Thanatophoric dysplasia is a lethal skeletal dysplasia. It is the most common lethal skeletal dysplasia followed by osteogenesis imperfecta type II.
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Epidemiology
The estimated incidence is around 1:25,000-50,000 3.
Associations
Pathology
Subtypes
There are two recognized subtypes:
-
type I
marked underdevelopment of the skeleton
telephone receiver deformities are more pronounced
-
type II
the presence of a cloverleaf skull may be a distinctive feature
limb shortening milder and bowing is not a feature 3
Genetics
It results from a mutation coding for the fibroblast growth receptor 3 (FGFR3) located on chromosome 4p16.3. The type of receptor mutation is different from the FGFR mutation in achondroplasia. Inheritance is thought to be sporadic.
Radiographic features
Plain radiograph
Plain films are usually done postmortem, if done at all. Features include:
Limbs
proximal portions of the long limbs are small, giving a rhizomelic appearance
long bones (typically humeri and femora) have a typical "telephone handle" - bowing of the diaphyses with metaphyseal flaring
Iliac bones
usually hypoplastic
small squared iliac wings
may show trident acetabula
Chest
narrow chest
short horizontal ribs
small scapulae
Skull and face
relative macrocephaly
nasal bridge flattening
kleeblattschaedel (cloverleaf) skull (with type II) 2-4
Spine
platyspondyly: flattening of vertebral bodies
normal trunk length
Ultrasound
It may be difficult to accurately diagnose before the 3rd trimester (~22 weeks) 4. Before that time it can be included in the differential if there is a short femur length measurement.
Sonographically-detectable features may include:
relatively narrow thoracic cavity 4
short, thick, bowed tubular bones, especially of lower extremities 4
thickened soft tissues of extremities 4
comparatively large head with frontal bossing
a cloverleaf skull appearance may also be seen: type II (see case 3)
Treatment and prognosis
The condition is uniformly fatal within a few hours of birth either from respiratory failure or from brainstem compression from a narrow foramen magnum.
History and etymology
The term thanatophoric derives from the Greek words "thanatos" (θάνατος), meaning "death" 2 and "phoros" (φόρος), meaning "bearing/carrying/bringing".
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