First-Trimester Cranial Ultrasound Markers of Open Spina Bifida.

Objective: 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.