OB II Unit 6 Fetal Skeleton 119- 142

What does the fetal skeleton look like?

• Skeleton appears as cartilaginous structures that undergo ossification.

What anomalies result from the fetal skeleton?

Anomalies result from genetic factors, unknown causes, or environmental factors

What is skeletal dysplasia? 

•Describes abnormal growth & density of cartilage & bone

What is dwarfism?

• Disproportionately short stature (occurs secondary to a skeletal dysplasia)

What is the lethal form of skeletal dysplasia?

• Lethal forms = extremely severe prenatal appearance

  • Severe Micromelia – shortening of limbs

What is the nonlethal form of skeletal dysplasia?

•- Nonlethal forms =  manifest milder form

What is the process of evaluating the skeletal system of a fetus?

• Assess limb shortening – measure all long bones

• Assess bone contour

• Estimate degree of ossification

• Evaluate thoracic shape & circumference

• Coexistent hand & foot anomalies

• Evaluate face & profile

• Survey for other anomalies

• Manifestation of skeletal dysplasias varies

What are the segmental patterns of long bones?

Rhizomelia

Mesomelia

What is the non-segmental pattern of long bones?

Micromelia

What is Rhizomelia?

• Shortening of proximal segment 

• Humerus and Femur 

What is Mesomelia?

• Shortening of distal segments

• Radius/Ulna and Tibia/Fibula 

What is Micromelia?

• Shortening of ENTIRE Extremity

What is the most common LETHAL skeletal dysplasia?

Thanatophoric Dysplasia

What are the 2 subdivisions of thanatophoric dysplasia?

• Type I: short, curved femurs, flat vertebral bodies

• Type II: short, straight femurs, flat vertebral bodies, cloverleaf skull

What type of thanatophoric dysplasia may be an autosomal recessive inherited trait?

Type 2 

What is the prognosis of thanatophoric dysplasia?

Extremely grim due to pulmonary hypoplasia

What are the US findings for thanatophoric dysplasia?

•Severe micromelia

•Cloverleaf deformity

•Narrow thorax with shortened ribs

•Protuberant abdomen

•Frontal Bossing – bulging forehead

•Hypertelorism

•Flat vertebral bodies

What are extra US findings for thanatophoric dysplasia?

•Severe Polyhydramnios

•Hydrocephalus

•Nonimmune hydrops

What is this image showing?

Thanatophoric Dysplasia

What are these images showing?

Thanatophoric Dysplasia

What is another name for dwarfism?

Achondroplasia

What is the most common NON-lethal dysplasia?

Achondroplasia/ Dwarfism

What is achondroplasia? 

• Decreased endochondral bone formation, producing SHORT, SQUAT BONES

Achondroplasia may not be evident until after ____ weeks when biometry becomes abnormal.

22 weeks 

What is the heterogeneous form of achondroplasia?

Good survival rate with normal intelligence & life span

What is the homozygous form of achondroplasia?

LETHAL, with most infants dying from respiratory problems

What are the US findings for achondroplasia?

• Rhizomelia

• Macrocephaly

• Trident hands

  • Short prox. & middle phalanges

• Depressed nasal bridge

• Frontal bossing

• Mild ventriculomegaly

What is a rare lethal skeletal dysplasia?

Achondrogenesis

What are the cartilage abnormalities of achondrogenesis?

• Cartilage abnormalities = abnormal bone formation & hypomineralization

What are the 2 types of achondrogensis?

• Type 1 = Parenti-Fraccaro

• Type 2 = Langer-Saldino (89% of cases)

What is the prognosis of achondrogenesis?

Grim due to pulmonary hypoplasia

What are the US findings for achondrogenesis?

•Severe micromelia

•Decreased or absent ossification of spine

•Macrocephaly

•Short trunk

•Short thorax & ribs

•Micrognathia

•Polyhydramnios

•Hydrops is possible

What are these images showing?

Achondrogenesis

What is osteogenesis imperfecta?

Collagen production problem which = Brittle Bones

Where does osteogenesis imperfecta manifest?

•Manifests in the teeth, skin, ligaments & blue sclera

What are the 4 types of osteogenesis imperfecta?

•Types 1 & 4 = mildest forms

•Type 3 = severe form

•Type 2 =  MOST SEVERE –LETHAL

Osteogenesis imperfecta has an increased translucency in what trimester?

1st trimester

what are the US findings for osteogenesis imperfecta?

• Generalized Hypomineralization of bones especially cranium

  • Skull = allows brain structures to be clearly visualized; compressible

• Multiple fractures of long bones, ribs, & spine

  • May leave bones bowed, thickened, & sharply angulated

• Narrow thorax

• Micromelia

• Polyhydramnios

What type is similar to type 2 but less severe?

Type 3

what is this image showing?

Osteogenesis Imperfecta

What are these images showing?

Osteogenesis Imperfecta

What is congenital hypophosphatasia?

Lethal disorder of diffuse hypomineralization caused by alkaline phosphatase deficiency

What is the US features of congenital hypophosphatasia?

• Diffuse hypomineralization of bone

• Moderate to severe micromelia

• Extremities may be bowed, fractured, or absent

• Poorly ossified cranium with well-visualized brain structures

• Small thoracic cavity

What is diastrophic dysplasia?

•Rare disorder with micromelia, talipes, cleft palate, micrognathia, scoliosis, short stature, earlobe & hand deformities,  (fixed abducted thumb = hitchhiker thumb)

What is this image showing?

Diastrophic dysplasia

What is Camptomelic Dysplasia?

•Group of LETHAL skeletal dysplasias

What is Camptomelic dysplasia characterized by?

• Characterized by BOWING of the long bones

  • Bowing of long bones (Legs affected worst)

  • Small thorax

  • Hypoplastic fibulas & scapulae

  • Hypertelorism

  • Cleft Palate

  • Micrognathia

  • Talipes

  • Hydrocephalus

  • Polyhydramnios

  • Hydronephrosis

What are these images showing?

Campomelic dysplasia