interventricular foramen between the 5th lumbar and the 1st sacral vertebrae
- May also arise directly from the posterior aspect of the internal iliac artery
Describe the lateral sacral arteries
- On each side, there is a superior and inferior branch, originating from the posterior branch of the internal iliac artery.
- Pass medially and descend anterior to sacral anterior rami.
- Give off spinal branches which pass through the anterior sacral foraminae to supply the vertebrae.
Describe the median sacral artery
- Small unpaired artery arising from the posterior aspect of the abdominal aorta, superior to its bifurcation.
- Runs anterior to the bodies of the last one or two lumbar vertebrae, the sacrum and the coccyx.
- Can give rise to the 5th pair of lumbar arteries
- As it descends over the sacrum, it gives off branches to anastomose with those of the lateral sacral arteries.
- These support the branches which enter the spinal canal via the anterior sacral foraminae
- Small periosteal branches and equatorial branches supply the anterior aspect of the sacrum, similar to the superior regions of the vertebral column.
What happens to blood vessels which surround the intervertebral disc during early development?
They gradually dissipate resulting in an avascular structure
How (generally) does the vertebrae receive its blood supply?
- Segmentally, from branches of vessels that lie adjacent to it.
- These branches anastomose with the anterior and posterior spinal arteries to supply the spinal cord.
Which parts of the vertebrae are vascularised?
- The part of the body immediately adjacent to the disc is avascular.
- The more central region is vascular.
Why is the central vascular region of the vertebrae zoned?
It is likely that diffusion of O2 and nutrients for disc metabolism is zoned because of the arrangement of the lamellae of the annulus fibrosus.
(Probably)
Describe the arterial supply to the central region of the vertebral column
- Central region can be divided into 3 zones:
- Innermost zone supplied by the tortuous nutrient artery
- Middle zone supplied by the metaphyseal arteries
- The most peripheral zone is supplied by the peripheral arteries
What happens to the nucleus pulposis with age?
- Dehydrates and loses its elastic property
- Loses proteoglycans
- Gains collagen
What does loss of proteoglycans in the nucleus pulposus result in?
- Loss of glycosaminoglycans
- This is responsible for reduced osmotic pressure of the disc matrix and so a loss of hydration
What happens when the disc matrix is dehydrated?
- The IV disc stiffens and loses its important ability to deform and reform under changing pressure.
- When load is applied, the disc will lose height.
What results from degeneration of the IV discs
- Necrotic appearance due to cell death
- Can put excess pressure on supporting structures:
- Apophyseal joints adjacent to the damaged disc
- Ligamentum flavum
What would result from reduced tensional force on the ligamentum flavum?
May result in thickening and remodelling and due to its inherent loss of elasticity, the ligament may bulge into the vertebral canal, resulting in spinal stenosis
When do IV discs degenerate?
- Far earlier than other musculoskeletal tissues
- About 20% of people in their teens have discs with mild signs of degeneration
- Degeneration increases steeply with age, particularly in males
- Around 10% of 50-year-old discs are severely degenerated
- Around 60% of 70-year-old discs are severely degenerated
What are Schmorl’s nodes?
- Vertical protrusion / herniation of the nucleus pulposus through the cartilaginous and bony end plate into the vertebral body.
- Causes a defect in the vertebrae superior and inferior to the herniated disc.
- Most common endplate defect.
List the types of Schmorl’s nodes
- Traumatic
- Idiopathic
- Developmental
- Genetic
- Decreased bone mineral density
Explain the immune response to a Schmorl’s node
When a disc herniates into the vertebral endplate it could be considered by the body as ‘non-self tissue’ and when it comes into contact with blood, will trigger an auto-immune reaction.
What are the symptoms associated with Schmorl’s nodes?
- Severe back pain
- Inflammation
- When the auto-immune response is not present, Schmorl’s nodes are often asymptomatic
Why is there a greater arterial supply to the cervical and lumbar vertebral regions?
Because there are cervical and lumbar enlargements
At what spinal level is the cervical enlargement?
C4-T1
At what spinal level is the lumbar enlargement?
T11-S1
What is the purpose of the cervical and lumbar enlargements?
They facilitate increased neural input from and output to the limbs
Which arteries supply the cervical and lumbar enlargements?
- Large caliber anterior segmental radiculmedullary arteries:
- The artery of Lazorthes (cervical enlargement)
- The artery of Adamkiewicz (lumbar enlargement)
Describe spinal cord infarction
- Rare - accounts for 1% of all strokes
- Emboli arises from anywhere in the circulatory system and moves into the:
- anterior spinal artery (most common)
- posterior spinal artery (rare)
- causing ischaemia and subsequent infarction.
- Early presentation:
- Numbness
- Aching
- Tingling
- Lower extremity weakness
- Cramping
- Bowel and bladder paralysis
- Pain
What results from involvement of the posterior horn in posterior spinal artery infarction?
May cause loss of sensory function
Why is posterior spinal infarction so rare?
Due to the extensive lateral vascular network
Describe Beck’s system
(Anterior spinal artery syndrome)
- One of the causes of spinal cord infarction
- Caused by hypo-perfusion of the anterior spinal artery due to an occlusion of the vessel, leading to ischemia in the anterior 2/3 of the spinal cord.
- The anterior spinal artery supplies the anterior 2/3 of the spinal cord via the sulcal (central) artery.
What are the common causes of Beck’s syndrome?
- Aortic aneurysms
- Direct trauma to the aorta
- Surgery on the aorta
- Acute disc herniation
- Cervical spondylosis
- Kyphoscoliosis
- Trauma to the spinal column
- Emboli
What is cervical spondylosis?
Neck pain caused by age-related damage to bones and tissues
What are the symptoms of Beck’s syndrome?
- Patient normally presents with:
- An acute and painful myelopathy with additional symptoms such as impaired bladder and bowel control.
- Pain and temperature sensation and bilateral motor function below the lesion are lost.
- Sense of vibration and position are intact because of the preservation of the dorsal columns.
- Autonomic dysfunction: orthostatic hypotension
What does the intrinsic venous system drain?
Involves only the spinal cord, not the spinal column itself
Where do the sulcal veins drain blood from?
Where do they drain to?
Collect blood from:
- Both halves of the medial aspects of the anterior horns
- Anterior grey commissure
- White matter of the anterior funniculus
Drain into the anterior median vein
How are the radial veins formed?
Where do they drain to?
- In the peripheral grey matter and adjacent white matter, capillaries travel towards the periphery of the spinal cord forming radial veins.
- Drain into a venous ring on the spinal surface which drains into components of the extrinsic venous system.
How is reflux regulated in the radiculomedullary veins?
-
Initially thought that bicuspid valves prevented the reflux of blood from the radiculomedullary veins back into the longitudinal veins.
- Human cadaver study showed no bicuspid valves.
-
Now understood that:
- Dural folds extend into the lumen of the vein
- Periradicular veins are tortuous, reducing venous reflux
- A bottleneck is created by a narrowed dural part and widened intra- and extra- dural parts
- Significant smooth muscle fibres in the walls of the intradural and extradural parts of the radiculomedullary veins
Describe Batson’s plexus
(Extradural vertebral venous plexus)
Has 3 major divisions:
- Internal vertebral plexuses
- External vertebral plexuses
- Basivertebral plexuses
What is Batson’s plexus responsible for?
- Draining blood from the radiculomedullary veins
- Draining the vertebral column itself
Describe the internal vertebral venous plexuses
- Anterior and posterior internal vertebral plexues communicate superiorly with the suboccipital venous systems.
- Has 4 longitudinal veins - 2 anteriorly ad 2 posteriorly
Describe the anterior internal vertebral plexus
Lies on either side of the posterior longitudinal ligament and connects to the basivertebral plexus via transverse branches.
Describe the posterior internal vertebral plexus
Anterior to the ligamentum flavum and connects to the posterior external vertebral plexus via perforating branches.
Describe the external vertebral plexuses
Has anterior and posterior parts.
-
Anterior external vertebral plexus:
- Formed from tributaries from the vertebral body
-
Posterior external vertebral plexus:
- Veins passing through the ligamentum flavum form the posterior external vertebral venous plexus, which surrounds the posterior elements of the vertebrae.
How do the internal and external venous plexuses communicate?
Via intervertebral veins, which accompany the spinal nerves through the intervertebral foramina
Describe the basivertebral plexus
- Form within the vertebral bodies and run horizontally within them
- Emerge from foraminae on the surfaces of the vertebral bodies , particularly on the posterior surface
- Some drain to and contribute to the anterior external vertebral plexus
- The majority of blood in these plexuses, however, drain to the anterior internal vertebral plexus
Describe the extradural venous drainage in the cervical region
Occurs via 3 major pairs of vessels:
- Vertebral veins
- Deep cervical veins
- Jugular veins
Describe the extradural venous drainage from the thoracic and lumbar regions
Occurs via the azygos system and ascending lumbar veins:
- The ascending lumbar vein joins the azygos vein on the right and the hemiazygos on the left
- The hemiazygos crosses to join the azygos around T9 level
- The accessory hemiazygos drains the upper left thoracic vertebral levels (T3-T8)
Describe the extradural venous drainage in the lumbosacral region
- Ascending lumbar veins communicate with the IVC via 4 horizontal lumbar segmental veins.
- Great variation in lumbar venous drainage; spinal venous blood has been shown to drain to:
- Left renal vein
- Vein of the crus of the diaphragm
- Sacral veins empty to:
- Lateral sacral veins
- Internal iliac veins
What are the four routes of metastasis via blood?
- Contiguous spread
- local invasion
- Compartmental spread
- direct seeding to body cavities
- Haematogenous spread
- via the vasculature of the body
- Lymphangitic spread
- through lymphatic vessels and ‘preferentially to regional lymph nodes and later to distant sites
What is step 1 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(1) Invade locally through surrounding extracellular matrix and stromal layer cells
What is step 2 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(2) Intravasate into the lumen of blood vessels
What is step 3 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(3) Survive the rigors of transport through the vasculature
What is step 4 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(4) Arrest at different organ sites
What is step 5 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(5) Extravasate into the parenchyma of distant tissues
What is step 6 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(6) Initially survive in these foreign microenvironments in order to form micrometastases
What is step 7 of the invasion-metastasis cascade?
Epithelial cells in primary tumours:
(7) Reinitiate their proliferative programs at metastatic sites, thereby generating macroscopic, clinically detectable neoplastic growths
List some primary cancers which often metastasise to bone
- Breast cancer
- Lung cancer
- Especially prostate cancer
