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Keywords:

  • associated defects;
  • congenital limb abnormalities;
  • fetal MRI;
  • upper extremities

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

Objective

In view of the increasing use of fetal magnetic resonance imaging (MRI) as an adjunct to prenatal ultrasonography, we sought to demonstrate the visualization of upper extremity abnormalities and associated defects on MRI, with regard to fetal outcomes and compared with ultrasound imaging.

Methods

This retrospective study included 29 fetuses with upper extremity abnormalities visualized with fetal MRI following suspicious ultrasound findings and confirmed by postnatal assessment or autopsy. On a 1.5-Tesla unit, dedicated sequences were applied to image the extremities. Central nervous system (CNS) and extra-CNS anomalies were assessed to define extremity abnormalities as isolated or as complex, with associated defects. Fetal outcome was identified from medical records. MRI and ultrasound findings, when available, were compared.

Results

Isolated upper extremity abnormalities were found in three (10.3%) fetuses. In 26 (89.7%) fetuses complex abnormalities, including postural extremity disorders (21/26) and structural extremity abnormalities (15/26), were demonstrated. Associated defects involved: face (15/26); musculoskeletal system (14/26); thorax and cardio/pulmonary system (12/26); lower extremities (12/26); brain and skull (10/26); and abdomen (8/26). Of the 29 cases, 18 (62.1%) pregnancies were delivered and 11 (37.9%) were terminated. MRI and US findings were compared in 27/29 cases: the diagnosis was concordant in 14 (51.9%) of these cases, and additional findings were made on MRI in 13/27 (48.1%) cases.

Conclusions

Visualization of upper extremity abnormalities on fetal MRI enables differentiation between isolated defects and complex ones, which may be related to poor fetal prognosis. MRI generally confirms the ultrasound diagnosis, and may provide additional findings in certain cases. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

Over the past several years, magnetic resonance imaging (MRI) has been used increasingly as an adjunct examination to ultrasonography for the evaluation of fetal anomalies1–5. The high soft-tissue contrast, high resolution and multiplanar imaging capabilities have been cited as advantages of prenatal MRI1–5.

MRI data about the normal and pathological development of diverse fetal organ systems have been presented in detail1, 5–9, whereas literature regarding the use of MRI for the diagnosis of musculoskeletal and, in particular, extremity abnormalities is scarce10–13. These anomalies may involve all limbs or be focal, involving a single distal digit. Since congenital malformations of the extremities may be isolated or can be associated with other defects, syndromes and skeletal dysplasias, a specific prenatal diagnosis is vital14–17. Detailed examination of the extremities, although not listed in the guidelines of the American Institute of Ultrasound in Medicine for standard obstetric sonography18, is a critical component of fetal imaging in the diagnosis of many syndromes, as has been emphasized by several ultrasound studies14–17. Prenatal ultrasound imaging is currently regarded as the method of choice for measuring long bones and examining distal limbs.

In view of the limited number of reported cases, our analysis aimed to provide initial data on the potential of fetal MRI for the characterization of congenital abnormalities of the upper extremities. We sought to demonstrate the visualization on fetal MRI of congenital abnormalities of the upper extremities, with a focus on associated defects. We describe in detail our imaging protocols, present the potential impact of a prenatal MRI diagnosis and compare MRI with ultrasound findings.

Patients and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

The protocol for this retrospective study was approved by our Institutional Review Board (EC No. 993/2009) and the procedure was performed in accordance with the Declaration of Helsinki.

Patients

This retrospective series included MRI studies of 29 fetuses, depicting unilateral or bilateral abnormalities of the upper extremities, either isolated or with associated defects (complex), carried out between January 2005 and September 2010. The gestational age ranged from 18 + 4 to 38 + 2 (mean, 26 + 2) weeks and there were 28 singletons and one twin pregnancy with one affected fetus. All cases were confirmed by clinical (clinical examination and imaging studies) or pathological (autopsy and histopathology) assessment.

In all cases, MRI had been indicated in order to delineate central nervous system (CNS) and extra-CNS findings after suspicious prenatal ultrasound findings, in order to confirm or possibly expand the diagnosis. Written, informed consent to undergo MRI was obtained from all mothers (maternal age range, 17–38 (mean, 29) years). Karyotype was determined in 13 fetuses, five by chorionic villus sampling and eight by amniocentesis, and postnatally in one individual, by fluorescent in-situ hybridization following intravenous blood sampling.

Imaging

Ultrasound

Routine prenatal two-dimensional (2D) transabdominal anomaly scans were performed in our hospital by an obstetric specialist using a GE Voluson 730 Expert (GE Medical Systems, Solingen, Germany) or a Toshiba Xario (SSA-680A) (Toshiba Medical Systems, Wiener Neudorf, Austria) ultrasound machine. Examinations were performed within 4 days prior to MRI.

Magnetic resonance imaging

Non-contrast enhanced MRI was performed on a 1.5-Tesla unit (Philips Medical Systems, Best, The Netherlands) using a five-element phased-array cardiac coil. There was no sedation of either mother or fetus. Our standard MRI protocol included the application of the following sequences to image the fetal extremities:

  • 1.
    Coronal and sagittal T2-weighted single-shot (SSh) turbo spin echo (TSE) sequences (repetition time (TR), shortest; echo time (TE), 140 ms; TSE factor, 92; field-of-view (FOV), 200–230 mm; matrix, 256 × 153; slice thickness, 3 mm; flip angle, 90°; duration, 18.7 s).
  • 2.
    Dynamic steady-state free precession (SSFP) sequences (TR, 3.14 ms; TE, 1.57 ms; FOV, 320 mm; matrix, 176 × 110; slice thickness, 30 mm; flip angle, 60°; 4–6 frames/s; duration, 34 s).
  • 3.
    A three-dimensional (3D), thick-slab T2-weighted sequence (TR, 8000 ms; TE, 400–800 ms; FOV, 210–320 mm; matrix, 256 × 205; slice thickness, 30 mm; flip angle, 90°; up to 15 projections (12°–15° angulation); duration, 8 s).
  • 4.
    In some cases: coronal and sagittal SSh fast field echo (FFE) sequences (‘echoplanar imaging’ (EPI)) (TR, 3000 ms; TE, shortest; FOV, 230 mm; matrix, 160 × 95; slice thickness, 4 mm; flip angle, 90°; duration, 12 s).

The fetal head was imaged by: axial, coronal and sagittal T2-weighted SSh TSE sequences in 3-mm thick slices; a 3D thick-slab T2-weighted sequence; coronal EPI; an axial T1-weighted sequence; and axial and coronal diffusion-weighted imaging (DWI).

The fetal body was imaged by: axial, coronal and sagittal T2-weighted SSh TSE sequences; coronal T1-weighted sequences; axial and coronal EPI; coronal DWI; and multiplanar SSFP sequences.

Evaluation

Images were reviewed by consensus by two fetal MRI specialists (both with 12 years' experience), who were aware of the abnormal ultrasound findings. Morphological assessment, including fetal biometry and visualization of extremity positioning, was performed using coronal and sagittal T2-weighted SSh TSE sequences, the 3D thick-slab T2-weighted sequence and EPI. The humerus length was measured bilaterally. Intrauterine growth restriction (IUGR) was defined as an SD of 2.5 below the mean for fetal humerus length measurements, in association with placental abnormalities19, 20. Evaluation of the extremity included its shape, form, number of extremity elements and composition. The dynamic SSFP sequence was performed at 5, 10, 15, 20, 25 and 35 min to study fetal movements and to detect contractures (isolated and multiple), based upon the fixed extremity position during the examination (total duration of examination, 40 min). The fetal movement patterns were analyzed according to modified ultrasound criteria21 that covered the qualitative aspects of movement (amplitude and speed or absence of movements) and number of participating body parts.

CNS and other abnormalities were reviewed to define extremity abnormalities as isolated (without other associated defects) or complex (with associated defects). The amount of amniotic fluid was assessed according to the maximum vertical pocket depth published for prenatal ultrasound22. The appearance of the placenta23 and the fetal positioning were also evaluated.

The fetal outcomes of the study population were identified from medical records and autopsy reports. Delivered pregnancies were differentiated from terminated pregnancies.

Statistical analysis

Descriptive statistics were used to analyze the number of fetal abnormalities in the study cohort. MRI and ultrasound findings were also compared using a descriptive approach.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

Magnetic resonance imaging findings

There was an isolated unilateral abnormality of the upper extremity in 3/29 (10.3%) fetuses (MRI diagnosis at 20 + 0 to 32 + 2 weeks). One fetus presented with right-sided ectrodactyly (Figure 1), a second fetus with adactyly (Figure 2) and the third fetus with lymphangioma of the right upper extremity (Figure 3).

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Figure 1. (a) Coronal T2-weighted magnetic resonance image in a 23 + 3-week fetus with isolated unilateral ectrodactyly, without other abnormalities and in breech presentation (karyotype unknown; liveborn). Note absence of several central phalanges with ‘lobster claw’-like appearance of the hand (arrow). (b) Hand X-ray at 3.2 years showing a metacarpal and phalangeal malformation, with two osseous phalanges of the right hand (R) and normal development of the left hand (L).

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Figure 2. Sagittal T2-weighted magnetic resonance image in a 32 + 2-week fetus with isolated unilateral limb deficiency of the right upper extremity, in breech presentation (46,XY; liveborn). Note complete absence of the fingers of the right hand (arrow), whereas the left hand appears to be normal (ellipse).

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Figure 3. Magnetic resonance images in a 20 + 0-week fetus with lymphangioma of the right upper extremity and shoulder girdle and with otherwise normal anatomy, in breech presentation (karyotype unknown; liveborn). (a) Coronal T2-weighted image showing a large cystic (hyperintense) tumor without solid components (+). (b) Thick-slab T2-weighted image showing the lesion in an oblique view, presenting with multiple septa (arrow).

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A complex abnormality of the upper extremity associated with other defects was demonstrated in the other 26 (89.7%) fetuses (MRI diagnosis 18 + 4 to 38 + 2 (mean, 26 + 2) weeks). The abnormality was unilateral in 9/26 (34.6%) fetuses and bilateral in the remaining 17/26 (65.4%) fetuses. Several fetuses had multiple findings.

Among the nine fetuses with complex unilateral abnormalities of the upper extremities, four fetuses had contractures of the arm and hand, three fetuses had polydactyly (Figure 4), one fetus had ectrodactyly and one fetus had finger contractures. Among the 17 fetuses with complex bilateral abnormalities of the upper extremities, eight fetuses had long-bone shortening, seven fetuses had contractures of the arms and hands (Figure 5), two fetuses had clenched fists, two fetuses had ectrodactyly (Figure 6), one fetus had adducted thumbs and two fetuses had finger contractures.

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Figure 4. Magnetic resonance images in a 23 + 5-week fetus with unilateral polydactyly, corpus callosum hypoplasia and bilateral kidney hypoplasia, in breech presentation (46,XX; infant death at 7.5 months). (a) Oblique T2-weighted image in which entire fetus is visible, showing detail of the left hand with two abnormally elongated digits (arrow). (b) Coronal T2-weighted image showing a hypoplastic corpus callosum (arrow) and a small cystic basal ganglia lesion (arrowhead). (c) Postnatal hand X-ray at 1 month showing six digits with dysmorphism of first (arrow head) and second (arrow) digits.

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Figure 5. Magnetic resonance imaging in a 32 + 0-week fetus with hand contractures, developmental disorder of the opercula, thoracic deformity and hepatomegaly, in cephalic presentation (images rotated) (46,XY; liveborn). (a) Thick-slab T2-weighted image showing bilateral abnormal deviation of the hands indicative of contractures (arrows). (b) Prenatal coronal T2-weighted image showing widening of the subarachnoid space (arrowheads). (c) This widening was also evident postnatally, on axial T2-weighted imaging at 4.5 months (arrowheads), resulting in underdevelopment of the opercula with distinct widening of the cisterns of the lateral cerebral fossa. (In this case, a postnatal chest X-ray showed a deformed thorax with ‘coat hanger’ appearance of the ribs, suggesting uniparental disomy 14 (genetic testing not performed)).

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Figure 6. Imaging in a 21 + 0-week fetus with ectrodactyly of both hands and left foot and bilateral hydronephrosis, in cephalic presentation (karyotype unknown; liveborn). (a) Three-dimensional ultrasound image showing ectrodactyly of the right hand (arrow). (b) Single image of a dynamic sequence showing a split malformation of the right hand (arrow) and the left foot (arrowhead), with only two phalanges present.

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Associated defects

Of the 26 fetuses with associated defects, facial/neck defects were found in 15 (57.7%) (MRI diagnosis at 18 + 4 to 36 + 3 (mean, 25 + 2) weeks). Mandibular retrognathia was seen in 11 fetuses, microphthalmia in two fetuses, nuchal cystic hygroma in two fetuses, frontal bossing in one fetus, cleft lip and palate in one fetus and dysplastic ears in one fetus.

Generalized musculoskeletal defects were found in 14/26 (53.8%) fetuses (MRI diagnosis at 18 + 4 to 31 + 2 (mean, 25 + 3) weeks). Long-bone shortening and thin extremity musculature apparently related to IUGR was seen in eight fetuses, arthrogryposis was seen in four fetuses (one of which had fetal akinesia sequence), multiple bone fractures with bent long bones caused by lethal osteogenesis imperfecta was seen in one fetus and caudal regression sequence with scoliosis was seen in one fetus.

Lower extremity defects were found in 12/26 (46.2%) fetuses (MRI diagnosis at 21 + 3 to 34 + 0 (mean, 27 + 2) weeks). There were bilateral clubfeet in four fetuses, unilateral clubfoot in three fetuses, rocker bottom feet in two fetuses, unilateral ectrodactyly in one fetus, bilateral lower extremity shortening in one fetus, unilateral lower extremity contracture in one fetus, missing toes in one fetus and bilateral foot deformities with missing bones in one fetus.

Thoracic and cardiopulmonary defects were found in 12/26 (46.2%) fetuses (MRI diagnosis at 18 + 4 to 36 + 3 (mean, 25 + 3) weeks). Lung hypoplasia (assessed by abnormal T2-weighted signal intensities)24 was seen in seven fetuses, cardiomegaly in four fetuses, thorax deformity in two fetuses, hydrothorax in two fetuses and esophageal atresia in one fetus.

Brain abnormalities were found in 9/26 (34.6%) fetuses (MRI diagnosis at 21 + 0 to 38 + 2 (mean, 28 + 2) weeks) and skull abnormalities were found in one (3.8%) fetus (MRI diagnosis at 34 + 0 weeks). Cerebellar hypoplasia was seen in three fetuses, lissencephaly in three fetuses, hydrocephaly in two fetuses (caused by aqueduct stenosis in one and choroid plexus hemorrhage in the other), corpus callosum hypoplasia in two fetuses, basal ganglia lesions in one (Figure 4), opercula development disorder in one (Figure 5), ventricular asymmetry in one; pons deformity in one, pons hypoplasia in one and microcephaly in one. In the fetus with a skull abnormality, this was a skull base deformity.

Abdominal defects were found in 8/26 (30.8%) fetuses (MRI diagnosis at 19 + 2 to 34 + 0 (mean, 25 + 2) weeks). An omphalocele with a small bowel ileus was seen in one fetus (Figure 7), hepatomegaly in two fetuses, bilateral kidney hypoplasia in two fetuses, ascites in two fetuses, bilateral hydronephrosis in one fetus, duodenal stenosis in one fetus and a diaphragmatic hernia in one fetus.

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Figure 7. Sagittal T2-weighted magnetic resonance imaging in a 34 + 0-week fetus with bilateral hand contractures, skull base deformity, omphalocele and bowel stenosis, hepatomegaly and rocker bottom feet, in cephalic presentation (image rotated) (46,XY unbalanced translocation (t/4q/7p); infant death at 3.5 months). An umbilical hernia (arrow) with a large hernia sac filled with a distended bowel section (arrowhead) is visible; postnatally this was identified during surgery as an obstructed Meckel's diverticulum.

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Hydrops fetalis was seen in 2/26 (7.7%) fetuses (MRI diagnosis at 21 + 2 and 23 + 0 (mean, 22 + 1) weeks).

Amniotic fluid, fetal positioning, placenta

There was a normal amount of amniotic fluid in 18/29 (62.1%) mothers, polyhydramnios in five (17.2%) and oligohydramnios in six (20.7%). The fetus was in cephalic presentation in 16/29 (55.2%) cases and in breech presentation in 13 (44.8%) cases. There was normal appearance of the placenta, according to age, in 19/29 (65.5%) cases, placental infarctions in eight (27.6%) and a placental hemorrhage in two (6.9%).

Outcomes

In 11/29 (37.9%) cases, the parents elected to terminate the pregnancy (MRI diagnosis at 18 + 4 to 30 + 0 (mean, 22 + 2) weeks), and 18/29 (62.1%) were delivered (MRI diagnosis at 19 + 2 to 38 + 2 (mean, 27 + 2) weeks). Ten of these, including one stillbirth, were delivered vaginally and eight were delivered by Cesarean section. Three individuals died within the first months of delivery. All three individuals with unilateral isolated extremity abnormalities were delivered. Table 1 gives detailed information on terminated cases and those which died during infancy.

Table 1. Details of terminations of pregnancy (TOP), stillbirths and infant deaths in cases of upper extremity abnormalities
 MRI findings  
GA (weeks)ExtremitiesOtherKaryotypeAge at death
  1. GA, gestational age at time of magnetic resonance imaging (MRI) diagnosis; IUGR, intrauterine growth restriction; MRSA, methicillinresistant Staphylococcus aureus.

18 + 4Fetal akinesia, arthrogryposis, clubfeetMicrognathia, lung hypoplasiaUnknownTOP 19 + 0 weeks
19 + 2Unilateral polydactylyMicrophthalmia, lung hypoplasia, diaphragmatic hernia, kidney hypoplasia46,XXTOP 20 + 1 weeks
21 + 0Unilateral polydactylyMicrocephaly, microphthalmia, corpus callosum hypoplasia, cystic hygroma, cardiomegaly, placental infarctionTrisomy 13TOP 23 + 5 weeks
21 + 2Bilateral hand contracturesCardiomegaly, lung hypoplasia, hydrops fetalis, hepatomegaly, polyhydramniosUnknownTOP 22 + 5 weeks
21 + 3Multiple fractures with bent bonesOsteogenesis imperfecta46,XXTOP 21 + 4 weeks
22 + 5IUGR, unilateral upper extremity contractures, clubfeetCardiomegaly, lung hypoplasia, placental infarction46,XYTOP 23 + 5 weeks
22 + 5IUGRHydrothorax, lung hypoplasia, ascites, placental hemorrhageUnknownTOP 23 + 3 weeks
23 + 0IUGR, adducted thumbs, clubfeetFacial dysmorphia, lung hypoplasia, hydrops fetalis, placental infarctionUnknownTOP 23 + 2 weeks
23 + 4IUGR, unilateral upper extremity contracturesLissencephaly, ventriculomegaly, cerebellar hypoplasia, placental infarction, oligohydramnios45,XX (13/14) (q10/q10) Robertsonian translocationTOP 24 + 3 weeks
27 + 2Finger contracturesLissencephaly, retrognathia, duodenal stenosis46,XXTOP 30 + 4 weeks
30 + 0IUGR, finger contracturesPontine/cerebellar hypoplasia, cleft lip and palateTrisomy 18TOP 32 + 1 weeks
21 + 3Bilateral ectrodactyly, foot deformityNuchal cystic hygroma, cardiomegaly, lung hypoplasia, ascites, placental infarction46,XYStillbirth 28 + 0 weeks
34 + 0Hand contractures, rocker bottom feetSkull base deformity, facial dysmorphia, thorax deformity, hepatomegaly, omphalocele, oligohydramnios46,XY unbalanced translocation (t/4q/7p)Died of cardiorespiratory decompensation with pulmonary infection at 3.5 months
21 + 0Unilateral polydactylyCorpus callosum hypoplasia, basal ganglia cysts, kidney hypoplasia46,XXDied of renal insufficiency and MRSA sepsis at 7.5 months
26 + 6Arthrogryposis, clenched fistsLissencephaly, cerebellar hypoplasia, polyhydramniosUnknownDied 2 days after Cesarean section at 28 + 2 weeks

In 17 children, MRI findings were confirmed by postnatal clinical examination and imaging studies (e.g. plain film radiographs/computed tomography/ultrasound/MRI). In 15 individuals (11 terminated cases, one stillbirth and three infant deaths), confirmation was by autopsy and histopathology findings.

Of the 14 cases with known karyotype, 10 had normal karyotype and four were abnormal. One case had a 45,XX (13/14) (q10/q10) Robertsonian translocation, one had a 46,XY unbalanced translocation (t/4q/7p), one had trisomy 18 and one had trisomy 13. In all other cases, karyotyping was unknown.

MRI vs ultrasound findings

Because of different national referring departments, ultrasound reports were not available for inclusion in the study in two cases. The diagnoses of MRI and ultrasound for extremity abnormalities and associated defects were concordant in 14/27 (51.9%) cases. The ultrasound diagnoses were expanded by the MRI results through additional findings in 13/27 (48.1%) cases (Table 2). MRI showed additional brain anomalies in eight cases, additional extremity abnormalities in three cases, both additional brain and additional extremity anomalies in one case and findings indicative of a Pena–Shokeir phenotype in one case.

Table 2. Details of imaging findings in fetuses with upper extremity abnormalities which had findings on magnetic resonance imaging (MRI) additional to those on ultrasound (US)
 Imaging findings
GA (weeks)Ultrasound*Additional on MRIUpper extremities (US/MRI)
  • *

    Excluding upper extremity findings.

  • Any finding on MRI additional to that found on US.

  • Comparison of upper extremity findings using the two modalities.

  • §

    This prenatal finding resulted in the postnatal finding of underdevelopment of the opercula (Figure 5). GA, gestational age at time of magnetic resonance imaging (MRI) diagnosis (ultrasound examinations performed within 4 days prior to MRI). IUGR, intrauterine growth restriction.

38 + 2Internal hydrocephalyChoroid plexus hemorrhage, unilateral hand contractureUnilateral hand contracture not described on US
32 + 0Thorax deformity, hepatomegaly, clubfeetSubarachnoid space widening§Bilateral hand contractures depicted on US and MRI
30 + 0Caudal regression, foot deformitiesUnilateral ectrodactylyUnilateral ectrodactyly not described on US
30 + 0Cleft lip and palate, bone shortening, IUGRPontine and cerebellar hypoplasiaBilateral finger contractures depicted on US and MRI
27 + 2Gyration disorder, retrognathia, duodenal stenosis, uterus bicornisLissencephalyUnilateral finger contractures depicted on US and MRI
26 + 6Slight internal hydrocephaly, arthrogryposis, polyhydramniosLissencephaly, cerebellar hypoplasiaContractures depicted on US and MRI
24 + 6Clubfoot (left)Slight ventricular asymmetryUnilateral hand contracture on US and MRI
23 + 5Hypoplasia of corpus callosum, kidney hypoplasiaBasal ganglia cystsPolydactyly depicted on US and MRI
23 + 4Ventriculomegaly, cerebellar hypoplasia, placental infarction, oligohydramniosLissencephalyIUGR and unilateral upper extremity contractures depicted on US and MRI
21 + 0Microcephaly, microphthalmia, cystic hygroma, cardiomegaly, placental infarctionCorpus callosum hypoplasiaUnilateral polydactyly depicted on US and MRI
21 + 0Retrognathia, hydronephrosisSplit left footBilateral upper extremity ectrodactyly depicted on US and MRI
19 + 0Microphthalmia, lung hypoplasia, diaphragmatic hernia, kidney hypoplasia,Unilateral polydactylyUnilateral polydactyly not described on US
18 + 4ArthrogryposisLung hypoplasia, micrognathia, Pena–Shokeir phenotypeContractures depicted on US and MRI

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

Demonstrating morphological and postural abnormalities in 29 fetuses, this retrospective investigation of anomalies of the fetal upper extremities is the largest such prenatal MRI study to date. We have demonstrated the visualization of upper extremity abnormalities on prenatal MRI and now discuss the potential role of MRI in musculoskeletal imaging of the fetus.

Fetal MRI of the musculoskeletal system was enhanced by using MR sequences more advanced than T2-weighted imaging5, 25, 26. The heavily T2-weighted thick-slab sequence allows a spatial impression of the whole fetus, and is especially effective for visualizing fetal proportions and surface25. In contrast to 3D ultrasound, thick-slab T2-weighted imaging is not limited by the FOV and, therefore, fetuses can be imaged even at advanced gestational ages. The graded spectrum of shades of gray provides a fetal ‘shine-through’ effect, whereas 3D ultrasound demonstrates only the fetal surface or bones. Thick-slab T2-weighted imaging seems to be useful in detecting abnormal proportions (IUGR, disproportionate dwarfism in skeletal dysplasias) and extremity positioning (arthrogryposis)25, whereas evaluation on 2D MRI may be complicated because of movement and lack of continuity in single slices.

In contrast to previous studies2, 27, in which MRI of the extremities was limited because of the lack of real-time information, dynamic sequences, as applied in our study, seem to allow visualization of movements. By using modified ultrasound criteria, these sequences were instrumental in evaluating malposition and confirming the lack of movement in contractures (Figure 8), and in providing information about fetal bulk motion5, 25. As quantitative fetal MRI movement studies are generally not performed, movement disorders should be evaluated in combination with other musculoskeletal features. Compared to quantitative and qualitative ultrasound assessment of fetal motility, which has been well investigated and is applied routinely during scanning21, dynamic fetal MRI is based on preliminary study results. On MRI, abnormal swallowing activity may also be observed in association with a lack of extremity movements in fetal akinesia.

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Figure 8. Magnetic resonance imaging in a 21 + 2-week fetus with bilateral hand contractures, lung hypoplasia, enlarged heart, hydrops fetalis and hepatomegaly, in breech presentation (karyotype unknown; terminated). The dynamic sequences (from left to right) show a consistent, abnormal deviation and fixed positioning of the hands (arrows).

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Although prenatal ultrasound has proven to be reliable in the visualization of bone ossification centers from 9 gestational weeks onwards27, 28, there is limited experience in the evaluation of bones on fetal MRI. Currently, only EPI sequences can depict the fetal skeleton on MRI before 27 weeks, demonstrating bones as hypointense and the cartilaginous epiphyses as hyperintense structures5, 26. EPI might be helpful in the detection of abnormal/absent bone ossification: there was one case of osteogenesis imperfecta with abnormal EPI signal intensities shown in our study. T2-weighted imaging is important for imaging of the musculoskeletal system. At all gestational ages these sequences depict excellently fetal anatomy, particularly the fetal surface and including hands and feet. Furthermore, case reports suggest that increased T2-weighted signal intensities indicate structural derangement in congenital muscular disorders on fetal MRI5. Further research into MRI is necessary to assess its potential to improve muscular imaging, as opposed to the simple biometric measurements which can be performed easily using prenatal sonography29.

Since limbs, joints and digits are visible on both transvaginal and transabdominal ultrasound imaging, and are well-visualized on 3D sonography when surrounded by amniotic fluid14–17, the value of fetal MRI as a diagnostic modality for the extremities could be questioned. However, there is a large number of cases with associated anomalies, including generalized fetal disease and CNS abnormalities; our data suggest the value of MRI to visualize these associated defects. In our series, the vast majority (26/29) of fetuses with anomalies of the upper extremities had other major anomalies, and a recent ultrasound study found similar results17.

Our data again underline the importance of assessment of the upper limbs in prenatal diagnosis, since any abnormalities may be part of chromosomal or monogenic disorders or syndromes. The recognition of a specific extremity defect might play a key role in correctly identifying the final diagnosis14–17. The differentiation between isolated and complex abnormalities is very important, as the latter may be associated with poor prognosis16, 17; in our study 11/29 pregnancies were terminated, one individual died in utero, and three additional children died during infancy. All of these were cases with complex abnormalities. The antenatal detection of extremity abnormalities should therefore alert the examiner to search for other major anomalies, and should trigger a complete work-up including anatomical imaging, as well as genetic counseling30. Our study revealed four abnormal karyotypes; three fetuses were terminated and the fourth infant died in early childhood. Prenatal diagnosis can serve as a prognostic tool and help in planning for pre- and postnatal care.

Our results show that MRI is a complementary tool that can not only confirm an ultrasound diagnosis, but also provide additional findings in certain cases, especially with regard to fetal neuroimaging. MRI can assess cortical development, the thinness of the pericerebral space and the brainstem much more easily than can sonography31. This is underscored by our results: in nine cases MRI visualized additional brain findings which were not detected on ultrasound (Table 2). Currently, T2-weighted imaging may be considered the best sequence for imaging fetal brain anatomy due to its use of a high tissue contrast5. We cannot objectively document effect on fetal outcome based on MRI, but it is noteworthy that four of nine pregnancies with brain anomalies were terminated, and two other individuals with brain anomalies died within the first months of postnatal life.

A drawback of our retrospective unblinded data is that this limited study cohort cannot be used to determine the sensitivity and specificity of the detection by MRI of extremity abnormalities; we are now planning a prospective study.

In conclusion, visualization of upper extremity abnormalities by fetal MRI enables differentiation between isolated and complex defects, which frequently are related to poor fetal outcome, with a potential impact on pre- and postnatal management. Fetal MRI can confirm the ultrasound diagnosis and may provide additional findings in specific cases. However, further validation must await future investigation to allow advanced imaging of normal and abnormal fetal bone and muscle development.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES

We would like to thank Ms Mary McAllister (Johns Hopkins University, Baltimore, MD) for her help in editing the manuscript.

REFERENCES

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES