Prenatal diagnosis of achondroplasia: new specific signs.
BACKGROUND
Achondroplasia is one of the most common forms of short limb dwarfism. It is usually suspected on third trimester routine ultrasound because of very shortened long bones. We have described two new prenatal sonographic signs of achondroplasia visible at the proximal femoral metaphysis.


METHODS
Over 5 years, five fetuses were diagnosed with achondroplasia at the Grenoble Prenatal Diagnosis Centre. Ultrasound and tomographic examinations were performed by specialists. To study the proximal metaphysis, the ultrasound transducer was positioned at a 45 degree angle to the diaphyseal axis. Postnatal diagnosis was confirmed.


RESULTS
On computed tomography and postnatal X-ray, proximal femoral metaphysis appeared rounded, with poor, uneven ossification. Connexion to diaphysis was abnormal, with relative overgrowth of the periosteum, creating a new diagnostic sign that we called the 'collar hoop' sign. On ultrasound, all fetuses had a very rounded metaphyseal-epiphyseal interface, with an angle connexion to diaphysis wider than expected. The 'collar hoop' sign was obvious on four of the fetuses. During the same period, proximal femoral metaphyses appeared normal in 653 healthy fetuses, suggesting high specificity of those two new signs.


CONCLUSIONS
Metaphysis examination is recommended if fetal femur length measures below the fifth percentile, as normal aspect may rule out achondroplasia.
Boulet
Stéphanie
S
Maternity Hospital, Chambéry 73000, France.
Althuser
Marc
M
Nugues
Frédérique
F
Schaal
Jean-Patrick
JP
Jouk
Pierre-Simon
PS
D000130:Achondroplasia / Q000000981:diagnostic imaging*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000254:growth & development; D006621:Hip Joint / Q000000981:diagnostic imaging; D006801:Humans; D007231:Infant, Newborn; D009929:Organ Size; D011247:Pregnancy; D014057:Tomography, X-Ray Computed; D016216:Ultrasonography, Prenatal