description
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.
diagnosis
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.
differential diagnosis
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.
sonographic features
ossified calvarium
severe micromelia
concave metaphyses
short, thin ribs without fractures
absent or minimally ossified vertebral bodies
absent or partly ossified pedicles
unossified ischium, pubis, calcaneus and talus
associated syndromes
references
1. van der harten hj, brons jtj, dijkstra pf, niermeyer mf, meijer cj, van giejh hp, arts nfa chondrogenesis-hypochondrogenesis: the spectrum of chondrogenesis imperfecta. a radiological, ultrasonographic, and histopathologic study of 23 cases pediatr pathol 8:571-597
2.mahoney bs, filly ra, cooperberg plantenatal sonographic diagnosis of achondrogenesisj ultrasound med 3:333-335
3. tongsong t, srisombom j, sudasna jprenatal diagnosis of langer-saldino achondrogenesisj clin ultrasound 23:56-58
4. soothill pw, vuthivong c, rees hachondrogenesis type ii diagnosed by transvaginal ultrasound at 12 weeks gestation prenat diagn 13:523-528
5. borochowitz z, ornoy a, lachman r, rimoin dlachondrogenesis ii-hypochondrogenesis: variability versus heterogeneityam j med genet 24:273-288
6. eyre dl, upton mp, shapiro fd, wilkinson rh, vawter gf nonexpression of cartilage type ii collagen in a case of langer-saldino achondrogenesisam j hum genet 39:52-67
7. lachman r, tiller ge, graham jm, rimoin dlcollagen, genes and skeletal dysplasias – on the edge of a new era: a review and update eur j radiol 14:1-10″