Cranial findings detected by second-trimester ultrasound in fetuses with myelomeningocele: a systematic review

Abstract

Background: Abnormal intracranial findings are often detected at mid-trimester ultrasound (US) in fetuses with myelomeningocele (MMC). It is unclear whether these findings constitute a spectrum of the disease or are an independent finding, which should contraindicate fetal surgery.

Objective: To ascertain the spectrum and frequency of US-detected cranial findings in fetuses with MMC.

Search strategy: MEDLINE, Embase, Web of Science and CENTRAL were searched from January 2000 to June 2020.

Selection criteria: Study reporting incidence of cranial US findings in consecutive cases of second-trimester fetuses with MMC.

Data collection and analysis: Publication quality was assessed by Newcastle-Ottawa Scale (NOS) and modified NOS. Meta-analysis could not be performed as a result of high clinical diversity and study heterogeneity.

Main results: Fourteen cranial US findings were reported in 15 studies. Findings in classic Chiari II malformation (CIIM) spectrum included posterior fossa funnelling (96%), small transcerebellar diameter (82-96%), 'banana' sign (50-100%), beaked tectum (65%) and 'lemon' sign (53-100%). Additional cranial findings were small biparietal diameter (BPD) and head circumference (HC) (<5th centile; 53 and 71%, respectively), ventriculomegaly (45-89%), abnormal pointed shape of the occipital horn (77-78%), thinning of the posterior cerebrum, perinodular heterotopia (11%), abnormal gyration (3%), corpus callosum disorders (60%) and midline interhemispheric cyst (42%).

Conclusions: We identified 14 cranial findings by second-trimester US in fetuses with MMC. The relatively high incidence of these findings and their unclear prognostic significance might not contraindicate fetal surgery in the case of normal fetal genetic testing. Some cranial findings may independently affect postnatal outcome, however. Long-term detailed follow-up is required to investigate this.

Tweetable abstract: A high rate of cranial abnormalities found on second-trimester ultrasound in fetuses with myelomeningocele.

Keywords: Chiari II malformation; fetal surgery; myelomeningocele; prenatal; spina bifida; spina bifida aperta; spinal dysraphism; ultrasonography.

Figure 1

Flow diagram of illustrated study selection (adapted from Preferred Reporting Items for Systematic Reviews and Meta‐Analysis, PRISMA).

Figure 2

Classic Chiari II malformation findings detected by ultrasound in fetuses with open spina bifida: (A) midsagittal view demonstrating a clivus–occipital bone angle of 69°; (B) transcerebellar view showing a ‘banana’ sign of the cerebellum and an effaced cisterna magna; (C) transcerebellar view showing prominent beaking and elongation of the tectum; (D) transventricular view demonstrating the scalloping of the frontal bones of fetal skull, known as the ‘lemon’ sign. Reprinted with permission of the UZ Leuven, Leuven, Belgium.

Figure 3

Additional cranial findings detected by ultrasound in fetuses with open spina bifida: (A) transventricular view showing a mild ventriculomegaly with a short distance between the posterior edge of the occipital horn and the occipital bone (calliper 1); (B) transventricular view showing a normal size lateral ventricle with a pointed occipital horn; (C) transventricular view demonstrating a midline anechoic interhemispheric cyst; (D) mid‐sagittal view of the same fetal brain showing a midline cyst situated below the splenium of the corpus callosum (S) and the column of the fornix (small arrow), and posterior to the thalamus (T). Reprinted with permission of the UZ Leuven, Leuven, Belgium.