Ultrasonography Flashcards
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 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
What is achondroplasia?
- Genetic disorder which results in short-limbed dwarfism
- Torso is the same length and there is bowing of long bones
- Thickened soft tissue surrounding long bones
- On 20 week scan
- Frontal bossing (forehead protuding is a characteristic of achondroplasia)
Describe the implications of a low-lying placenta
- Implantation of the placenta over the internal os (or lower region of uterus)
- If placenta is within 2.5cm of cervix = more scans required
- IMPLICATION
- If placenta is not raised then a C-section may be required
Describe Talipes (club foot)
- Where the foot turns inwards
- Can affect one or both feet
- Causes
- Mechanical → Due to position in the womb, foot may be trapped
- Chromosomal abnormalities (Downs syndrome-21, Patau Syndrome-13, Edwards Syndrome-18)
- Causes
- Can affect one or both feet
What is the treatment of Talipes (club foot)
Ponseti Method
Ligaments, joints and tendons are stretched after gentle manipulations. A plaster cast is applied after each manipulation to retain the degree of correction and soften ligaments
What is the umbilical arterial doppler assesment used for?
Used as a marker of placental insufficiency (failure of nutrient delivery) and consequent intrauterine growth restriction (IUGR) or suspected pre-eclampsia
What is an ectopic pregnancy?
What are some causes?
An ectopic pregnancy is when the egg has implanted outside the uterus, usually in the fallopian tubes
Causes
- Surgery
- PIDS (pelvic inflammatory disease)
- Endometriosis
How do multiple pregnancies occur?
They are caused by the delay in the fertilized egg reaching the womb before implanting
What is the difference between dichorionic and monochorionic twins?
Dichorionic = Type of twin pregnancy where each twin has its own chorion (membrane surrounding amniotic sac), amniotic sac and placenta
Monochorionic = Twins will share the same placenta
What prenatal diagnostic test genetic screening can be carried out for chromosomal abnormalities
- Chorionic villus sampling = placental sample taken
- Aminocentesis = Amniotic fluid sample is taken
From this we can test the genetics of the baby from what we pick up in the sample but also comes with a miscarriage risk.
Reminder of non-invasive technique → cffDNA (cell free foetal DNA) DNA fragments in maternal plasma (10 weeks onwards), foetal DNA can be separated from maternal DNA and amplified via PCR/NGS
Describe fibroids
- Are benign tumours of the uterus
- Muscular and can be caused by pregnancy
- Can become a mechanical obstruction to babys exist in pregnancies
- Many can grow until the blood supply they recieve can no longer support further growth, but others can get very large and require surgical intervention
What is an AAA and what is characterised by?
What is the treatment of an AAA?
Abdominal aortic anuerysm - when the aorta becomes abnormally large or balloons outward
- Defined as aneurysmal when reaching 3cm
- Surgery required when aneurysm meets 5.5cm in AP (anteroposterior) diameter
Treatment
- EVAR = endovascular aortic repair, stent is inserted in areas of weakness
How do gallstones come about?
What is required for a gallstone ultrasound?
They are caused by an imbalance in the chemical makeup within the bile (high cholsterol/bilirubin).
Patients will need to fast for 4 hours before, so gallbladder fills up with bile giving us the black space (fluid) which allows us to see the stones (bright white dots which are dense)
What can a urinary tract ultrasound used to test for?
- Polycystic kidney disease
- Renal calculi (kidney stones)
- Enlarged prostate
- Ectopic kidney
What can a testicular ultrasound be used to detect?
What can a breast ultrasound be used for?
- Under the age of 35, breast tissue tends to be denser.
-
Difficulty diagnosing breast lumps on mammograms as differentiation between solid and fluid filled areas is relatively poor.
- Ultrasound can make differentiation at an improved rate (about 30% increased).
Ultrasound also enables core biopsies to be taken of breast lumps to allow for histological investigation for classification of the lump.
How can an ultrasound be used in DVT?
- Can be used to exclude or confirm the presence of a deep vein thrombosis in cases of pain or swelling in lower limbs
- It is often used as a screening tool for DVT in post operative patients and those with pulmonary embolus
Explain POCUS (point of care) ultrasound FAST (focus assesment with sonography of trauma)
POCUS-FAST
-
Focused Assessment with Sonography for Trauma (FAST) scan is a point-of-care ultrasound examination performed at the time of presentation of a trauma patient.
- Ultrasound is becoming first and foremost prevalent over going to CT for trauma patients.
- Ultrasounds can detect as little as 20ml of free fluid compared to 200ml required with plain X-rays
