Skeletal Dysplasias Flashcards
List of most common skeletal dysplasias
- Achondroplasia
- Cleidocranial dysostosis
- Dactyly (Brachydactyly, Camptodactyly, Polydactyly, Syndactyly)
- Enchondromatosis (Ollier)
- Fibrous dysplasia
- usual form (Jaffe-Lichtenstein)
- with skin pigmentation and precocious puberty (McCune-Albright) - Gaucher’s
- Hypophosphatemic rickets
- Marfan’s
- Multiple hereditary exostoses
- Neurofibromatosis
- Osteogenesis imperfecta
- Osteopetrosis (with osteopetrosis, you get pyknodysostosis for free)
- Osteopoikilosis
What is achondroplasia
Achondroplasia is a congenital genetic disorder resulting in rhizomelic dwarfism and is the most common skeletal dysplasia.
Occurs due to sporadic mutations in the majority of cases but can be inherited as an autosomal dominant condition.
Imaging features of achondroplasia (cranial)
- frontal bossing/delayed closure of anterior fontanelle
- small/non-existent cisterna magna
- enlarged suprasellar cistern +/- empty sella due to normal brain and brainstem size but a short clivus
- communicating hydrocephalus (typically dilated supratentorial ventricles) due to small jugular foramen which can result in elevated venous pressures and reduced flow in the superior sagittal sinus
- more vertical course of the straight sinus
- foramen magnum narrowed ++
- obliteration of the CSF space around the cervicomedullary junction
- cervical cord increased intramedullary T2 signal sometimes seen, representing myelomalacia and gliosis
Treatment: Surgical decompression may be required, with resection of the posterior aspect of the foramen magnum, the posterior arch of C1 and duroplasty.
Imaging features of achondroplasia (spine)
- posterior vertebral scalloping
- progressive decrease in the interpedicular distance in the lumbar spine. Decreased L5-S1 is pathognomnic. => spinal stenosis
- gibbus deformity: thoracolumbar kyphosis
- bullet-shaped/hypoplastic vertebra (not to be confused with Hurler syndrome)
Imaging features of achondroplasia (pelvis)
- small squared (tombstone or mickey mouse ear) iliac wings
- horizontal acetabular roof (decreased acetabular angle)
- trident acetabulum (small bony spurs at the medial and lateral acetabular margins )
- champagne glass type pelvic inlet
Imaging features of achondroplasia (limbs)
- metaphyseal flaring: can give a trumpet bone type appearance [NORMAL BONE DENSITY]
- the femora and humeri are particularly shortened (rhizomelic shortening)
- long fibula: the fibular head is at the level of the tibial plateau
- bowing of legs
- trident hand (splaying/gap between middle and ring finger)
- the metacarpal and metatarsal bones, and in some cases the proximal phalanges, are short and of similar length
Treatment varies and is usually orthopaedic, particularly to correct kyphoscolioses, as well as neurosurgical, to decompress the foramen magnum or shunt hydrocephalus
Imaging features of achondroplasia (limbs)
- metaphyseal flaring: can give a trumpet bone type appearance [NORMAL BONE DENSITY]
- the femora and humeri are particularly shortened (rhizomelic shortening)
- long fibula: the fibular head is at the level of the tibial plateau
- bowing of legs
- trident hand (splaying/gap between middle and ring finger)
- the metacarpal and metatarsal bones, and in some cases the proximal phalanges, are short and of similar length
What is Osteogenesis imperfecta (OI)?
refers to a heterogeneous group of congenital, non-sex-linked, genetic disorders of collagen type I production, involving connective tissues and bones.
In general, four hallmark feature:
1. osteoporosis with abnormal bone fragility
2. blue sclera
3. dentinogenesis imperfecta
4. hearing impairment from otosclerosis
Other features include ligamentous laxity and hypermobility of joints, short stature and easy bruising.
Plain radiography is the first line examination of osteogenesis imperfecta. what would you see in the limbs?
- Overtubulation of long bones (narrow, gracile bones) and metacarpals/metatarsals/phalanges
- generalised osteoporosis, thinned out cortex, severe bowing deformity, multiple fractures with hyperplastic callus formation.
- If treated with bisphosphonates, you may see zebra stripe sign in the long bone metaphyses (esp in distal femur)
Treatment of osteogenesis imperfecta
Prognosis is very variable depending on type ranging from being uniformly lethal from type II to a slight reduction in life expectancy for type I.
Management options for non-lethal types include:
- surgical correction of deformities and the prevention of fractures
- intramedullary rods with osteotomy are used to correct severe bowing of the long bones
- intramedullary rods are also recommended for children who repeatedly fracture long bones
- bisphosphonates
- growth hormone therapy
Treatment of osteogenesis imperfecta
Prognosis is very variable depending on type ranging from being uniformly lethal from type II to a slight reduction in life expectancy for type I.
Management options for non-lethal types include:
- surgical correction of deformities and the prevention of fractures
- intramedullary rods with osteotomy are used to correct severe bowing of the long bones
- intramedullary rods are also recommended for children who repeatedly fracture long bones
- bisphosphonates
- growth hormone therapy
Plain radiography is the first line examination of osteogenesis imperfecta. what would you see in the head, neck and spine?
basilar invagination (dens above Chamberlain’s line- line between hard palate and opisthion)
wormian bones
kyphoscoliosis
vertebral compression fractures
codfish vertebrae
platyspondyly
Plain radiography is the first line examination of osteogenesis imperfecta. what would you see in the chest and pelvis?
chest:
pectus excavatum or carinatum
accordion ribs
pelvis:
protrusio acetabuli
coxa vara
Plain radiography is the first line examination of osteogenesis imperfecta. what would you see in the chest and pelvis?
chest:
pectus excavatum or carinatum
accordion ribs
pelvis:
protrusio acetabuli
coxa vara
The differential diagnosis for Osteogenesis Imperfecta (esp milder forms) is Non-accidental injury (NAI). What are some clues of NAI?
HIGHLY SUSPICIOUS INJURIES:
1) metaphyseal corner fractures AKA classical metaphyseal lesions (CML) or bucket handle fractures, are observed in young children, less than 2 years old. It is the injury thats most specific for NAI.
2) Rib fractures, esp posterior ribs.
3) skull fracture: suspicious features include:
-non-parietal skull fracture (a parietal fracture is more suggestive of accidental injury)
-involves multiple bones
-diastatic sutures
-crosses sutures
-depressed fracture (fracture a la signature)
4) scapular fractures
5) sternal fractures
6) outer third clavicular fractures
Fractures which are MODERATELY SPECIFIC for NAI:
- bilateral fractures with fractures of differing ages
- digital fractures in non-ambulant children
- vertebral fractures or vertebral subluxation
- spiral humeral fractures
- separation of epiphysis
- complex skull fractures
Fractures which have LOW SPECIFICITY for NAI are:
- middle clavicular fractures
- linear simple fractures of parietal bone
- single fractures in diaphysis (spiral humeral fracture is an exception)
- greenstick fractures
