First-Trimester Cranial Ultrasound Markers of Open Spina Bifida.

OBJECTIVES

To evaluate cranial ultrasound markers during a first-trimester routine ultrasound examination for screening for open spina bifida (OSB).

METHODS

Midsagittal and axial images of the fetal head obtained from fetuses with spina bifida and unaffected control fetuses at 11 weeks to 13 weeks 6 days were analyzed retrospectively. The observed markers of the posterior brain included the 4- versus 3-line view, the brain stem (BS)-to-brain stem-occipital bone (BSOB) distance ratio (BS/BSOB), the position relationship between the maxillo-occipital (MO) line and the midbrain-BS junction, and the crash sign status.

RESULTS

This study included 9 OSB cases, 2 closed spina bifida (CSB) cases, and 200 unaffected controls. Eight of 9 OSB cases had informative midsagittal views of the head. The 3-line view (abnormal) and BS/BSOB greater than 1 (abnormal) were observed in 87.5% (7 of 8) and 100% (8 of 8), respectively. The midbrain-BS junction was below or nearly on the MO line (abnormal) in 100% (8 of 8). Seven of the cases had informative axial views of the head. The crash sign (abnormal) was observed in 85.7% (6 of 7). A 3-line view was seen in all of the cases that had a positive crash sign. Neither of the 2 cases of CSB and none of the controls had any of the 4 first-trimester intracranial ultrasound markers of OSB.

CONCLUSIONS

The 4 first-trimester intracranial ultrasound markers investigated in this study appear to be very good markers of OSB, especially a BS/BSOB greater than 1 and an abnormal MO line. The crash sign and 3-line view were observed in the same fetus. In our study, these ultrasound findings were not helpful in CSB.