- Open Access
The skeleton and musculature on foetal MRI
© European Society of Radiology 2011
- Received: 19 October 2010
- Accepted: 27 January 2011
- Published: 19 February 2011
Magnetic resonance imaging (MRI) is used as an adjunct to ultrasound in prenatal imaging, the latter being the standard technique in obstetrical medicine.
Initial results demonstrate the ability to visualise the foetal skeleton and muscles on MRI, and highlight the potentially useful applications for foetal MRI, which has significantly profited from innovations in sequence technology. Echoplanar imaging, thick-slab T2-weighted (w) imaging, and dynamic sequences are techniques complementary to classical T2-w imaging.
Recent study data indicate that foetal MRI may be useful in the imaging of spinal dysraphism and in differentiating between isolated and complex skeletal deformities with associated congenital malformations, which might have an impact on pre- and postnatal management.
More research and technical refinement will be necessary to investigate normal human skeletal development and to identify MR imaging characteristics of skeletal abnormalities.
- Foetal MRI
- Congenital abnormalities
Foetal magnetic resonance imaging (MRI) has become an increasingly used imaging technique, serving as an adjunct to ultrasound in prenatal diagnosis [1–4]. Numerous recent studies have emphasised the benefits of MRI for the demonstration of congenital abnormalities of the brain and lungs, or complex syndromes [1–7].
However, there are almost no reports in the literature describing MRI for the prenatal visualisation and diagnosis of skeletal and muscular abnormalities, with the exception of spinal dysraphism [8–10]. Therefore, the authors sought to demonstrate and summarise their preliminary results for the visualisation of the skeleton in utero on MRI. The imaging techniques are described in detail, and the potential impact of a prenatal MRI diagnosis is discussed.
In addition to commonly used T2-weighted (w) imaging to depict foetal anatomy and anomalies at all gestational ages, MRI protocols should include imaging techniques such as echo planar imaging (EPI), thick-slab T2-w sequences, and dynamic steady-state free precession (SSFP) sequences to visualise the developing musculoskeletal system [1, 11, 12].
Application of T2-w single-shot (SSh) turbo-spin-echo (TSE) sequences
Axial, coronal, and sagittal planes; repetition time (TR): shortest; echo time (TE): 100 ms; TSE factor: 92; field of view: 200–230 mm; matrix: 256 × 153; slice thickness: 3–4 mm; slices: 18; flip angle: 90°; duration: 18.7 s
Whole body evaluation
Head size and shape (microcephaly; encephaloceles)
Brain (associated malformations; acquired anomalies) (TE: 140 ms in GW 18–29)
Face and foetal profile (facial clefts)
Orbits (content; interorbital distance)
Teeth buds and hard palate (cleft palate)
External ear size, shape, and position; and fluid-filled inner ears
Thorax shape and lung volume (lung hypoplasia in skeletal dysplasias)
Spine (content/extent of spinal dysraphism)
Arms and legs; hands and feet (size, shape, number of fingers/toes)
Musculature (decreased thickness; fatty atrophy after GW 30)
Application of single-shot fast-field-echo (SSh FFE) sequences (echo-planar imaging)
Coronal and sagittal planes; repetition time (TR): 3,000 ms; echo time (TE): shortest; field of view: 230 mm; matrix: 160 × 95; slice thickness: 4 mm; flip angle: 90°; duration: 12 s
Facial profile (after GW 28; delineation enhanced because of chemical shift by subcutaneous fat)
Hard palate (cleft palate)
Imaging of normal hyperintense cartilaginous epiphysis and hypointense diaphysis
Bone length and shape (bent bones; skeletal dysplasias)
Ossification disorders (osteogenesis imperfecta)
Application of thick-slab T2-w imaging
Coronal and sagittal planes; repetition time (TR): 8,000 ms; echo time (TE): 400–800 ms; field of view: 210–320 mm; matrix: 256 × 205; slice thickness: 30–50 mm; flip angle: 90°; up to 15 projections (12°–15° angulation); duration: 8 s
Foetal proportions and surface, whole foetus from different angles
Facial features (micrognathia; dysmorphic features)
Intrauterine growth restriction (IUGR)
Dwarfism, mesomelia or rizomelia (skeletal dysplasias)
Extremity positioning (contractures, arthrogryposis)
Extremity thickness (hydrops; subcutaneous oedema; muscle mass)
Limb deformity/deficiency (amniotic bands; clubfeet; skeletal dysplasias)
External masses (extensive lymphangiomas)
Discontinuity of the body surface (omphalocele; spina bifida)
Application of dynamic steady-state free precession (SSFP) sequences
Repetition time (TR): 3.14 ms; echo time (TE): 1.57 ms; field of view: 320 mm; matrix: 176 × 110; slice thickness: 30 mm; gap: 0; flip angle: 60°; 4–6 frames per second; up to 8 repetitions; duration: 34 s
Imaging of movement patterns of extremities, head, and body; swallowing; and diaphragm excursions
Akinesia (foetal akinesia deformation sequence; neuromuscular disorders)
Foetal bulk motion
On MRI, the skull base and cranio-cervical junction should be examined in detail, particularly the width and content of the foramen magnum, as a narrow foramen magnum may occur in some skeletal dysplasias, and cerebellar herniation occurs in Chiari malformations .
Magnetic resonance imaging is the most accurate method of delineating any kind of muscular abnormalities in paediatric populations , but MRI of the foetal musculature is only in the early stages of investigation. With regard to the structure, normal individual muscles (with few exceptions, e.g., the diaphragm) cannot be delineated, because muscles display a homogeneous T2-w hypointensity . However, tissue composition changes with advancing gestation, as evidenced by EPI sequences. MRI can show the thickness and contours of the skeletal muscles, and atrophy (Fig. 5) , which may indicate the presence of a neuromuscular disorder. In addition, T1- and T2-w signals may be pathological with increased T2-w signal intensities (Table 1) . It has been stated that impairment of muscle development must reach a critical stage, occurring relatively late in pregnancy, to result in significant changes in foetal motility and morphology . Overall, abnormal muscular development may be observed with limb abnormalities, such as arthrogryposis, spinal muscle dystrophy, or muscle dystrophy [37, 38].
Foetal skeletal dysplasias are usually recognised by ultrasound [41, 44–46]. However, published reports have described ultrasound as only moderately accurate in the detection of foetal musculoskeletal anomalies and specific skeletal dysplasias [45, 46], which may indicate a potential future role of MRI in these conditions. Foetal MR imaging may complement the use of molecular genetics to diagnose skeletal dysplasias . After 30 weeks of gestation, conventional radiography of the maternal abdomen may also help to identify possible bone abnormalities . Recent case series report the application of prenatal computed tomography with 3D reconstructions as an adjunct to ultrasound in the diagnosis of lethal skeletal dysplasias .
Initial results demonstrate the visualisation of the normal and abnormal skeleton on foetal MRI, which highlights the use of MRI as an adjunct to prenatal ultrasound. MRI may be helpful in foetal spinal imaging, and in the differentiation between isolated and complex abnormalities, which might have an impact on pre- and postnatal management, as complex abnormalities may be related to an unfavourable outcome. Preliminary experience suggests an improvement in diagnosis through additional MRI findings in specific cases compared with ultrasound. However, increased efforts are needed to refine MRI techniques for the visualisation of the foetal skeleton and to clarify the value of MRI compared with standard ultrasound.
U.N. and S.F.N. co-wrote the manuscript; both authors contributed equally to this work. The authors would like to thank Ms. Mary McAllister for her help in editing the manuscript.
The authors have indicated they have no financial relationships relevant to this article to disclose.
Conflict of interest
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