Fetal Skeletal Dysplasias Flashcards
Endochondral ossification begins at how many weeks?
10 menstrual weeks
What are the first bones to ossify? 5
- Mandible and maxilla
- Clavicle
- Calvarium
- All long bones
- Vertebral laminate
When does the mandible and maxilla finish ossifying?
8-19 menstrual weeks
Calvarium is finish ossification when?
12-13 weeks
All long bones finish ossification when?
End of the 1st trimester
Vertebral laminae finish ossification when?
18 weeks
What are some secondary ossification centres?
Epiphyses
Secondary ossification centres are separated from the shaft of the long bone by what?
A layer of cartilage
Secondary ossification centres develop when?
Late in pregnancy and in the neonatal period
What aids in the determination of fetal maturity?
Visual aids
When is the distal femur visible?
32-35 weeks
When is the distal humorous finished ossifying?
> 38 weeks
What might delay secondary ossification centres development?
IUGR
Femoral growth is 3mm/week until when?
27 weeks
Femoral growth is 1mm/week from when?
28 weeks to term
How do we measure the femur?
Only the shaft of the femur
Femur is measured as part of what?
Part of the anatomy scan and all biometry scans
What is the routine assessment for bones? 8
- Femur length
- Humerus length
- Lower limbs
- Upper limbs
- Foot/Ankle angles
- Feet palmer view
- Hands
- Spine and calvarium
What do we assess for in terms of ossification/ bones? 5
- Size
- Presence
- Shape
- Contour
- Density
What are 3 errors of morphogenetic?
- Malformation
- Deformation
- Disruption
What is malformation?
Abnormal formation of tissue (genetic and telegenic drugs)
What is deformation?
Normally developed, but abnormal force alters structure shape
What is an example of deformation? 2
- Oligohydraminos causing clubbed feet
- Features of potter’s sequence
What is disruption?
Normally developed, but abnormal interference causes tissue destruction
What are two examples of disruptions?
- Vascular occlusion = limb reduction
- Tearing amniotic membrane = Tissue destruction
What is skeletal dysplasia?
The abnormal development of the cartilaginous and osseous tissues, resulting in bones that appear shortened, thin, deformed or that fail to form at all.
What is another name of skeletal dysplasia?
Osteochondrodysplaisa
What are indications of skeletal dysplasia? 4
- Specific genetic risks (Previous pregnancy, family history)
- Apparent limb abnormality
- Associated abnormality
- Abnormal amniotic fluid
What does family history of skeletal dysplasia warrant?
Extensive screening of target areas
Extensive screening for skeletal dysplasia can help identify what?
The types of skeletal dysplasia as many disorders inherit as AR or AD
What is consanguinity?
Couples that are relatives
What presents from consanguinity?
AR traits more prevalent
What are four patterns of limb shortening?
- Rhizomelia
- Mesomeilia
- Mircomeilia
- Acromeilia
What is rhizomelia?
Proximal portion of limb is shortened (fever and humerus)
What is mesomelia?
Middle portion of limb is shortened (Radius/ ulna and tibia/fibula)
What is micromelia?
All portions of the limb are shortened
What is acromelia?
Distal portion of limb (hands/ feat)
What is phocomeilia? 2
- Abscesses of the proximal portion of the extremity
- Hands or feet attached to trunk of the body
What does phocomelia resemble ?
Presemnil flipper
Shortened long bones are routinely measured when?
FL and HL at detailed scan
What is the routine for measurements of FL and HL at detailed scan? 4
- Cross-reference to BPD/long bone chart
- Marker is <0.9 of expected)
- Or <5%
- 2 SD for fetal age
In terms of shortened long bones, once a skeletal abnormality is identified, what happens to the long bones.
Once a skeletal abnormalities is identified, all bones should be measured
What classifies as severely shortend long bones?
> 4 standard deviation
If the bones are -2-4 SD, what needs to be done?
F/U in 3-4 weeks to ensure normal growth
In terms of shortened bones, when can we expected normal lengths?
- Normal lengths early in 2nd trimester
Dysplasia’s that manifest later mean what?
Less severe features that have a better prognosis
What is another name for sporadic dominant?
AR inherithence pattern
What are some common lethal skeletal dysplasia? 3
- Thanathorphic dysplasia a
- Achonoderognesis
- Osteogenesis imperfects II
What are some rare lethal skeletal dysplasias? 3
- Congenital hypophophastasia
- Camptomelic dysplasia
- Homozygous achondroplasia
There are how many different types of skeletal dysplasia
436
What does this image represent?
Patterns of limb shortening
What does this image represent?
Phocomelia
What are some common lethal dysplasia’s? 3
- Thanatophoric dysplasia
- Achondrogenesis
- Osteogenesis imperfects
60% of common lethal dysplasia’s are what? 2
- Thanatophoric
- Achondrogenesis
Dysplasia’s are considered lethal with what? 2
- Decreased thoracic circumference
- Severe micromelia
What does decreased thoracic circumference do with lethality?
It causes pulmonary hypoplasia
What do we need to determine thoracic circumference and lethality? 2
- Compare chest and abdomen
- Compare femur length and abdomen
What is abnormal narrow chest ratios? 2
- Chest/ Abdoment ratio <0.79
- FL/AC <0.6
Indicative of hyperplasticity thorax
Thanatophoric means what in Greek?
Death bearing
What is the most common lethal skeletal dysplasia?
Thanatophoric dysplasia
Thanatophoric dysplasia is believed to be autosomal what? Why?
Dominant, because it is caused by mutations of the FGFR3 gene
What is the FGFR3 gene?
Fibroblast growth factor receptor
In terms of Thanatophoric dysplasia, around 50% present how?
Clinically as large for gestational age (LGA) due to polyhydraminos
What are some general abnormalities of Thanatophoric dysplasia? 7
- Micromelia
- Redundant skin folds
- Clover leaf skull deformity (Kleeblattschadel)
- Frontal bossing
- Bowed limbs (Telephone receiver)
- Narrow thorax
- Platyspondyly
What is Platyspondyly? 2
- Flatness of the vertebral bodies
- Thin vertebrae bodies
What is seen with TD type 1? 4
- Extreme rhizomelia
- Bowed bones
- Platyspondyly
- Frontal bossing
What is seen with TD type 2? 3
- Straighter long bones
- Taller vertebral bodies
- Kleeblattschadel
Between TD Type 1 and 2 which is more common?
Type 1
If the vertebral bodies appear flattened or less than the intervertebral space, what has happened?
Platyspondyly
How do we find the expected FL?
Check the BPD to the expected FL
What is the second most common lethal skeletal dysplasia?
Achondrogenesis