Ultrasonography Flashcards
(47 cards)
What are ultrasound waves?
Sound waves with frequencies higher than the human audible range (20kHz)
How far do ultrasound waves travel in a patient?
Only a few centimetres
Describe the pulse echo principle
The ultrasound/ probe transducer has two functions:
- Emits a soundwave
- Recieves echos from the original wave
When ever an ultrasound passes through a tissue it can
- be reflected
- OR
- pass through and continue propagating
What is the fate of ultrasound waves when they can pass through tissue?
- Can be reflected
- OR
- Pass through and continue propagating
What affects how much of the sound wave is reflected?
TISSUE DENSITY
- Dense tissue (like bone, gas) will reflect the sound waves at a high amplitude producing a white image
- Less dense tissue (fluid, amniotic fluid, urine) will not reflect, and ultrasound waves propagate producing a black image
List some advantages of ultrasound use?
- No radiation
- No documented side effects
- Usually non-invasive (sometimes invasive if trans-vaginal or endo-anal)
- Widely accessible
- Results available immediately
- ‘Real time’ imaging
- Well tolerated
List some disadvantages of ultrasound use?
- Ultrasound image is highly dependant on patient habitus (e.g weight)
- Effectiveness is operated dependant
- No known side effects
- Training is more resource intensive
What are some clinical applications of ultrasounds?
Mainly:
- Obstetrics (pregnancy, childbirth, postpartum period)
- Gynaecology
- Abdominal
- Urinary
Also:
- Trauma = POCUS
- Testicular
- Breast
- Head and Neck
- Vascular
- Cardiology
- Musculo-skeletal
- Lungs
Describe the advantage of using an ultrasound over X-ray/CT scans in obstetric imaging
Doesnt use ionising radiation
Describe the 12 week scan ultrasound scan in obstetrics
- Foetus is approximately 45-84mm in length
- First routine scan offered to most low risk pregnancies
- Detects ‘viability’, number of foetus’, gross anatomy, detectable major abnormalities, morphology of ovaries and an accurate gestational age of foetus
Describe some pathologies picked up on a 12 week scan
Anencephaly = Some or all foetal brain, skull and scalp is missing
Omphalocele/ exomphalos = Herniation of abdominal tissue (part of the intestine will protude through the abdominal wall at birth)
Body stalk defect = Extreme form of herniation, where abdominal organs will have herniated through abdomen and develop outside of the cavity
What does a blighted ovum/ missed miscarriage on an ultrasound represent?
- Something may have gone wrong in the pregnancy that has prevented the foetus from growing and there is scanning of an empty sac
- The empty sac will have caused all the same symptoms of pregnancy + positive pregnancy test
- Hence Ultrasound (12 week scan) is the first sign that something in the pregnancy has gone wrong
What is the probabillity of getting a miscarriage?
High at 3 weeks
Decreases after that, once we get to 12 weeks the probabillity is extremely low
What is a cystic hygroma and molar pregnancy?
- Cystic hygroma = fluid filled cysts of resulting from blockage in the lymphatic vessels will not form properly
- Molar pregnancy = Non-viable fertillised egg implants in uterus and fails to come to term, foetus doesnt form properly and baby doesnt develop
Both picked up on 12 week scan
What genetic disease can we also screen for at 12 weeks?
We can scan for DOWNS SYNDROME (needs a blood test + scan)
- Scan we carry out a foetal nuchal translucency screening
- Measures size of nuchal pad at the nape of the foetal neck
What is the frequency of Down’s Syndrome?
Around 2 per 2000 births
However increased risk in older women
- 1:1500 at 20 years
- 1:800 at 30 years
- 1:270 at 35 years
- 1:100 at 40 years
- 1:50 at 45 years and over
At around what time do we need to carry out the foetal nuchal translucency screening for downs syndrome?
Between 11 weeks and 13 weeks (+ 6 days)
After 13 weeks the lymphatic system will have developed and drained the fluid from the back of the neck
(Reminder nuchal translucency should not be confused with nuchal fold thickness test which is carried out between 16-24 weeks)
Describe what a nuchal translucency is?
Appearance of the collection of fluid under the skin behind the foetal neck in the first trimester of pregnancy.
THE MORE FLUID THERE IS THE INCREASED CHANCE OF A GENETIC ABNORMALITY
This fluid will go on to form part of the lymphatic system
What is another marker of Down’s Syndrome at 12 weeks?
No nasal bone
What is the purpose of a 20 week scan?
Helps to identify abnormalities which
- May indicate the baby has a life-limiting condition
- May benefit from antenatal treatment
- May require early intervention following delivery
Other standard aims:
- placenta localisation
- foetal biometry
- fibroid monitoring
- liquor assessment
What are some abnormalties that can be picked up from a 20 week scan?
- Spina bifida - neural tube defect, incomplete closing of the spine and membranes around the spinal cord, gap in lumbar- sacral spine
- Achondroplasia - short limbed dwarfism (torso is normal length)
- Low lying placenta - implantation os placental over cervical opening
- Talipes (Club foot) - foot turns inwards
- Anhydraminios (complete or near complete lack of aminiotic fluid), Oligohydramnios (not enough aminiotic fluid)/ Polyhydramnios (too much amniotic fluid)
What is spina bifida?
What can severe spina bifida lead to?
- Neural tube defect, where the baby’s spine and spinal cord doesnt develop properly
- There is incomplete closing of the spine and the membranes surrounding the spinal cord
- There is a gap in the lumbar sacral spine
- Can lead to:
- Paralysis
- Incontinence
- Difficult walking
- Other chromosomal abnormalities
How is an ultrasound used to detect for spina bifida?
Detected via a skull ultrasound before getting to the spine
- The cerebellum will be pulled down because the spinal cord is protuding through the back which will pull at the base of the brain and disrupt the shape
How do we treat spina bifida?
Carried out in utero to repair gaps in the babys spine so they are closed before the baby is born
Not taking folic acid can be one of the causes of an increased risk of spina bifida