fetal mri in cns abnormalities. relevant issues for obstetricians

Obstetrics

Revision ArticleInternational colaboration

Fetal MRI in CNS abnormalities. Relevant issues for obstetriciansManuel Recio Rodríguez*, Vicente Martínez de Vega Fernández, Pilar Martínez Ten**, Javier Pérez Pedregosa**, Daniel Martín Fernández-Mayoralas***, Mar Jiménez de la Peña

ResumenLa resonancia magnética (RM) fetal es una técnica deimagen en auge, útil en la valoración del cerebro ycolumna fetal. Ayuda a estudiar el desarrollo cerebralfetal y se puede realizar un diagnóstico precoz de lasanomalías congénitas. La imagen de RM muestra granresolución de contraste y permite diferenciar mejorque la ecografía entre hallazgos normales y patológi-cos. Además, algunas malformaciones cerebrales olesiones destructivas ocultas en la ecografía prenatalpueden ser detectadas por RM. Revisamos las indica-ciones, utilidad, seguridad, aspectos técnicos de la RMfetal y la apariencia del desarrollo cerebral fetal, y eva-luamos su contribución en el diagnóstico de las patolo-gías de las diferentes regiones cerebrales y de la pato-logía espinal fetal.

AbstractFetal MRI in CNS abnormalities. Relevant issues forobstetriciansFetal MR imaging (MRI) is an increasingly available tech-nique used to evaluate the fetal brain and spine, because itprovides a unique opportunity to evaluate fetal brain develop-ment and to make an early diagnosis of congenital abnormal-ities. MRI allows a better differentiation between normal andabnormal signal intensity of fetal tissues due to its higher con-trast resolution compared to prenatal sonography (US).Therefore, structural abnormalities such as brain malforma-tions and destructive lesions that could be sonographicallyoccult on prenatal sonography can be detected at fetal MRI. We review indications, utility, safety, and technical aspectsof fetal MR imaging and the appearance of normal fetalbrain development evaluating its contribution in the diag-nosis of fetal diseases of different brain regions and spinaldisorders.

INTRODUCTION

The main purpose of prenatal diagnosis is togather genetic, anatomical, biochemical and physiolo-gical information about the fetus to detect potentialabnormalities that may have impacts both during thefetal period and after birth. Thus, we can providefamilies with information, genetic counseling, and/ortherapeutic alternatives for any anomalies detected.

Since the first use of magnetic resonance imaging(MRI) in pregnancy reported in the Lancet in 1983 bySmith FW et al (1), over 3,000 articles on fetal MRI havebeen published.

MRI is a complementary method to ultrasound(US), useful for fetal assessment, which is helpful informulating prognosis and perinatal management,and can detect occult abnormalities in up to 50% ofcases for certain indications(2).

Our aim is to show the safety, advantages, limita-tions, indications and clinical applications of fetalbrain MRI.

SAFETY

Many MRI safety studies have been conducted inanimals, but there is a lack of consensus as to theextrapolation of results to human subjects (3). TheSafety Committee of the Society for MagneticResonance Imaging concluded 17 years ago that fetalMRI was indicated when other non-ionizing diagnos-tic imaging methods were inadequate or when MRIexamination would provide important information onpregnancy. However, owing to the potential risks tothe developing fetus and the limitations of MRI, it isadvisable to wait until the second trimester.Nevertheless, in 2002, the American College ofRadiology, based on a risk-benefit assessment, appro-ved the use of MRI at any gestational age (4).

The use of intravenous contrast is not acceptedbecause gadolinium chelates cross the placenta; theyappear in the fetal bladder and then in amniotic fluid,to be subsequently swallowed by the fetus.Furthermore, the half-life of gadolinium in the fetus isunknown (5). Some authors have recently reported thepotential nephrotoxicity risk of gadolinium (nephro-genic systemic fibrosis) (6).

*Hospital Quirón Madrid. Diego de Velázquez. Pozuelo de Alarcón.28223 Madrid. España. Email: [email protected]**Delta Ecografía. Centro de Diagnóstico por la Imagen en Obstetriciay Ginecología, Madrid.*** Servicio de Neurología Infantil. Hospital Quirón Madrid.

Correspondencia: Manuel Recio Rodrí[email protected]: julio 2010; aceptado: octubre 2010Received: july 2010; accepted: october 2010©SAR-FAARDIT 2010

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Fetal MRI in CNS abnomalities

ADVANTAGES AND LIMITATIONS

Ultrasound is the method of choice for routinescreening in the fetus and for examination of the cen-tral nervous system (CNS) anatomy. However, even inexpert hands, some abnormalities may be overlookeddue to technical problems (reverberation artifacts),maternal or fetal conditions (maternal obesity, inap-propriate fetal position, oligohydramnios) or becausefindings are very subtle.Fetal MRI has several advantages over perinatal US:- Improved spatial resolution (due to the use of

multi-channel receiver arrays and parallel ima-ging techniques).

- Direct visualization of both sides of the brain(while on ultrasound, the anterior margin of thecerebral hemisphere is shadowed because ofreverberation from overlying structures, there arelimitations in the case of oligohydramnios, inade-quate fetal positioning for US or acoustic shado-wing from the ossifying calvarium).

- More detailed assessment of brain development,including direct visualization of the developingcortex and sulcation pattern, which is extremelydifficult, and sometimes impossible, to visualizeon ultrasound.

Fetal MRI’s leading limitations include:- Fetal motion artifacts, reduced with the new ultra-

fast imaging sequences (images are acquired inless than 1 second) and with maternal fasting 4hbefore the study.

- Low spatial resolution at early gestational agebecause of the small size of the fetus.

- Maternal claustrophobia and discomfort duringthe scan (particularly at advanced gestational age).

INDICATIONS

As we have previously mentioned, ultrasound isthe method of choice for routine screening in the fetusand for examination of fetal brain anatomy. In ourcentre, we perform MRI as from the second trimesterto avoid the period of fetal organogenesis, preferablyat ?20 weeks gestational age, when the size of the fetusis large enough to obtain good spatial resolution.

MRI should always be performed after an ultra-sound examination by a skilled sonographer. SalomonLJ et al (7) report the main indications:• A history of severe brain abnormality in a pre-

vious pregnancy, but ultrasound examination isconsidered normal; MRI is performed in order tolook for subtle signs of recurrence.

• An abnormality identified on ultrasound exami-nation that appears to be isolated (typically ventri-culomegaly or corpus callosum agenesis); MRI isperformed to look for associated abnormalitiesthat may have been overlooked by ultrasound.

• An abnormality diagnosed on ultrasound exami-

nation, but the examination cannot be completedbecause of technical problems (e.g. maternal obe-sity or fetal position); MRI is performed to supple-ment ultrasound.

• A high risk of development of brain abnormality,especially in cases of fetal infection (cytomegalovi-rus, varicella and toxoplasmosis) or ischemicdamage (in-utero death of a monochorionic twinor twin-to-twin transfusion syndrome).

IMAGING PROTOCOL

It is advisable to perform MRIs using a high-fieldMRI scanner (1.5T) with high spatial resolution arraysto obtain good diagnostic imaging (such as an 8-chan-nel cardiac array); higher magnetic fields are unaccep-table. The examination is performed in supine decubi-tus position, except at advanced gestational ages, whenthe patient lies in the left lateral decubitus position.

In most centers, the examination is performedwith no maternal sedation, given the use of ultrafastimaging sequences. The patient should fast for 4 hbefore the examination to reduce bowel peristalsisartifacts. Centers that perform fetal MRI with sedationusually administer 1 mg flunitrazepam 20 minutesbefore the examination (8).

Written informed consent should always be obtainedfrom the patient. It is advisable that the examination beperformed by trained operators. Previous ultrasoundinformation allows better planning of the examination.

Three orthogonal planes with respect to themother are identified to obtain sagittal, coronal andaxial slices of the fetus, always taking as reference thelast sequence used to plan the following sequencebecause of fetal movements.

The main sequences used are: • T2-weighted images such as Single Shot Fast Spin

Echo T2 (SSFSE T2) and balanced sequences (FIES-TA) are useful to assess fetal anatomy. Balancedsequences or Steady-State Free Precession sequen-ces are less susceptible to fetal movements and cere-brospinal fluid (CSF) artifacts, mainly at early gesta-tional ages. CSF is hyperintense in these sequences.

• T1-weighted images (dual echo gradient or FastSpoiled Gradient Echo T1) allow for identificationof hemorrhage, calcification or fat and provideinformation on myelination. CSF is hypointense inthese sequences.

• Diffusion-weighted imaging: this sequence isparticularly useful in detecting acute ischemiclesions as well as in the differential diagnosis ofarachnoid and epidermoid cysts (Fig. 1) (9)

Relevant imaging parameters:• Single Shot Fast Spin Echo T2 (SSFSE T2): TR =

1088 ms, TE = minimum (90 ms), matrix = 256 x256, FOV = 34 cm, bandwidth = 20.83 KHz. NEX =0.5, slice thickness = 3 mm, spacing = 0 mm.

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• Balanced sequences (FIESTA): TR = 3.9 ms, TE =minimum (1.7 ms), matrix = 256 x 256, FOV = 35cm, bandwidth = 125 KHz. NEX = 2, slice thick-ness = 5.1 mm, spacing = 0 mm and angle = 45º.

• T1-weighted images (3D dual echo gradient): TR= 8.5 ms, TE = minimum (2.4 ms), matrix = 336 x256, FOV = 39 cm, bandwidth = 62.5 KHz, NEX =0.69, slice thickness = 6 mm, spacing = 0 mm andangle = 12°.

• Diffusion-weighted imaging: TR = 2500 ms, TE =minimum (69 ms), matrix = 128x128, FOV = 36 cm,bandwidth = 62-250 KHz, NEX = 6, slice thickness= 4 mm, spacing = 0 mm and b = 1000 s/mm2.

ANALYSIS AND INTERPRETATION

Fetal BiometryBrain volume estimation is performed using the

fronto-occipital, cerebral biparietal and bone biparie-tal diameters as well as the craniocerebral index andthe cephalic index (Fig. 2).

For assessment of the cerebellum, the transversecerebellar diameter, anteroposterior diameter, andheight and surface of the vermis are used (Fig. 3) (10, 11).Ventricular size assessment is performed using theanteroposterior diameter of the fourth ventricle, thewidth of the third ventricle, and the transversal dia-


Fig. 1 (a) Coronal SSFE T2; (b)Sagittal SSFE T2; (c) Coronal T1-weighted gradient dual echo; (d)Coronal FIESTA; (e) SagittalFIESTA; (f) Axial diffusion.

Fig. 2. (a) Sagittal SSFSE T2, fronto-occipital diameter (FOD); (b)sagittal FIESTA, corpus callosum length (CCL); (c) Coronal FIESTA,cerebral biparietal diameter (cerebral BPD); (d) Coronal FIESTA, bonebiparietal diameter (bone BPD).

Fig. 3 (a) Sagittal SSFSE T2: anteroposterior diameter of the vermis; (b)Sagittal SSFSE T2: height of the vermis; (c) Sagittal SSFSE: surface ofthe vermis; (d) Axial SSFSE T2: Transverse Cerebellar Diameter (TCD)


meter of the lateral ventricles measured on the coronalslice at the level of the atria (12).

The corpus callosum is assessed using the lengthof the corpus callosum measured on the sagittal slicefrom the genu to the splenium.

Cortical sulci analysisAssessment of cortical sulci is the second step.

Sulcal development is an important marker of fetalmaturation.- At 20 gestational weeks, only the lateral sulci

(Sylvian fissures) and the interhemispheric fissurewill be visible.

- At 25 gestational weeks, the lateral sulci, the inter-hemispheric fissure, the hippocampal and calcari-ne fissures, and the cingulate and internal parieto-

occipital sulci become visible (Fig. 4).- At 27 gestational weeks, the lateral sulcus, the inter-

hemispheric fissure, the hippocampal and calcarinefissures, the cingulate, internal parieto-occipital andcentral sulcus should already be present (10,13).

- At 29 gestational weeks, marginal, pre- and pos-tcentral, intraparietal, collateral, superior temporaland superior frontal sulci should be visible and thecentral sulcus should reach half of the cerebralhemisphere (10,13).

- At 31 weeks, the inferior frontal sulcus should bevisible.

- At 35 weeks, the temporal lobe should have all itssulci, including the inferior temporal sulci and theoccipitotemporal sulci. The pattern at this gestatio-nal age is the definitive pattern (Fig. 5) (10,13, 14).


Fig. 5 (a) Sagittal SSFSE T2; (b)Axial SSFSE T2; (c) CoronalSSFSE T2. At 29 weeks, the margi-nal (6), precentral (7), central (8),postcentral (9) intraparietal, colla-teral (10), superior temporal (11)and superior frontal (12) and infe-rior frontal (13) sulci would bevisible and the central sulcuswould reach half of the cerebralhemisphere in depth. (d) SagittalSSFSE T2; (e) Axial SSFSE T2; (f)Coronal SSFSE T2; at 35 weeks,the temporal lobe should have all itssulci, including the inferior tempo-ral sulci (14) and the occipitotem-poral sulci (15). The pattern at thisgestational age is the definitive pat-tern. Interhemispheric fissure (1),Sylvian fissures (2), parieto-occipi-tal sulci (3), calcarine fissures (4)and hippocampal fissures (5).

Fig. 4 (a) Sagittal SSFSE T2, (b)Axial FIESTA; (c) Coronal FIES-TA at 20 gestational weeks, onlythe interhemispheric fissure (1)and the Sylvian fissures (2) wouldbe visible. (d) Sagittal SSFSE T2,(e) Axial FIESTA; (f) CoronalFIESTA, at 25 weeks, only theinterhemispheric fissure (1),Sylvian fissures (2), parieto-occipi-tal sulci (3), calcarine fissures (4),and hippocampal fissures (5)would be visible.


Myelination analysisMyelination is a good indicator of fetal cerebral

maturation. The increase in cholesterol and glycolipidsaccompanying the formation of myelin results in anincrease in water, thus leading to a shortening of T1 andT2 sequences, visible as a hypersignal on T1-weightedimages or a hyposignal onT2-weighted images.

Such signal changes can be seen in the white mat-ter, starting at 20 weeks’ gestation in the posteriorbrainstem. At 27 weeks, some myelin is visible in thevermis and the middle cerebellar peduncles. A mode-rate signal is also visible at the central basal ganglia(10,13), and at 33 weeks, the myelination of the posteriorlimbs of the internal capsules occurs, extending pro-gressively to the globus pallidus at 35–36 weeks (Fig.6) (14). Myelination of the corona radiata occurs at theend of gestation.

Neuronal migration analysisThe development of the cerebral cortex is divided

into 3 stages: cell proliferation, cell migration and,finally, cortical organization.

Neuronal migration occurs between the third andfourth month of gestation and is complete by approxi-mately 24 weeks. Neuronal migration occurs from theperiventricular germinal zone to the pial surface in sixsuccessive layers. The first neurons occupy the deepestportion within the cerebral cortex, whereas those migra-ting later occupy the most superficial layers. Migrationis regulated by radial fibers and mediators (15).

In MRI, neuronal migration is determined by themultilayered appearance on T2-weighted images:

- At 16-18 weeks, three layers are observed (innergerminal matrix, intermediate layer of migratingneurons and outer immature cortex).


Fig. 7 (a) Coronal SSFSE T2; (b) Coronal SSFSE T2; (c) Coronal FIES-TA; (d) Coronal FIESTA. Three layers: inner germinal matrix (brokenarrows), intermediate layer of migrating neurons (black arrows) and outerimmature cortex (curved arrows) at 20.4 weeks. Two layers: inner whitematter (white arrow) and outer cortex (white arrowhead) at 35 weeks.

Fig. 8 GA: 29 weeks. Corpus callosum agenesis. Diamniotic and bicho-rionic twin pregnancy. (a) Coronal FIESTA; (b) Axial Single Shot FastSpin Echo T2 (SSFSE T2); (c) Sagittal SSFSE T2. Total agenesis of thecorpus callosum in the twin in left dorsal cephalic position: elevation ofthe third ventricle connecting with the interhemispheric fissure (whitearrow), separated frontal horns (arrowhead) and colpocephaly (curvedarrow). The other twin shows no abnormalities.

Fig. 6 Normal myelination of the brainstem in a 25-week fetus. (a)Axial FIESTA T2; (b) Axial FIESTA T2. Myelination has not begun inthe supratentorial brain. Myelination of the posterior border of the pons(arrowhead). The signal intensity of the pallidum and the thalamus issimilar to that of white matter (curved arrow). (c) Axial SS FSE T2.The signal intensity of the pallidum and thalamus is hypointense in T2-weighted sequences at weeks 27 to 34 (arrow). (d) Coronal FSPGR T1.Myelination of the internal capsule, of the globus pallidus and thalamusincreases at 35 weeks with hyperintensity in T1 (arrow).


- At 34 weeks, two layers are identified (inner whitematter and outer cortex) (Fig. 7) (16).

CLINICAL APPLICATIONS

Central nervous system malformations accountfor one third of fetal anomalies and are found in 75%of dead fetuses. The incidence of CNS malformationsis estimated at 1 out of 100 live births. Approximately

10% of brain abnormalities are secondary to chromo-somal aberrations, 20% to genetic factors, 10% toadverse effects in the uterus (e.g., infection) and 60%have no identifiable etiology.

We will divide diseases according to the differentbrain areas involved:

Midline abnormalities: total or partial agenesis ofthe corpus callosum (Fig. 8), alobar, semilobar or lobarholoprosencephaly (Fig. 9), septo-optic dysplasia,lipoma of the corpus callosum, cysts of the cavumseptum pellucidum, of the cavum vergae or of thevelum interpositum or absence of the cavum.

Assessment of the corpus callosum is one of themain indications of fetal MRI. While the diagnosis oftotal agenesis is usually based on ultrasound, MRI isparticularly useful in the investigation of partial age-nesis or for the identification of associated abnormali-ties. MRI should be performed when the developmentof the corpus callosum is complete, after week 20. Inapproximately 20% of cases in which callosal agenesiswas suspected on ultrasound, MRI was able todemonstrate an intact corpus callosum (17). In over 63%of cases there are associated abnormalities such as cor-tical malformations, heterotopia, Dandy-Walker mal-formation, Chiari II malformations, schizencephalyand encephalocele (17, 18).

Ventricles: ventriculomegaly is the most commonfinding on ultrasound and therefore the most com-mon indication for fetal MRI. It is classified as mild(10-12 mm), moderate (12-15 mm) and severe (> 15mm). Fetal MRI can detect sonographically occultabnormalities in up to 40-50% of cases, such as neuraltube defects (Fig. 10), agenesis of the corpus callosum,Dandy-Walker complex, lissencephaly, polymicrogy-ria, holoprosencephaly, subependymal heterotopia,intraventricular or subependymal hemorrhage, peri-ventricular leukomalacia or porencephaly (2).


Fig. 9 (a) Sagittal SSFSE T2; (b)Axial SSFSE T2; (c) Axial SSFSET2. GA: 27.2 weeks. Agenesis of thegenu and of 2/3 of the anterior bodyof the corpus callosum (whitearrow). Anteroinferior fusion ofboth frontal lobes (arrowhead) andabsence of frontal horns (brokenarrow). Normal right kidney.Multicystic dysplastic left kidney(curved arrow). (d) Coronal SSFSET2; (e) Axial SSFSE T2; (f) AxialSSFSE T2. GA: 21.4 weeks.Semilobar holoprosencephaly withfusion of thalamus (curved arrow)and frontal lobes (arrowhead).Temporal and occipital horns forma-tion (white arrow). Rudimentaryfalx cerebri (broken arrow).

Fig. 10 Hydrocephalus and occipital meningocele. (a) Sagittal SSFSET2; (b) Axial SSFSE T2; (c) Sagittal FIESTA; (d) Axial FIESTA. GA:21 weeks. Occipital meningocele (white arrow) with cerebellar hypopla-sia. Hydrocephalus with septum pellucidum defect (arrowhead).Arcuate uterus (curved arrow) with uterine myomas (broken arrow).


Periventricular area: MRI can detect subependy-mal heterotopia, small germinal matrix hemorrhagesas well as subependymal nodules in tuberous sclerosis(Fig. 11). Non-visualization of subependymal nodulescannot rule out a diagnosis of tuberous sclerosis (19, 20, 21).

Cerebral parenchyma: MRI can detect small brainhemorrhages or ischemic lesions, determining iflesions are acute or not based on diffusion sequence(Fig. 12) (22, 23).

In infectious diseases, MRI allows detection ofparenchymatous lesions that may be overlooked byultrasound, especially cytomegalovirus infection (24, 25).

Cortical surface: The development of the cerebralcortex is divided into 3 stages: cell proliferation (2 to 4months of gestation), neuronal migration (from 3-4months of gestation to 24 weeks’ gestation) and corti-

cal organization (from 22 weeks’ gestation to 2 yearsof age) (15). Malformations are classified into:

Cell proliferation disorders: decreased prolifera-tion (microlissencephaly), increased proliferation(hemimegalencephaly) and abnormal proliferation(cortical dysplasia).

Disorders of neuronal migration: decreased migra-tion (classic lissencephaly) (Fig. 13), increased migra-tion (congenital muscular dystrophy), ectopic migra-tion (heterotopia).

Disorders of cortical organization: polymicrogyria(patterns I and II), polymicrogyric syndromes (bilate-ral frontal, bilateral perisylvian, bilateral frontoparie-tal, bilateral parasagittal parietooccipital and diffusebilateral) and schizencephaly type I (fused lips) andtype II (open lips) (Fig. 14) (26).


Fig. 11. GA: 30 weeks. Tuberoussclerosis with cardiac rhabdomyo-ma. (a) and (d) Sagittal SSFSE T2;(b) Coronal SSFSE T2; (c) AxialSSFSE T2. Right subependymalnodule adjacent to the interventri-cular foramen (arrow). (e) Echo-Doppler: 4-chamber view of largerhabdomyoma in the left ventricle(arrowhead); (f) Axial FIESTA.Cardiac rhabdomyoma of the leftventricle (arrowhead). Outcome:delivery at 36 weeks.

Fig. 12. GA: 17 weeks. Subacutevenous infarction with intraventri-cular hemorrhage and germinalmatrix hemorrhage. (a) and (b)Sagittal and axial T1 gradientecho; (c) Sagittal SSFSE T2; (d)Axial SSFSE T2; (e) Coronal SSFSE T2; (f) Axial diffusion imaging.Subacute hemorrhagic infarction(arrow), germinal matrix hemor-rhage (arrowhead) and intraventri-cular hemorrhage (asterisk). Full-term delivery with motor sequels.


Pericerebral spaces: While enlarged, extra-axialspaces are normally visible on ultrasound, somelesions such as subdural hematoma require furtherexamination by MRI (27).

Posterior fossa: Most abnormalities discoveredduring pregnancy that involve the posterior fossa

have a poor prognosis. MRI allows better visualiza-tion of this structure than ultrasound, especially incases of non-cephalic presentations, when an endova-ginal probe cannot be used as a complement.Posterior fossa abnormalities evaluated by fetal MRimaging include Dandy-Walker malformation (Fig.15), hypoplasia and/or rotation of the vermis (Fig. 16),Blake pouch cyst, mega cisterna magna, arachnoidcyst, cerebellar dysplasia, cerebellar hypoplasia, cere-bellar hemorrhage, Walker-Warburg syndrome,Chiari malformation and other less common abnor-malities such as the Pascual Castroviejo type 2Syndrome (PHACE Syndrome) (28, 29).

Special reference should be made to two indica-tions for fetal MRI:

Complications of monochorionic twin pregnan-cies: Intrauterine death of one monochorionic twin isassociated with an increased risk of survival in theother twin because of acute cerebral hypoperfusionsecondary to thromboembolic events (30).

Twin-twin transfusion syndrome (TTTS) is charac-terized by abnormal flow from the time when thedonor twin develops oligohydramnios to the timewhen the recipient twin develops polyhydramnios.The morbidity of TTTS is very high and both twins areat risk for cerebral ischemia. Approximately 50 % ofsurviving twins experience abnormalities (31).

Congenital infections: the most common cause ofbrain abnormality in cases of infection is cytomegalo-virus (CMV) and secondly toxoplasmosis. Other viru-ses that can also affect the fetal brain include: varicellazoster virus, parvovirus B19, rubella, and lymphocyticchoriomeningitis virus. They cause diffuse or focalwhite matter abnormalities and, with time, cortical


Fig.13. Type 1 Lissencephaly and callosal agenesis. Woman with nor-mal first pregnancy (gender: female). (a) Sagittal FIESTA; (b) AxialFIESTA. Second pregnancy. GA: 23 weeks. Severe hydrocephalus withSylvian fissure, parieto-occipital sulci and calcarine fissures not visible.Corpus callosum agenesis (arrow). Gender: male. (c) Coronal SSFSET2; (d) Axial SSFSE T2. Third pregnancy. GA: 21.1 and gender male.Findings are similar to those of the second pregnancy (lissencephaly andcallosal agenesis).

Fig. 14. Open lip schizencephaly.GA: 25 weeks (a) Coronal SSFSET2; (b) Coronal SSFSE T2; (c)Axial SSFSE T2; (d) SagittalSSFSE T2. Right insular cleft(white arrow) with pial-ependymalcommunication is suggestive ofopen lip (type II) schizencephaly.Thin septum that appears tocorrespond to ventricular wall(black arrow). (e) Coronal FIR; (f)Axial 3D reconstruction FSPGR.

MRI is performed at 6 years of age because of seizures as from 5 years of age, controlled with valproic acid, and mild spastic monoparesis of the leftarm. We can see how the open lip schizencephaly has progressed to fused lip schizencephaly with polymicrogyria lining the cleft (white arrowhead).Opercularization occurs between weeks 22 and 38. Associated with subependymal heterotopia in inferior and posterior location (black arrowhead).


atrophy and ventricular enlargement. Hemorrhagesare also observed in association with CMV and parvo-virus B19. They may be associated with cortical mal-formations such as lissencephaly, polymicrogyria, anddelayed cortical maturation (24, 25, 32).

MRI also allows assessment of spinal and medu-llar abnormalities: Chiari II with myelomeningoceles,sacrococcygeal teratoma, caudal regression syndro-me, myeloschisis, meningocele and lipomeningocele,tethered spinal cord or diastematomyelia.

The most common indication is myelomeningoce-le associated with Chiari II (Fig. 17); MRI is particu-larly helpful when ultrasound is limited (in cases ofmaternal obesity, inadequate fetal position, oligohy-dramnios). MRI is useful in identifying additional

associated anomalies: corpus callosum agenesis orhypoplasia, periventricular nodular heterotopia, cere-bellar dysplasia, hydrocephalus, syringohydromyeliaand diastematomyelia (33, 34).

Sacrococcygeal teratoma is the most commontumor of the neonate, with an incidence of one in35,000 to 40,000 live births (35). Malignant degenerationis the primary cause of postnatal death and is rare inutero. The high mortality rate is related to tumor sizeand associated dystocia, preterm labor secondary topolyhydramnios and placentomegaly (secondary tocardiac failure associated with arteriovenous shun-ting) (36, 37, 38). MRI is better than ultrasound in assessingthe extension of the teratoma. The American Academyof Pediatrics Surgical Section Classification is used:


Fig. 15. GA: 22 weeks. ClassicDandy-Walker complex. (a) and(b) ultrasound; axial planes (c)Sagittal SSFSE T2; (d) SagittalFIESTA; (e) Axial SSFSE T2; (f)Axial FIESTA. Dandy-Walkerwith partial cerebellar vermis age-nesis (arrow) and hydrocephalus(arrowhead).

Fig. 16. GA: 25 weeks. Hypoplasiaand/or rotation of the vermis (a)Coronal FIESTA; (b) SagittalFIESTA, fetus 1; (c) Axial SSFSET2 fetus 1; (d) Sagittal FIESTA,fetus 2; (e) Sagittal FIESTA, fetus3; (f) Coronal FIESTA, fetus 3.Multiple pregnancy in 42-year-oldwoman with OVODON IVF andtransference of 3 embryos. Twomonochorionic diamniotic males(fetus 1 in cephalic presentationand fetus 3 in breech presentation)with hypoplasia and rotation of thevermis (white arrow) and opencommunication of the fourth ven-tricle and the cisterna magna(arrowhead). The twin in transver-se position (female) has a normalvermis (black arrow).


type I (external component and minimal presacralcomponent), type II (external component and signifi-cant presacral component), type III (minimal externalcomponent and predominantly intrapelvic compo-nent) and type IV (located entirely within the pelvisand abdomen) (Fig. 18) (39, 40).

Finally, another clinical application of MRI is theassessment of craniofacial abnormalities, including:cleft lip, cleft palate (Fig. 19), hypotelorism, hypertelo-rism, anophthalmia, microphthalmia, nasal bone age-nesis or hypoplasia (Down syndrome or fronto-nasaldysplasia) (Fig. 20) or midline abnormalities (maxi-llary hypoplasia, cyclopia, proboscis, ethmocephalyor cebocephaly) (41,42,43).

CONCLUSIONS

MRI is evolving as a useful complimentary tool toultrasound that allows assessment of fetal brain deve-lopment as from the second trimester. It has a moreaccurate diagnostic capability than ultrasound in theidentification of brain development abnormalities orother destructive lesions. MRI is helpful in formula-ting prognosis and perinatal management, since it candetect occult abnormalities in up to 50% of cases forcertain indications.


Fig. 17. GA 20 weeks: Chiari IIwith myelomeningocele. (a)Sagittal SSFSE; (b) CoronalSSFSE; (c) Axial SSFSE T2.Ventriculomegaly. Chiari II malfor-mation (arrow). Myelomenigocele(arrowhead). GA: 26.5 weeks.Chiari II with myeloschisis. (d)Coronal SSFSE; (e) Axial SSFSE;(f) Sagittal FIESTA. Chiari IIMalformation (arrow). Myeloschisis(arrowhead). Ventriculomegaly(asterisk).

Fig. 18. GA: 20 weeks. Type Isacrococcygeal teratoma (arrow).(a) Sagittal SSFSE T2; (b) EcoDoppler; (c) 3D ultrasound, surfa-ce reconstruction; (d) SagittalFIESTA. Predominantly skin-cove-red exophytic lesion. Minimal pre-sacral component. Surgery at 48 h.(e) Picture of the preoperative tera-toma; (f) Postoperative picture.


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Fig. 19. GA: 29.4 weeks (a), (b) and(c) Coronal SSFSE T2; (d) AxialSSFSE T2; (e) and (f) SagittalSSFSE T2. Type II cleft lip andpalate (arrow). Microphthalmiawith absent lens and right orbithypoplasia (arrowhead).

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fetal mri in cns abnormalities. relevant issues for obstetricians

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