What are the characteristic radiological features and management options for skeletal dysplasia?

Radiological Features of Skeletal Dysplasia

Ultrasound is the primary imaging modality for prenatal diagnosis of skeletal dysplasia, with most severe cases detected at the routine 18-20 week anatomical survey, while postnatal diagnosis relies on plain radiography skeletal surveys. 1

Prenatal Radiological Features

Timing of Detection

• Increased nuchal translucency at 10-14 weeks gestation accompanied by shortened/bowed limbs, abnormal chest/ribs, or undermineralized skull is highly suggestive of severe skeletal dysplasia 1
• 18-20 weeks gestation is the optimal time for detecting most skeletal dysplasias during routine anatomical screening 1
• Earlier detection generally correlates with worse clinical phenotype and prognosis 1

Key Ultrasound Findings

• Short limb length: femur or humerus length <5th percentile or >2 SD below mean 1
• Angular deformities of long bones (bowing) 1
• Cupped and flared metaphyses with widened, irregular physes (growth plates) at sites of rapid growth 1
• Abnormal chest configuration: bell-shaped thorax, short ribs, or abnormal costochondral junctions 1
• Widened distal metaphyses at wrist and ankle levels 1
• Craniofacial abnormalities: dolichocephaly, frontal bossing, widened sutures 1

Lethality Indicators

The combination of multiple ultrasound findings predicts lethality better than any single feature: 1

• Thoracic circumference to abdominal circumference ratio <0.6 suggests pulmonary hypoplasia with poor prognosis 2
• Severe micromelia (though not the single best predictor) 1
• Polyhydramnios combined with skeletal findings 1
• Decreased lung volume on ultrasound 3

Imaging Modality Limitations

• Plain radiographs are NOT helpful prenatally due to maternal structures obscuring the fetal skeleton and radiation concerns 1
• CT scanning provides excellent skeletal detail but is avoided prenatally due to ionizing radiation exposure 1
• 3D ultrasound can assist with facial feature assessment when available 1
• MRI may be useful in select cases as a safer alternative to CT 1

Postnatal Radiological Features

Primary Imaging Approach

Plain radiography skeletal survey is the standard postnatal imaging modality for diagnosing skeletal dysplasia 1, 4, 5

Systematic Radiographic Assessment

Long Bones

• Rachitic changes: cupped and flared metaphyses, widened irregular physes preferentially at distal femora, distal tibiae, and distal radii 1
• Cortical thickening (distinguishes from nutritional rickets where bone resorption features are present) 1
• Bowing deformities: primarily affecting lower limbs (varus or valgus deformity with torsional components) 1
• Epiphyseal dysplasia: irregular, delayed, or abnormal ossification of epiphyses 1, 5

Spine

• Vertebral body abnormalities: irregular shape, flattening (platyspondyly), anterior beaking 1
• Scoliosis and kyphosis from anatomically different-sized vertebrae 1
• Spinal canal stenosis (common in achondroplasia) 1
• Intervertebral disc prolapse and interspinal ligament thickening 1

Thorax

• Rachitic rosary: beading at costochondral junctions 1
• Harrison's groove: horizontal indentation of lower chest 1
• Short ribs with abnormal configuration 1

Skull

• Dolichocephaly: parietal flattening with frontal bossing 1
• Widened sutures from premature fusion of parietal and frontal bones 1
• Craniofacial bone involvement affecting nasopharynx and craniocervical junction 1

Hands and Feet

• Metaphyseal widening at wrists and ankles 1
• Specific patterns visible on hand/spine radiographs (e.g., anterior vertebral beaking and generalized epiphyseal dysplasia in pseudoachondroplasia) 1

Pattern Recognition Approach

Use a stepwise diagnostic strategy: 5

1. Categorize into dysplasia families based on pattern recognition (e.g., achondroplasia family, spondyloepiphyseal dysplasia congenita family, dysostosis multiplex family) 5
2. Identify severity variations within the pattern and subtle distinctive findings 5
3. Focus radiography on knees, wrists, and/or ankles as these are usually sufficient to diagnose rickets 1

Adult Radiographic Features

• Pseudofractures (Looser zones) frequently observed 1
• Early osteoarthritis: osteophytes, joint space narrowing in spine, hips, and knees 1
• Enthesopathies: bone proliferation at ligament attachments, ligament calcification 1
• Osteomalacia-related changes (though true fractures are rare) 1

Management Implications

Diagnostic Workup

• Refer suspected cases to centers with high-level ultrasound expertise and maternal-fetal medicine specialists 1
• Offer prenatal next-generation skeletal panel gene sequencing or whole exome/genome testing to increase diagnostic yield (requires expert interpretation) 1
• Retain fetal DNA for further evaluation until correct diagnosis is established 1
• Perform postnatal skeletal survey on all terminated fetuses with suspected skeletal dysplasia 1

Critical Pitfalls to Avoid

• Do NOT rely on plain radiographs prenatally - they add minimal value and expose the fetus to radiation 1
• Do NOT assume micromelia alone predicts lethality - use combination of findings 1
• Do NOT interpret genomic test results without qualified expert involvement - filtering steps are required to determine clinical significance 1
• Do NOT perform cesarean delivery solely for fracture prevention in skeletal dysplasia - vaginal delivery exerts more uniform pressure than extraction through small uterine incision 1

Anesthesia Planning Considerations

Radiographic findings have direct implications for delivery planning: 1

• Spinal canal stenosis makes regional anesthesia technically difficult or dangerous 1
• Craniocervical junction abnormalities and nasopharyngeal narrowing complicate intubation for general anesthesia 1
• Advanced anesthesia consultation is mandatory, not optional 1