Prenatal diagnosis of Kniest dysplasia with three-dimensional helical computed tomography.

OBJECTIVE: Fetal three-dimensional helical computed tomography (3D-CT) has attracted attention in the diagnosis of fetal skeletal dysplasias because of limited diagnostic capabilities of standard ultrasonography to delineate the skeleton. Here we report the first instance of diagnosing Kniest dysplasia with 3D-CT. METHODS: Fetal 3D-CT was performed for a fetus at 28 weeks' gestation after ultrasonography at 24 weeks had shown moderate shortening of the limbs, mild narrow thorax, and polyhydramnios. The imaging parameters were set so as to reduce estimated fetal irradiation dose to 12.39 mGy of the CT dose index volume and 442 of the dose length product. RESULTS: Fetal 3D-CT revealed dumbbell-shaped femora and platyspondyly with coronal cleft of the lumbar vertebral body. This warranted a diagnosis of Kniest dysplasia and corresponded well with postnatal radiographic findings. In retrospect, however, spinal deformation was somewhat underestimated due to image smoothing associated with image processing in 3D-CT. Genetic testing for COL2A1 confirmed Kniest dysplasia; i.e., a de novo mutation of A-C transversion at the splice acceptor site of the 3' end of intron 16. CONCLUSIONS: The combined use of 3D-CT with ultrasonography is a power tool for the prenatal diagnosis of congenital skeletal dysplasias.