Sphenofrontal distance on three-dimensional ultrasound in euploid and trisomy-21 fetuses at 16-24 weeks' gestation

The first 3D analysis of the sphenoid morphogenesis during the human embryonic period

The sphenoid has a complicated shape, and its morphogenesis during early development remains unknown. We aimed to elucidate the detailed morphogenesis of the sphenoid and to visualize it three-dimensionally using histological section (HS) and phase-contrast X-ray CT (PCX-CT). We examined 54 specimens using HS and 57 specimens using PCX-CT, and summarized the initial morphogenesis of the sphenoid during Carnegie stage (CS) 17 to 23. The 3D models reconstructed using PCX-CT demonstrated that some neural foramina have the common process of "neuro-advanced" formation and revealed that shape change in the anterior sphenoid lasts longer than that of the posterior sphenoid, implying that the anterior sphenoid may have plasticity to produce morphological variations in the human face. Moreover, we measured the cranial base angle (CBA) in an accurate midsagittal section acquired using PCX-CT and found that the CBA against CS was largest at CS21. Meanwhile, CBA against body length showed no striking peak, suggesting that the angulation during the embryonic period may be related to any developmental events along the progress of stages rather than to a simple body enlargement. Our study elucidated the normal growth of the embryonic sphenoid, which has implications for the development and evolution of the human cranium.

Sphenofrontal distance in euploid and aneuploid fetuses

OBJECTIVE

To examine the sphenofrontal distance (SFD) in a large series of aneuploid fetuses in the second and third trimesters and compare findings with those of a euploid population.

METHODS

The database at our unit was searched to identify pregnancies with a diagnosis of trisomy 21, 18 or 13, triploidy or Turner syndrome after 15 weeks' gestation. Stored ultrasound images obtained between 19 and 22 weeks were reviewed. For the normal population, two euploid fetuses matched for gestational age were selected randomly for each aneuploid case. The SFD was measured from the anterior edge of the sphenoid bone to the lowest posterior edge of the frontal bone using on-screen calipers. The SFD measurement was parallel to the long axis of the maxilla. If the sphenoid bone did not extend superiorly enough for direct measurement of the SFD, a tangential line was drawn at the anterior wall of the sphenoid bone and extended cranially. In these cases, the distance between the extended line and the frontal bone was measured. One operator measured the SFD twice and was blinded to the results and karyotype.

RESULTS

The study population consisted of 591 pregnancies: 394 euploid fetuses, 122 fetuses with trisomy 21, 45 with trisomy 18, 16 with trisomy 13, eight with Turner syndrome and six with triploidy. For both euploid and aneuploid groups, mean gestational age at examination was 22.8 (range: euploid, 15.0-40.7; aneuploid, 15.0-40.3) weeks. For euploid fetuses, mean SFD was 1.27 cm and measurements ranged from 0.53 cm to 2.56 cm. SFD was significantly dependent on gestational age (SFD = 0.138 + 0.005 × gestational age, P < 0.001, r = 0.802). Mean SFD was significantly smaller in each aneuploid group compared with the euploid population (trisomies 21, 18 and 13: all P < 0.001; triploidy: P = 0.026; Turner syndrome: P = 0.047). For 32 (26.2%), nine (20.0%) and six (37.5%) fetuses with trisomy 21, 18 and 13, respectively, SFD was < 5^th percentile. Only one (12.5%) fetus with Turner syndrome and none with triploidy had SFD < 5^th percentile.

CONCLUSION

In aneuploid fetuses, the SFD is smaller than in their euploid counterparts. However, for a false-positive rate of 5%, the detection rate of trisomy 21 is only 26%. Therefore, using the method we have proposed, it is unlikely that this marker will play a major role in second- and third-trimester screening for aneuploidy. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.