Prenatal evaluation of the conus medullaris position in normal fetuses and fetuses with spina bifida occulta using three-dimensional ultrasonography

Utility of routine mid-trimester fetal ultrasound scan in detecting filar cysts and follow-up outcomes

PURPOSE

To assess the value of routine mid-trimester fetal ultrasound scans in detecting FCs, as well as the related ultrasound and clinical follow-up outcomes.

METHODS

A retrospective analysis was conducted on 1064 fetuses who underwent standardized ultrasound screening during the mid-trimester. During the examination, high-frequency ultrasound was used to examine the fetal spine. Different frequency ultrasound probes were used to compare and analyze the detection rates of FCs. We conducted follow-up ultrasound observations on all FCs and conducted long-term follow-up observations in terms of the motor function of the children after birth.

RESULTS

Among 1064 fetuses detected by ultrasound, a total of 910 fetuses were completely evaluated using high-frequency and low-frequency ultrasound, and 24 FCs were found. In all 24 cases of FCs, 7 cases were detected using low-frequency ultrasound, while high-frequency ultrasound detected all cases. There was a significant difference in the detection rates between the two groups (χ2 = 26.323, P = 0.000). Of all the 24 FCs, 21 cysts disappeared spontaneously (87.5%); one fetus was induced for abortion due to a concurrent cleft lip; after multiple ultrasound examinations, it was found that the cyst persisted in one fetus; one case was not followed up by ultrasound. There was no statistically significant difference in the start of sitting and crawling time between the control group and the FCs group.

CONCLUSION

Routine mid-trimester fetal ultrasound scan detect FCs, particularly when high-frequency ultrasound probes were routinely applied. Most FCs detected by prenatal ultrasound spontaneously disappear and have no impact on the motor function of the fetus after birth (with the conus medullaris located at or above the L3 level). The shortest time interval from the detection to the disappearance of the cyst was 11 days.

Comparison between MRI and the Combination of 2D and 3D US in the Prenatal Diagnosis of Closed Spina Bifida

INTRODUCTION

Closed spina bifida (CSB) is a rare condition with a challenging prenatal diagnosis. Herein, we assess the conventional two-dimensional (2D) ultrasound (US) combined with three-dimensional (3D) ultrasound (US) and magnetic resonance imaging (MRI) in the prenatal diagnosis of CSB.

METHODS

In this retrospective study, we included 20 cases of fetal CSB confirmed by postnatal MRI, post-mortem pathological examination, or postpartum surgery. Prenatal 2D US complemented with the 3D US was performed in all fetuses to evaluate the characteristics of the conus, vertebral arch, and scoliosis. Moreover, MRI was performed to establish the split vertebrae, with or without a bulging mass. Thereafter, we compared the performance of the US and MRI.

RESULTS

Diagnosis accuracy of US was comparable with MRI (70% vs. 75%, κ = 0.62); US detected more cases with interpediculate distance ≥95% (55% vs. 35%, κ = 0.22) than MRI. On the other hand, MRI had a superior capacity for identifying vertebral arch fissures (20% vs. 35%, κ = 0.39). MRI and ultrasound had good agreement in the conus medullaris (65% vs. 70%, κ = 0.42) and scoliosis (45% vs. 35%, κ = 0.59). Both US and MRI detected 1 (5.0%) case with "lemon sign" and "banana sign." The missed diagnosis rates of US and MRI were 15% (3/20) and 5% (1/20), respectively. The misdiagnosis rates of US and MRI were 15.0% (3/20) and 20.0% (4/20), respectively.

CONCLUSION

Both MRI and 2D US combined with the 3D US had excellent performance in prenatal diagnosis of CSB.

Fetal Tethered Spinal Cord: Diagnostic Features and Its Association with Congenital Anomalies

OBJECTIVE

We assessed the frequency and type of associated congenital anomalies encountered with fetal tethered spinal cord (TSC) determined prenatally.

METHOD

A retrospective review was conducted based on the associated fetal abnormalities following diagnosis of low-lying fetal conus medullaris during the prenatal ultrasound.

RESULTS

Of the 26 fetuses with low-lying conus medullaris, four were solitary TSC and 22 had TSC combined with associated congenital malformations, including four cases with spina bifida occulta, four cases with spina bifida aperta, one case with severe hydrocephalus, and 13 cases with multisystem congenital malformations. Among all the 13 cases with combined multisystem congenital malformations, four cases had vertebral defects, anal anomalies, cardiac defects, trachea-esophageal fistula, renal anomalies, and limb anomalies (VACTERL) syndrome, two cases had combined kidney development abnormalities, one case had cloacal exstrophy (OEIS syndrome), and six cases had chromosomal abnormalities (one case of chromosome 7q deletion, two cases of trisomy 13 syndrome, one case of trisomy 18 syndrome, one case of trisomy 9 syndrome, and one case of chromosome 4p deletion).

CONCLUSIONS

Low-lying conus medullaris found during prenatal ultrasound examination were often associated with neural tube malformations or multi-systemic complex developmental malformations. The frequency of chromosomal abnormalities was 23.1%.

Prenatal assessment and pregnancy outcomes of foetal low-lying conus medullaris using 3D ultrasound

OBJECTIVES

This study aims to follow up on low-lying conus medullaris (CM) cases and explore the correlation between the CM location and the final prognosis.  METHODS: We retrospectively collected 37 cases diagnosed with low-lying CM during pregnancy in the Peking University First Hospital from January 2019 to December 2020. The location of CM was confirmed by 3D ultrasonography, and clinical data, including postnatal outcomes, were recorded. When the conus medullaris was below L3 (excluding L3), it was diagnosed as low-lying conus medullaris, regardless of gestational age. The short-term postnatal outcome included assessment of symptoms and signs of motor and sensory neuron dysfunction.

RESULTS

The average gestational weeks of low-lying diagnosis was between 23 and 24 weeks. Among 37 cases, nine (24.3%) were complicated with spine dysraphism (3 cases of open spina bifida, 6 cases of tethered cord syndrome). Apart from 7 cases of pregnancy termination, the remaining 30 live births had a good prognosis in the short term, though 5 out of 6 cases of tethered cord syndrome underwent surgical release. The mean location of cases of open spinal dysraphism (n = 3) and those of closed dysraphism/tethered cord syndrome (n = 6) was at Lumber vertebra 5 (L5) and between L5 and Sacral vertebra 1 (S1), respectively, which showed statistical significance compared with the postnatally normal group. When we set Lumber 4.25 as the cut-off value to predict the diagnosis of spine dysraphism (mainly involving open spinal dysraphism and closed spinal dysraphism/tethered cord syndrome), the sensitivity was 66.7. At the same time, the specificity was 96%, along with the area under the curve (AUC) at 0.877.

CONCLUSION

The second trimester finding of low CM is associated with spinal defects, mainly open spinal dysraphism and closed spinal dysraphism/tethered cord syndrome. Careful assessment of the fetal spine should be considered especially when the location of CM is lower than L4.

Ascent of the conus medullaris in human foetuses: a systematic review and meta-analysis

The aim of the present systematic review and meta-analysis was to identify when the ascent of the conus medullaris occurs in human foetuses considering differences in evaluation methods and sample characteristics. Five databases were searched for relevant articles using different combinations of keywords. Article selection and data extraction were performed independently by two reviewers. Disagreements were resolved by a third reviewer. The variables were distributed into four groups according to the gestational age of the specimens: I (13-18 weeks); II (19-25 weeks); III (26-32 weeks); IV (33 weeks to the probable date of birth). Eighteen articles were included. The majority used imaging exams as the evaluation method. Cadaveric dissections were reported in the remaining articles. Only morphological studies were included in the meta-analysis. Significant ascent occurs between groups I and III as well as groups II and IV. Despite the considerable heterogeneity among the studies included in the present review, the findings enabled the determination that the conus medullaris reaches its normal birth level by the 26th week. Further analyses should be performed based on nationality and ethnicity to diminish the heterogeneity of the data.

Three-Dimensional Sonographic Evaluation of the Position of the Fetal Conus Medullaris at First Trimester

OBJECTIVE

The objective of this study was to assess the position of the conus medullaris (CM) at the first trimester 3D ultrasound in a cohort of structurally normal fetuses.

METHODS

This was a multicenter prospective study involving a consecutive series of structurally normal fetuses between 11 and 13 weeks of gestation (CRL between 45 and 84 mm). All fetuses were submitted to 3D transvaginal ultrasound using a sagittal view of the spine as the starting plane of acquisition. At offline analysis, the position of the CM was evaluated by 2 independent operators with a quantitative and a qualitative method: (1) the distance between the most caudal part of the CM and the distal end of the coccyx (CMCd) was measured; (2) a line perpendicular to the fetal spine joining the tip of the CM to the anterior abdominal wall was traced to determine the level of this line in relation to the umbilical cord insertion (conus to abdomen line, CAL). Interobserver agreement for the CCMd was evaluated. Linear regression analysis was used to determine the association between the CMCd and CRL, and a normal range was computed based on the best-fit model. The absence of congenital anomalies was confirmed in all cases after birth.

RESULTS

In the study period between December 2019 and March 2020, 143 fetuses were recruited. In 130 fetuses (90.9%), the visualization of the CM was feasible. The mean value of the CMCd was 1.09 ± 0.16 cm. The 95% limits of agreement for the interobserver variability in measurement of the CMCd were 0.24 and 0.26 cm. The interobserver variability based on the intra-class correlation coefficient (ICC) for the CCMd was good (ICC = 0.81). We found a positive linear relationship between the CCMd and CRL. In all these fetuses, the CAL encountered the abdominal wall at or above the level of the cord insertion.

CONCLUSION

In normal fetuses, the assessment of the CM position is feasible at the first trimester 3D ultrasound with a good interobserver agreement. The CM level was never found below the fetal umbilical cord insertion, while the CMCd was noted to increase according to the gestational age, confirming the "ascension" of the CM during fetal life.

MRI characteristics of the fetal tethered spinal cord: a comparative study

Purpose: To compare fetuses and children with confirmed tethered cord syndrome to age-matched controls to provide a reference for prenatally identifying tethered spinal cord and to identify salient points on MRI for diagnosis.Materials and Methods: This retrospective study enrolled 13 fetuses and 20 children with tethered cord syndrome, and age-matched counterparts were included as controls. The MRI features including concomitant malformations, position of the conus medullaris, and thickened filum terminale of the two patient groups were evaluated and compared. Levels of the conus medullaris were discriminated between patients and an equivalent number of controls.Results: Various concomitant malformations manifested on the MRI of all patients, and there were differences between the two patient groups. Significant differences of the level of the conus medullaris were found between the fetal and child patients (U, 26.50; Z, -3.87; p < 0.001) and between the normal fetus and child controls (U, 23.50; Z, -4.13; p < 0.001). The position of the conus medullaris was visibly lower in the patient groups than in the control groups. No significant difference in the diameters of the filum terminale was found between the fetal and child patients (p = 0.67).Conclusions: The current study's results indicate that tethered spinal cord syndrome can be diagnosed in utero with MRI combined with several characteristics, particularly the position of the conus medullaris. Special attention should be paid to the gestational age of the fetus because normal changes in spinal cord position occur with gestational development.

Measurement of fetal conus distance with 3D ultrasonography as a reliable prenatal diagnosis method for tethered cord syndrome

AIM

The aim of this study is to investigate if three-dimensional (3D) ultrasonography is a reliable diagnosis method for prenatal tethered cord syndrome (TCS) by measuring fetal conus distance (CD) in comparison to two-dimensional (2D) ultrasonography and magnetic resonance imaging (MRI).

METHODS

This retrospective study included 468 normal fetuses as control group and 14 TCS fetuses as tethered group. CD were measured by 2D, 3D ultrasonography and MRI, and the reliability and repeatability of CD measurement was compared between two experienced ultrasound specialists or among the multiple measurements for each specialist.

RESULTS

The results showed that 3D ultrasonography was superior to 2D ultrasonography in the repeatability of measuring CD. The CD were positively correlated to gestational ages in control group (P < 0.05). The CD of TCS group (-1.342 ± 0.124) was significantly shorter than that of normal control group (0.013 ± 0.965) (P < 0.01). There were no significant differences in the effectiveness of locating conus medullaris and measuring CD between 3D ultrasonography and MRI.Conclusion Measurement of fetal CD with 3D ultrasonography can serve as a reliable and cost-effective prenatal diagnosis method for TCS.

A method for quantitative 2-dimensional sonographic analysis of the fetal conus medullaris position

OBJECTIVE

This study explored the use of 2-dimensional (2D) ultrasound scans for the quantitative assessment of the fetal conus medullaris (CM) position and its correlation with gestational age (GA).

METHODS

This was a prospective study. We identified the first sacral vertebra (S1) by intersection of 2 lines in 2D scans, then counted upward from S1 to determine the CM level and recorded the number of ossified sacral vertebral bodies. A quantitative assessment of the CM position was performed by measuring the distance between the CM and the midpoint of the S1 (CM-S1). The correlation between the CM-S1 distance and GA was evaluated.

RESULTS

We determined the CM level by identifying S1 first in 521 fetuses (GA, 20-38 weeks). The CM position in 70% of cases was at the L2 and L2-3 level, and at the L2 level or above after 37 weeks. The number of ossified sacral veterbral bodies was not consistent. CM-S1 measurements were easy to perform. A significant positive correlation between CM-S1 distance and GA was observed (R²  = .89, P < .05). The best-fit formula was: CM-S1 distance = 1.57 × GA - 16.43. The normal reference range was established and the fifth percentile was calculated for each GA.

CONCLUSIONS

S1 was easily identified, and the CM position relative to S1 was useful. There was a substantial correlation between CM-S1 and GA. Below the fifth percentile it was suggested that tethered cord may exist.

Prenatal Assessment of the Position of Fetal Conus Medullaris as a Predictor of Fetal Spinal Lesions

OBJECTIVES

The aim of this study is to compare two different methods in assessment of the position of fetal conus medullaris (CM) and to explore the significance for assessment of CM.

METHODS

This study included both normal fetuses and those with the diagnosis of fetal spinal lesions. The position of fetal CM was performed sonographically using two methods: location of CM in relation to the vertebral body (CM level) and measurement of the conus sacrum (CS) distance.

RESULTS

The results showed that intra-observer and interobserver concordance was high for the two methods, both in the normal and abnormal groups. There was significant association between femur length and CS distance (R²  = 0.917) and between gestational age and CS distance (R²  = 0.892).

CONCLUSIONS

We propose the combined use of CM level location and CS distance measurement for the prenatal diagnosis of fetal spinal lesions for complementary needs.

Evaluation and management of tethered cord syndrome in occult spinal dysraphism: Recommendations from the international children's continence society

AIMS

As awareness and frequency of tethered spinal cord (TSC) related to occult spinal dysraphism (OSD) has increased with magnetic resonance imaging (MRI), variability exists in its evaluation and management. Due to no published level I data, we summarize the current International Children's Continence Society (ICCS) recommendations for diagnosis and treatment of OSD.

METHODS

Guidelines were formulated based on analysis of pertinent literature and consensus among authors. This document was vetted by the multidisciplinary members of the ICCS via its website before submission for peer review publication.

RESULTS

The more frequent diagnosis of OSD is associated with increased operative intervention. Spinal cord untethering (SCU) has a highly variable risk profile, largely dependent on the specific form of OSD. Progressive neurological deterioration attributed to "tethered cord" may occur, with or without surgery, in selected forms of OSD whereas other cohorts do well.

CONCLUSION

Infants with classic cutaneous markers of OSD, with progressive neurologic, skeletal, and/or urologic findings, present no diagnostic or therapeutic dilemma: they routinely undergo MRI and SCU. Conversely, in asymptomatic patients or those with fixed, minor abnormalities, the risk profile of these OSD cohorts should be carefully considered before SCU is performed. Irrespective of whether or not SCU is performed, patients at risk for progression should be followed carefully throughout childhood and adolescence by a multidisciplinary team.

Localization of the fetal conus medullaris by oblique view extended imaging

OBJECTIVE

To evaluate the accuracy of oblique view extended imaging (OVEI) in locating the position of the fetal conus medullaris.

METHODS

One hundred and twenty-two normal fetuses and five counterparts with spinal bifida received prenatal ultrasound examination. The vertebral body at the terminal of the conus medullaris and the coronal section of over five vertebral bodies were reconstructed using OVEI. Development of the nervous system of normal fetuses was assessed at postnatal day 28. For spinal bifida cases, pathological examination was performed.

RESULTS

Among 127 fetuses, the conus medullaris was accurately positioned in 120 (94.0%) cases according to OVEI. OVEI failed to locate the conus medullaris in three healthy fetuses due to obesity of the mother and four cases with spinal bifida due to abnormal fetal position. The conus medullaris was located at L3 or above in 115 healthy fetuses. The conus medullaris was positioned below L4 in five fetuses with spinal bifida, including L5 in two, S1 in two, and S3 in one, which was consistent with the findings of pathological examination.

CONCLUSIONS

OVEI can display the 12th rib, T12, and conus medullaris simultaneously. OVEI is applicable to precisely locate the position of the conus medullaris and useful for prenatal evaluation of spinal bifida.

Three-dimensional ultrasound of the fetus: how does it help?

Three-dimensional ultrasonography (3-D US) was introduced to the field of fetal imaging in the early 1990s. Since then several publications have described potential applications for the diagnosis of congenital malformations as well as organ volumetry. This article reviews basic principles of 3-D US as well as its clinical applicability to prenatal diagnosis of abnormalities involving the face, spine and skeletal system, as well as potential applications of 3-D US for fetal cardiovascular and neuroimaging. Limitations related to motion artifacts, acoustic shadowing and barriers to clinical implementation of 3-D US in clinical practice are addressed.

Prenatal Evaluation of the Fetal Conus Medullaris on a Routine Scan

Objective: To assess the ability to identify the conus medullaris (CM) and measure the conus-sacrum distance (CS distance) on a routine scan and the relationship with maternal and fetal factors. Methods: This was a prospective study. The assessment of the CM and the CS distance and the influence of the body mass index (BMI), gestational age (GA) and fetal position were analyzed. The correlation between the femur length (FL) and the GA with the CS distance was evaluated. Results: A total of 696 fetuses were analyzed. The CM could be visualized in 82.3% of the cases, and the CS distance could be analyzed in 81.2% of the cases. The CM assessment was statistically associated with BMI and fetal position but not with GA. The CS distance assessment was statistically associated with BMI and GA but not with fetal position. We determined a significant association between the FL/CS distance and between the GA/CS distance. Conclusions: Assessment of the CM is possible on most routine scans. The CS distance could be introduced to routine scans for the assessment of prenatal skin-covered spinal dysraphism. High BMI, advanced GA and breech presentation could be potential factors limiting the feasibility of evaluating the CM.

Physical model from 3D ultrasound and magnetic resonance imaging scan data reconstruction of lumbosacral myelomeningocele in a fetus with Chiari II malformation

Rapid prototyping is becoming a fast-growing and valuable technique for physical models in case of congenital anomalies. Manufacturing models are generally built from three-dimensional (3D) ultrasound, computed tomography, and fetal magnetic resonance imaging (MRI) scan data. Physical prototype has demonstrated to be clinically of value in case of complex fetal malformations and may improve antenatal management especially in cases of craniosynostosis, orofacial clefts, and giant epignathus. In addition, it may enhance parental bonding in visually impaired parents and have didactic value in teaching program. Hereby, the first 3D physical model from 3D ultrasound and MRI scan data reconstruction of lumbosacral myelomeningocele in a third trimester fetus affected by Chiari II malformation is reported.