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KEY POINTS

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KEY POINTS

  1. Sonographic evaluation of the vertebral column and the spine is a requirement of almost all governing bodies.

  2. Starting the 13th postmenstrual weeks it is possible to ascertain a normal spine as well as a number of its anomalies.

  3. 3D ultrasound is increasingly used and became instrumental in imaging the vertebral column in the three orthogonal planes using the X-ray or maximum mode rendering.

  4. MRI may at times be necessary to complete the workup.

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The assessment of the fetal vertebral column by transabdominal ultrasound (US) is an essential part of the second-trimester anatomical scan. The possibility of evaluating the spine at as early as 13 weeks of gestation by transvaginal high-resolution US has greatly improve its diagnostic capabilities and enabled the diagnosis of some of the common vertebral anomalies at this stage of pregnancy. Because not all spinal anomalies may be diagnosed during the late first or early second trimester, transabdominal US continues to be the "everyday" tool in the diagnosis of spinal and spinal cord malformations.1 One example of this is the tethered cord that may be visible, in some but not all the cases, from the the midsecond trimester as the terminal spinal cord becomes more clearly defined.

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The introduction of volume US with minimum intensity projection, or radiograph mode, contributes to projecting and locating the exact level of the malformation.2 The additional value of this technology is still controversial, and the projection of a three-dimensional (3D) acquisition of the spine is not always reassuring, as it may miss small lesions in the lower spine.3

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Magnetic resonance imaging (MRI) has been proposed as an additional tool in the diagnosis and counseling of patients with spinal cord anomalies, particularly regarding the evaluation of the spinal canal and its contents. So far this technology has not been widely used, but initial reports appear promising.4,5 In this chapter, the terms spine, spinal column, and vertebral column are used interchangeably.

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DEVELOPMENT OF THE SPINE AND SPINAL CORD

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The vertebrae develop during the sixth postmenstrual week of gestation, when chondrification centers appear for each mesenchymal vertebra. Each vertebral body has two primary ossification centers, one dorsal and one ventral. These centers fuse to form the centrum, which creates three primary ossification loci by the end of embryonic development; one develops in the vertebral body and the other two on each half of the vertebral arch.6 According to US studies, by 16 postmenstrual weeks, S1 and S2 ossification centers are almost all visualized in coronal planes, but S3 is present in only about half of these fetuses; the nucleus of S4 develops slightly later and is observed in all fetuses at 21 weeks.7 The posterior arch synchondrosis is not ossified in fetuses.

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Closure of the neural tube seems to begin separately at several different levels. Progressive folding ...

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