Session 1 embryology and radiology Flashcards
Which genes control segmentation in embryology?
Hox genes
What is segmentation in the embryonic period?
Patterning and segregation of cells into repeating units (segments) along the longitudinal axis.
- what limb develops from a limb bud
- how many fingers
What is a homeotic mutation?
What does it cause?
Mutation of a Hox gene?
The tissue to alter their differentiation pattern.
E.g. a 6th lumbar vertebra develops instead of the 1st sacral vertebra / 6th didgit develops
What causes thoracic outlet syndrome?
What is it?
Compression of nerves and vessels from the neck to the armpit due to extra cervical ribs (Hox gene/ homeotic mutation)
When do the limb buds develop?
How do they elongate?
4th week of development
mesenchyme proliferation
When does endochondrial ossification begin in embryonic development?
12th week
Describe how the limbs rotate in development?
Upper limbs externally rotate through 90 degrees
Lower limbs internally rotate through almost 90 degrees
Why does sartorius muscle follow an oblique path?
Due to internal rotation of the lower limbs during development
Why does bone appear whiter than tissue on an X ray?
Bone is more radiodense so absorbs more electrons (radiation)
What is ‘joint space’ on an X-ray?
The place where articular cartilage is present. The cartilage is radiolucent so can’t be seen on an X-ray
Two fractures which only occur in children?
- Green stick fracture
(bone bends and cracks) - Epiphyseal separation fracture
(epiphysis slips off the metaphysis)
Most common place for a compression fracture?
Lumbar vertebrae
looks like a squashed can
How does an epiphyseal separation fracture occur?
Which patients do they commonly occur in?
The fracture extends through an unfused growth plate (epiphyseal plate) so the epiphysis is removed from the metaphysis
Overweight, adolescent boys during a rapid growth spurt. In the femur; presents as hip pain and limp
What can affect the cell proliferation and transformation within the epiphyseal growth plate?
Growth hormone - increased
Thyroid deficiency- reduced
Excess corticosteroids - reduced
How do you calculate a bone age?
X-ray of the hand to determine the ossification of the carpal bones in the wrist as they gradually ossify from birth until 12 years old
8 steps in a fracture healing
(fracture) haematoma necrosis inflammation granulomatous tissue/ angiogenesis soft callus (fibrocartilaginous) hard callus (woven bone) lamellar bone remodelling
Benefits of CT scanning compared to X ray
(Both use X ray beams
CT is a polo mint)
- CT images can be assembled to produce 3D images
- Better for soft tissues
- Ability to manipulate the image afterwards allows you to see tissues of different density in the same image slice
- High resolution; can be used in real time
Negatives of CT
- higher radiation dose
- motion artefact if the patient moves
- some patients are allergic to intravenous contrast
- very obese patients can’t always fit the polo
Units of tissue density in a CT scan?
Density > 100 HU appears ____?
Density < 0 appears____?
Hounsfield Units (HU)
Above 100 is white (bone)
Below 0 is dark
How does MRI work?
- Magnets produce a strong magnetic field which causes protons in the body (in hydrogen atoms) to align with the field. (No radiation in MRI)
- Radiofrequency signal pulses are applied which deflects the protons from their equilibrium position
- The pulses are stopped and the protons realign with the magnetic field, releasing energy
- Energy released and time taken to return are measured and used to create the images (vary with molecule and environment).
How do fluid and fat appear in these types of MRI images?
T1
T2
STIR
T1- fat bright, fluid dark
T2- fat bright, fluid bright
STIR- fluid bright, fat dark
When is a STIR MRI useful and why?
Useful to see oedema because fluid appears bright and signal from fat is suppressed (fat appears dark)
What is gadolinium and when is it used?
Chemical element used as a contrast media during MRI. It enhances image clarity and can be injected into a joint or intravenously
How does ultrasound work?
High frequency sound waves travel through the patient and are deflected by tissue and tissue planes. The deflected signals are measured by the transducer and analysed to create an image
Ultrasound benefits and disadvantages
Good things; No radiation exposure Good at soft tissue Useful for imaging tendons and muscles Used to locate fluid collections/ haematomas
Bad things;
Need a skilled operator
Poor resolution of deep tissues
Limited use for bone and intra-articular (in the joint) imaging
Who are especially sensitive to damage from ionising radiation?
Children and foetuses because they have rapidly dividing cells
What is nuclear medicine?
Use radiolabelled biologically active drugs to measure biological activity.
E.g. measure areas of metabolically active bone
Why do veins appear dark in the DR?
Blood drains into the veins from the arteries (appear bouncy and hollow) and clots
veins look dark or collapsed
Where is the intercostal neurovascular bundle?
What does it consist of?
Beneath each rib
Intercostal vein
Intercostal artery
Intercostal nerve
