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This document discusses ultrasound evaluation of the fetal musculoskeletal system. It begins by describing development of the fetal skeleton from various cell types and then discusses limb bud development. It describes the process of skeletogenesis and factors involved in patterning. It provides details on qualitative assessment of long bones and differential diagnosis of various skeletal dysplasias based on ultrasound findings. Key skeletal dysplasias discussed in detail include achondroplasia, thanatophoric dysplasia, achondrogenesis, osteogenesis imperfecta, and hypophosphatasia.
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- 1. Ultrasound Evaluation of the Fetal Musculoskeletal System
- 2. Development of the Fetal Skeleton 1. Cranial neural crest cells 2. Paraxial mesoderm cells or somites 3. Lateral plate mesoderm
- 3. Limb buds-4th week of embryonic life Mesenchymal models of bone-5th week of embryonic life Development of the upper limbs precedes the lower limbs Limbs develop in a proximo-distal sequence Osteogenesis-7th week of embryonic life
- 4. Skeletogenesis Fours steps: 1. Patterning 2. Organogenesis 3. Growth 4. Homeostasis
- 5. Signalling Regions of Patterning 1. Apical ectodermal ridge 2. An area consisting of ectoderm covering the sides of the bud 3. A zone of polarizing activity
- 6. Other Genes Involved in Patterning Sonic hedgehog(Shh) GLI-Kruppel family member GLI3 (Gli3) Sallike 1 (Sall 1) Hoxd 13 Bone morphogenetic/cartilage-derived morphogenetic protein (CDMP) Growth differentiation factors (GDFs) Noggin(Nog) Wn7-a Engrailed (en) LIM homeobox transcription factor 1 beta (Lmx1b)
- 7. Three Phases of Organogenesis 1. Condensation 2. Cell differentiation 3. Histogenesis
- 8. Endochondral ossification Axial and appendicular skeleton SOX9 plays an important role in chondrogenesis -Mutations in this gene cause campomelic dysplasia Procollagen type II alpha 1 (COL2A1), which encodes collagen type II
- 9. Bone Marrow Formation 1. Degradation of hypertrophic cartilage matrix 2. Chondrocytes undergo apoptosis 3. Osteoblasts replace the disappearing cartilage with trabecular bone 4. Bone marrow is formed
- 10. Osteoblasts in the perichondrium begin to deposit a collar of compact bone matrix along the diaphysis. -Osteoblast differentiation is controlled by RUNX2 and Osterix. Proliferation is controlled by the LDL receptor related protein 5 (LPR5) signaling pathway. Eventually, cartilage in the center of the anlagen degrades, mineralizes, and is removed by osteoclasts.
- 11. Secondary ossification centers begin to appear at the extremities of bones(epiphysis) later in pregnancy The growth plate is formed by a cartilaginous component, a bony component, and fibrous tissue -responsible for longitudinal growth of long bones until definitive fusion of epiphyses and diaphysis occurs at the end of puberty
- 12. Only the diaphyses are measured when doing UTZ of long bones DFE-32-33 weeks PTE-34-35 weeks PHE-37-38 weeks
- 13. Intramembranous Ossification Craniofacial skeleton and clavicles develop by this process Direct differentiation of mesenchymal cells into osteoblasts which produce a bone matrix rich in type I collagen Bone remodeling is accomplished by continuous and concerted action of osteoblasts and osteoclasts
- 14. Skeletal Dysplasia Heterogenous group of disorders affecting the development of the chondro-osseous tissues and resulting in abnormalities in the size and shape on the various segments of the skeleton.
- 15. Skeletal Dysplasia Results from abnormal development , growth or maintenance of cartilage and bone tissues Estimated in 2.4 births 23% of infants were stillborn and 32% died during the first week of life Overall frequency among perinatal deaths was 9.2 per 1000.
- 16. Clinical Presentation Usually presents in one of two ways: 1. A patient has delivered an infant with a skeletal dysplasia and desires antenatal assessment in a subsequent pregnancy 2. Incidental finding of shortened, bowed or anomalous extremity during a routine sonographic examination.
- 17. Role of diagnostic imaging 1. To narrow the differential diagnosis of skeletal dysplasia so that appropriate confirmatory molecular tests can be selected 2. To predict lethality 3. To identify the fetus early enough in the pregnancy so that the diagnostic workup can be completed before fetal viability.
- 19. Approach to the Diagnosis of Musculoskeletal Dysplasia - Requires a multistep total body ultrasound which should include assessment of the following: 1. Measure all long bones To assess the anatomy of the limbs, two types of views should be sought: regional views – aiming at visualization of the three components to ascertain whether the anomaly involves the whole limb or predominantly a part of it
- 20. Approach to the Diagnosis of Musculoskeletal Dysplasia focal, higher-magnification views – to study in detail the anomaly of the affected segment, in order to characterize possible focal defects and/or anomalies of the extremities
- 26. Approach to the Diagnosis of Musculoskeletal Dysplasia 2. Compare with other segments and classify based on the shortening of the extremities: • Micromelia – entire limb • Rhizomelia – proximal segment • Mesomelia- intermediate segment • Acromelia - distal segment
- 27. Evaluation of the Long Bones
- 28. Evaluation of the Long Bones and Extremities
- 29. Ultrasound differential diagnosis of skeletal dysplasias characterized by severe micromelia Index Sign Severe Micromelia Additional signs Thoracic hypoplasia (no cloverleaf skull) Thanatoporic dysplasia type I Additional signs Ubiquitous fractures ± hypomineralization Osteogenesis imperfecta type II Additional signs Throracic hypoplasia ± hypomineralization Achondrogenesis Additional signs Severe ubiquitous hypomineralization Hypophosphatasia Additional signs Throracic hypoplasia ± CHD polydactyly ± hypomineralization Short rib polydactyly syndromes
- 31. Ultrasound differential diagnosis of skeletal dysplasias characterized by rhizomelia of variable severity Index Sign Rhizomelia Additional signs Frontal bossing ± mild macrocrania Achondroplasia Additional signs Thoracic hypoplasia ± polydactyly ± renal anomalies Asphyxiating thoracic dystrophy (Jeune Syndrome) Additional signs Postural deformities + ‘hitch- hiker’s thumb’ ± micrognathia Diastrophic dysplasia
- 32. 3. Qualitative assessment of long bones ‘Degree of Mineralization – assessed by acoustic shadow behind the bone and the echogenicity of the bone itself
- 34. Ultrasound differential diagnosis of skeletal dysplasias characterized by diffuse hypomineralization Index Sign Hypomineralization Additional signs Micromelia + fractures Osteogenesis imperfecta type II Additional signs Micromelia Hypophosphatasia (clavicle-spring hypomineralization) Additional signs Micromelia + thoracic hypoplasia ± micrognathia Achondrogenesis Additional signs Micromelia + CHD + polydactyly Short-rib polydactyly syndromes
- 35. 3. Qualitative assessment of long bones Fractures
- 36. 3. Qualitative assessment of long bones
- 37. 3. Qualitative assessment of long bones Degree of long bone curvature (e.g. bowing) Bowing of the lower extremities Thanarophoric dysplasia Campomelic dysplasia
- 38. Metaphyseal flaring – denotes widening at the level of the metaphyseal growth plate
- 39. Approach to the Diagnosis of Musculoskeletal Dysplasia 4. Measure chest dimensions to determine the risk of pulmonary hypoplasia a. Evaluation of thorax and lungs by 2d ultrasound
- 41. Index sign Thoracic hypoplasia Additional signs Micromelia (no cloverleaf skull) Thanatoporic dysplasia type I Additional signs Rhizomelia ± renal anomalies/polydactyly Asphyxiating thoracic dystrophy (Jeune Syndrome) Additional signs Micromelia ± hypomineralization Achondrogenesis Additional signs Micromelia ± hypomineralization Hypophosphatasia Additional signs Micromelia + polydactyly + CHD ± hypomineralization Short-rib polydactyly syndrome(s)
- 42. 5. Evaluation of Hands and Feet
- 43. 5. Evaluation of Hands and Feet
- 44. Evaluation of Hands and Feet
- 45. Evaluation of Hands and Feet
- 47. Ultrasound Differential Diagnosis of Conditions possibly associated with Clubfoot Index sign Clubfoot Additional signs Neural tube defects + Chiari II Complex spina bifida Additional signs Bowed tibias and femurs + micrognathia Campomelic dysplasia Additional signs Focal femoral hypoplasia + micrognathia Femoral hypoplasia – unusual facies syndrome Additional signs Arthrogryposis + pterygia Multiple Pterygium Syndrome Additional signs Arthrogryposis + micrognathia Hydrops FADS
- 48. Polydactyly
- 49. Ultrasound Differential Diagnosis of Conditions possibly associated with Polydactyly Index Sign Polydactyly Additional sign Micromelia + thoracic hypoplasia + CHD Short-rib polydactyly syndrome(s) Additional sign CHD + micrognathia + multiple anomalies Trisomy 13 Additional sign Thoracic hypoplasia + renal anomalies Asphyxiating thoracic dystrophy (Jeune syndrome) Additional sign Polycystic Kidney + cephalocele Meckel-Gruber Syndrome Additional sign CHD + acromesomelia Ellis-van Creveld Syndrome
- 50. Evaluation of Hands and Feet
- 51. Erodactyly
- 52. Ultrasound Differential Diagnosis of Conditions possibly associated with Ectrodactyly Index sign Ectrodactyly Additional signs Phocomelia + cleft lip/ palate Robert’s Syndrome Additional signs Aplasia radii + micrognathia + multiple anomalies Trisomy 18 Additional signs Cleft lip/palate or malar hypoplasia EEC Syndrome Additional signs Micrognathia + external ear anomalies Nager Syndrome Additional signs None SHFM
- 53. Evaluation of Hands and Feet
- 54. Evaluation of the Fetal Cranium Poor ossification Frontal bossing Cloverleaf deformity
- 55. Ultrasound Differential Diagnosis of Conditions possibly associated with Hypomineralization Index sign Hypomineralization Additional signs Micromelia + fractures Osteogenesis Imperfecta type II Additional signs Micromelia Hypophosphatasia Additional signs Micromelia + Thoracic hypoplasia ± micrognathia Achondrogenesis Additional signs Micromelia + CHD + Polydactyly Short-rib polydactyly syndrome
- 57. Ultrasound Differential Diagnosis of Conditions possibly associated with Hydrops/hygroma Index sign Hydrops Additional signs Micromelia ± hypomineralization + micrognathia Achondrogenesis Additional signs Micromelia (no cloverleaf skull) Thanatophoric dysplasia type I Additional signs Micromelia + fractures + hypomineralization Osteogenesis Imperfecta type II Additional signs Rhizomelia + polydactyly/renal anomalies Asphyxiating thoracic dystrophy (Jeune Syndrome) Additional signs Micromelia + CHD + Polydactyly Short-rib polydactyly syndrome(s)
- 58. Evaluation of the Fetal Spine
- 59. Evaluation of the Fetal Spine
- 60. Skeletal Dysplasias 3 different groups 1. Osteochondrodysplasias (abnormalities of cartilage and or bone growth and development) 2. 2. Disorganized development of cartilaginous and fibrous components of the skeleton 3. Idiopathic osteolysis
- 61. Achondroplasia Most common non lethal skeletal dysplasia An autosomal dominant condition with complete penetrance and estimated prevalence renging from 1:10,000 to 1:50,000 births Characteristics: • Rhizomelic shortening of the limbs and mild limb bowing, exagerrated lumbas lordosis • Bones of hand and feet are brachydactyly • Head is large (macrocephaly), with frontal bossing, midface hypoplasia, flatted nasal bridge, and broad mandible Normal lifespan. No risk of mental retardation. Orthopedic and pulmonary long term sequalae due to relatively small thorax
- 62. Achondroplasia
- 63. Achondroplasia
- 64. Achondroplasia Trident hand – an increased interspace between the third and fourth digit – specific finding for achondroplasia
- 65. Achondroplasia
- 66. Thanatophoric Dysplasia Most common lethal skeletal dysplasia Autosomal dominant Occurs in 0.24 to 0.69 of 10,000 births Characteristics: • Severe rhizomelia • Normal trunk length with narrow thorax • Large head with prominent head • Prognosis: uniformly lethal disorder
- 70. Thanatophoric Dysplasia 2 subtypes – phenotypically differentiated with skull shape and femur morphology 1. Type I
- 71. Thanatophoric Dysplasia 2 subtypes – phenotypically differentiated with skull shape and femur morphology 1. Type I
- 74. Thanatophoric Dysplasia Type II
- 75. Achondrogenesis Also known as anosteogenesis A lethal chondrodystrophy characterized by severe micromelia, a short trunk and macrocrania Occurs in 0.09 to 0.23 in 10,000 births
- 78. Osteogenesis Imperfecta Heterogenous group of disorders caused, in most cases, by mutations in one or two genes for type I procollagen Occurs in 0.18 per 10,000 births Extraskeletal malformations are variably associated with the disorder and include blue sclera, dentino-genesis imperfecta, hyperlaxity of ligaments and skin, hearing impairment and presence of wormian bones
- 86. Hypophosphatasia Rare autosomal recessive inherited disorder with incidence of 1:100,000 Characterized by demineralization of bones and low alkaline phosphatase (ALP) in serum and other tissues
- 87. Hypophosphatasia Types (according to age of onset) 1. Perinatal (lethal) – associated with stillbirth or early neonatal death due to either intracranial hemorrhage or respiratory insufficiency secondary to poorly developed ribs and reduced thoracic cavity volume 2. Infantile – may involved craniosynostosis and nephrocalcinosis from hypercalcemia and hypercalciuria during the first year of life and is often fatal. 3. Childhood – premature loss of deciduous teeth and rickets
- 88. Hypophosphatasia 4. Adult – recurrent metatarsal structural stress fractures abd pseudofratures in long bones 5. Odontohypophosphatasia – mildly affected individuals who have dental, but no skeletal manifestations. The teeth are predisposed to cavities and may lost prematurely. 6. Pseudohypophosphatasia- very rare. Same as infantile but with increased or normal ALP. - Perinatal and infantile – autosomal recessive - Adult, childhood and odontohyphophosphatasia – autosomal dominant or autosomal trait
- 89. Hypophosphatasia
- 90. Hypophosphatasia
- 91. Diastrophic Dysplasia Autosomal recessive Very rare but prevalent in Finland with a carrier frequency of 1 to 2%. Generalized disorder of cartilage leading to destruction of cartilage matrix, formation of fibrous scar tissue and subsequent ossification Not universally lethal Intelligence and sexual development are unaffected
- 92. Diastrophic Dysplasia Characterized by rhizomelic type-micromelia, joint contractures, clubfoot, hand deformities, multiple joint contrcatures, hand deformities, spine disorders (e.g. scoliosis, kyphosis, spina bifida oculta, spinal stenosis, lumbar lordosis), severe talipes equinovarus Head is normal but may have micrognathia and cleft palate
- 93. Diastrophic Dysplasia Joint contractures and painful osteoarthroses are associated with severe physical handicaps that require corrective orthopedic surgery Increased mortality in neonates and infants due to upper airway obstruction secondary to tracheobronchomalacia and medullary compression caused by severe cervical kyphosis
- 96. Campomelic Dysplasia Rare lethal disorder Occurs in 0.05 to 1.6 in 10,000 Thorax is narrow, can be bell shaped and 11 pairs of ribs are usually present Cervical vertebrae are hypoplastic and poorly ossified
- 97. Campomelic Dysplasia Chracterized by bowing of long bones of the lower extremities, enlarged and elongated skull with peculiarly small face, hypoplastic scapulae and several anomalies such as micrognathia, cleft palate, talipes equinovarus, congenital dislocation of the hip, macrocephaly, hydrocephalus, hydronephrosis and congenital heart defects
- 98. Campomelic Dysplasia Two short bone varieties: 1. Kyphomelic dysplasia – normocephalic form 2. Craniostenotic dysplasia – appears to be identical to Antley-Bixler syndrome 75% affects male with sex reversal syndrome and have female or ambiguous genitalia Frequently lethal in infancy Cause of death is usually respiratory distress due to tracheomalacia
- 100. Campomelic Dysplasia
- 101. Campomelic Dysplasia
- 102. Skeletal Dysplasias Characterized by a Hypoplastic Thorax A. Asphyxiating Thoracic Dysplasia (Jeune Syndrome) - Rare autosomal recessive condition - Occurs in 0.14 in 10, 000 births - Characterized by a combination of a small thorax, varying degrees of brachymelia, polydactyly, pelvic abnormalities and renal involvement - Prognosis varies from neotal death, due to pulmonary hypoplasia, to normal survival
- 103. Asphyxiating Thoracic Dysplasia (Jeune Syndrome)
- 104. Asphyxiating Thoracic Dysplasia (Jeune Syndrome)
- 105. Short Rib-Polydactyly Syndromes (SRP) Heterogenous group of disorders inherited as autosomal recessive trait 4 types 1. Type I - Saldino - Noonan 2. Type II – Majewski 3. Type III – Verma-Naumoff 4. Type IV – Beemer-Langer Lethal in newborn due to severe pulmonary hypoplasia and associated anomalies Characterized by short limbs/micromelic dwarfism, constricted thorax, usually polydactyly and multiple anomalies of major organs
- 106. Short Rib-Polydactyly Syndromes (SRP)
- 108. Limb Deficiency or Congenital Amputations Limb defieciency – absence of an extremity Congenital amputation – absence of a segment of extremity Overall incidence – 0.49 to 3.5 per 10,000 births 50% - simple transverse reduction deficiencies of one forearm or hand without associated anomalies 23 % - consist of reduction with additional anomalies of the internal organs or craniofacial structures
- 109. Limb reduction abnormalities Amelia – absence of a limb or limbs Hemimelia – absence of longitudinal segment of a limb (redial aplasia, radial hypoplasia) Phocomelia – hypoplasia of the limbs, with hands and feet attached to the shoulders and hips Acheira – absence of the hands Apodia – absence of a foot or feet Acheiropodia – absence of hands and feet
- 113. Rockerbottom foot
- 115. Thank you and Good Day!
Editor's Notes
- The skeleton is formed by 206 skeletal elements constituted by 2 tissues, bone and cartilage, and 3 cell-types (osteoblasts, osteoclasts, and chondrocytes. The craniofacial skeleton originates form cranial neural crest cells, the paraxial mesoderm gives rise to the axial skeleton, and the lateral plate mesoderm is the embryonic precursor of the limbs
- The anlagen of the humerus and femur forming 1st, followed by the radius and ulna, the tibia and fibula, the metacarpal and metatarsal bones, and phalanges Osteogenesis-developing by either endochondral or membranous ossification.
- Patterning is the process by which the final size, shape, and number, and arrangement of bones are determined. Homeostasis is the process that controls the continuing remodeling of bones.
- The apical ectodermal ridge consists of densely-packed ectodermal cells located at the tip of the limb bud, w/c express several fibroblast growth factors (FGFs) that initiate and control limb outgrowth The ectoderm covering the sides of the bud regulates dorsoventral patterning The zone of polarizing activity is located on the posterior limb bud margin. It is responsible for AP patterning and thus, the formation of digits.
- Condensation is of great importance in skeletal development because the templates for future bones are defined at this stage.
- The axial skeleton (eg. Vertebrae and the dorsal part of the ribs) originates from the somites. campomelic dysplasia-a severe skeletal disorder characterized by congenital bowing and angulation of the long bones(especially of the tibia), hypoplastic scapulae, sex reversal in male fetuses, and a high lethality rate due to respiratory insufficiency
- The portion of the cartilage trapped between the expanding primary and secondary ossification centers known as the growth plate or physis Indian hedgehog (Ihh)- a stimulator of chondrocyte proliferation at the growth plate
- The epiphyses are hypoechoic and are not always visualized. Secondary ossification centers are visualized in the third trimester. These ossification centers may be seen earlier in female fetuses than in male fetuses
- The challenge of antenatal diagnosis of skeletal dysplasias generally presents itself in one of two ways: In patients at risk, the examination is easier when the particular phenotype is known. The inability to obtain a reliable information about skeletal mineralization and the involvement of other system (eg skin) with sonography is a limiting factor in the establishment of an accurate diagnosis after the identification of the incidental finding. Another limitation is the paucity of information about the in utero natural history of this disorder.
- Despite the increasing availability of molecular testing, a comprehensive molecular diagnostic search for all skeletal dysplasias is not possible at this time. Indeed, as mentioned, only about one third of skeletal dysplasias have their molecular basis defined. Therefore the role of diagnostic imaging in the prenatal investigation of skeletal dyspalsias are:
- The US appearance of the bones changes significantly during gestation, due to progressive mineralization. Limb buds are first seen by ultrasound at about the 8th week of gestation; the femur and humerus are seen from 9 weeks, the tibia/fibula and radius/ulna from 10 weeks and the digits of the hands and the feet from 11 weeks. All long bones are consistently seen from 11 weeks. Body movements (wiggling) are seen at 9 weeks and, by 11 weeks, limbs move about readily. The lengths of the humerus, radius/ulna, femur and tibia/fibula are similar and increase linearly with gestation. At the 18–23-week scan, the three segments of each extremity should be visualized, but it is only necessary to measure the length of one femur.
- Ultrasound (US) assessment of the fetal musculoskeletal apparatus requires a global approach to the fetal body, given that skeletal dysplasias and neuromuscular diseases involve more or all anatomic regions simultaneously, because of the ubiquitous distribution of bones and muscles. The only exceptions are reduction defects of the limbs, congenital or acquired (amniotic band syndrome), which are regional by definition. Therefore, unlike other systems, assessment of the fetal musculoskeletal apparatus requires a multistep total body US approach, which should include assessment of the following: To assess the anatomy of the limbs, two types of views should be sought: (1) regional views, aiming at visualization of the three components (rhizomelic, mesomelic, and acromelic), to ascertain whether the anomaly involves the whole limb or predominantly a part of it—this is generally carried out with low-magnification sagittal US views of the whole limb
- Humerus. Long bone length is the measurement of the ossification center of bone diaphysis All three portions of the upper limb must be distinguished proximal (humerus *), middle (ulna and radius **) and distal (hand ***), with five fingers
- Ulna (*) and radius (**). Ulnar diaphysis is longer than radial one. Proximal noncalcified epiphyses may be assessed, as round anechogenic structures (arrows) Upper limb. For a correct ultrasonographic assessment, all three portions of fetal limbs must be visualized (proximal, middle and distal) aligned following the same axis. Fetal posture and shoulder, elbow and wrist movement must be assessed
- All three portions of the lower limb must be distinguished: proximal (femur *), middle (tibia and fibula **) and distal (foot ***) Lower limb showing all three portions. All of them responsible of a posterior shadow effect (*). One must assess the femur, tibia and foot normally aligned and the hip, knees and elbows motility
- Tibia (*) and fibula (**). Tibial diaphysis is longer and thicker than fibular diaphysis. Nonmineralized fibular epiphysis (arrows) Femoral diaphysis. A normal degree of mineralization is indirectly assessed by the appearance of a posterior shadow (arrows) that enables a clear visualization of all diaphyseal thickness (discontinued line). For this reason bone appears thinner than soft tissues that surround it
- it is important to assess that both femurs have the same length (arrows) Lower extremity uniformly shortened, with a correct degree of mineralization and no angulations or fractures (*)
- Upper limb, flexed: the image shows the rhizomelic segment (humerus), the mesomelic segment (ulna and radius) and the acromelic segment (hand). Lower limb, abducted: the rhizomelic (femur), mesomelic (tibia and fibula) and acromelic segments (foot)
- Note the absence of the hyperechoic rim due to the normal mineralization of the skull and the evidence of the CNS structures due to the unblocked penetration of the US waves. The lateral ventricle and choroid plexus in the near field are well seen due to lack of normal mineralization of the calvarium.
- The presence or absence of hypomineralization in this group of syndromes varies in the four types
- 1. Multiple fractures in the ribs are present. Note the severe bowing and shortening of the left femur and humerus. 2. In utero fracture in OI II. The arrows indicate the hypoechogenic fracture line.
- Long bone shortening and angulation due to multiple fractures (arrows)
- At present there is no objective means of assessing long bone curvature and experience is the only tool assisting the operator in discerning the boundary between the normality and abnormality
- Antenatal ultrasound image showing short femur (white arrow) and humerus (dashed arrow) with metaphyseal flaring. It can be observed in many condition such as achondroplasia, hypochondroplasia, hypochondrogenesis, asphyxiating thoracid dysplasia, hypophosphatasia, OI etc
- Severe skeletal dysplasia are associated with a hypoplastic thorax. This is extremely important because of chest restriction leads to pulmonary hypoplasia, a frequent cause of death in these conditions. When a severe skeletal dysplasia is diagnosed, the presence of marked thoracic involvement and pulmonary hypoplasia will allow the clinician to counsel the parents regarding the diagnosis
- Hands and feet should be examined to exclude polydactyly, brachydactyly. Hands are best assessed when they are open so one can confirm the integrity of all the phalanges and the normal separation of fingers Forefoot. Arrows showing metatarsal and phalanges. Fetal tarsus completes its calcification process at 26 weeks of gestation
- Hand, high-magnification: the five rays are visible, with all digits extended Foot, high magnification: the toe (arrow) and the other digits are visible. The calcaneus and metatarsus are also visible.
- Table 12-15 shows a normogram of the fetal foot throughout gestation. Disproportion between the hands and feet and other part othe extremity may also be a sign of skeletal dysplasia.
- This table illustrates the relationship between the femur and foot length. The femur length/foot length ratio is nearly constant from 14 to 40 weeks of gestation, with a mean value of 0.99 + 0.06. A ratio below 0.87 is considered abnormal.
- In clubfoot, the axis of the foot is no longer that of the lower leg, and therefore on the sgittal view of the leg, the sole is also visible with the foot drawn up and bent inward.
- Arthrogyrposis is a condition characterized by fixed abnormal contractures of all muscles within a given anatomic area.
- Polydactyly is defined as postaxial if the sixth digit which may or may not present a bony phalanx, is on the ulnar of fibular after the 5th digit. On the contrary if the additional digit is located o the radial/tibial side, before the thumb/toe, it is called preaxial. Care muust be taken in the diagnosis of suspected polydactyly. The hand has to be imaged either with the digits upward or with its radial aspect proximity to the transducer; in these positions , soft appendices would also be spotted on the ulnar margin of the hand.
- Jeune syndrome-polydactyly is found in only 20% of cases.
- Erodactyly is the absence of one or more digits although the term is used almost synonymously with thumb aplasia. However it should be emphasized that the absence of one or more digit or the fusion of any (syndactyly) into two gross digits (lobster-claw anomaly) are highly indicative of very rare conditions such as Nager syndrome or erodactyly-ectodermal dysplasoa (EEC) and split hand and foot malformation.
- Ectrodactyly consists mainly of ‘lobster claw’ anomaly Ectrodactyly-ectodermal dysplasia Split-hand and foot malformation
- Several skeletal dysplasias are associated with defects of membranous ossification and therefore affect skull bones. Examination of the skull bones may reveal poor ossification, frontal bossing or cloverleaf deformities. The US detection of hypomineralization is usually made on the axialtransthalamic view of the fetal head or, alternatively, on the midsagittal view of the fetal profile. A peculiar feature, in the case of hypomineralization of the calvarium, is the perfect depiction of the fetal brain due to the lack of US absorption by the underossified proximal parietal bone; in addition, the usually bright rim of the calvarium is barely visible. An additional feature is the softness of the calvarium: it is possible to deform the fetal head significantly by applying moderate pressure with the transducer. Once the occurrence of hypomineralization has been established, the next step is to evaluate the involved regions. The selective involvement or, on the contrary, the selective sparing of a given region may contribute to the differential diagnosis. As an example, in hypophosphatasia, the hypomineralization spares the clavicles. A flow chart assisting in the differential diagnosis of the most common skeletal dysplasias characterized by hypomineralization
- The spine is electively evaluated using the midsagittal view, possibly performed with an spine up position, in order to assess the vertebral bodies and the cutaneous contour, taking care to reduce the pressure on the transducer to leave some amniotic fluid between the proximal uterine wall and the spine, which greatly enhances the acoustic window (Figure 9.3). This sagittal view allows display of neural tube defects as well as possible fusions of vertebral bodies. (a) Two-dimensional sagittal view: the regular aspects of all the neural arches, together with the continuous cutaneous contour, are evident. By confirming the integrity of the cutaneous contour on this view, it is possible to exclude open spina bifida. In front of the sacrum, the bladder (Bl) is visible.
- Coronal scan of the fetal spine by 2D US showing scoliosis The most common osseous anomaly causing scoliosis is unilateral unsegmented bar with contralateral hemivertebrae. Spinal dysraphism with congenital scoliosis and this should be examined carefully.
- Postmortem photography of an achondroplasic fetus showing frontal bossing, depressed nasal bridge and rhizomelia
- Macrocrania and low nasal bridge
- The skin is redundant in comparison with short phalanges, leading the hand to have this curved appearance.
- View of the head. Note the double contour of the skull (arrows) that suggests a generalized lymphatic drainage defect. The skull is compressible by the transducer, which permits a good visualization of the intracranial structures
- Prominent skull, hypoplastic thorax, severe micromelia. Short and curved thighs
- Characteristic bowing of the femur (arrow).The classical “bent” bone on ultrasound may mimic a fracture as a result of the acute angulation, Middle portion of lower extremity showing long bone bowing (arrow) but no fractures are seen
- Coronal view of the trunk. The thorax is bellshaped, and the ribs are shortened (but normally mineralized). A normal abdomen appears protuberant compared to the small thorax (arrows) Fetal thorax oblique section. Rib shortening, with a wrinkled appearance and angulation caused by multiple fractures (arrows)
- Total body surface rendering showing: severe thoracic hypoplasia, with thoracoabdominal indentation, macrocrania, and limb shortening.
- Bowed “telephone receiver” femurs
- The ribs are very short and, on the midsagittal low-magnification view of the fetal trunk, a dip typical of severe thoracic hypoplasia can be seen at the level of the thoraco-abdominal junction.
- Head is large, with frontal bossing and a low nasal bridge
- Axial transthalamic view demonstrating the abnormal shape of the skull and the early closure of some sutures (arrowheads). Cloverleaf skull
- Note the double contour of the skull (arrows) that suggests a generalized lymphatic drainage defect. The skull is compressible by the transducer, which permits a good visualization of the intracranial structures. Frontal and lateral views. There is no mineralization of the spine and ischial bones. The thorax is bell shaped with short and straight ribs with no fractures. Long bones are short, with metaphyseal flaring and cupping.
- Transverse axial sonogram. The lack of ossification of the spine makes the determination of anterior and posterior aspects of the fetus difficult to view.
- On transvaginal ultrasound, the complete hypomineralization of the calvarium is evident (arrowheads). Sagittal section. Abnormal ossification of the fetal skull as shown by the absence of posterior shadowing
- Ventriculomegaly (between calipers) secondary to a reduced magnum foramen. When no CNS anomalies are prenatally detected, psychomotor development is normal
- Axial view of the thorax: abnormal ribs with thoracic hypoplasia.
- The four-chambers view. Narrow chest caused by fractures of the ribs and wrinkling of the surface of the bones due to multiple fractures Multiple fractures of the ribs. The callous formation may be assessed microscopically (arrows)
- Fractured and bowed femur (arrow). Fractured tibia, with an acute angle deformation (arrow).
- Osteogenesis imperfecta type II. Long bone shortening and angulation due to multiple fractures
- Hypophosphatasia (14 weeks of gestation). The transvaginal shows severe micromelia and hypomineralization of the upper limb. Neither the humerus nor the ulna/radius is visible in the rhizomelic and mesomelic segments of the arm, due to severe hypomineralization (h: hand).
- Hypophosphatasia (14 weeks of gestation). The transvaginal scan shows: (a) complete absence of calvarial mineralization (arrowheads); (b,c) multiplanar imaging of the fetal body demonstrating complete absence of mineralization involving virtually all districts with the significant exception of the clavicles, which are spared (arrows). In the sagittal plane (b), due to the transparent ribs, the moderately hyperechoic lung is also visible below the clavicle. On the coronal view (c), the complete absence of mineralization of the calvarium and the spine allows a neat unobscured demonstration of the spinal cord and the brain, with the two lateral ventricles and the choroid plexuses (arrows: clavicles).
- The left image shows the classic “hitchhiker’s thumb” (arrowhead) typical of this disorder, which is due to contracture of the extensor of the thumb and the flexors of the other digits. The right image shows a less typical case on three-dimensional surface-rendering: the thumb is extended, but the other digits show only partial flexion contracture.
- Rhizomelia Postural deformities
- Campomelic dysplasia (22 weeks of gestation). Two-dimensional imaging (a) significantly bowed and short femur; (b) mildly bowed tibia.
- Campomelic dysplasia (22 weeks of gestation). (a) Three-dimensional maximum-mode rendering of the lower limb demonstrates evident bowing of femur and tibia (arrows). In addition, the smaller than normal iliac wing is shown; this represents an additional sign of campomelic dysplasia; (b) three-dimensional maximum mode rendering of the calvarium demonstrates a large anterior fontanelle (c: coronal suture; m: metopic suture; s: sagittal suture); (c) three-dimensional surface-rendering of the fetal profile demonstrates moderate micrognathia; (d) autoptic confirmation (arrows: bowed femur and tibia).
- Coronal view of the scapula showing its poor mineralization
- Coronal view of the thorax, showing severe thoracic hypoplasia (arrows), with the heart (H) squeezed into the center of the thorax. Axial view of the abdomen, showing the horseshoe kidney (arrowheads).
- Confirmation at autopsy. Note the severe thoracic hypoplasia (arrowheads) Axial view of the thorax, confirming severe hypoplasia: the heart is almost outside the ribcage due to the extremely reduced dimensions of the thorax.
- Short-rib polydactyly syndrome (20 weeks of gestation). (a) Severe thoracic hypoplasia. (b) Postaxial polydactyly of one hand (arrow). (c) Confirmation of polydactyly at autopsy. (d) Specimen after termination of pregnancy, showing severe thoracic hypoplasia (arrowheads). Note also the dip at the thoracoabdominal junction (arrowheads).
- There is severe shortening of all long bones, very short and horizontal ribs, and postaxial polydactyly in all four extremities. Note the angulation of bone in the forearm.
- Sonogram of a fetus with radial aplasia. The hand deviates toward the side of the absent bone (radius).
- the absent part of the limb involves the hand and part of the forearm (arrowheads),
- Terminal transverse reduction defect (acheiria): all digits and part of the metacarpus are completely absent. (b) Severe hypoplasia of the lower half of the calf and the foot (arrow). (c) Confirmation at autopsy: compare with the size of the normal contralateral limb and foot.
- This deformation is typical of trisomy 18 and of other muscular and chromosomal anomalies. On ultrasound, the most typical feature is the prominent calcaneus (arrow).
- Phocomelia of upper fetal extremity. Anomalous hand (between callipers) directly inserted in the trunk without evidence of middle or proximal portions of the upper limb (arrow)