The comparative study of antenatal magnetic resonance imaging and ultrasound in the evaluation of fetal central nervous system abnormalities

Peerzada Ziaulhaq; Naseer A Khan; Saba Banday

doi:10.4103/cjhr.cjhr_52_20

ORIGINAL ARTICLE

Year : 2020 | Volume : 7 | Issue : 3 | Page : 188-192

The comparative study of antenatal magnetic resonance imaging and ultrasound in the evaluation of fetal central nervous system abnormalities

Peerzada Ziaulhaq¹, Naseer A Khan¹, Saba Banday²
¹ Department of Radiology, Government Medical College, Srinagar, Jammu and Kashmir, India
² Department of Obstetrics and Gynecology, SKIMS, Srinagar, Jammu and Kashmir, India

Date of Submission	14-May-2020
Date of Decision	24-Jun-2020
Date of Acceptance	03-Sep-2020
Date of Web Publication	25-Jan-2021

Correspondence Address:
Peerzada Ziaulhaq
Department of Radiology, Government Medical College, Srinagar, Jammu and Kashmir
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/cjhr.cjhr_52_20

Abstract

Background: The role of fetal magnetic resonance imaging (MRI) was studied in antenatal anomalies detected by ultrasound. Materials and Methods: The study was conducted in the Department of Radiodiagnosis and Imaging, Government Medical College, Srinagar, over a period of 12 months including all pregnant women with suspected fetal anomalies on ultrasonography (US). Results: In 9/23 cases (39.1%), the US findings and MRI findings were similar. MRI changed the diagnosis in 11/23 cases (47.8%). MRI provided additional information than US in 2/23 cases (8.69%), and there was 1/23 (4.3%) cases in which US provided additional information to that provided by MRI in terms of intrauterine growth restriction. Conclusions: US and MRI are complementary to each other in reaching a diagnosis in the fetal central nervous system abnormalities, and MRI is a major problem-solving modality where the US findings are inconclusive. The major role for fetal MRI was found in confirmation of inconclusive sonographic findings and the evaluation of sonographically occult diagnoses.

Keywords: Congenital fetal anomalies, fetal magnetic resonance imaging, fetal ultrasound

How to cite this article:
Ziaulhaq P, Khan NA, Banday S. The comparative study of antenatal magnetic resonance imaging and ultrasound in the evaluation of fetal central nervous system abnormalities. CHRISMED J Health Res 2020;7:188-92

How to cite this URL:
Ziaulhaq P, Khan NA, Banday S. The comparative study of antenatal magnetic resonance imaging and ultrasound in the evaluation of fetal central nervous system abnormalities. CHRISMED J Health Res [serial online] 2020 [cited 2021 Mar 2];7:188-92. Available from: https://www.cjhr.org/text.asp?2020/7/3/188/307823

Introduction

The most commonly used screening modality for fetal imaging is ultrasonography (US), however, this modality of imaging has its own limitations, for example, limited soft-tissue contrast, small field of view, poor visualization of fetal parts in reduced amniotic fluid and in fatty patients, and limited visualization of the posterior fossa in advanced gestational age, because of calvarial calcification.^[1],[2],[3]

Magnetic resonance imaging (MRI) usually complements the US if any additional anatomical information is needed to confirm or refute a diagnosis. Few recently introduced, fastly acquired MRI sequences allow us to obtain fetal images during maternal breathhold, without necessity of fetal or maternal sedation. The quality of superior contrast resolution of MRI has made it possible to easily distinguish individual fetal organ anatomy with greater detail.^[4] MRI also has the added advantage of multiplanar acquisition and a large field of view, which makes it a greatly valuable investigation in the evaluation of the fetuses with large or complex anomalies, and allows us to look at the fetal abnormalities in the context of the entire fetus.^[5] MRI also helps us in situations, such as maternal obesity and oligohydramnios where US has been proven to be difficult, due to its technical limitations and operator dependence.^[6] MRI has a great advantage in evaluating anomalies of the central nervous system (CNS), particularly in the later stages of gestation when ossification of the calvarium has occurred and US has a disadvantage of limited visibility of the intracranial structures. However, certain limitations of the fetal MRI are also there. MRI may not provide us much anatomical information in the early period of gestation due to the small size of the fetus and excess fetal movement.^[7]

The advantage of MRI, among others, is its safety in the evaluation of the fetus. MRI, being a noninvasive technique, does not have the side effects of the ionizing radiation, and no known delayed sequelae have been reported till date.^[8] No deleterious effects have been conclusively documented till date. Although currently, there is no evidence in the literature that MRI has any harmful effects on the fetus, long-term safety has yet to be demonstrated. There is a lack of consensus, among various authors, as to whether the risk to the fetus is real.^{[9],[10],[11],[12]} The American College of Radiology (ACR) has stated that fetal MRI can be performed at any stage of pregnancy.^[13] However, it is better to perform the MRI after 17–18 weeks of gestation, as there is a potential risk to the developing fetus as well as the excessive motion of younger fetuses does not allow us to perform an MRI examination.^[14]

Materials and Methods

The study was conducted in the Department of Radiodiagnosis and Imaging, Government Medical College, Srinagar, a multispecialty tertiary care hospital, over a period of 12 months from July 2017 to July 2018. All pregnant women with an abnormal level II scan on US and pregnant women with confirmed diagnosis of congenital anomalies of the fetus in utero who were scheduled for termination were included in the study.

Pregnant women having a history of claustrophobia, metallic implant insertion, cardiac pacemakers, and metallic foreign body were excluded from the study.

A total of 23 patients underwent fetal MRI examination in our hospital during the study period. Siemens 3 Tesla Magnetom Skyra MRI machine was used. The patient particulars were collected in a prescribed format. The USG was performed by a certified radiologist and where the US was incomplete, and the repeat scan was performed by the authors on GE S8 equipment. The MRI examination was carried out using a 12-channel body coil. With as small as the field of view as possible, the acquisition was performed by taking 3–5 mm thick slices. Multiple sequences were taken predominantly T2 single-shot fast spin-echo in three orthogonal planes. The mother was preferably kept fasting for about 4 h before the MRI to reduce fetal motion. Written informed consent was obtained before the study in all cases. Although MRI examination can be performed with the mother in the left lateral decubitus, this results in lower image quality. Fetal MRI was performed by obtaining an initial localizer in three orthogonal planes with respect to the mother, using 6- to 8-mm thick slices with a 1- to 2-mm interslice gap and a large field of view. The localizer helps us to visualize the position of the fetus and determine fetal sidedness, as well as to ensure that the coil is centered over the region of interest. Typically, 3-mm thick ultrafast T2-weighted images of the fetal brain were then prescribed from the localizer with no skip. Images were acquired in the axial, sagittal, and coronal planes. Diffusion-weighted imaging was also performed wherever found necessary using a b value of 0 s/mm² and 600 s/mm². The data were collected on predesigned study pro forma. All the data were entered into the Microsoft Excel program and checked for any inconsistencies. Data were presented in terms of percentages and proportions.

Results

A total number of 23 patients underwent MRI in our department for different indications. US was performed in all the patients. In 20/23 cases, MRI was done within 2 weeks of US. The age of the patients included in this study ranged between 22 and 37 years, with an average age of 33 years. All MRI examinations were performed in the second and third trimesters. MRI examination was avoided in the first trimester in accordance with ACR guidelines in order to avoid potential risk to the developing fetus. The participants included in this study were pregnant females with a gestational age of 19–36 weeks with an average gestational age of 25 weeks.

History of previous pregnancy with congenital anomalies was elicited in 4 patients.

One out of 23 cases was a twin pregnancy.

In 9/23 cases (39.1%), the US findings and MRI findings were similar. MRI changed the diagnosis in 11/23 cases (47.8%). MRI provided additional information than US in 2/23 cases (8.69%), and there was 1/23 (4.3%) cases in which US provided additional information to that provided by MRI in terms of intrauterine growth restriction.

The criteria used to define ventriculomegaly in our study were when the diameter of the atria of the lateral ventricle, measured at the posterior margin of the glomus of the choroid plexus on an axial image through the thalami, was ≥10 mm. Ventriculomegaly was further characterized into mild (10–15 mm), moderate (>15 mm and residual cortex larger than 2 mm), and severe (residual cortex thickness <2 mm).^[15] In our study, we found ventriculomegaly in 11/23 (47.8%) cases. Seven out of 11 cases (63%) were bilateral, and the rest 4/11 (36.4%) were unilateral. Three out of 11 cases of ventriculomegaly were found to be of moderate severity and 7/11 cases of ventriculomegaly were of mild severity. One out of 11 cases of ventriculomegaly was of severe category. In 9/11 cases (81.8%), we found various associated CNS anomalies which included Arnold–Chiari malformation, agenesis of corpus callosum, Dandy–Walker continuum, sulcation abnormality, and TORCH infection [Figure 1], [Figure 2], [Figure 3], [Figure 4]. Three cases of enlarged cisterna magna were included in our study. One of the cases was suspected by ultrasound and the other two were not detected by ultrasound and the patients were referred to MRI for confirmation of congenital cystic adenomatoid malformation picked up on USG, in one of the cases and the other case was referred for evaluation of complex maternal adnexal cyst. Five out of 23 cases (21.7%) had abnormalities of the corpus callosum diagnosed on MRI: 2/5 of the cases were suspected/diagnosed on USG and 3/5 cases were diagnosed as ventriculomegaly. Four out of 23 cases (17.3%) had Arnold–Chiari malformation, two out of whom were diagnosed as ventriculomegaly on US. One out of 23 cases had Lissencephaly. One out of 23 cases had holoprosencephaly, which was wrongly diagnosed as hydrocephalus on US.

Figure 1: Fetal magnetic resonance imaging showing Arnold–Chiari malformation with dilated ventricular system

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Figure 2: Fetal magnetic resonance imaging showing colpocephaly in a fetus with agenesis of the corpus callosum

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Figure 3: (a) Axial magnetic resonance imaging of a fetus with agenesis of the corpus callosum. (b) Coronal magnetic resonance imaging of a fetus with agenesis of the corpus callosum

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Figure 4: Fetal magnetic resonance imaging in a patient with Lissencephaly and Dandy–Walker continuum

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In all these cases, the diagnosis was made on MRI. One out of 23 patients had Dandy–Walker continuum, which was wrongly diagnosed as a case of arachnoid cyst on USG. Two out of 23 patients had encephalocele, both were correctly picked up by USG, and MRI confirmed the diagnosis [Figure 5]. One out of 23 patients had hydranencephaly which was wrongly diagnosed as a case of ventriculomegaly on USG [Figure 6]. Intracranial cysts were visualized in 3/23 cases: two of the cysts were diagnosed as arachnoid cysts and one was diagnosed as a cyst of the cavum velum interpositum. All of them were diagnosed on MRI. One out of 23 cases was a twin pregnancy. In 16/23 cases, pregnancy was continued. In 7/23 cases, the patient underwent termination or pregnancy terminated spontaneously or pregnancy had to be terminated due to maternal indication.

Figure 5: Fetal magnetic resonance imaging in a patient with large encephalocele

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Figure 6: Fetal magnetic resonance imaging in a fetus diagnosed as hydranencephaly

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Discussion

US is an effective modality in the evaluation of the fetal brain and detection of its anomalies. However, ultrasonographic evaluation of the fetal brain is bounded by nonspecific appearance of some fetal CNS anomalies and some technical factors that limit the visualization of the part of the brain near the transducer.^[16] The reduced accuracy of ultrasound in evaluation of fetal CNS abnormalities can be explained by several factors including difficulties in transmission of ultrasonographic wave through the ossified fetal skull, the maternal obesity, and the descent of the fetal head into the maternal pelvis.^[17] There is a need for a reliable alternative imaging modality to get us to the diagnosis where USG diagnosis is difficult, for example, holoprosencephaly.^[18] Fetal MRI can provide useful information that cannot be provided by ultrasound and guide us in making a therapeutic plan.^[16] The patients referred for fetal MRI in our setup are usually for the confirmation of sonographic findings and evaluation of occult sonographic findings.

Whitby et al., 2003, performed an observational study on 21 pregnant women with suspected fetal CNS abnormality on the basis of antenatal US.^[19] They found that the MRI findings were different from that of US in 10/21 (47.6%); MRI provided additional information than the US in 5/21 (23.8%) and US and MRI results agreed in 6/21 (28.6%). In our study, 9/23 cases (39.1%), the US findings and MR findings were similar. MRI changed the diagnosis in 11/23 cases (47.8%). MRI provided additional information than US in 2/23 cases (8.69%), and there was 1/23 (4.3%) cases in which US provided additional information to that provided with MRI. This can be explained by the technological advances in the USG as well as improvement in the radiologist's skills.

MRI provided additional information than US in 2/23 cases (8.69%) in our study which was 23.8% in the abovementioned study performed by Whitby et al. which can be explained by more number of patients having spinal involvement in their study. MRI changed the diagnosis in 11/23 cases (47.8%) which was similar to their study.

Hamisa et al.^[20] in 2013 conducted a study on 23 pregnant women. In their study, they found that MRI and ultrasound showed similar findings in six cases. MRI changed the diagnosis in 14 cases and provided additional information in 2 cases. Ultrasound was superior to magnetic resonance imaging in one case at the second trimester due to fetal motion. Our results were also similar to the study conducted by Hamisa et al.

Hosny and Elghawabi in 2010 performed MRI of 25 pregnant women with fetal congenital anomalies detected on USG.^[21] In their study, MRI findings altered the diagnosis in 2/25 cases; MRI added additional information in the form of occult spinal diastematomyelia in two out of four cases of Chiari/meningocele malformation. In 18 cases, MRI confirmed the diagnosis of USG. MRI findings altered the diagnosis of 2/25 (8%) cases. MRI added additional findings in two out of four cases. In the remaining 18/25 (72%) cases, MRI confirmed the diagnosis of US. In our study, in 9/23 cases (39.1%), the US findings and MRI findings were similar. This can be explained by the fact that Hosny and Elghawabi had not limited their study to only CNS anomalies.

Evaluation of anomalies such as abnormalities of the corpus callosum, aqueductal stenosis, and abnormalities of the posterior fossa, particularly in the third trimester of pregnancy, is much better with MRI where direct visualization is possible, unlike US which relies on indirect signs. In our study in patients in whom corpus callosal abnormalities were suspected on US, MRI was superior and confirmed the diagnosis.

Conclusions

Tremendous progress that has been made in MR sequences and developments in USG has helped in reaching a diagnosis in fetal CNS abnormalities. Our study leads us to the conclusion that fetal MRI is a very useful modality in evaluation of fetal CNS anomalies. Both of these modalities are complementary to each other in reaching a diagnosis, and MRI is a major problem-solving modality where the US findings are inconclusive.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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