Fetal skeletal computed tomography: when? How? Why?

PURPOSE: To study the additional role of fetal skeletal computed tomography in suspected prenatal bone abnormalities. MATERIALS AND METHODS: Two centers included in a retrospective study all fetuses who benefited from skeletal computed tomography for a suspected constitutional bone disease or focal dysostosis. RESULTS: A total of 198 patients were included. CT was performed in 112 patients (56%) for an isolated short femur below the third percentile (group A), in 15 patients (8%) for bowed or fractured femur (group B), in 23 patients (12%) for biometric discrepancy between a short femur and increased head circumference (group C) and in 48 patients (24%) for suspected focal dysostosis (group D). CT was interpreted as normal in 126 cases (64%), i.e. 87% in group A, 0% in group B, 65% in group C and 25% in group D. When including only cases with postnatal or postmortem clinical and/or radiological confirmation was available, CT provided additional and/or more accurate information than ultrasound in 20% of cases in group A, 66% in group B, 30% in group C and 72% in group D. Sixty-seven percent of patients in whom CT was interpreted as normal were lost to follow-up. CONCLUSION: In isolated short femur, fetal skeletal CT is normal in the great majority of cases although protocolized follow-up of these babies is absolutely compulsory, as a large proportion is lost to follow-up. Fetal skeletal CT can confirm or improve imaging for the suspected diagnosis in suspected focal dysostosis or constitutional bone disease.

Isolated intrauterine femoral fracture in an otherwise normal fetus.

Multiple fractures of the long bones can be seen in the intrauterine period as a result of disorders such as skeletal dysplasias or maternal trauma, but isolated intrauterine femoral fracture is an extremely rare condition. Congenital short femur should be kept in mind, especially during the intrauterine period in the differential diagnosis. We report a case diagnosed as isolated femoral fracture in the 34th gestational week with post-partum confirmation of the diagnosis by X-rays and physical examination.

Variable prenatal appearance of osteogenesis imperfecta.

Osteogenesis imperfecta is a heterogeneous group of disorders of type I collagen with both lethal and nonlethal forms. Prenatal sonographic findings in affected fetuses are variable and depend on the severity of the disease. Six cases of osteogenesis imperfecta in which prenatal sonography had been performed were reviewed. Two cases of lethal type II osteogenesis imperfecta revealed short femurs at 16 to 17 weeks' gestation with development of bowing and fractures by 19 weeks' gestation. Four fetuses with the nonlethal type III or IV had femoral bowing with or without shortening in the late second or third trimester with grossly normal mineralization. Fractures in this latter group did not develop until 1 to 12 months after delivery. Understanding the progressive nature and variability of osteogenesis imperfecta is crucial in the prenatal diagnosis and management of this disease.