by Dr Noreen Norfaraheen Lee Abdullah MD (UKM), MMed Radiology (UKM), AM(Mal)

Answer to Case Of the Month 
Achondroplasia

Discussion of Findings
In the skull radiograph, there is a large calvarium with prominence of the frontal and parietal bones. These give the appearance typically described as frontal bossing. The skull base is small when compared to the large cranium. The nasal bridge is flat and the mid-face is small.

In the upper and lower limbs, the long bones demonstrate proximal shortening (also known as rhizomelic shortening) and are tubular shaped. The tibia and the femur are of equal length. The metaphyseal ends of the long bones are flared; hence the appearance of cupped bone shaft ends. The pelvis has prominent sacrosciatic notches bilaterally. The ilium assumes a tombstone appearance and the pelvis, a champagne glass configuration.

In the spine, there is posterior vertebral scalloping and platyspondyly. In the babygram, a relatively long trunk is observed (when compared to the limbs). The 2nd, 3rd and 4th fingers are of the same length sometimes described in books as the trident hand.

The diagnosis is achondroplasia.

Achondroplasia is the most common short-limbed dwarfism observed in our community. It has autosomal dominant transmission. It manifests at birth by rhizomelic micromelia and craniofacial abnormalities.

Typically the child has short and stubby upper and lower limbs. The trunk is relatively long, the root of the nose is depressed and there is a prominent forehead.

A babygram initially would be helpful. Radiographically the features are as described above. In addition, bowing of the limbs are observed and this will become apparent as the child grows and begin to ambulate.

Increased lordosis, scoliosis and gibbus deformity are some features of the spine that may occur. The ribs sometimes are short and cupped at the ends. The interpediculate distances abnormally decrease down the lumbar spine. This feature is not apparent in the newborn but becomes increasingly prominent as the child grows. There is also relative increase in the intervertebral disc space height. The height and anteroposterior diameter of vertebral bodies are decreased and therefore, likely to cause neurological symptoms later in life. MRI of the lumbar spine would then be helpful.
 

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Last Updated:
Tuesday, 04 January 2005