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Radiologic Findings: : (a) short flat vertebral bodies, lack of normal increase in interpediculate distance from upper lumbar vertebrae caudally, short pedicles with narrow vertebral canal; (b) squared iliac wings, short narrow sciatic notch, flat acetabular roof; ( c ) micromelia, short and thick tubular bones, notched (V-shaped) growth plates creating ball-in-socket epiphyseal-metaphyseal junctions, flared metaphyses, fibular overgrowth.

Diagnosis:Achondroplasia.

Discussion: Achondroplasia is the most common nonlethal skeletal dysplasia with a frequency of approximately 1 per 13,500-26,000 live births. The mode of inheritance is autosomal dominant with spontaneous mutations accounting for 80-85% of cases. The patient's mentality is usually normal. Other radiologic manifestations include a large skull with a relatively small base, a narrow foramen magnum and a small posterior fossa. In the infant, the normal sharp demarcation of the cartilage-shaft junction is lacking in the long bones, the cartilage space between opposing bones is excessively wide and, in the spine, the intervertebral spaces are often as high as the ossified portions of the bodies. With increasing age, posterior scalloping of the vertebral bodies is noted. Clinical complications of achondroplasia include hydrocephalus and paraplegia from the constrictive effects of the skull and spine.

References:
1. Taybi H, Radiology of Syndromes, Metabolic Disorders, and Skeletal Dysplasias,
4th ed., Mosby 1996.

2. Silverman F, Caffey's Pediatric X-ray Diagnosis: An Integrated Imaging Approach,
9th ed., Mosby 1993

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