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Science to Practice |
Department of Radiology, Indiana University, Riley Hospital for Children, 702 Barnhill Rd, Rm 1053b, Indianapolis, IN 46202. e-mail: kiappleg@iupui.edu.
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The detection of skeletal anomalies and the accurate prenatal diagnosis of skeletal dysplasias remain problematic with ultrasonography (US). There is almost no literature describing the use or potential use of magnetic resonance (MR) imaging for the diagnosis of fetal musculoskeletal abnormalities. In this issue of Radiology, however, Connolly et al (1) elegantly describe the use of MR imaging to define normal musculoskeletal development in fetal pig specimens.
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While some controversy remains, the current literature overall supports the safety of fetal MR imaging. Software and hardware improvements have become widely available, allowing us to perform fast and very fast MR imaging, such as that with echo-planar and single-shot fast spin-echo techniques. Connolly et al (1) used a wrist coil and MR imaging techniques that were not limited to fast or very fast sequences since they analyzed pathologic specimens of fetal pig femurs. The authors described the MR imaging appearances of the fetal pig femur at each trimester and with histologic analysis correlated the evolution of the signal intensity, size, and shape of the femur, including the early appearance and differentiation of the epiphysis, physis, and metaphysis, and corticomedullary differences. MR imaging depicted contour changes of the developing femoral intercondylar notch, changes in cartilage composition such as development of the epiphyseal ossification center, and changes in the signal intensity and shape of the bone and bone marrow.
The Practice
Clinical use.—Published reports have described US as only moderately accurate in the detection of fetal musculoskeletal anomalies and as inaccurate in the diagnosis of specific skeletal dysplasias (2,3). One study reported a sensitivity of 25% (95% confidence interval: 14%, 36%) for the prenatal US detection of limb anomalies in 26 203 births (4). In another report, investigators found 40% of cases to be false-positive for the detection of isolated clubfoot, all of which were diagnosed in the third trimester of pregnancy (5). Yet a third report described the difficulty in distinguishing between isolated bowed femurs and true dysplasia, making parental counseling a challenge (6).
MR imaging has an increasing and complementary role with US for fetal imaging. Improvements in MR imaging—the most important being fast and very fast sequences with gradient-echo techniques—have allowed the increased use of this modality for fetal imaging and have obviated the use of sedation to decrease fetal motion. MR imaging incrementally influences the treatment management for patients who are being considered for fetal intervention (7). While the uses and outcomes of fetal MR imaging and fetal surgery remain under investigation, there is little understanding of the role of fetal MR imaging in the detection of musculoskeletal abnormalities, and, as yet, fetal surgery has not been performed for such indications.
Future opportunities and challenges.—The study by Connolly et al is a first step in defining and developing the role of MR imaging in the characterization of the normal fetal musculoskeletal anatomy. Additional animal and clinical research will be needed to optimize MR imaging techniques, define normal human fetal musculoskeletal development, and identify abnormal development. Challenges include those related to fetal motion, the often complex position of the fetal limbs, and distinguishing what may be a normal variant from an abnormality.
Fetal MR imaging may enable earlier identification of abnormalities so that families can obtain earlier fetal genetic diagnoses, be referred to appropriate pediatric orthopedic specialists, and plan prenatal and immediate postnatal care. With increasing antenatal detection of musculoskeletal abnormalities, it is critical that parents receive adequate antenatal counseling by specialists in congenital musculoskeletal anomalies. MR imaging potentially may enable (a) earlier and more precise identification of skeletal anomalies and dysplasias versus normal development, (b) quantification of bone marrow abnormalities, and (c) identification of teratogenic and drug-induced metabolic bone disorders. Fetal MR imaging may complement the use of molecular genetics—for example, specific mutation analysis to diagnose many skeletal dysplasias.
Summary
Connolly et al have shown that MR imaging can depict normal musculoskeletal development in fetal pig specimens. Future use of fetal MR imaging will likely include refinement of current techniques to allow better investigation of normal and abnormal fetal musculoskeletal MR imaging characteristics.
FOOTNOTES
See also the article by Connolly et al in this issue.
REFERENCES
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