The FetalSkeletal System

Carol B. Benson, MD

Ultrasound Assessmentof Fetal Skeletal System

Extremities

Spine

Calvarium

Long Bone Development

Ossify by the end of the first trimester

Late third trimester2° ossification centers visible

distal femurproximal tibiaproximal humerus

Tole 41w epiphysis

Epiphysis41 weeks

Drachman & Rousseau nlSpine 3D

ExtremitiesAssess To Exclude

Size Skeletal dysplasia

Presence Absent limbAmniotic band

syndrome

Bones of forearms Radial hypoplasia

Hand position Clenched fists

Foot position ClubfootRockerbottom foot

Calderon Femur length Michel arm 3 bones

Caraballo nl hand

Foot

Femur Length

Normal for GA = Mean ± 2 SD

FL falls 2 - 4 SD below meanMost are growth restrictedWithout skeletal dysplasia

FL falls > 4 SD below meanUsually a skeletal dysplasiaBones appear abnormal by US

Long Bones are Too Short

Skeletal dysplasia

Dysotosis

Malformation

Deformationamniotic band syndromerestrictive uterine environment

Ultrasound assessment

Degree of shortening of long bonestypically > 4 SD below mean for GA

Distribution of involved bonesextremities, spine, calvarium, ribs

Bony abnormalities

↓ mineralization, fractures, bowing

Polydactyly

Skeletal Dysplasias Lethal Skeletal Dysplasias

Neonate cannot surviveusually due to respiratory failure

Ultrasound diagnosis typicallymade in 2nd trimester

Thanatophoric dysplasia Osteogenesis imperfecta Type 2 Achondrogenesis Congenital hypophosphatasia Short rib – polydactyly syndrome

Nonlethal Skeletal Dysplasias

Infants typically surviveUltrasound diagnosis typically

not made in 2nd trimestersometimes made in 3rd trimester

Heterozygous achondroplasia Osteogenesis imperfecta Types 1&4 Asphyxiating thoracic dystrophy

Thanatophoric Dwarf

Most common lethal skeletal dysplasiaSevere rhizomelia

(proximal shortening)Bowed long bonesNarrowed thorax – short ribsFlattened vertebral bodiesCloverleaf skullMegalencephaly – temporal lobe

with excess sulcation/fissures

Cole thanatophoric dwarf

Thanatophoric dysplasia

Kristian 19wthanatophoric

Thanatophoric dysplasia

Kristian 19wthanatophoric

FEM

Osteogenesis ImperfectaType 2

Type 2 — Autosomal recessiveLethal

Ultrasound findings — Type 2FracturesDeformitiesPoor mineralizationSoft skull

Types 1, 3, & 4 — Autosomal dominantNonlethal

Lopez OI

Osteogenesis Imperfecta Type 2

Lopez OI

Osteogenesis Imperfecta Type 2

Osteogenesis ImperfectaType 1 & 4

Type 1 & 4 — Autosomal dominantNonlethal

Ultrasound findings — Type 1 & 4Lagging growth of long bones

3rd trimesterBowing of long bonesMild deformitiesPoor mineralizationSoft skull

McBride OI type 4

Osteogenesis Imperfecta Type 1

Al-Owfi OI type 4

Osteogenesis Imperfecta Type 4

Jones fem fxOI 4

Osteogenesis Imperfecta Type 4

2.4 cm 2.0 cm

18 weeks

Achondrogenesis

Autosomal recessive -- lethal dysplasia

Severely or absent ossification

Marked limb shortening

Absent vertebral body ossification

Normal calvarial ossification

Cooperachondrogenesis

Achondrogenesis

Lyuachondrogenesis

AchondrogenesisArthrogryposis

Multiple joint contracturesEtiologies

Limitation to movementOligohydramniosMultiple gestationBicornuate uterus

Abnormal nerve function Abnormal musculature Defective connective tissue

ArthrogryposisMultiplex Congenita

Ultrasound findingsContracturesIntrauterine growth restrictionPolyhydramniosHydrops

Beausoleil arthrogryposis

Arthrogryposis

McGuiganarthrogryposis

Banerjee Larsen synarthrogryposis

Arthrogryposisfrom

Larsen syndrome(rare genetic syndrome)

Zaiats clubfeet CMV

Clenched Hands – Cytomegalovirus

VentriculomegalyIntracranial calcifications

Zaiats clubfeet CMV

Clubfeet – Cytomegalovirus

Abnormal Hands & Forearms

Inherently abnormalMalformationDysplasia

Normal tissues effected by externalfactors

Deformationuterine constraintsamniotic band syndrome

Disruption (e.g., teratogen)

Radial Ray AnomaliesAssociated with

SyndromesCornelia de LangeFanconi anemiaHolt-OramRadial aplasia-ThrombocytopeniaPoland syndromeNager acrofacial dysostosisVACTERL

Trisomies 13 & 18

Henebry VACTERLabnl thumb

Radial Ray DefectAbnormal Thumb

VACTERL

Castrodad VACTERLhypopl rad

Hypoplastic Radius – VACTERL

Double-outletright ventricle

& transpositionof the great arteries

Colon absent radius tri 18

Absent radius – Trisomy 18Limb Reduction Defects

Terminal transverse deletions(e.g., absent hands)

Isolatedsporadic, unilateralamniotic band syndromevascular accident

SyndromesOrofacial (e.g., Poland)Amniotic bands

Osgood absent hand

Osgood absent hand 3D bones

PolydactylySupernumerary fingers or toesSkeletal dysplasias

Short-rib polydactylyChondroectodermal dysplasiaAsphyxiating thoracic dysplasia

Trisomy 13Meckel-Gruber syndromeAutosomal dominant polydactyly

usually post-axial

MacGowan polydactyly withMeckel Gruber

Polydactyly with Meckel-Gruber

Hand Foot

Malenko dup thumbpolydactyly

Duplicated thumbClinodactyly &

Overlapping Digits

Deviation or deflection of finger(s)

Curving of 5th finger towards 4th

Trisomy 21

Overlapping digitsTrisomy 13Trisomy 18

Dixonclinodactyly

Clenched hands – Trisomy 18Clubfoot

EtiologyGenetic

A variety of syndromesChromosomal defects

EnvironmentalSevere oligohydramniosUterine anomalies

Ultrasound findingsBones of the foot lie in parallel

to bones of lower leg

Lashley clubfeet

Clubfoot

21 weeks

13 weeks

Amniotic Band Syndrome

Early rupture of amnion

Fibrous bands entrap or adhere to fetus

Limb amputations or deformities

EncephalocelesFacial clefts

Ventral wall defectsEctopia cordis

Ultrasound Findings

Fetal deformitiesSkeletalCraniofacialVentral wall

Adherent bands

DDx: Amniotic “sheets”

Amniotic Band Syndrome

Dailey ABS anomalous hand

Amniotic BandSyndrome

Lukina ABS indents calf

Amniotic BandSyndrome

Spinal Abnormalities

Meningomyelocele

Hemivertebra

Scoliosis

Diastomatomyelia

Caudal regression / sacral agenesis

Sacrococcygeal teratoma

Meningomyelocele

Normal

Meningomyelocele

Bardales tri 18Meningomyelocele

Belleveaumeningomyelocele

Meningomyelocele – 18 weeks

Meningocele

Spina bifida

Protrusion of membranes & fluid

No protrusion of nerve roots

Often skin covered

Ultrasound findingssplaying of posterior elementscystic mass protruding

Cabral 19wMeningocele

19 weeks

Reif 20w Meningocele

Hemivertebrae

Associated with a variety of syndromes

Ultrasound findingsKink in spineMismatch of posterior

ossification centers

Johnson hemivertebrae

Hemivertebrae

Hazen Hemivert

Hemivertebrae

1

5

10

13

Sacral Agenesis

Hypoplasia / absence2 or more sacral vertebrae

In fetuses of diabetic motherswith poor glucose control

MacDougall sacral agen

Sacral agenesis

Bensonsacral agenesis

Sacral agenesis

Cranial Anomalies

Craniosynostosis Trigonocephaly (Trisomy 13) Cloverleaf skull (Thanatophoric

dysplasia)

Lemon sign (Chiari II malformation)

Strawberry skull (Trisomy 18)

Craniosynostosis

Premature closure of one or morecranial sutures; Male:Female = 2:1

Complications:Abnormal head shapeAbnormal facesNeurologic deficits

e.g., hearing lossPrenatal diagnosis

Typically not possible before 3rd trimester

Foundas craniosyn

Craniosynostosis

34 weeks

Cloverleaf Skull

Craniosynostosis causing

trilobed shape

prominent forehead

Associated with

Thanatophoric dysplasia

Cole thanat skull

Cloverleaf skull – Thanatophoric dysplasia

20 weeks

Strawberry-Shaped Cranium

Associated with Trisomy 18

Barnatstrawb sk

Strawberry-Shaped CraniumTrisomy 18

16 weeks

Blackman 3D hands