A quantitative study on the spatial and temporal ossification patterns of vertebral centra and neural arches and their relationship to the fetal age

An Easy and Effective Method for Evaluating the Position of Conus Medullaris: Counting the Number of Vertebral Ossification Center Below the End of Conus Medullaris

OBJECTIVE

This study aimed to ascertain the conus medullaris position by counting the number of ossification centers in the vertebral bodies below the conus medullaris endpoint (N) and assess its utility in screening for closed spinal dysraphism and tethered cord syndrome.

METHODS

A total of 900 normal fetuses and 146 fetuses with closed spinal dysraphism or tethered cord syndrome were included in this study. The N values were tallied and compared along the spinal longitudinal plane. The receiver operating characteristic curve was utilized, and the cut-off value of N was analyzed.

RESULTS

The counting of N was successfully performed in 856 normal and 146 abnormal fetuses. In the normal group, an increase in N with gestational age was observed. Specifically, in the subgroup of 17-20 wk fetuses, N was ≥6 in 117 out of 131 cases. This figure increased to 211 out of 213 in 21-24 wk and 512 out of 512 in 25-41 wk, respectively. Cases with N ≥7 accounted for 715 out of 856 fetuses in the 17-41 wk range. In the abnormal group, N was less than 7 in 152 out of 163 fetuses, showing statistical differences between the two groups. With a cut-off value of 6.5, specificity and sensitivity reached 93.3% and 83.5%.

CONCLUSIONS

The counting of N was found to be a straightforward and efficient method for evaluating the position of the conus medullaris.

Regionalization, constraints, and the ancestral ossification patterns in the vertebral column of amniotes

The development of the vertebral column has been studied extensively in modern amniotes, yet many aspects of its evolutionary history remain enigmatic. Here we expand the existing data on four major vertebral developmental patterns in amniotes based on exceptionally well-preserved specimens of the early Permian mesosaurid reptile Mesosaurus tenuidens: (i) centrum ossification, (ii) neural arch ossification, (iii) neural arch fusion, and (iv) neurocentral fusion. We retrace the evolutionary history of each pattern and reconstruct the ancestral condition in amniotes. Despite 300 million years of evolutionary history, vertebral development patterns show a surprisingly stability in amniotes since their common ancestor. We propose that this stability may be linked to conservatism in the constraints posed by underlying developmental processes across amniotes. We also point out that birds, mammals, and squamates each show specific trends deviating from the ancestral condition in amniotes, and that they remain rather unchanged within these lineages. The stability of their unique patterns demonstrates a certain homogeneity of vertebral developmental constraints within these lineages, which we suggest might be linked to their specific modes of regionalization. Our research provides a framework for the evolution of axial development in amniotes and a foundation for future studies.

Normal development of sacrococcygeal centrum ossification centers in the fetal spine: a postmortem magnetic resonance imaging study

PURPOSE

To describe the temporal pattern of the appearance of the S1-Co1 centrum ossification centers (COCs) and provide reference data for the S1-S5 COCs and sacral length at various gestational ages (GAs).

METHODS

Postmortem magnetic resonance imaging (MRI) was performed on 71 fetuses (GA, 17-42 weeks) using the 3D dual-echo steady-state with water excitation T2 sequence in the sagittal plane. To confirm the reliability of this sequence, the MRI data were compared with the CT and histologic data obtained from two fetuses (GAs, 21 and 30 weeks). The presence or absence of each sacrococcygeal COC was recorded. Sacral length and S1-S5 COC height, sagittal diameter, transverse diameter, cross-sectional area, and volume were measured.

RESULTS

All fetuses showed S1-S3 COCs by 17 weeks, S4 COCs by 19 weeks, and S5 COCs by 28 weeks. The S4, S5, and Co-1 COCs were visualized in 70 (98.59%), 51 (71.83%), and 21 (29.58%) fetuses, respectively. Sacral length, height, sagittal, and transverse diameters increased linearly, while cross-sectional area and volume increased exponentially with advancing GA. Mean growth rates of the sagittal and transverse diameters, cross-sectional area, and volume, but not of height, significantly differed among the S1-S5 vertebrae.

CONCLUSION

We have presented the timing of appearance of individual sacrococcygeal COCs and the age-specific, normative MRI reference values for sacral length and the morphometric parameters of the sacral COCs, which are of clinical importance in the diagnosis of congenital sacral abnormalities and skeletal dysplasia.

How to Explore Fetal Sacral Agenesis Without Open Dysraphism: Key Prenatal Imaging and Clinical Implications

The estimated prevalence of fetal caudal dysgenesis is 1 per 100,000 births. The functional prognosis of sacral agenesis is dominated by the large spectrum of associated caudal malformations. Except for cases associated with hydrocephalus secondary to open spinal dysraphism or chromosomal anomalies, association with mental deficiency is rare. We propose a systematic prenatal approach to cases of fetal sacral agenesis based on 9 etiologic items: clinical context, type of sacral dysgenesis, associated spinal cord malformations, mobility of lower limbs, investigation of the presacral region, analysis of the gastrointestinal tract, analysis of the genitourinary tract, associated vertebral defects, and cytogenetic analysis.

Avian tail ontogeny, pygostyle formation, and interpretation of juvenile Mesozoic specimens

The avian tail played a critical role in the evolutionary transition from long- to short-tailed birds, yet its ontogeny in extant birds has largely been ignored. This deficit has hampered efforts to effectively identify intermediate species during the Mesozoic transition to short tails. Here we show that fusion of distal vertebrae into the pygostyle structure does not occur in extant birds until near skeletal maturity, and mineralization of vertebral processes also occurs long after hatching. Evidence for post-hatching pygostyle formation is also demonstrated in two Cretaceous specimens, a juvenile enantiornithine and a subadult basal ornithuromorph. These findings call for reinterpretations of Zhongornis haoae, a Cretaceous bird hypothesized to be an intermediate in the long- to short-tailed bird transition, and of the recently discovered coelurosaur tail embedded in amber. Zhongornis, as a juvenile, may not yet have formed a pygostyle, and the amber-embedded tail specimen is reinterpreted as possibly avian. Analyses of relative pygostyle lengths in extant and Cretaceous birds suggests the number of vertebrae incorporated into the pygostyle has varied considerably, further complicating the interpretation of potential transitional species. In addition, this analysis of avian tail development reveals the generation and loss of intervertebral discs in the pygostyle, vertebral bodies derived from different kinds of cartilage, and alternative modes of caudal vertebral process morphogenesis in birds. These findings demonstrate that avian tail ontogeny is a crucial parameter specifically for the interpretation of Mesozoic specimens, and generally for insights into vertebrae formation.

Sonographic Evaluation of Fetal Conus Medullaris and Filum Terminale

Background: Sonographic evaluation of the fetal conus medullaris (CM) level is not reproducible. The objectives of this study were to determine the normal position of the fetal CM during pregnancy as well as the normal intradural filum terminale (FT) length and to evaluate their use in detecting tethered cord. Methods: This is a prospective evaluation of normal singleton pregnancies examined by sonography from 17 weeks of gestation to term. Each sonographer had to identify the top of the first sacral vertebra (S1) to measure the distance between it and the conus extremity (CM-S1 distance). The intradural FT distance was measured with 5- to 8-MHz probes. Results: 194 consecutive pregnant women were included. The CM and intradural FT were demonstrated clearly in 164 (84%) cases. The mean CM-S1 distance was 20.6 mm (range 0.5-42). The mean intradural FT distance was 27.9 mm (range 6.6-49.3). Linear regression analysis showed a significant association between both those distances and gestational age (p < 0.05). In cases of tethered cord, the mean CM-S1 distance and the mean intradural FT distance were both below the 5th percentile. Conclusion: Prenatal evaluation of the CM and the intradural FT is feasible and reproducible and seems useful in detecting tethered cord.

Cross-sectional study of C1-S5 vertebral bodies in human fetuses

INTRODUCTION

Knowledge on the normative spinal growth is relevant in the prenatal detection of its abnormalities. The present study determines the height, transverse and sagittal diameters, cross sectional area, and volume of individual C1-S5 vertebral bodies.

MATERIAL AND METHODS

Using the methods of computed tomography (CT), digital image analysis, and statistics, the size of C1-S5 vertebral bodies in 55 spontaneously aborted human fetuses aged 17-30 weeks was examined.

RESULTS

All the 5 examined parameters changed significantly with gestational age (p < 0.01). The mean height of vertebral bodies revealed an increase from the atlas (2.39 ±0.54 mm) to L2 (4.62 ±0.97 mm), stabilized through L3-L4 (4.58 ±0.92 mm, 4.61 ±0.84 mm), and then was decreasing to S5 (0.43 ±1.06 mm). The mean transverse diameter of vertebral bodies was increasing from the atlas (1.20 ±1.96 mm) to L1 (6.24 ±1.46 mm), so as to stabilize through L2-L3 (6.12 ±1.65, 6.12 ±1.61 mm), and finally was decreasing to S5 (0.26 ±0.96 mm). There was an increase in sagittal diameter of vertebral bodies from the atlas (0.82 ±1.34 mm) to T7 (4.76 ±0.85 mm), its stabilization for T8-L4 (4.73 ±0.86 mm, 4.71 ±1.02 mm), and then a decrease in values to S5 (0.21 ±0.75 mm) was observed. The values for cross-sectional area of vertebral bodies were increasing from the atlas (2.95 ±5.25 mm(2)) to L3 (24.92 ±11.07 mm(2)), and then started decreasing to S5 (0.48 ±2.09 mm(2)). The volumetric growth of vertebral bodies was increasing from the atlas (8.60 ±16.40 mm(3)) to L3 (122.16 ±74.73 mm(3)), and then was decreasing to S5 (1.60 ±7.00 mm(3)).

CONCLUSIONS

There is a sharp increase in size of fetal vertebral bodies between the atlas and the axis, and a sharp decrease in size within the sacral spine. In human fetuses the vertebral body growth is characterized by maximum values in sagittal diameter for T7, in transverse diameter for L1, in height for L2, and in both cross-sectional area and volume for L3.

New patterns of the growing L3 vertebra and its 3 ossification centers in human fetuses - a CT, digital, and statistical study

Background

This study describes reference data for L3 vertebra and its 3 ossification centers at varying gestational ages.

Material/Methods

Using CT, digital-image analysis and statistics, the growth of L3 vertebra and its 3 ossification centers in 55 spontaneously aborted human fetuses aged 17–30 weeks was examined.

Results

Neither sex nor right-left significant differences were found. The height and transverse and sagittal diameters of the L3 vertebral body increased logarithmically. Its cross-sectional area followed linearly, whereas its volume increased parabolically. The transverse and sagittal diameters of the ossification center of the L3 vertebral body varied logarithmically, but its cross-sectional area and volume grew linearly. The ossification center-to-vertebral body volume ratio gradually declined with age. The neural ossification centers increased logarithmically in length and width, and proportionately in cross-sectional area and volume.

Conclusions

With no sex differences, the growth dynamics of the L3 vertebral body follow logarithmically in height, sagittal and transverse diameters, linearly (in cross-sectional area), and parabolically (in volume). The growth dynamics of the 3 ossification centers of the L3 vertebra follow logarithmically in transverse and sagittal diameters, and linearly (in cross-sectional area and volume). The age-specific reference intervals of the L3 vertebra and its 3 ossification centers present the normative values of clinical importance in the diagnosis of congenital spinal defects.

Morphometric study of the T6 vertebra and its three ossification centers in the human fetus

Purpose

Knowledge on the normative growth of the spine is critical in the prenatal detection of its abnormalities. We aimed to study the size of T6 vertebra in human fetuses with the crown-rump length of 115–265 mm.

Materials and methods

Using the methods of computed tomography (Biograph mCT), digital image analysis (Osirix 3.9) and statistics, the normative growth of the T6 vertebral body and the three ossification centers of T6 vertebra in 55 spontaneously aborted human fetuses (27 males, 28 females) aged 17–30 weeks were studied.

Results

Neither male–female nor right–left significant differences were found. The height, transverse, and sagittal diameters of the T6 vertebral body followed natural logarithmic functions as y = −4.972 + 2.732 × ln(age) ± 0.253 (R² = 0.72), y = −14.862 + 6.426 × ln(age) ± 0.456 (R² = 0.82), and y = −10.990 + 4.982 × ln(age) ± 0.278 (R² = 0.89), respectively. Its cross-sectional area (CSA) rose proportionately as y = −19.909 + 1.664 × age ± 2.033 (R² = 0.89), whereas its volumetric growth followed the four-degree polynomial function y = 19.158 + 0.0002 × age⁴ ± 7.942 (R² = 0.93). The T6 body ossification center grew logarithmically in both transverse and sagittal diameters as y = −14.784 + 6.115 × ln(age) ± 0.458 (R² = 0.81) and y = −12.065 + 5.019 × ln(age) ± 0.315 (R² = 0.87), and proportionately in both CSA and volume like y = −15.591 + 1.200 × age ± 1.470 (R² = 0.90) and y = −22.120 + 1.663 × age ± 1.869 (R² = 0.91), respectively. The ossification center-to-vertebral body volume ratio was gradually decreasing with age. On the right and left, the neural ossification centers revealed the following models: y = −15.188 + 6.332 × ln(age) ± 0.629 (R² = 0.72) and y = −15.991 + 6.600 × ln(age) ± 0.629 (R² = 0.74) for length, y = −6.716 + 2.814 × ln(age) ± 0.362 (R² = 0.61) and y = −7.058 + 2.976 × ln(age) ± 0.323 (R² = 0.67) for width, y = −5.665 + 0.591 × age ± 1.251 (R² = 0.86) and y = −11.281 + 0.853 × age ± 1.653 (R² = 0.78) for CSA, and y = −9.279 + 0.849 × age ± 2.302 (R² = 0.65) and y = −16.117 + 1.155 × age ± 1.832 (R² = 0.84) for volume, respectively.

Conclusions

Neither sex nor laterality differences are found in the morphometric parameters of evolving T6 vertebra and its three ossification centers. The growth dynamics of the T6 vertebral body follow logarithmically for its height, and both sagittal and transverse diameters, linearly for its CSA, and four-degree polynomially for its volume. The three ossification centers of T6 vertebra increase logarithmically in both transverse and sagittal diameters, and linearly in both CSA and volume. The age-specific reference intervals for evolving T6 vertebra present the normative values of potential relevance in the diagnosis of congenital spinal defects.

Cross-sectional study of the neural ossification centers of vertebrae C1-S5 in the human fetus

Purpose

An understanding of the normal evolution of the spine is of great relevance in the prenatal detection of spinal abnormalities. This study was carried out to estimate the length, width, cross-sectional area and volume of the neural ossification centers of vertebrae C1–S5 in the human fetus.

Materials and methods

Using the methods of CT (Biograph mCT), digital-image analysis (Osirix 3.9) and statistics (the one-way ANOVA test for paired data, the Kolmogorov–Smirnov test, Levene’s test, Student’s t test, the one-way ANOVA test for unpaired data with post hoc RIR Tukey comparisons) the size for the neural ossification centers throughout the spine in 55 spontaneously aborted human fetuses (27 males, 28 females) at ages of 17–30 weeks was studied.

Results

The neural ossification centers were visualized in the whole pre-sacral spine, in 74.5 % for S1, in 61.8 % for S2, in 52.7 % for S3, and in 12.7 % for S4. Neither male–female nor right–left significant differences in the size of neural ossification centers were found. The neural ossification centers were the longest within the cervical spine. The maximum values referred to the axis on the right, and to C5 vertebra on the left. There was a gradual decrease in length for the neural ossification centers of T1–S4 vertebrae. The neural ossification centers were the widest within the proximal thoracic spine and narrowed bi-directionally. The growth dynamics for CSA of neural ossification centers were found to parallel that of volume. The largest CSAs and volumes of neural ossification centers were found in the C3 vertebra, and decreased in the distal direction.

Conclusions

The neural ossification centers show neither male–female nor right–left differences. The neural ossification centers are characterized by the maximum length for C2–C6 vertebrae, the maximum width for the proximal thoracic spine, and both the maximum cross-sectional area and volume for C3 vertebra. There is a sharp decrease in size of the neural ossification centers along the sacral spine. A decreasing sequence of values for neural ossification centers along the spine from cervical to sacral appears to parallel the same direction of the timing of ossification. The quantitative growth of the neural ossification centers is of potential relevance in the prenatal diagnosis and monitoring of achondrogenesis, caudal regression syndrome, diastematomyelia and spina bifida.

Cross-sectional study of the ossification center of the C1-S5 vertebral bodies

Purpose

Knowledge on the normative growth of the spine is relevant in the prenatal detection of its abnormalities. This study describes the size of the ossification center of C1–S5 vertebral bodies.

Materials and methods

Using CT, digital-image analysis, and statistics, the size of the ossification center of C1–S5 vertebral bodies in 55 spontaneously aborted human fetuses aged 17–30 weeks was examined.

Results

No sex significant differences were found. The body ossification centers were found within the entire presacral spine and in 85.5 % of S1, in 76.4 % of S2, in 67.3 % of S3, in 40.0 % of S4, and in 14.5 % of S5. All the values for the atlas were sharply smaller than for the axis. The mean transverse diameter of the body ossification center gradually increased from the axis to T12 vertebra, so as to stabilize through L1–L3 vertebrae, and finally was intensively decreasing to S5 vertebra. There was a gradual increase in sagittal diameter of the body ossification center from the axis to T5 vertebra and its stabilization for T6–T9 vertebrae. Afterward, an alternate progression was observed: a decrease in values for T10–T12 vertebrae, an increase in values for L1–L2 vertebrae, and finally a decrease in values for L3–S5 vertebrae. The values of cross-sectional area of ossification centers were gradually increasing from the axis to L2 vertebra and then started decreasing to S5 vertebra. The following cross-sectional areas were approximately equivalent to each other: for L5 and T3–T5, and for S4 and C1. The volumetric growth of the body ossification center gradually increased from the axis to L3 vertebra and then sharply decreased from L4 to S5.

Conclusions

No male–female differences are found in the size of the body ossification centers of the spine. The growth dynamics for morphometric parameters of the body ossification centers of the spine follow similarly with gestational age.

New anatomical data on the growing C4 vertebra and its three ossification centers in human fetuses

PURPOSE

Detailed knowledge on the normative growth of the spine is of great relevance in the prenatal diagnosis of its abnormalities. The present study was conducted to compile age-specific reference data for vertebra C4 and its three ossification centers in human fetuses.

MATERIALS AND METHODS

With the use of CT (Biograph mCT), digital image analysis (Osirix 3.9) and statistical analysis (Wilcoxon signed-rank test, Kolmogorov-Smirnov test, Levene's test, Student's t test, one-way ANOVA, post hoc RIR Tukey test, linear and nonlinear regression analysis), the normative growth of vertebra C4 and its three ossification centers in 55 spontaneously aborted human fetuses (27 males, 28 females) aged 17-30 weeks was examined.

RESULTS

Significant differences in neither sex nor laterality were found. The height and transverse and sagittal diameters of the C4 vertebral body increased logarithmically as: y = -3.866 + 2.225 × ln(Age) ± 0.238 (R(2) = 0.69), y = -7.077 + 3.547 × ln(Age) ± 0.356 (R(2) = 0.72) and y = -3.886 + 2.272 × ln(Age) ± 0.222 (R(2) = 0.73), respectively. The C4 vertebral body grew linearly in cross-sectional area as y = -7.205 + 0.812 × Age ± 1.668 (R(2) = 0.76) and four-degree polynomially in volume as y = 14.108 + 0.00007 × Age(4) ± 6.289 (R(2) = 0.83). The transverse and sagittal diameters, cross-sectional area and volume of the ossification center of the C4 vertebral body generated the following functions: y = -8.836 + 3.708 × ln(Age) ± 0.334 (R(2) = 0.76), y = -7.748 + 3.240 × ln(Age) ± 0.237 (R(2) = 0.83), y = -4.690 + 0.437 × Age ± 1.172 (R(2) = 0.63) and y = -5.917 + 0.582 × Age ± 1.157 (R(2) = 0.77), respectively. The ossification center-to-vertebral body volume ratio gradually declined with age. On the right and left, the neural ossification centers showed the following growth: y = -19.601 + 8.018 × ln(Age) ± 0.369 (R(2) = 0.92) and y = -15.804 + 6.912 × ln(Age) ± 0.471 (R (2) = 0.85) for length, y = -5.806 + 2.587 × ln(Age) ± 0.146 (R(2) = 0.88) and y = -5.621 + 2.519 × ln(Age) ± 0.146 (R(2) = 0.88) for width, y = -9.188 + 0.856 × Age ± 2.174 (R(2) = 0.67) and y = -7.570 + 0.768 × Age ± 2.200 (R(2) = 0.60) for cross-sectional area, and y = -13.802 + 1.222 × Age ± 1.872 (R(2) = 0.84) and y = -11.038 + 1.061 × Age ± 1.964 (R(2) = 0.80) for volume, respectively.

CONCLUSIONS

The morphometric parameters of vertebra C4 and its three ossification centers show no sex differences. The C4 vertebral body increases logarithmically in height and both sagittal and transverse diameters, linearly in cross-sectional area, and four-degree polynomially in volume. The three ossification centers of vertebra C4 grow logarithmically in both transverse and sagittal diameters, and linearly in both cross-sectional area and volume. The age-specific reference intervals for evolving vertebra C4 may be useful in the prenatal diagnosis of congenital spinal defects.

Contribution of the anterior longitudinal ligament to ossification and growth of the vertebral body: an immunohistochemical study using the human fetal lumbar vertebrae

Using 15 mid-term human fetuses, we examined the role of the spine anterior and posterior longitudinal ligaments (ALL, PLL) in ossification of the lumbar vertebral body. By 18 weeks, a pair of calcified tissue or cortical walls had developed on the anterior and posterior sides of the ossification center. These calcified cortical walls were more highly eosinophilic than trabecular or woven bone in the ossification center. Vimentin-positive osteoblasts were arranged in line along the outer surface of the walls. However, few CD68-positive osteoclasts were evident around the walls, suggesting that the calcification in the walls was similar to periosteal ossification. The anterior cortical wall was connected tightly with the ALL by fiber bundles, but the posterior wall was separated from the PLL by the basivertebral (central) vein and loose tissues. Notably, by 30 weeks, the anterior cortical wall had become attached to and incorporated into the ALL. Thus, the ALL seemed to act as an active periosteum for ossification. Although our materials were limited in number and stage, we hypothesized that, in contrast to the PLL, the mature anterior cortical wall corresponds to a calcified fibrocartilage adjacent to the ALL and forms a bone-ligament interface maintaining an ossification potential.

An immunohistochemical study of the tissue bridging adult spondylolytic defects--the presence and significance of fibrocartilaginous entheses

Introduction Spondylolytic spondylolisthesis is an osseous discontinuity of the vertebral arch that predominantly affects the fifth lumbar vertebra. Biomechanical factors are closely related to the condition. An immunohistochemical investigation of lysis-zone tissue obtained from patients with isthmic spondylolisthesis was performed to determine the molecular composition of the lysis-zone tissue and enable interpretation of the mechanical demands to which the tissue is subject.

METHODS

During surgery, the tissue filling the spondylytic defects was removed from 13 patients. Twelve spondylolistheses were at the L5/S1 level with slippage being less than Meyerding grade II. Samples were methanol fixed, decalcified and cryosectioned. Sections were labelled with a panel of monoclonal antibodies directed against collagens, glycosaminoglycans and proteoglycans.

RESULTS

The lysis-zone tissue had an ordered collagenous structure with distinct fibrocartilaginous entheses at both ends. Typically, these had zones of calcified and uncalcified fibrocartilage labelling strongly for type II collagen and aggrecan. Labelling was also detected around bony spurs that extended from the enthesis into the lysis-zone. The entheses also labelled for types I, III and VI collagens, chondroitin four and six sulfate, keratan and dermatan sulfate, link protein, versican and tenascin.

CONCLUSIONS

Although the gap filled by the lysis tissue is a pathological feature, the tissue itself has hallmarks of a normal ligament-i.e. fibrocartilaginous entheses at either end of an ordered collagenous fibre structure. The fibrocartilage is believed to dissipate stress concentration at the hard/soft tissue boundary. The widespread occurrence of molecules typical of cartilage in the attachment of the lysis tissue, suggests that compressive and shear forces are present to which the enthesis is adapted, in addition to the expected tensile forces across the spondylolysis. Such a combination of tensile, shear and compressive forces must operate whenever there is any opening or closing of the spondylolytic gap.

Fetal spine ossification: the gender and individual differences illustrated by ultrasonography

The spatial and temporal pattern of manifestation of ossification nuclei of the spinal column in fetal life have been well established by histologic and radiologic studies. Sonographic evaluation of the fetal spine depends on visualization of the ossification centers, but the sequence of development of ossification centers in the vertebral column obtained by embryologists and sonographers and radiology are conflicting. We carried out a longitudinal study to establish the ultrasonographic appearance and timing of development of primary ossification centers of the fetal spine in the first and second trimesters of pregnancy. A total of 80 mothers were evaluated during their pregnancy with two echographic controls; in the first trimester, the spine length was measured and, in the second trimester of pregnancy, the timing of ossification of the bodies and neural arches of sacral vertebrae and the difference in appearance between the female and male genders were evaluated. Spinal length measurements obtained in the first trimester and percentage of detection of sacral vertebral structures increased progressively with a regular pattern in relation to gestational age. Spinal length at first ultrasound examination was slightly correlated with time of appearance of sacral bodies and arches. Ossification timing was significantly earlier in females than in males. The study has attempted to improve our understanding of the sonographic detection of the spinal ossification. Data presented give some further information on the stages of appearance of sacral vertebrae body centers during intrauterine development. Differences between genders and interindividual variations in ossification timing were observed at a very early stage of development. This could be of value when fetal growth is evaluated. Moreover, further knowledge of spinal development may be useful for early diagnosis of spinal abnormalities and for fetal biometrics.

Ossification timing of sacral vertebrae by ultrasound in the mid-second trimester of pregnancy

OBJECTIVES

The aim of the study was to establish the ossification timing of sacral vertebrae by ultrasonography in the second trimester of pregnancy, for the diagnosis of caudal regression syndrome with isolated sacral agenesis.

METHODS

The study was carried out on 77 normal single pregnancies, at gestational ages ranging from 15 to 21 weeks, using high-resolution transabdominal echography. The sacral region was visualized in a coronal plane, when the fetus was in anterodorsal position. The level of ossification of sacral vertebrae (S1 to S5) at each gestational age was recorded. Each sacral region was examined three times by the same observer and the nucleus was considered as present when it was visualized at least two times out of three. Blind assessment was performed three times by a second observer, who was not present at the previous examination, for interobserver and intraobserver error analysis.

RESULTS

Interobserver and intraobserver error calculation demonstrated the reproducibility of the method. Concordance between the two observers as evaluated by Cohen Kappa index was 0.77 (C.I. 95%, 0.69-0.85).S1 ossification nuclei were visualized in all fetuses at 15 weeks and S2 nucleus was found in all fetuses within 17 weeks. S3 nucleus was detected in 45% of fetuses by the beginning of the 16th week. S4 was visualized in 55% of the cases at 18 weeks and progressively in a higher percentage of cases during the following weeks of gestation.

CONCLUSION

The data obtained showed that the sequence of development of sacral region ossification was related to gestational age. This observation allows clinicians to accurately exclude isolated sacral agenesis at 16 to 17 weeks of gestation, when the S1-S2 ossification nuclei are visualized. This opportunity may be of particular value in the offspring of diabetic mothers.

Spine length measurement in the first trimester of pregnancy

OBJECTIVES

The aim of the study was to evaluate spine length as an indicator of skeletal growth in the first trimester of pregnancy and to provide a nomogram of spine length at the end of the first trimester of pregnancy.

METHODS

The study was carried out on 420 single pregnancies, at gestational ages ranging from 11 to 14 weeks, using high-resolution transabdominal echography. Biparietal diameter and crown-rump length (CRL) were measured to date the pregnancy. Using the same scanning plane used to measure CRL, the whole spine length in antero-dorsal position can be visualized as a double hyperechoic line from 10 weeks of gestation onwards. Spine length was measured three times by one observer and the mean of the three measurements was considered as definitive. Forty fetuses had multiple measurements for interobserver and intraobserver error analysis.

RESULTS

Linear relationship between spine length, and gestational age, biparietal diameter and CRL were demonstrated. Spine length (millimetres) as a function of gestational age (days) was expressed by the regression equation: spine length = 1.09 x (gestational age in days) -60.56, with a determination coefficient of R(2) = 0.744. Spine length ranged from 21.5 mm at 11 weeks to 41.9 mm at 14 weeks.

CONCLUSION

The data obtained showed that spine length increased progressively from the end of the first trimester to the beginning of the second. A high correlation between spine length, gestational age, biparietal diameter, and CRL was observed. Spine length measurement could therefore be considered a good indicator of fetal growth.

Prenatal development of the normal human vertebral corpora in different segments of the spine

STUDY DESIGN

Vertebral columns from 13 normal human fetuses (10-24 weeks of gestation) that had aborted spontaneously were investigated as part of the legal autopsy procedure. The investigation included spinal cord analysis.

OBJECTIVES

To analyze the formation of the normal human vertebral corpora along the spine, including the early location and disappearance of the notochord.

SUMMARY OF BACKGROUND DATA

Reference material on the development of the normal human vertebral corpora is needed for interpretation of published observations on prenatal malformations in the spine, which include observations of various types of malformation (anencephaly, spina bifida) and various genotypes (trisomy 18, 21 and 13, as well as triploidy).

METHODS

The vertebral columns were studied by using radiography (Faxitron X-ray apparatus, Faxitron Model 43,855, Hewlett Packard) in lateral, frontal, and axial views and histology (decalcification, followed by toluidine blue and alcian blue staining) in and axial view. Immunohistochemical marking with Keratin Wide Spectrum also was done.

RESULTS

Notochordal tissue (positive on marking with Keratin Wide Spectrum [DAKO, Denmark]) was located anterior to the cartilaginous body center in the youngest fetuses. The process of disintegration of the notochord and the morphology of the osseous vertebral corpora in the lumbosacral, thoracic, and cervical segments are described. Marked differences appeared in axial views, which were verified on horizontal histologic sections. Also, the increase in size was different in the different segments, being most pronounced in the thoracic and upper lumbar bodies. The lower thoracic bodies were the first to ossify. The morphologic changes observed by radiography were verified histologically.

CONCLUSIONS

In this study, normal prenatal standards were established for the early development of the vertebral column. These standards can be used in the future--for evaluation of pathologic deviations in the human vertebral column in the second trimester.

Neuro-osteology

Neuro-osteology stresses the biological connection during development between nerve and hard tissues. It is a perspective that has developed since associations were first described between pre-natal peripheral nerve tissue and initial osseous bone formation in the craniofacial skeleton (Kjaer, 1990a). In this review, the normal connection between the central nervous system and the axial skeleton and between the peripheral nervous system and jaw formation are first discussed. The early central nervous system (the neural tube) and the axial skeleton from the lumbosacral region to the sella turcica forms a unit, since both types of tissue are developmentally dependent upon the notochord. In different neurological disorders, the axial skeleton, including the pituitary gland, is malformed in different ways along the original course of the notochord. Anterior to the pituitary gland/sella turcica region, the craniofacial skeleton develops from prechordal cartilage, invading mesoderm and neural crest cells. Also, abnormal development in the craniofacial region, such as tooth agenesis, is analyzed neuro-osteologically. Results from pre-natal investigations provide information on the post-natal diagnosis of children with congenital developmental disorders in the central nervous system. Examples of these are myelomeningocele and holoprosencephaly. Three steps are important in clinical neuro-osteology: (1) clinical definition of the region of an osseous or dental malformation, (2) embryological determination of the origin of that region and recollection of which neurological structure has developed from the same region, and (3) clinical diagnosis of this neurological structure. If neurological malformation is the first symptom, step 2 results in the determination of the osseous region involved, which in step 3 is analyzed clinically. The relevance of future neuro-osteological diagnostics is emphasized.

Sequential order of appearance of ossification centers in the opossum Didelphis albiventris (Didelphidae) skeleton during development in the marsupium

Pouch-young of the opossum Didelphis albiventris were studied. They were removed from the marsupium at a crown-rump length (CRL) of 9.0 to 100.0 mm and submitted to differential staining of the bone and cartilage. Newborn D. albiventris of 9.0 to 10.0 mm CRL have a cartilaginous skeleton, with no macroscopic evidence of ossification. In 10.5 to 13.0 mm CRL pouch-young, ossification occurs in the bones surrounding the oral cavity, clavicle, ribs, cervical and thoracic vertebrae and thoracic limbs, structures necessary to ensure the survival and maintenance of the newborn in the marsupium. Ossification of most of the skull begins in 15.5 to 16.0 mm CRL pouch-young. The ossification in the pelvis and the pelvic limbs is observed at 18.0 mm CRL and in the sternum and the epipubic bone at 25.0 to 28.0 mm CRL. Most of the skeleton is ossified in 45.0 to 58.0 mm CRL pouch-young, except in the carpus, tarsus and epiphyses of the long bones where ossification occurs in 60.0 to 100.0 mm CRL pouch-young. In the skeleton of D. albiventris the omosternum, haemal arches, prepollex, prehallux and parafibula, are present. These are inconstant or absent elements in eutherian mammals.

The architecture of internal blood vessels in human fetal vertebral bodies

The internal vascular system of vertebral bodies was investigated in 17-24 wk human fetuses by acrylic dye injection and by corrosion casting/scanning electron microscopy. The regions of intervertebral spaces did not contain blood vessels. The radial metaphyseal vessels were at the stage of centripetal ingrowth into the vertebral body cartilage and their terminal, blindly ending segments had a form of cuff-like capillary plexuses. The anterolateral equatorial arteries communicating with the vessels of the ossification centre were only rarely found. The centre was usually supplied by 2 posterior (nutrient) arteries which branched into an arcade-like array of arterioles equipped with occasional sphincters and giving origin to a dense network of peripherally located capillaries. Numerous blind capillary buds formed the advancing border of the ossification centre. The veins usually accompanied the arteries. In the ossification centre the venous compartment consisted of sinuses drained by larger posterior veins. In the 17 wk fetus, an axial avascular area was observed in the place of notochord localisation, indicating the formation of a ring-shaped ossification centre around the notochord remnants at earlier stages of fetal development.

On the assessment of the growth patterns in human fetal limbs: longitudinal measurements and allometric analysis

The total length (TL) and length of the ossified part (OL) of some long bones of the upper (humerus, ulna, radius) and lower limb (femur, tibia, fibula) were evaluated in 58 aborted human fetuses (crown-rump length, CRL, between 38 and 116 mm, developmental age from 8 to 14 weeks). The specimens, without any detectable malformation, were cleared and double-stained with alcian blue and alizarin red S to obtain a differential detection of the ossified part within the comprehensive outline between the cartilaginous epiphyses. The correlation between the values of TL and OL and those of CRL emphasized that the systematic OL measurement in limb long bones correlated better than TL with development age, since OL increased faster than TL. TL and OL also correlated with the CRL by bivariate allometry (ln y = ln a + b ln x) and the data obtained showed that they grew with positive allometry. The comparison between the cumulative values of the bones examined in each limb showed that both TL and OL grew relatively faster in the lower limb than the upper; the greatest growth rate was found for OL in the lower limb. These results many provide a tool for a comprehensive assessment of long bone growth patterns and may be useful in determining fetal growth even in incomplete specimens, in which one or some long bones can still be measured.