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. 2024;32(3):1371-1382.
doi: 10.3233/THC-230332.

Ultrasound-based horizontal ranging in the localization of fetal conus medullaris

Xiuping Liu  1 , Ping Li  1 , Yuemin Yang  1 , Cheng Tian  2
Affiliations

Ultrasound-based horizontal ranging in the localization of fetal conus medullaris

Xiuping Liu et al. Technol Health Care. 2024.

Expression of concern in

  • Expression of concern.
    [No authors listed] [No authors listed] Technol Health Care. 2025 Nov 12:9287329251392360. doi: 10.1177/09287329251392360. Online ahead of print. Technol Health Care. 2025. PMID: 41223024 No abstract available.

Abstract

Background: Currently, there are a variety of methods for ultrasound to localize the conus medullaris. A concern is that measured values can be influenced by variations in spinal flexion and extension.

Objective: To overcome this limitation, the present study measures the horizontal distance (HD) between the end of the conus medullaris and the caudal edge of last vertebral body ossification in normal fetus at different gestational weeks, and analyzes the relationship between the measured value and fetal growth, as well as the utility of these measurements in assessing the position of the conus medullaris.

Methods: A total of 655 fetuses at gestational weeks 18-40, who underwent routine prenatal ultrasound, were selected in the study. We measured the distance between the end of the cone of the fetal spinal cord and the caudal end of the final vertebral ossification center (Distance1, D1), the distance between the end of the spinal cord cone and the intersection of the extension of D1 with the caudal skin (Distance2, D2), and HD. We analyzed the correlation between the measurements and gestational weeks, established normal reference values, the ratio of D1, D2 and HD to the commonly used growth parameters was calculated. The ratios of D1, D2, HD and the application value of each ratio phase were analyzed, and the reliability analysis of repeated measurement results among physicians was performed.

Results: D1, D2 and HD exhibited strong linear correlations with gestational weeks. Among the ratios of D1, D2 and HD to common growth parameters, D2/FL stabilized after 20 weeks of gestation and consistently exceeded 1. Repeatability tests between D1, D2 and HD showed good reliability (P> 0.05).

Conclusion: D1, D2 and HD are significantly correlated with gestational age. Horizontal distance measurement can effectively determine the position of fetal conus medullaris, enabling rapid prenatal evaluation of low position of conus medullaris and excluding the possibility of tethered cord.

Keywords: Fetus; conus medullaris; tethered spinal cord; ultrasonic examination.

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Conflict of interest statement

None of the authors has any personal, financial, commercial, or academic conflicts of interest to report.

Figures

Figure 1.
Figure 1.
Measurement of D1, D2 and HD ultrasound schematic diagram. The distance between A and B is D1. The distance between A and C is D2. The distance between a and b is HD. Point A (also marked as “a”) stands for the end of the fetal conus medullaris, point B stands for the caudal end of the ossification center of the terminal vertebral body, point C is the intersection of the D1 extension and the caudal skin, point b is the intersection of the horizontal line passing through point A (or a) and the vertical line passing through point B.
Figure 2.
Figure 2.
Correlation between D1 and gestational age and reference range.
Figure 3.
Figure 3.
Correlation between D2 and gestational age and reference range.
Figure 4.
Figure 4.
Correlation between HD and gestational age and reference range.
See this image and copyright information in PMC

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