Fetal Skeletal Anomalies Overview

Overview

This lecture covers the ultrasound diagnosis of various fetal skeletal anomalies, focusing on diagnostic features, types, and distinguishing characteristics of different skeletal dysplasias.

Approach to Prenatal Diagnosis of Skeletal Dysplasia

• Skeletal dysplasias are rare conditions with unique recurrence risks and neonatal outcomes.
• Diagnosis on routine ultrasound requires systematic examination of limbs, head, thorax, and spine.

Achondrogenesis

• Severe limb shortening, narrow thorax, short trunk, large head, micronathia, nuchal edema, and polyhydramnios.
• Type 1: autosomal recessive, poor skull/vertebral mineralization, rib fractures.
• Type 2: sporadic, poor vertebral mineralization, no skull involvement or rib fractures.

Achondroplasia

• Short limbs, hands, fingers, large head with frontal bossing, depressed nasal bridge, lumbar scoliosis.
• Features noticeable after 22 weeks gestation.

Asphyxiating Thoracic Dystrophy (Jeune Syndrome)

• Short, narrow chest, short ribs, rhizomelic limb shortening appearing after 22 weeks.

Adolosteogenesis

• Severe limb shortening, narrow thorax, club feet, joint dislocations, prominent forehead, hypertelorism, micronathia, cleft palate, hitchhiker thumbs.

Campomelic Dysplasia

• Bowed long bones, acute femoral angulation, narrow chest, hypoplastic scapulas, large calvarium, small face, micronathia.

Craniosynostosis

• Premature cranial suture fusion, abnormal cranial shapes.

Diastrophic Dysplasia

• Severe shortening/bowing of long bones, joint contractures, scoliosis, club feet, hitchhiker thumb.

Ellis van Creveld Syndrome

• Shortness of limbs, postaxial polydactyly, narrow chest, ectodermal dysplasia, heart defects.

Hypophosphatasia

• Severe micromelia, thoracic hypoplasia, diffuse bone hypomineralization, normal clavicles.

Yarcolovin Syndrome

• Fused vertebral bodies/ribs, short trunk, normal limb length.

Osteogenesis Imperfecta

• Spectrum from mild (type I: blue sclera, deafness, fractures) to severe (type II: short limbs/ribs, fractures, hypomineralized skull).
• Types II and III usually diagnosed prenatally; Type III: multiple fractures, scoliosis, short stature.

Short-Rib Polydactyly Syndrome

• Micromelia, short ribs, hypoplastic thorax, polydactyly.
• Multiple types with distinct features (e.g., metaphyseal changes, cleft lip, ambiguous genitalia).

Thanatophoric Dysplasia

• Severe limb shortening, narrow thorax, normal trunk, large head with prominent forehead.
• Type I: curved femurs (telephone receiver); Type II: straight femurs, cloverleaf skull.

Key Terms & Definitions

• Skeletal Dysplasia — a group of disorders characterized by abnormal bone and cartilage development.
• Micromelia — abnormal shortness of limbs.
• Rhizomelia — proximal limb shortening.
• Polydactyly — presence of extra fingers or toes.
• Hypomineralization — reduced bone mineral content seen as decreased bone echogenicity on ultrasound.
• Hitchhiker Thumb — thumb positioned away from the hand due to joint abnormality.

Action Items / Next Steps

• Review distinguishing ultrasound features for each skeletal dysplasia.
• Practice identifying anomalies in sample ultrasound images.
• Prepare for quizzes on key terms and classification of skeletal anomalies.