Highlights
In a 12-year tertiary-centre cohort of 187 fetuses with open spinal dysraphism, the motor level was more caudal than the anatomical level in 85.0% of cases.
The median anatomical-motor discrepancy was two vertebral segments, but the range was wide, extending from -3 to +15 segments.
Myeloschisis was associated with a larger discrepancy than myelomeningocele, while bilateral talipes and kyphosis were linked to smaller differences.
Higher anatomical lesions correlated with ventriculomegaly and vertebral anomalies, supporting the prognostic value of targeted prenatal imaging.
Study Background
Open spinal dysraphism, most commonly myelomeningocele and myeloschisis, remains one of the most important congenital neurologic conditions diagnosed prenatally. The exact spinal level of the lesion carries major prognostic implications because it influences lower-limb motor function, ambulatory potential, bladder and bowel outcomes, and the likelihood of associated complications such as hydrocephalus and Chiari II malformation. For parents considering fetal surgery, accurate prenatal level assessment is also central to counselling and eligibility discussions.
In clinical practice, however, the level seen on ultrasound does not always equal the neurologic level that will ultimately determine function. Anatomical level refers to the highest vertebra that is not fully closed, whereas motor level reflects the most caudal muscle group that remains active. These are related but not identical constructs. A fetus may have a higher anatomic defect with relatively preserved caudal motor function, or, less commonly, the apparent imaging level may underestimate neurologic involvement. Understanding this discrepancy matters because families and care teams often interpret prenatal reports as if anatomical and motor levels were interchangeable.
The study by Arévalo and colleagues addresses an important gap: how often does discordance occur, how large is it, and which prenatal findings help explain it?
Study Design
This was a retrospective observational study conducted at a single tertiary referral centre over 12 years, from 2011 to 2022. The cohort included 187 fetuses diagnosed with open spinal dysraphism on prenatal ultrasound.
The investigators defined the anatomical level as the highest non-closed vertebra identified by ultrasound. Motor level was determined through dynamic fetal assessment of the most caudal active muscle group. The primary endpoint was the difference between anatomical and motor levels. The study also examined whether lesion type and other prenatal characteristics were associated with the magnitude of the discrepancy after adjustment for anatomical level. In addition, the authors explored associations between anatomical level and ultrasound findings such as ventriculomegaly, vertebral anomalies, bilateral talipes, and kyphosis.
Because the analysis was retrospective and based on a tertiary referral cohort, the results are most directly applicable to specialist fetal imaging settings rather than unselected obstetric populations.
Key Findings
The principal result is clinically striking: in 85.0% of fetuses, the motor level was more caudal than the anatomical level. In practical terms, this means that the functional neurologic impairment inferred from dynamic fetal movement was often less severe than the structural lesion level might suggest. The median discrepancy was two vertebral segments, though the range was broad, from -3 to +15. That range indicates that some fetuses had motor levels more cranial than the anatomical level, while others had much more extensive discordance.
The magnitude of the discrepancy was not random. It was significantly greater in fetuses with myeloschisis compared with those with myelomeningocele, with an adjusted coefficient of 0.78 and a p value below 0.001. This suggests that lesion morphology matters when interpreting prenatal imaging. Myeloschisis is typically considered a more severe open defect, and the finding that it is associated with larger anatomical-motor gaps may reflect both developmental biology and the challenges of ultrasound-based functional inference in more severe lesions.
Two other prenatal features were associated with smaller discrepancies: bilateral talipes and kyphosis. These findings are important because they may signal more extensive functional involvement, narrowing the gap between visible structural abnormality and actual motor impairment. In other words, when deformities such as clubfeet or spinal curvature are present, the motor level may be closer to the anatomical level than in fetuses without these signs.
The study also showed that higher anatomical levels were significantly associated with ventriculomegaly and vertebral anomalies. This is consistent with the known phenotype of more cranially extensive open spinal dysraphism, which is often accompanied by more complex central nervous system and skeletal abnormalities. For prenatal counseling, this reinforces the concept that spinal level should not be interpreted in isolation; associated brain and vertebral findings contribute to the overall risk profile.
Interpretation of the discrepancy
The fact that the motor level is often more caudal than the anatomical level has several possible explanations. First, structural closure failure does not always translate linearly into segmental motor loss, especially in early gestation when movement patterns may be altered but not absent. Second, fetal compensatory movement can make preserved function appear more robust on ultrasound than it will be postnatally. Third, the relationship between the spinal cord lesion and downstream motor outcomes may be influenced by tethering, tissue integrity, and associated neural injury that are not fully captured by vertebral anatomy alone.
Importantly, this does not mean that prenatal ultrasound is inadequate. Rather, it shows that ultrasound captures complementary dimensions of the defect. Anatomical level provides structural mapping, while motor assessment adds a functional layer. The challenge is to integrate both rather than treat one as a surrogate for the other.
Expert Commentary
This study is valuable because it addresses a real-world question faced by fetal medicine specialists: how should a prenatal lesion level be interpreted when counselling families about prognosis? The answer, supported by these data, is that a structural lesion level alone may overstate functional impairment in many cases. That has direct implications for discussions about postnatal mobility, the need for assistive devices, and expectations after prenatal or postnatal repair.
Several strengths deserve emphasis. The sample size is relatively large for a single-centre fetal imaging study, and the 12-year study window increases clinical relevance. The use of adjusted regression analyses improves interpretability by accounting for anatomical level when examining factors associated with discrepancy. The focus on clinically recognizable ultrasound features also makes the findings translatable to daily practice.
At the same time, limitations are important. Retrospective design introduces selection and information bias, and the study reflects the expertise and referral patterns of a tertiary centre, which may not generalize to community settings. The abstract does not report interobserver reliability, exact gestational age at imaging, or postnatal correlation with neurologic outcomes. That last point is particularly important: a prenatal motor level is a useful estimate, but its ultimate prognostic accuracy depends on how it aligns with postnatal exam and long-term function. Without that linkage, the study mainly clarifies prenatal imaging discordance rather than definitive outcomes.
Another limitation is that the abstract does not specify whether dynamic motor assessment was standardized across sonographers over the entire 12-year period. In a long retrospective cohort, subtle changes in equipment, expertise, and reporting practice may influence results. Nevertheless, the consistency of the main finding across a large sample suggests that the signal is real.
From a counseling standpoint, the study supports a nuanced message: a higher anatomic lesion does not automatically mean equivalent motor loss. Families should be told that structural level, movement assessment, and associated anomalies all contribute to prognosis. This is especially relevant in fetal surgery programs, where prenatal imaging determines not only eligibility but also expectations regarding functional benefit.
Clinical Implications
For maternal-fetal medicine specialists and fetal neurologic imaging teams, the practical takeaway is to report both anatomical and motor levels whenever possible, and to describe the degree of discrepancy rather than assuming equivalence. In fetuses with myeloschisis, a larger gap between anatomy and function may be expected. Conversely, the presence of bilateral talipes or kyphosis may indicate more severe functional involvement.
For counseling, a multidisciplinary approach remains essential. Ultrasound findings should be integrated with fetal MRI where available, as well as with genetic, neurosurgical, and neonatal assessments. The reported association between higher anatomical levels and ventriculomegaly or vertebral anomalies also argues for careful screening for associated abnormalities that may change prognosis and management.
For research, the next logical step is prospective validation with standardized imaging protocols and postnatal neurologic follow-up. It would also be useful to determine whether prenatal anatomical-motor discrepancy predicts long-term ambulation, orthopedic surgery burden, bladder outcomes, or response to fetal repair. Such evidence would move the field from descriptive imaging toward outcome-driven prenatal stratification.
Conclusion
This 12-year retrospective study shows that in open spinal dysraphism, prenatal motor level is frequently more caudal than the anatomical level, with discordance present in more than four-fifths of fetuses. The magnitude of this difference varies by lesion type and is influenced by associated ultrasound findings. The core message is clinically important: structural and functional assessments are related but not interchangeable, and both should be incorporated into prenatal counseling and decision-making.
Funding and ClinicalTrials.gov
The abstract does not report funding details or ClinicalTrials.gov registration. No trial registration is evident from the study design, which was retrospective observational.
References
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2. Adzick NS, Thom EA, Spong CY, et al. Fetal surgery for myelomeningocele: trial results and a follow-up study. N Engl J Med. 2011;364(11):993-1004.
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