Pictorial review: imaging of the spinal manifestations of achondroplasia

Achondroplasia is the commonest hereditary skeletal dysplasia exhibiting dwarfism with characteristic rhizomelic (proximal) shortening of the limbs. It is predominantly linked with an autosomal dominant inheritance, but sporadic mutations can occur which are associated with advanced maternal age. Approximately 1 in every 25 000-30 000 live births are affected, and the overall life expectancy is marginally reduced by ~10 years. Mutations in the fibroblast growth factor receptor causes a decrease in endochondral ossification, which results in stunted growth of cartilaginous bones. A resultant narrowed foramen magnum and a short clivus are seen which predisposes to craniocervical spinal canal stenosis. Apnoeic events arising from the compression of the vertebral arteries at the level of the craniocervical junction lead to fatality in the young, with a death rate as high as 7.5%. Decrease in the caudal inter-pedicular distance is characteristic and a contributory factor for cervical, thoracic and lumbar spinal canal stenosis, most pronounced in the lumbar spine with patients often requiring surgical intervention to ease symptoms. Thoracolumbar kyphoscoliosis and sacral manifestations such as small sacro-sciatic notches and a horizontal pelvis are seen. The aim of this pictorial review is to demonstrate the imaging findings of the spinal and pelvic manifestations of achondroplasia.