Autosomal dominant disturbance in epiphyseal chondroblastic growth and maturation The major abnormality is failure of normal enchondral cartilage growth at the physis. Periosteal and membranous ossification are normal. Some enchondral ossification centers are affected more than others, particularly those at the base of the skull and at the ends of long bones.
Antenatal ultrasoundAntenatally detectable sonographic featuresinclude short femur length measurement : often well below the 5th centile the femur length (FL) to biparietal diameter (BPD) is taken as a useful measurement trident hand 11: 2,3 and 4 fingers appearing separated and similar in length separation of 1st and 2nd, 3rd and 4th fingers protruding forehead : frontal bossing
Radiologic features: skull Narrowing of the spinal canal is the pathologic hallmark of achondroplasia. The base of the skull (which is formed by enchondral ossification) is small, often with a stenotic foramen magnum. Basilar impression is frequent. The cranium is large, though short in its anteroposterior (AP) dimension (brachycephaly). The frontal bones are prominent and the nasal bones are small. The mandible forms normally and, therefore, gives the impression of prognathism. Cervico medullary kink relative elevation of the brainstem resulting in a large suprasellar cistern and vertically-oriented straight sinus communicating hydrocephalus
Relatively largecranial vaultwith small skullbase.Prominentforehead withdepressednasal bridgenarrowedforamenmagnum
There is a relatively large cranial vault with small skull base. There is a prominent forehead with depressed nasal bridge. The foramen magnum is narrowed , and there is a cervicomedullary kink. Relative elevation of the brainstem gives rise to a large suprasellar cistern and a vertically-oriented straight sinus.
The clivus is short such that the tip ofthe odontoid is elevated tothe level of the posterior lip of foramenmagnum. At this point, theAP diameter of the bonycraniocervical junction measures only7 mm.The cord fills the availablesubarachnoid space at this level, andthere is impingement on the cord bythe posterior lip of foramenmagnum. Subtle T2 hyperintensity isshown in the medulla and in theupper cord down to the level ofjunction of odontoid with body of C2.Some T2 hyperintensity within or belowthe cruciform ligament raises apossibility of a little fluid but noevidence of ligamentous disruptionis shown.
Limbs There is symmetric shortening of all long bones. The femora and humeri are particularly shortened (rhizomelic shortening) metaphyseal flaring : can give a trumpet bone type appearance The bone ends are often splayed, with metaphyseal cupping. V shaped growth plates are seen. Because periosteal ossification proceeds normally, there is relative widening of the shafts. The ulna and tibia are often shorter than the radius and fibula. The tubular bones of the hands and feet are short and thick. The fingers are all the same length, with separation of the middle and ring fingers (trident hand).
rhizomelic shortening of the humeruswith posterior bowing and anincomplete glenoid fossa.
Image showsinverted femoralphyses (inverted Vconfiguration),which contributes toa waddling gait.
Genu varum. Image shows rhizomelic shortening of the bilateral femurs with metaphyseal flaring. The bones are wide because of unaffected appositional growth.
thesplayed and cupped metaphyses as well as the shortening of the leg
characteristictrident hand, with separation of the third and fourth digits. The fingers are all the same length.
Spinal Posterior vertebral scalloping Progressive decrease in interpedicular distance in lumbar spine Gibbus : thoracolumbar kyphosis with bullet- shaped / hypoplastic vertebra (not to be confused with Hurler syndrome) Short pedicle canal stenosis Laminar thickening Widening of intervertebral discs Increased angle between sacrum and lumbar spine The lumbar lordosis is often exaggerated, complicated by a horizontally oriented sacrum
Note the posterior scalloping of the vertebral bodies. The pedicles are short and thick and contribute to the development of lumbar spinal stenosis. COMMENT: These individuals are usually hyperlordotic.
Notethe increased disc height and bullet-nosed vertebrae.
19 year old achondroplastic patient. Findings include: short pedicles, posterior vertebral scalloping, thoracolumbar kyphosis, tombstone iliac wings
Pelvis and hips The entire pelvis is small(trident pelvis) The ilia are shortened caudally and flattened, with small sciatic notches. The acetabula are horizontally oriented (decreased acetabular angle), and there is excessive thickening of the Y cartilage. The pelvis assumes a characteristic champagne glass appearance. (champagne glass type pelvic inlet) Small squared (tombstone) iliac wings Short sacroiliac notches
The characteristic champagne glass pelvis. The ilii are short and flat. Also observe that the acetabular roofs are horizontally oriented. Of incidental notation is retention of barium in two colonic diverticula (arrows).
Chest anterior flaring of ribs anteroposterior narrowing of ribs Shortened ribs
Pseudoachondroplasia Pseudoachondroplasia (PSACH) is a rare form of short-limbed dwarfism with a reported prevalence of approximately four per million individuals. Autosomal dominant inheritance has been reported in most cases. Usually children at 2–3 years of age presents with delay in walking or waddling gait.
Physical examination reveals normal facies and intelligence. The adult height usually ranges between 82–130 cm with marked shortening of limbs. Associated deformities include genu valgum/varus, genu reccurvatum, limited elbow extension, kyphoscoliosis or increased lumbar lordosis, and joint laxity with secondary osteoarthritic changes.
The radiographic features include dramatically rhizomelic type of dwarfism, with flared and irregular metaphysis. Epiphyses are small, irregular, and often fragmented with delayed appearance, and the femoral capital and humeral epiphysis are most affected. Medial beaking of the femoral neck is one of the characteristic features. The hand and foot bones (metacarpals, metatarsals and phalanges) are broad and shortened with small and rudimentary epiphysis. Madelung deformity can be seen. Pelvis appears squared with broad iliac wings and narrow sacrosciatic notches. The acetabulum is poorly formed with horizontal roofs. The skull and facial bones are normal. Platyspondyly, anterior “beaking,” persistent oval shape, odontoid dysplasia, and disc space widening may also be present. Interpedicular distance is characteristically normal.
8 year old. (a) Radiograph (AP view) of pelvis reveals squared ilium, narrow sacrosciatic notches, dysplastic acetabuli, and a characteristic medial beak at femoral neck. (b) Radiograph (AP view) of upper limb showing markedly flared and irregular metaphysis with deformed, irregular, and fragmented epiphyses. (c) Lateral radiograph of Lumbosacral spine showing platyspondyly with central beaking. (d) Radiograph (AP view) of hand shows underdeveloped carpals with short and broad metacarpals and phalanges
2 year old.(a) Radiograph (AP view) of pelvis showing milder changes compared to previous case.(b) Radiograph (Lateral view) of Lumbosacral spine (in younger child) showing platyspondyly
in spine platyspondyly, flame- shaped vertebrae with anterior projections. The interpedicular distance does not progressively decrease in the lumbar spine. At CV junction odontoid hypoplasia.
Exaggerated thoracolumbar kyphosis, mild to moderate scoliosis.
Achondroplasia patients have a large head with prominent frontal bones and a narrow base. The interpedicular distance decreases caudally in lumbar region but with normal vertebral height. The pelvis is square with small sciatic notches and shows classic champagne glass appearance. PSACH patients, on the other hand, have a normal skull and interpedicular distance with marked platyspondyly.
In MED, epiphyses are abnormal, but there are near normal metaphysis, pelvis, and spine unlike in PSACH, where metaphyseal and spinal changes are more marked. In SED, congenital epiphyseal changes mimic PSACH; however, spinal changes are more pronounced with marked kyphoscoliosis. Hip joints are affected disproportionately in relation to nearly normal distal limbs.
In Morquio syndrome, the spinal changes are prominent with flat vertebrae, central beaking, and marked kyphosis. Metacarpals show proximal tapering with short, wide tubular bones. Epiphysis may be affected, but metaphyseal widening and irregularity as seen in PSACH is absent. In hypothyroidism, epiphyseal changes may simulate PSACH, but the dwarfism is symmetrical involving all long bones with slender shafts and endosteal scalloping. Metaphyses are normal. The skull shows wormian bones, J-shaped sella in young children, and cherry sella in older children. Bullet-shaped lumbar vertebra with kyphosis is seen, but general platyspondyly is lacking. Classical pelvis changes of PSACH are also lacking
Hypochondroplasia Hypochondroplasia, a chondrodystrophy with autosomal dominant inheritance, is a form of short stature. FGFR3 gene mutation is known to be associated with hypochondroplasia. Infants are usually born of low-normal weight and length, but in early childhood fall far below the average for their age. 10- 12% have mental retardation.
Physical features The most common clinical features of hypochondroplasia: Short stature (adult height 128 - 165 cm; 2-3 SD below the mean in children) Stocky build Shortening of the proximal (rhizomelia) or middle (mesomelia) segments of the extremities Limitation of elbow extension Broad, short hands and feet (brachydactyly) Generalized, mild joint laxity Large head (macrocephaly) with relatively normal facies Less common but significant clinical features: Scoliosis Bow legs (genu varum) (usually mild) Lumbar lordosis with protruding abdomen Mild to moderate intellectual disability Learning disabilities Adult-onset osteoarthritis
. Radiologic features Shortening of long bones with mild metaphyseal flare (especially femora and tibiae) Narrowing of or failure to widen in the inferior lumbar interpedicular distances Mild to moderate brachydactyly Short, broad femoral neck Squared, shortened iliaLess common but significant radiologic features: Elongation of the distal fibula Shortening (anterior-posterior) of the lumbar pedicles Dorsal concavity of the lumbar vertebral bodies Shortening of the distal ulna Long ulnar styloid (seen only in adults) Prominence of muscle insertions on long bones Shallow "chevron" deformity of distal femur metaphysis Low articulation of sacrum on pelvis with a horizontal orientation Flattened acetabular roof
Short and broad femoral neck. Squared and shortened iliium and acetabular roof.
Lumbar stenosis. Intrapedicular distance narrowerat L4 than L3.
Spinal stenosis. Lateral radiograph lumbar spine shows narrow A-P diameter of the lumbar spine.
Differential diagnosis Mild achondroplasia Mild forms of metaphyseal chondrodysplasias Mild forms of mesomelic dwarfism Mild forms of spondylo-epiphyseal-metaphyseal dysplasias Leri-Weill dyschondrosteosis Pseudohypoparathyroidism and pseudopseudohypoparathyroidism Short stature caused by disturbances in the growth hormone axis Constitutive short stature