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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