P15.05: Prenatal diagnosis of achondroplasia with ultrasound, three-dimensional computed tomography and molecular methods

Achondroplasia is one of the best known and common chondrodysplasia. The golded standard method of diagnosis is DNA testing for mutation of fibroblast growth factor receptor III (FGFR3). If no presence of past or family history, early diagnosis is hard because of late appearance of ultrasound findings of this disease, we report a case of prenatal diagnosis of achondroplasia with ultrasound, three dimensional helical computed tomography (3DCT). A 29 year-old woman, gravida 2 para 0, was transferred to our clinic for further examination because of short femurs (< 2%). This woman had unremarkable medical and obstetrical history. The ultrasound scan at 32 weeks of gestational age revealed rhizomelic shortening of the extremities, frontal bossing and the over rounded metaphyseal–epiphyseal interface at the femur ends with wide angle 143.55° while connecting to diaphysis. This also called ‘collar hoop’ sign. After 6 days, 3D helical CT scan was done, which also revealed rhizomelic limbs, narrowing of the interpediculate distance of the lumbosacral spine, rounded iliac wings and bilateral ‘collar hoop’ sign of the proximal femurs. All these findings lead to diagnosis of achondroplasia. Achondroplasia was confirmed because point mutation on the exon 8 of FGFR3 was found. After counseling, patient and her husband chose to keep pregnancy. A male baby was born by elective cesarean section with body weight: 3435 gm, height 48 cm and Apgar score: 8/9. Postnatal X-ray also confirmed antenatal findings of ultrasound and 3DCT. Nowadays, achondroplasia is suspected at third trimester due to late appearance of this disease. We presented this case to show new prenatal ultrasound finding of ‘collar hoop’ sign at the proximal end of the femur in achondroplasia. Besides, the result of intrauterine 3DCT is also compatible with ultrasound finding. This new sign may provide us a new method for earlier diagnosis of achondroplasia.