test 4 Flashcards
what are the 2 tissues that skeleton is composed of?
- bone
- cartilage
what are the cell types of the skeleton?
- osteoblasts
- osteoclasts
- chrondrocytes
what are the 3 embryonic cell linages?
- cranial neural crest cells
- paraxial mesoderm cells or somites
- lateral plate mesoderm
what is formed from the cranial nural crest cells?
craniofacial skeleton
what is formed from the paraxial mesoderm cells or somites?
axial skeleton
what is formed from the lateral plate mesoderm?
responsible for limb formation
when do limb buds begin to develop?
during the 4th week of embryonic life (th mentral week)
do the upper limbs or lower limbs form first?
upper limbs do (bud appearance, develpment, differentiation and establishment of final relative limb size)
what is the order of development of the fetal limbs?
- humerus and femur
- radius, ulna, tibia, and fibula
- metacarpal and metatarsal bones
- phalanges
what are the 4 steps of skeltognesis?
- patterning
- organogenesis
- growth
- homeostasis
what is patterning?
final size, shape, number and arrangment of bones are determined
what is organogenesis?
bone and cartillage are formed
what is homeostasis?
the tendency of the body to seek and maintain a condition of balance or equilibrium within its internal environment, even when faced with external changes
where are the long bones measured?
between the distal and proximal ossification centers
what should the cardio-thoracic circumference be less than throughtout gestation?
slowly increases through gestation but should always be less than 0.5
why may cardio-thoracic circumferance be increased?
cardiac=fetal cardiomegaly
thoracic=pulmonary hypoplasia
what is the thoracic/abdominal circumferance after 20 weeks?
> 0.8
what are the indications for careful survey of the fetal skeleton?
- fam history with a known genetic risk
- detection of a fetal anomaly during a routine OB study
what is skeletal dysplasia?
medical term for what most people refer to as “dwarfism” It is am umbrealla term for a group of hundreds of conditions affecting bone and cartilage growth
a child born with skeletal dysplasia will have an abnormal difference in what?
shape of:
- legs
- arms
- trunk
- skull
how is classification of skeletal dysplasia made?
underlyinh molecular abnormalities
what is prenatal sonographic diagnosis of skeletal dysplasia centered on?
combinations of abnormal finding of the limbs, rib cage, skull, and spine
what is the most common severe skeletal dysplasia manifest with?
- severe micromelia (shortening of all limbs)
- variabel degrees of thoracic dysplasia
what is the most common way skeletal dysplasia is detected?
measurment of FL
what does it mean when FL is 1-4 mm below 2 SD point?
further serial measurments are required to determine if a skeletal dysplasia is present
what does it mean when FL is 5mm below the 2 SD point?
there is a high liklihood of skeletal dysplsia
what is used to determine skeletal dysplasia versus severe IUGR?
femur length to feet length ratio
what does the femur length and foot length ratio tell us with sever IUGR?
femur length is abnormally small however the femur length to foot length ratio remains essentially normal
what does the femur length and foot length ratio tell us with skeletal dysplasia?
the femur length to foot length ratio decreases, since foot length is unaffected and the femur is shortened to different angles
what are the 4 patterns of shortnening of the long bones?
- rhizomelia
- mesomelia
- acromelia
- micromelia
what is rizomelia?
shortening of proximal segment (femur, humerus)
what is mesomelia?
shortnening of middle segment (radius, ulna, tibia, fibula)
what is acromelia?
shortnening of distal segment (hands and feet)
what is micromelia?
shortnening of entire limb (mild, mild/bowed, severe)
with skeletal dysplasia, severe ________ are lethal
micromelia
what is thoracic dysplasia associated with?
abnormally snall misshapen chest and is associated with pulmonary hyperplasia
what is frontal bossing?
the development of an unusually pronounced forehead which may also be associated with a heavier than normal brow ridge
what causes frontal bossing?
enlargement of frontal bone
what is the most common LETHAL skeletal dysplasia?
thanatophoric dysplasia
what is the most common NONLETHAL skeletal dysplasia?
achondroplasia
what are the prevalance of disorders of muscoskeletal?
- Thanatophoric dysplasia
- Achondrogenesis
- Osteogenesis imperfecta
- Achondroplasia
what disroders are caused by different lutations in the fibroblast growth factor receptor 3 gene?
- Achondroplasia
- Hypochondroplasia
- Thanatophoric dwarfism
achondroplasia is autosomal ___________
dominant
what is associated with achondroplasia?
- Rhizomelic shortening
- mild limb bowing
- exaggerated lumbar lordosis
- enlarged head
- bones of hand and feet are short (trident hand)
- frontal bossing
- mid face hypoplasia
- flattened nasal bridge
- broad mandible
what is homozygous achondroplasia?
early shortnening of femurs
-letal in first 2 years of life
what is associated with heterozygous achondroplasia?
- short fingers and toes
- large head with prominent forehead
- small midface with a flattened nasal bridge
- spinal kyphosis or lordosis
- varus ir valgus
- ear infections
- sleep apnea
- hydrocephalus
what is spinal kyphosis?
convex curvature
what is spinal lordosis?
concave curvature
what is varvus?
bow leg
what is valgus?
knock knee
why does macrocephaly occur?
large head associated with hydrocephalus due to obstruction at the level of the foramen magnum
at what gestatinal age might the shortened limbs be detected?
varies between 21-27 weeks
hypochondroplasia is autosomal __________
dominant
what does hypochondroplasia resemble?
achondroplasia but features are milder
- sparing of the head
- lack of tibial bowing
what is Thanatophoric dwarfism characterized by?
- Extremely short limbs
- Folds of extra (redundant) skin on the arms and legs
- Narrow chest
- Short ribs
- Underdeveloped lungs
- Enlarged head with a large forehead
- Prominent, wide-spaced eyes.
what is type 1 of Thanatophoric dwarfism?
thanatophoric dysplasia is distinguished by the presence of curved thigh bones and flattened bones of the spine (platyspondyly)
what is type 2 of Thanatophoric dwarfism?
straight thigh bones and a moderate to severe skull abnormality called a cloverleaf skull
do most infants with Thanatophoric dwarfism survive?
no
what is associated with Thanatophoric Dysplasia?
- severe micromelia
- severe thoracic dysplasia
- polyhydramnois
- cloverleaf skull deformity
what are additional findings of Thanatophoric Dysplasia?
- Ventriculomegaly
- Macrocranium
- Cerebellar hypoplasia
- Prominent forehead
- Saddle nose
- Hypertetorism
- Short ribs
- Platyspondyly
what is Platyspondyly?
a radiographic feature and refers to flattened vertebral bodies throughout the axial skeleton
what is the most common spinal abnormality?
skelteal dysplasia
what does Thanatophoric Dysplasia look like?
significant narrowing of the chest and prominent abdomen
- shortened bowed limbs
- narrow thorax with short ribs
- large head
what is the 2nd most common lethal skeltal dysplasia?
achondrogenesis
what has the most severe degree of limb shortnening?
achondrogenesis
how is achondrogenesis type 1 characterized?
- inadequate ossification of the skull, spine, and pelvis
- extensive shortnening of tubular bones
- multiple rib fractures
how is achondrogenesis type 2 characteried?
- various degrees of calcification of the pelvis, skull, and spine
- without rib fractures
- most type 2 cases are sporadic (new autosomal dominant mutations)
which achondrogenesis is autosomial dominant and whic is recessive?
recessive=type 1
dominant=type 2
what are the sonographic features of Achondrogenesis?
- short femur length (below 5th percentile)
- trident hand and 4 fingers appearing separated and similar in length
- protruding forehead (frontal bossing)
what is taken as a useful measurement for Achondrogenesis?
femur length (FL) to biparietal diameter (BPD)
what is Hypophosphatasia?
an inherited disorder that affects the development of bones and teeth (disupts mineralization)
what are infants affected with Hypophosphatasia born with?
- short limbs
- abnormally shaped chest
- soft skull bones
with Hypophosphatasia the spine is usually ______________
hypomineralized
what are the 2 conditions most commonly associated with hypomineralization of the spine?
achondrogenesis type 1
hypophosphatasia
what is not affected with achondrogensis type 1?
skull
what does hypomineralized look like?
less echogenic than normal and attenuation of the vertebrae and enhanced visualiation of the spinal cord
what is osteogenesis imperfecta?
a congenital bone disorder characterized by brittle bones that are prone to fracture
what is associated with osteogenesis imperfecta type 1?
- blue sclera
- hyper laxity of ligaments and skin
- hearing impairment
- no prenatal deformities