Physical Characteristics of Thanatophoric Dysplasia

Thanatophoric Dysplasia is characterized by a severe growth deficiency. At birth, children are on average 40 cm long. Thanatophoric Dysplasia Type 1 is more common and is characterized by curved long bones, especially the femur, and flat vertebral bodies. A straight femur, taller vertebral bodies, and a cloverleaf skull are typical of Thanatophoric Dysplasia Type 2.

Face and Skull:

Type I:

• Large cranium and fontanelle
• Disproportionately full and pronounced forehead
• Protruding eyes
• Depressed nasal bridge

Type II:

• Cloverleaf skull
• Secondary skull deformities due to premature closure of cranial sutures

Trunk, Chest and Spine:

• Narrow thorax, owing to the shortened ribs
• Protuberant abdomen
• Short spine with flattened vertebrae

Arms and legs:

• Disproportionatly short extremities compared to a relatively average-sized trunk
• Stunted limbs with small fingers
• Bowed long bones in type I

What are the x-ray characteristics?

The major radiographic feature of infants with Thanatophoric dysplasia is a narrow thorax. Ribs are short with the rib ends appearing wide and cupped. Vertebral bodies are flat with a wide intervertebral disk space. The interpediculate distances narrow in the lumbar spine.

The pelvis has a short and square configuration. A small sciatic notch and medial spurs are typical. The long bones of the extremities are characteristically short and broad. The metaphyses exhibit cupped, spur-like flaring. Marked bowing of the femur is characteristic in Thanatophoric Dysplasia, Type I. Fibulae are markedly shorter than the tibiae. The phalanges, metacarpals, and metatarsal bones are characteristically short (3).