ACHONDROPLASIA, PSEUDOCHONDROPLASIA & HYPOCHONDROPLASIA

DR.ANKIT BENIWAL

ACHONDROPLASIA• Autosomal dominant disturbance in epiphyseal chondroblastic growth

and maturation. Homozygous achondroplasia is lethal. It is most common skeletal dysplasia and leads to rhizomelic dwarfism i.e. dwarfism where the dominant feature is proximal limb shortening (i.e. femoral, humeral).

• The major abnormality is failure of normal enchondral cartilage growth at the physis. Periosteal and membranous ossification are normal. Some enchondral ossification centres are affected more than others, particularly those at the base of skull and at the ends of long bones.

• Its prevalence is approx 1 in 25,000 to 50,000 births with males more frequently affected. It is most common type of disproportionate dwarfism.

ANTENATAL ULTRASOUND• Antenatal detectable sonographic features include:

Short femur length measurement: often well below 5th centile.

The femur length (FL) to biparietal diameter (BPD) is taken as

a useful measurement.

Trident hand: 2nd ,3rd and 4th fingers appears similar in length.

Protruding forehead: frontal bossing.

RADIOLOGICAL FEATURESSKULL

• These changes are mandatory to the diagnosis of achondroplasia.

• 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 magnus.

• Basilar impression is frequent.

• The cranium is large, though short in its antero-posterior

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 is seen.

• Relative elevation of the brainstem resulting in a large

suprasellar cistern and vertically-oriented straight sinus.

• Communicating hydrocephalus.

Relatively large cranial vault with small skull base. Prominent forehead with depressed nasal bridge is seen. Narrow foramen magnum is noted

• Cranial vault is relatively large with small base.

• Prominent forehead with depressed nasal bridge.

• Narrow foramen magnum.

• Cervico-medullary 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 of the odontoid is elevated to the level of the posterior lip of foramen magnum. At this point, the AP diameter of the bony cranio-cervical junction measures only 7mm.

• The cord fills the available subarachnoid space at this level, and there is impingement on the cord by the posterior lip of foramen magnum. Subtle T2 hyperintensity (shown by arrow) is seen in the medulla and in the upper cord down to the level of junction of odontoid with body of C2.

• LIMBS• There is symmetric shortening of all long bones. The

femur and humerus are particularly shortened.

• 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 middle

and ring fingers (Trident hand)

• Show prominent muscle insertions.

• Image shows femoral physes with ‘inverted V’ (Chevron sign) configuration of distal physes which causes waddling gait.

• Genu varum: rhizomelic shortening of both femurs with metaphyseal flaring. The bones are wide because of unaffected appostional growth.

The splayed and cupped metaphyses as well as the shortening of the leg

Characteristic trident hand, with separation of the 3rd and 4th digits(divergent digits). The fingers are all the same in length.

Short and thick tubular bone.

Carpal and tarsal bones are little affected.

SPINE

• Posterior vertebral scalloping.

• Progressive decrease in interpedicular distance in lumbar

spine (L1 to L5).

• Gibbus: thoracolumbar kyphosis with

bullet-shaped/hypoplastic vertebra

• Short interapedicle distance causing canal stenosis.

• Laminar thickening.

• Widening of intervertebral discs.

• Increased angle between sacrum and lumbar spine.

• L5 is deeply set and excessive pelvic tilt causes

prominence of the buttocks and an illusion of lordosis.

• Note the posterior scalloping of the vertebral bodies.

• The pedicles are short and thick and contribute to the development of lumbar spinal stenosis.

• Note the increased disc height and bullet-nosed vertebrae.

This is a 19yr old patient of achondroplasia.Findings noted are: 1. Short pedicle.2. Posterior vertebral scalloping3. Thoracolumbar kyphosis4. Tombstone iliac wings(square shaped)

PELVIS & HIPS

• The entire pelvis is small.

• 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/triradiate cartilage of acetabulum.

• The pelvis assumes a characteristic champagne glass

appearance (champagne glass type pelvic inlet).

• Small squared (tombstone) iliac wings.

• Short sacroiliac notches.

1. Dysplastic or square iliac bones 2. Narrow sacro-sciatic notches3. Flat bilateral acetabular roofs 4. Short both femoral necks5. Champagne glass-shaped pelvic cavity

CHEST•Anterior flaring

of ribs.

•Antero-posterior narrowing of ribs.

• Shortening of ribs

PSEUDOACHONDROPLASIA• Pseudoachondroplasia (PSACH) develop short-limbed

dwarfism with notable features of joint laxity, early onset degenerative joint disease, metaphyseal and epiphyseal maldevelopment, and vertebral malformations.

• It has autosomal dominant inheritance pattern.

• It presents between 2 and 4 years of age. It has a prevalence of approximately 4 per million.

KEY PHYSICAL EXAMINATION FEATURES ARE:

1. Normal facial appearance and intelligence.

2. The adult height ranges from 82 to 130 cm with a mean

height of approximately 118 cm.

3. There is marked shortening of the limbs with limited elbow

extension.

4. Patients are also noted to have deformities secondary

to osteoarthritis and joint laxity, including cervical spine

instability, genu valgum, genu varum, and genu

recurvatum.

5. Deformities of the back may include scoliosis, lumbar

lordosis, and thoracolumbar kyphosis.

6. Of importance, disturbance of gait (waddling gait) or a

deformity of the legs at approximately 2 years of age.

KEY RADIOLOGICAL FEATURES ARE:

• A normal skull and variable vertebral findings.

• There may be a persistent oval shape to the vertebral bodies during

childhood. Characteristic ‘central anterior tongues’ are seen.

• Anterior "beaking," platyspondyly, triangular outline, odontoid

dysplasia, and disc space widening may also be present.

• The long bones are shortened, have flared metaphyses, and have

small epiphyses that appear flared and irregular. These

manifestations are most notable in the hands and feet, but may

also be seen proximally.

• The development of the epiphyses is also delayed.

• The acetabulum is usually poorly formed and reveals a

widened triradiate cartilage.

• One finding very characteristic is the medial beaking seen in

the medial portions of the proximal femoral neck.

• The hands and wrists show delayed maturation, and there is

shortening and widening of the phalanges, metacarpals, and

metatarsals.

X ray PBH reveals:

Square ilia with short pubis and ischia.

Dysplastic acetabuli.

Characteristic medial beak of femur bilaterally

• X ray Tibia-fibula with ankle reveals:

• Short bones.

• Marked flared epiphysis.

• Irregular and deformed epiphysis

• X ray spine reveals:

• Tongue-like projections of the vertebral bodies, also called central beaking

• Superior and inferior defects.

• Platyspondyly is seen throughout the spine.

• X ray hands reveals:

• The phalanges are stubby and the epiphyses angular and irregular. • The metacarpals short. • The carpal bone epiphyses

appear late (delayed) and irregular• In both the hands-the

radius and ulna are flared at the metaphyses.

• Exaggerated Kypho-scoliosis is noted in a patient of pseudoachondroplasia

• Normal skull of pseudoachondroplasia patient.

• No skull bossing, depressed nose or small skull base noted.

HYPOCONDROPLASIA

• It is condrodystrophy with autosomal dominant inheritance, is a form of short stature.

• FGFR3 gene mutation is known to be associated with it.

• In it skull in never involved. Always appears normal.

Physical Features:

• Short stature.• Shortening of proximal (rhizomela) or middle

(mesomelia) segment of the extremities.• Broad, short hands and feet (brachydactyly).• The abdomen and buttocks are prominent.• Bow legs (genu varus).• Mild to moderate intellectual disability.• Scoliosis.

Radiological fetaures:

• Shortening of long bones with metaphyseal flaring.• Narrowing of interpedicular distance from L1 to

L5 with short pedicles.• Brachydactyly.• Short and broad femoral neck.• Distal fibula overgrows as compared to distal

tibia.• Small iliac bones.

• Short and broad femoral neck is seen here.

• Narrowing of interpedicular distance from L1 to L5, which leads to canal stenosis

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