Towards Detecting Open Spina Bifida in the First Trimester: The Examination of the Posterior Brain

Abstract

Introduction: Our aim was to examine the value of indirect signs of open spina bifida in the mid-sagittal view of the posterior brain at the 11-13 weeks' ultrasound examination and to summarize the current evidence for the first-trimester diagnosis of spina bifida. Methods: This was a prospective study in routine obstetric population.The presence of four almost parallel lines (four-line view) in the posterior brain was recorded. Biparietal diameter (BPD), intracranial translucency (IT) and cisterna magna (CM) were measured. The ratio of IT to CM (R ratio) was calculated. Results: 2,491 pregnancies were examined prospectively. Updated reference ranges for IT and CM were constructed. There were 3 cases with open spina bifida, and the four-line view was abnormal in 2 of them. The abnormal fetuses had smaller BPD as well as pronounced reduction in the CM and increase in the R ratio. Discussion: Examination of the posterior brain was feasible in all fetuses in the setting of the routine 11-13 weeks' ultrasound examination. Indirect signs of spina bifida are visible in the mid-sagittal view of the posterior brain, and the assessment of these structures can be a reliable tool in the early identification of this abnormality.

Cranial sonographic markers of fetal open spina bifida at 11 to 13 weeks of gestation

“…Similarly, authors have suggested qualitative evaluation of the posterior fossa in the sagittal view for the presence of three spaces, highlighting the presence of only two spaces in cases of spina bifida . In a similar approach and prospectively evaluating the posterior fossa in over 2000 pregnancies (looking for four parallel lines in the sagittal view), Kappou et al reported abnormal views in two out of three cases of open spina bifida.…”

Non‐visualization of choroid plexus of fourth ventricle as first‐trimester predictor of posterior fossa anomalies and chromosomal defects

“…were the first to suggest that assessment of the fourth ventricle, also called intracranial translucency, at the time of the 11–13‐week ultrasound scan could be a method of early screening for open spina bifida (OSB). Subsequent studies have confirmed this observation and have also reported an association between other posterior fossa abnormalities and OSB, including increased diameter of the brainstem (BS) and abnormal BS diameter‐to‐BS‐to‐occipital‐bone distance (BS/BSOB) ratio, obliteration of the cisterna magna, and posterior displacement of the aqueduct of Sylvius. These ultrasound features are almost invariably present in first‐trimester fetuses with OSB and are thought to be the result of early backward displacement of the posterior brain as a consequence of chronic leakage of cerebrospinal fluid through the spinal defect and hypotension of the cerebral ventricular system.…”

Intracranial translucency assessment at first trimester nuchal translucency ultrasound

“…The normal appearance of the posterior fossa in the mid‐sagittal plane has been described by various authors as consisting of three intra‐cranial hypoechoic ‘layered’ structures, representing the brainstem, intra‐cranial translucency (IT) of the fourth ventricle and cisterna magna, with a fourth extracranial hypoechoic layer formed by the NT (referred to as the four‐line view, see Fig. ) . The echogenic choroid plexus of the fourth ventricle forms the border between the IT and the cisterna magna …”

“…5 Over recent years, an abnormal posterior fossa on the mid-sagittal view of the face at the first trimester nuchal translucency scan, performed at 11-13+6 weeks' gestation, has been associated with the presence of OSB. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] The mid-sagittal view of the face has been routinely obtained in order to measure nuchal translucency (NT) thickness and assess the nasal bones as part of screening for chromosomal abnormalities.…”

“…1). 10,12,13 The echogenic choroid plexus of the fourth ventricle forms the border between the IT and the cisterna magna. 6 The Women's Imaging Department at the Royal Brisbane and Women's Hospital performs approximately 1000-1500 routine first trimester screening ultrasound scans every year.…”