achondrogenesis type ii (langer-saldino) is an autosomal dominant disorder with severe micromelia, a short trunk with barrel-shaped thorax, distended abdomen and a disproportionately large head. it has been postulated that achondrogenesis type ii and hypochondrogenesis are phenotypic variants of the same disorder; clinically and radiographically, achondrogenesis type ii, hypochondrogenesis and neonatal spondyloepiphyseal dysplasia congenita do form a continuum of disease. the fundamental biochemical disorder seems to be allelic mutations of the gene coding for type ii procollagen.
achondrogenesis type ii is characterized by an enlarged calvarium with normal ossification, micromelia and lack of mineralization of many or all of the vertebral bodies. the posterior ossification centers may or may not be formed and there is usually a lack of ossification of the sacrum, ischium, pubis, calcaneus and talus. the iliac wings are small and have concave inferior and medial margins. the metaphyses are concave. the ribs are variably shortened but there are no fractures. the combination of micromelia, normal calvarial mineralization and absent vertebral body ossification is highly suggestive of this condition.
in achondrogenesis type ia the calvarium is unossified and normally ossified in type ib. there is a variable pattern of vertebral ossification, the long bones are extremely short with metaphyseal spiking or spurring, and the ribs have cupped ends with (ia) or without (ib) fractures. in fibrochondrogenesis there is occasionally a poorly ossified calvarium, there are no rib fractures, the metaphyses are dumbbell-shaped and all segments of the spine are ossified. severe cases of hypochondrogenesis may present with micromelia and occasionally unossified cervical or sacral vertebral bodies. the calvarium is ossified, there are no rib fractures, the thoracolumbar spine has all three ossification centers and the long bones are better developed with only mild to moderate metaphyseal irregularity. severe congenital hypophosphatasia is characterized by a diffuse mineralization defect with an irregularly ossified skeleton, micromelia and multiple fractures. spinal involvement usually affects all three ossification centers in a similar fashion. osteogenesis imperfecta type ii can present with absent calvarial ossification, multiple fractures and micromelia but all segments of the spine are ossified. in thanatophoric dysplasia all spinal segments are ossified.
short, thin ribs without fractures
absent or minimally ossified vertebral bodies
absent or partly ossified pedicles
unossified ischium, pubis, calcaneus and talus
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