Achondroplasia

Achondroplasia is a type of genetic disorder that is a common cause of dwarfism. People with this condition have short stature, usually reaching a full adult height of around 4'0" (1.22 metres). The disorder is a result of an autosomal dominant mutation in the fibroblast growth factor receptor gene 3 (FBFR3), which causes an abnormality of cartilage formation. It occurs at a frequency of about 1 in 20,000 to 1 in 40,000 births.

Radiologic Findings

A skeletel survey is useful to confirm the diagnosis of achondroplasia. Skull films demonstrate a large skull with a narrow foramen magnum, and relatively small skull base. The vertabral bodies are short and cuboidal, and there is congenitally narrowed spinal canal. The iliac wings are small and squared, with a narrow sciatic notch. The tubular bones are short and thick with metaphyseal cupping and flaring and irregular growth plates. Fibular overgrowth is present. The hand is broad with short metacarpals and phalanges, and a trident configuration. The ribs are short with cupped anterior ends. If the radiographic features are not classic, a search for a different diagnosis should be entertained.

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Fig. 1 T2-weighted MR showing severe spinal stenosis, particularly at the foramen magnum.

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The diagnosis can be made on by fetal ultrasound by progressive discordance between the femur length and biparietal diameter by age. The trident hand configuration can be seen if the fingers are fully extended.

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