Ultrasonographic Evaluation of Neural Tube Defects at 11–14 Weeks

Abstract

Fetal neural tube defects are the second most common serious fetal birth defects. In fetuses with open spina bifida there is leakage of cerebrospinal fluid into the amniotic cavity which causes hypertension in the subarachnoid space leading to caudal displacement of the brain. The cranial signs (lemon and banana) are detectable during the second trimester scan. In the first trimester, there are alterations in the appearance of the posterior brain at 11–13 weeks. In fetuses with open spina bifida, the posterior shift of the brain is evident from the first trimester, resulting in compression of the fourth ventricle and alteration of the normal intracranial translucency. In the midsagittal view of the face, if the fourth ventricle is not visible, it should arouse the suspicion of the possibility of an underlying open spina bifida and hence, a detailed examination of the fetal spine should be performed. Also, because of the posterior shift of the brain, the brainstem (BS) appears relatively enlarged and shifted backwards. The BS to brainstem to occipital bone distance (BSOB) [BS/BSOB] ratio is increased and it is usually more than one. At 11–13-week scan, the midsagittal view of the face is the standard view obtained in every fetus and it is feasible to visualize the posterior region of brain in this view. Suspicious cases should undergo a detailed assessment of the spine, especially on transvaginal scan followed by targeted examination of the spine at 16–18 weeks.

Keywords

Neural tube defects - Posterior fossa - Intracranial translucency - Brainstem to occipital bone distance - Transvaginal scan

Publication History

Received: 28 April 2016

Accepted: 23 June 2016

Article published online:
08 May 2023