Fetal Skeleton

“-melia” definition

limb or extremity

amelia definition

absence of limbs

rhizomelia definition

shortening of proximal segment (humerus and femur)

**proximal=close to core of body

mesomelia definition

shortening of middle segment (rad/uln and tib/fib)

micromelia definition

shortening of entire limb

acromelia

shortening of distal segment (hands/feet)

campomelia

bowed legs

skeletal dysplasia

• abnormal growth and density of bone and cartilage

• over 450 different dysplasias

• rare

• many incompatible with life

  • lethal forms characteristically are extremely severe in their prenatal appearance

  • ex. you can easily see severe micromelia

thanatophoric dysplasia

• severe skeletal disorder characterized by extremely short limbs and folds of extra skin on arms and legs

• MC lethal skeletal dysplasia

• lethal prognosis

• subdivided into 2 types

  • type I: short, curved femurs and flat vertebral bodies

  • type II: straight, but short femurs, flat vertebral bodies, and a cloverleaf skull (AKA Kleeblattschädel skull)

**”thanatos” means death, so remember that thanatophoric dysplasia is LETHAL

SONO: thanatophoric dysplasia

• severe micromelia

• cloverleaf deformity

• narrow thorax with shortened ribs (bell-shaped)

• rhizomelia

• protuberant abdomen

• frontal bossing

• hypertelorism

• flat vertebral bodies

what do you see?

very narrow chest

achondroplasia

• defect in formation of cartilage and converting it to bone through ossification

  • produces short, squat bones

• MC nonlethal skeletal disorder

• 2 types:

  • heterozygous: gene inherited from one parent; good prognosis

  • homozygous: gene inherited from both parents; lethal prognosis

achondroplasia

• rhizomelia

• microcephaly

• trident hands

• depressed nasal bridge

• frontal bossing

• mild ventriculomegaly (sometimes)

• long bone shortening after 22 weeks (best diagnostic clue)

achondrogenesis

• rare lethal disorder resulting in absent mineralization of skeletal bones

  • affects cartilage and bone development

  • characterized by a small body, short limbs, and other skeletal abnormalities

• poor prognosis

• 2 forms:

  • type I: autosomal recessive; more severe

  • type II: spontaneous mutation; less severe; more common

SONO: achondrogenesis

• severe micromelia

• small thorax and ribs

• protuberant abdomen

• hypomineralization (spine)

• macrocephaly

• micrognathia

• polyhydramnios

• hydrops (possibly)

osteogenesis imperfecta

• rare bone disorder characterized by abnormal collagen production leading to brittle bones

• highly variable prognosis; can be lethal

• 4 types:

  • I: no prenatal deformities; mild

  • II: most severe form; lethal

  • III: severe; fractures at birth are common

  • IV: mildest form

SONO: osteogenesis imperfecta

• hypomineralization

  • especially in cranium

  • compressible skull

• multiple fractures of long bones, ribs, and spine

• narrow thorax (bell-shaped)

• micromelia

congenital hypophosphatasia

• condition that presents with diffuse hypomineralization of bone caused by alkaline phosphatase deficiency

• SONO features similar to osteogenesis imperfecta and achondrogenesis

• diagnosis can be confirmed with alkaline phosphatase assay

  • through fetal blood sampling or chorionic villus sampling, or through DNA analysis

• lethal-respiratory complications

campomelic dysplasia

• aka bent bone (bowed)

• rare lethal skeletal disorder characterized by bowing of the long bone (bent bones)

  • normal ossification without fractures

  • curvature of long bones

• most spontaneous but could be inherited

• associated with:

  • renal, cardiac, and CNS anomalies

  • ambiguous genitalia

SONO: camptomelic dysplasia

• bowing of long bones

  • low extremities severely affected

• small, narrow thorax (bell-shaped)

• hypertelorism

• hypoplastic fibulas, scapulae

• cleft palate

• micrognathia

• talipes

• abnormal genitalia

• hydrocephalus, hydronephrosis, and polyhydramnios

Roberts’ syndrome

• rare condition characterized by phocomelia and facial anomalies

• caused by mild to severe disruption of cell division

  • leads to malformed bones of the skull, face, arms, and lags

• characterized by:

  • symmetrical limb reduction

  • craniofacial anomalies

  • slow growth

• associated with…

  • cardiac, renal, and genital abnormalities

• poor prognosis

SONO: Roberts’ syndrome

• phocomelia

  • absent or severely shortened limbs

  • MC in upper extremities

• bilateral cleft lip and palate

• hypertelorism

• microcephaly

• cardiac, renal, and GI anomalies (possibly)

short-rib polydactyly syndrome

• lethal skeletal dysplasia

• pulmonary hypoplasia

• characterized by short ribs, short limbs, and polydactyly

• inherited in autosomal-recessive manner

SONO: short-rib polydactyly syndrome

• narrow thorax with short ribs

• polydactyly

• micromelia

• midline facial cleft

Ellis-Van Creveld syndrome

• increased frequency in Amish community

• characteristics:

  • narrow thorax → pulmonary hypoplasia

  • heart defects—MC is atrial septal defect (ASD)

• half will die during infancy from cardiorespiratory complications

SONO: Ellis-Van Creveld syndrome

• limb shortening

• narrow thorax

• polydactyly

• heart defects

caudal regression

• rare disorder that represents a range of malformations of caudal end of neural tube

  • complete or partial agenesis of the sacrum and coccyx

• associated with

  • VACTERL

  • GI, GU, CNS, and cardiac anomalies

• poor prognosis

SONO: caudal regression

• sacral agenesis

• talipes

• abnormal lumbar vertebrae

• abrupt termination of the spine

• lower extremity contractures

sirenomelia

• most severe form of causal regression syndrome

• affected infants are born with a single lower extremity or with two legs that are fused together

  • “mermaid” syndrome

• associated with:

  • maternal diabetes

  • renal agenesis

• lethal prognosis

SONO: sirenomelia

• variable fusion of the lower extremities

• bilateral renal agenesis

• oligohydramnios

• single umbilical artery

radial ray abnormalities

• hypoplasia or aplasia of the radius and ulna

• extreme angulation of the hand to the forearm

• associated with chromosomal anomalies

  • T13, T18, VACTERL

club foot

• malformation and/or malposition of the foot and ankle bones

• aka talipes

• male>female

• usually unilateral

• associated with a variety of chromosomal anomalies

• SONO:

  • persistent abnormal inversion of the foot perpendicular to lower leg

rocker-bottom foot

• characterized by prominent heel bone and convex rounded bottom of foot

  • 70% bilateral; 30% unilateral

• associated with:

  • chromosomal anomalies

  • T18

• surgical interventions needed

• SONO:

  • sole of foot is convex/rounded

sandal gap foot

• big toe angled medially

• large gap between 1st and 2nd toe

polydactyly

one or more extra digits

syndactyly

partial or complete fusion of digits

clinodactyly

• tip of the 5th finger (pinky) turns in open hand; overlapping digits

• strong association with T21

spalding’s sign

• overlapping of fetal skull caused by collapse of the brain

• appears usually a week or more after fetal death in utero

• indicated fetal demise

what are “lethal” pathologies usually associated with?

;pulmonary hypoplasia (because if lungs can’t develop, baby cannot survive)