MR imaging of the fetal musculoskeletal system

Fetal Skeletal Dysplasia

Skeletal dysplasias (SDs) are a diverse group of genetic disorders. Diagnosis can be difficult as many are rare and with varied presentations, but with knowledge of the most common SDs presenting prenatal and with an algorithm that uses both sonographic and MR imaging techniques, directed genetic testing and counseling can be provided for many families.

Susceptibility-weighted imaging to evaluate normal and abnormal vertebrae in fetuses:a preliminary study

OBJECTIVE

To evaluate the performance of Susceptibility-weighted imaging (SWI) in visualizing normal and abnormal fetal vertebrae in vivo and in utero.

METHODS

Ninety-seven women with normal fetal vertebrae and 127 women suspected fetal vertebral anomalies on ultrasound were included in our study. SWI, TrueFISP and HASTE of the fetal spine were performed on 1.5-T MRI. The image quality and diagnostic performance between HASTE/TrueFISP and SWI were compared. Pearson correlations to correlate the L1 centrum ossification center (COC) measurements with gestational age (GA) were performed.

RESULTS

The visibility of the fetal vertebral structures on the SWI images (3.58 ± 0.69) was significantly greater than those on the HASTE (1.98 ± 0.51, P < 0.001) and TrueFISP (2.63 ± 0.52, P < 0.001). The diagnostic accuracy of SWI (89.0%) was superior to HASTE/TrueFISP (48.0%) (P < 0.001) and the area under the curve (AUC) for SWI was 0.909 (P < 0.001). The height, transverse, sagittal diameter and area of L1 COC were linearly correlated with GA (all P < 0.001).

CONCLUSION

SWI proved to be a reliable method for depicting fetal vertebral structure and growth, which can significantly improve the diagnostic performance of vertebral anomalies in fetuses. This article is protected by copyright. All rights reserved.

Magnetic resonance imaging of the fetal musculoskeletal system

Diagnosing musculoskeletal pathology requires understanding of the normal embryological development. Intrinsic errors of skeletal development are individually rare but are of paramount clinical importance because anomalies can greatly impact patients' lives. An accurate assessment of the fetal musculoskeletal system must be performed to provide optimal genetic counseling as well as to drive therapeutic management. This manuscript reviews the embryology of skeletal development and the appearance of the maturing musculoskeletal system on fetal MRI. In addition, it presents a comprehensive review of musculoskeletal fetal pathology along with postnatal imaging.

Demonstration of Human Fetal Bone Morphology with MR Imaging: A Preliminary Study

Purpose:

CT is a useful modality for the evaluation of fetal skeletal dysplasia but radiation exposure is unavoidable. The purpose of this study is to compare the usefulness of MRI and CT for evaluating the fetal skeletal shape.

Methods:

This study was approved by our Institutional Review Board. Fetal specimens (n = 14) were scanned on a 3T MRI scanner using our newly-developed sequence. It is based on T2*-weighted imaging (TR, 12 ms; TE for opposed-phase imaging, 6.1 ms, for in-phase imaging, 7.3 ms; flip angle, 40°). The specimens were also scanned on a 320 detector-row CT scanner. Four radiologists visually graded and compared the visibility of the bone shape of eight regions on MRI- and CT-scans using a 5-point grading system.

Results:

The diagnostic ability of MRI with respect to the 5th metacarpals, femur, fibula, and pelvis was superior to CT (all, P < 0.050); there was no significant difference in the evaluation results of observers with respect to the cervical and lumbar spine, and the 5th metatarsal (0.058 ≤ P ≤ 1.000). However, the diagnostic ability of MRI was significantly inferior to CT for the assessment of the bone shape of the thoracic spine (observers A and C: P = 0.002, observers B and D: P = 0.001).

Conclusion:

The MRI method we developed represents a potential alternative to CT imaging for the evaluation of the fetal bone structure.

Fetal MRI at 3T-ready for routine use?

Fetal MR now plays an important role in the clinical work-up of pregnant females. It is performed mainly at 1.5 T. However, the desire to obtain a more precise fetal depiction or the fact that some institutions have access only to a 3.0 T scanner has resulted in a growing interest in performing fetal MR at 3.0 T. The aim of this article was to provide a reference for the use of 3.0 T MRI as a prenatal diagnostic method.

Prenatal diagnosis of congenital upper limb differences: a current concept review

Congenital upper limb differences are frequently associated with complex syndromes. Ultrasonography is considered as the first-line diagnostic modality, and fetal MRI can be useful to further evaluate ill-defined areas. Genetic and non-invasive prenatal testing help to identify the underlying genetic disorder. The diagnostic assessment is a multidisciplinary task that should involve early prenatal consultations with specialists involved in case management and treatment planning. Obstetricians, geneticists, radiologists, psychologists and dedicated surgeons are needed to provide good parental education, prenatal and postnatal care, and successful outcomes. The purpose of this review is to provide an overview of the clinicopathologic background, current diagnostic and imaging procedures in affected fetuses.

Prenatal diagnosis of musculoskeletal conditions

Ultrasonography is a safe, cost-effective tool used to prenatally detect common musculoskeletal conditions, including clubfoot, skeletal dysplasias, limb-length discrepancies, spinal abnormalities, and hand and other upper extremity deformities. With increased detection of such abnormalities, prenatal parental counseling by orthopaedic surgeons is being requested more frequently. Counseling is important for family education on prognosis and treatment options. A thorough understanding of the common musculoskeletal conditions diagnosed on prenatal ultrasonography, classification of these conditions, and the correlations of these classifications to postnatal severity allows the orthopaedic surgeon to conduct well-informed counseling sessions with families. Accurate information and counseling aids parents in understanding their child's diagnosis, assists clinicians in planning treatment algorithms, and optimizes family preparedness.

Fetal MRI: A Technical Update with Educational Aspirations

Fetal magnetic resonance imaging (MRI) examinations have become well-established procedures at many institutions and can serve as useful adjuncts to ultrasound (US) exams when diagnostic doubts remain after US. Due to fetal motion, however, fetal MRI exams are challenging and require the MR scanner to be used in a somewhat different mode than that employed for more routine clinical studies. Herein we review the techniques most commonly used, and those that are available, for fetal MRI with an emphasis on the physics of the techniques and how to deploy them to improve success rates for fetal MRI exams. By far the most common technique employed is single-shot T2-weighted imaging due to its excellent tissue contrast and relative immunity to fetal motion. Despite the significant challenges involved, however, many of the other techniques commonly employed in conventional neuro- and body MRI such as T1 and T2*-weighted imaging, diffusion and perfusion weighted imaging, as well as spectroscopic methods remain of interest for fetal MR applications. An effort to understand the strengths and limitations of these basic methods within the context of fetal MRI is made in order to optimize their use and facilitate implementation of technical improvements for the further development of fetal MR imaging, both in acquisition and post-processing strategies.

Fetal MRI: the sonographer's view

Fetal magnetic resonance imaging (MRI) is used with increasing frequency as a complementary imaging modality to ultrasound (US) in prenatal diagnosis. Fetal MRI displays the fetal, uterine, and extrauterine anatomy in ways that allow confirmation of normal anatomy and the diagnosis of pathological entities that were formerly very difficult to detect prenatally. Comparison of US views with standard orthogonal plane MR images reinforces the understanding of fetal anatomy as visualized with US. Technological advances in US equipment have allowed the recent description of subtle fetal anatomical structures. Similarly, knowledge of the MRI appearances of pathological conditions has opened opportunities for the sonographic diagnosis of entities such as brainstem malformations and alterations in the normal transient laminar pattern that occur during development of the fetal cerebrum. Fetal MRI can confirm suspicious US findings and thus add confidence in a particular prenatal diagnosis before performing invasive and interventional procedures. Specific MRI sequences can be used to add information about the chemical composition of fetal structures, such as fat, blood, and meconium. Dynamic MRI sequences have increased understanding of gestational age-dependent behavior, and assist the sonographer in assessment of fetal structural anomalies that cause abnormal movement and behavior. The technological ability of US to demonstrate very small structures complements the lower resolution of fetal MR images, whereas the ability of MR to visualize the whole fetus improves the limited views necessitated by US. Therefore, both US and fetal MRI have complementary strengths and weaknesses that can be used to full advantage in prenatal diagnosis.

Skeletal development on fetal magnetic resonance imaging

Prenatal magnetic resonance imaging (MRI) is being increasingly used, in addition to standard ultrasound, for the diagnosis of congenital diseases beyond the central nervous system. Previous studies have demonstrated that MRI may be useful for the in utero visualization of spinal dysraphism and for differentiating between isolated and complex skeletal disorders with associated abnormalities. More recently, attention has focused on the visualization of the human fetal skeleton for the delineation of normal and pathological development of skeletal structures. On 1.5 T, in particular, echoplanar imaging enables the delineation of various epimetaphyseal structures and morphometric measurements of the fetal long bones from 18 gestational weeks until term. This information gathered from prenatal MRI might be helpful in the diagnosis of focal bone abnormalities and generalized skeletal disorders, such as bone dysplasias. Further clinical research, along with the refinement of the newest techniques, will enable expansion of the preliminary findings and help in determining the impact of fetal magnetic resonance bone imaging in the routine clinical setting. This review summarizes the current data in the literature and the authors' clinical experience with the magnetic resonance visualization of the developing fetal skeleton and also comments on the potential future applications of this technique.

[Indications and technique of fetal magnetic resonance imaging]

CLINICAL/METHODICAL ISSUE

Evaluation and confirmation of fetal pathologies previously suspected or diagnosed with ultrasound.

STANDARD RADIOLOGICAL METHODS

Ultrasound and magnetic resonance imaging (MRI).

METHODICAL INNOVATIONS

Technique for prenatal fetal examination.

PERFORMANCE

Fetal MRI is an established supplementary technique to prenatal ultrasound.

ACHIEVEMENTS

Fetal MRI should only be used as an additional method in prenatal diagnostics and not for routine screening.

PRACTICAL RECOMMENDATIONS

Fetal MRI should only be performed in perinatal medicine centers after a previous level III ultrasound examination.

Human long bone development in vivo: analysis of the distal femoral epimetaphysis on MR images of fetuses

PURPOSE

To investigate human long bone development in vivo by analyzing distal femoral epimetaphyseal structures and bone morphometrics on magnetic resonance (MR) images of fetuses.

MATERIALS AND METHODS

An institutional review board approved this retrospective study, and informed consent was waived. Included were 272 MR imaging examinations (April 2004-July 2011) in 253 fetuses with a mean gestational age (GA) of 26 weeks 6 days (range, 19 weeks 2 days to 35 weeks 6 days) without known musculoskeletal abnormalities. Two independent readers qualitatively analyzed epiphyseal and metaphyseal shape, secondary ossification, and the perichondrium on 1.5-T echo-planar MR images and correlated the results with the GA that was derived from previous fetal ultrasonography (US). Diaphyseal and epiphyseal morphometric measurements were correlated with GA by means of the Pearson correlation and linear regression. MR imaging measurements of diaphyseal length and US normative values were compared graphically. Interreader agreement analysis was performed with weighted κ statistics and the intraclass correlation coefficient.

RESULTS

With advancing GA, the epiphyseal shape changed from spherical (r(2) = 0.664) to hemispherical with a notch (r(2) = 0.804), and the metaphyseal shape changed from flat (r(2) = 0.766) to clearly undulated (r(2) = 0.669). Secondary ossification (r(2) = 0.777) was not observed until 25 weeks 3 days. The perichondrium decreased (r(2) = 0.684) from 20 weeks onward. Correlation coefficients were 0.897 for diaphyseal length, 0.738 for epiphyseal length, and 0.801 for epiphyseal width with respect to GA. The range of measurements of diaphyseal length was larger than that of the reported US normative values. Interreader agreement was good for bone morphometrics (intraclass correlation coefficient, 0.906-0.976), and moderate for bone characteristics (weighted κ, 0.448-0.848).

CONCLUSION

Prenatal MR imaging allows visualization of human bone development in vivo by means of epimetaphyseal characteristics and bone morphometrics.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13112441/-/DC1.