Ratio of fetal choroid plexus to head size: simple sonographic marker of open spina bifida at 11–13 weeks' gestation

Abstract

CONTRIBUTIONWhat are the novel findings of this work? Increased fetal choroid-plexus-to-head-size ratio is a new sign for the easy detection of spina bifida in the first trimester. What are the clinical implications of this work?This sign should facilitate detection of spina bifida during the routine first-trimester scan. ABSTRACTObjectives To measure the ratio of choroid plexus (CP) size to head size in normal fetuses and to compare it to that in fetuses with open spina bifida (OSB) and quantify the subjective sign of a 'dry brain'.Methods This was a retrospective study of ultrasound images, obtained during first-trimester screening between 11 and 13 weeks of gestation, from 34 fetuses with OSB and 160 normal fetuses. From the hospital databases, we retrieved images of the fetal head in the transventricular axial plane. We measured the areas of both CPs and the head and calculated the ratio between them. We also measured the longest diameter of each CP and calculated their mean (CP length), and measured the occipitofrontal diameter (OFD) and calculated the ratio of CP length to OFD. Measurements from the OSB fetuses were plotted on crown-rump length (CRL) reference ranges constructed using data from the normal fetuses, and Z-scores were calculated. ResultsIn the normal fetuses, the CP area increased, while the ratios of CP area to head area and CP length to OFD decreased, with increasing CRL. In 30 of the 34 (88%) fetuses with OSB, both ratios were increased significantly and the CPs filled the entirety of the head, Correspondence to: Prof. R. Chaouigiving the impression of a dry brain. In these cases, the borders of the lateral ventricles could not be identified.Conclusions At 11-13 weeks, the majority of fetuses with OSB have reduced fluid in the lateral ventricles such that the CPs fill the head. The dry brain sign is easily visualized during routine first-trimester ultrasound examination while measuring the biparietal diameter, and can be quantified by comparing the size of the CPs to the head size. Until prospective data confirm the usefulness of this sign in screening for OSB, it should be considered as a hint to prompt the examiner to assess thoroughly the posterior fossa and spine.

Reference ranges for the fetal mesencephalon to occiput measurement at 11 to 13+6�weeks of gestation

“…At 11-13 weeks, the fetuses with OSB shows a reduction of the cerebrospinal fluid, due to its leakage at the level of the spinal defect ( 3 ). Consequently, others have proposed that there is a reduction of pressure in the spinal cord, cisterna magna, and fourth ventricle, compared with choroid ventricles, which produces a posterior and caudal displacement of the mesencephalon ( 4 , 8 ).…”

“…In the last 10 years, there is an increasing interest in diagnosing OSB at 11-13 weeks of gestation. This interest has been promoted by advances of the ultrasound equipment and progressive understanding of the abnormal arrangement of the posterior fossa because of the continuous leakage of cerebrospinal fluid (CSF) ( 2 , 3 ). The local pressure gradient leads to caudal displacement of the brainstem (BS) with the obliteration of the cisterna magna ( 4 , 5 ).…”

“…In the mid-sagittal view of the head, the most extensively researched markers for OSB were intracranial translucency (IT) ( 6-8 ), BS diameter, brainstem to occipital bone (BSOB) distance, BS/BSOB ratio and the junction between the midbrain and the BS below the maxilla-to-occipital line ( 5 , 9 , 10 ). OSB markers in the axial view of the head are less studied: ratio of choroid plexus size to head size ( 3 ), biparietal diameter (BPD) ( 11 ), posterior displacement of the midbrain ( 4 , 12 ) and the distance between the occipital bone and the aqueduct of Sylvius (AoS) ( 12 , 13 ).…”

“…Recently there is an increasing interest in the evaluation of the fetal head in the axial view through description of simple signs, which can be easily recognized at the time of BPD measurement: the dry brain and the crash sign ( 3 , 4 ). However, the posterior displacement of the midbrain and its impact with the occipital bone could vary and may not be present in all cases in the first trimester ( 4 ).…”

Accuracy of qualitative and quantitative cranial ultrasonographic markers in first‐trimester screening for open spina bifida and other posterior brain defects: a systematic review and meta‐analysis

“…Figure S2 shows the flow diagram of the study selection (see Supplementary material). The initial electronic search yielded 145 citations, from which 23 relevant publications 4,[9][10][11][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] were selected for the meta-analysis. Studies were published between 2009 and 2020, including 69 510 fetuses with 389 cases of OSB and 12 cases of oPBD (five DWM, two BPC, four mega CM and one arachnoid cyst).…”