Prenatal stage and neonatal diagnostics
Screening for developmental anomalies begins long before birth. The primary method is fetal ultrasound at 18–21 weeks of gestation. It allows the detection of lethal skeletal dysplasias, such as limb shortening or a pathologically narrow thorax. However, ultrasound does not always possess sufficient specificity for a precise genetic diagnosis. If a pregnancy is terminated for medical indications, the protocol requires mandatory radiography of the entire fetus (so-called babygrams) in two projections and histopathological analysis. Postmortem evaluation increasingly employs MRI and micro-CT.
In liveborn infants with dysmorphic features or short stature, a complete skeletal survey is performed. The standard set includes radiographs of the skull (capturing the atlas and axis), chest, pelvis, spine, and one upper and one lower extremity. A posteroanterior radiograph of the hand, typically the left, is mandatory for bone age determination.
Imaging modalities and complication monitoring
The diagnostic imaging method is always selected for the specific clinical task and the probable natural history of the disease:
- Dual-energy X-ray absorptiometry (DXA): used to assess bone mineral density, including the diagnosis of vertebral compression fractures in children with osteopenia.
- MRI: indispensable for monitoring hydrocephalus, structural brain anomalies (agenesis of the corpus callosum), and detecting spinal cord compression.
- Whole-body MRI: utilized as a safe alternative without ionizing radiation to search for multifocal lesions. Fat-suppression sequences (STIR) and diffusion-weighted imaging (DWI) are applied.
- Vertical biplanar imaging systems (EOS) and CT scanograms: necessary for the accurate assessment of long bone asymmetry and varus/valgus deformities.
Radiological patterns of genetic syndromes
Radiography enables the highly accurate recognition of manifestations of chromosomal aberrations and gene mutations:
- Trisomy 21 (Down syndrome): characterized by flared iliac wings (flared iliac wings), shallow acetabular sockets, the presence of 11 pairs of slender ribs, and two ossification centers in the manubrium sterni. A dangerous condition in this syndrome is atlantoaxial instability against the background of odontoid hypoplasia.
- Turner syndrome (45,X0): radiographs reveal shortening of the 4th metacarpals, osteoporosis, a decrease in the angle between the radial and ulnar metaphyses (resembling Madelung deformation), and flattening of the medial tibial condyle.
- Osteogenesis imperfecta: the clinical and radiological picture depends on the Sillence classification type. It is characterized by bone fragility and deformities. During bisphosphonate therapy in patients, specific radiodense «bisphosphonate lines» appear on radiographs.
Localized skeletal disorders
Developmental dysplasia of the hip (DDH) is frequently associated with breech presentation, female sex, and oligohydramnios. The optimal screening method is ultrasound using a high-frequency linear transducer at approximately 6 weeks of age, evaluating the joint according to Graf. When the proximal femoral epiphysis begins to ossify (usually at 9–12 months), ultrasound loses its informative value, and radiography is initiated to monitor treatment.
Perthes disease is idiopathic avascular necrosis of the femoral head. The disease manifests at 5–8 years of age with pain and a limp. The process goes through four stages: devascularization, collapse with fragmentation, reossification, and final remodeling. Involvement is more often unilateral.
Genetic mechanisms in radiology
Understanding the inheritance pattern is important for interpreting radiographs. Most systemic bone dysplasias are inherited in an autosomal dominant or recessive manner, but many severe forms result from spontaneous mutations (e.g., in achondroplasia).
Of special interest is somatic mosaicism — the presence of multiple cell lines derived from a single zygote. Radiologically, mosaicism manifests as asymmetric or strictly focal lesions (e.g., local overgrowth). Another important phenomenon is imprinting, where disease manifestation depends on which parent the chromosome was inherited from. A prime example is paternal disomy of chromosome 15 causing Angelman syndrome, whereas maternal disomy causes Prader-Willi syndrome.
Briefly: answers to topical questions
What types of osteogenesis imperfecta are distinguished by the Sillence classification, and how do they differ?
According to the Sillence classification, five types of osteogenesis imperfecta (Osteogenesis Imperfecta) are distinguished, which differ in their clinical and radiological manifestations.
| Sign | Type I | Type II | Type III | Type IV | Type V |
|---|---|---|---|---|---|
| Severity | Mild | Lethal | Severe | Mild to moderately severe | Moderate |
| Sclerae | Blue | Blue | Blue, then gray | White | White |
| Teeth | Normal or DI | — | DI | Normal or DI | Normal |
| Fractures at birth | <10% | Multiple | Frequent | Rarely | Rarely |
| Deformity | Mild | — | Severe | Variable | Moderate/severe |
Which angles are measured and what joint types are distinguished during hip ultrasound using the Graf method?
During ultrasound examination of the hip joints, the Graf angles (Graf angles) are measured: the alpha angle (alpha) and the beta angle (beta). Normally, the femoral head is centered, its adequate coverage by the acetabulum is determined, and the angles themselves are within normal limits. Information regarding which specific joint types are distinguished according to this method is absent in the presented materials.
Which specific lethal skeletal dysplasias can be detected on prenatal fetal ultrasound?
The presented materials indicate that prenatal fetal ultrasound at 18–21 weeks of gestation allows one to suspect lethal skeletal dysplasias based on signs such as short or bowed limbs and a narrow thorax.
However, the sources also emphasize that ultrasound findings are significant but insufficiently specific to establish a precise diagnosis. A specific list of lethal skeletal dysplasias that can be reliably detected specifically on prenatal ultrasound is not provided in the presented materials.
To distinguish Perthes disease from systemic epiphyseal dysplasias (e.g., Morquio syndrome) on a pelvic radiograph, use the «Asymmetric Perthes» rule: bilateral avascular necrosis of the femoral head always proceeds at different stages (asymmetrically), whereas genetic dystrophies affect both joints evenly.
Class and exam questions
Why is a radiograph of the left hand included in the standard skeletal examination protocol?
A posteroanterior hand radiograph is essential for accurately determining a child's bone age, making it possible to assess skeletal maturation rates and identify delayed or advanced development.
When is hip ultrasound replaced by radiography in dysplasia monitoring?
Ultrasound is replaced by radiography at 9–12 months of age. During this period, ossification of the proximal femoral epiphysis begins, preventing the ultrasound beam from adequately penetrating the joint.
What are "bisphosphonate lines" on a radiograph?
These are characteristic transverse radiodense bands in the metaphyses of bones. They appear in patients (e.g., with osteogenesis imperfecta) as a result of cyclic bisphosphonate therapy that inhibits osteoclast activity.
What else to study on this topic
- Radiological criteria for osteogenesis imperfecta (Sillence types I–V).
- Cervical spine imaging protocols in mucopolysaccharidoses and achondroplasia.
- Syndromes accompanied by asymmetric bone overgrowth (Klippel-Trenaunay syndrome, Beckwith-Wiedemann syndrome).
- Differential diagnosis of Madelung deformity in Leri-Weill dyschondrosteosis.
- Features of whole-body MRI protocols in childhood: STIR and diffusion-weighted imaging.
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