Highlights
In this 12-year single-center retrospective study of 187 fetuses with open spinal dysraphism, the prenatal 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, underscoring substantial heterogeneity in fetal neurologic expression.
Myeloschisis was associated with a larger discrepancy than myelomeningocele, while bilateral talipes and kyphosis were linked to smaller discrepancies.
Higher anatomical lesion levels correlated with ventriculomegaly and vertebral anomalies, reinforcing the value of a structured fetal ultrasound assessment beyond the spine alone.
Clinical Background and Unmet Need
Open spinal dysraphism, most commonly represented by myelomeningocele and myeloschisis, remains one of the most important congenital causes of lifelong neurologic disability. Prenatal diagnosis is no longer limited to detecting the presence of a spinal defect; it increasingly informs prognosis, delivery planning, parental counseling, and eligibility for fetal surgery in selected cases.
Two related but distinct concepts are central to counseling: the anatomical level of the spinal lesion and the motor level of neurologic impairment. The anatomical level refers to the highest vertebral segment that remains unclosed, whereas the motor level reflects the most caudal muscle group showing preserved active movement. In clinical practice, these levels are often assumed to align, but they do not necessarily do so. This distinction matters because motor outcome is usually more relevant to postnatal function than the bony extent of the defect itself.
Prenatal ultrasonography is the main imaging modality used to identify open spinal dysraphism and to estimate lesion severity. However, its ability to approximate future motor function is imperfect. The present study addresses a clinically important gap: how often anatomical and motor levels differ before birth, what factors are associated with a greater discrepancy, and which ultrasound findings track with higher anatomical lesions.
Study Design and Methods
This was a retrospective observational study conducted at a single tertiary referral center over 12 years, from 2011 to 2022. The study included 187 fetuses diagnosed prenatally with open spinal dysraphism.
Investigators defined the anatomical level as the highest non-closed vertebra on ultrasound. The motor level was assessed by dynamic ultrasound evaluation of the most caudal active muscle group. The difference between these two measures was then calculated in vertebral segments. Linear regression models were used to identify clinical and ultrasound variables associated with this discrepancy, with adjustment for anatomical level.
The authors also examined which ultrasound features were associated with the anatomical level itself. This is important because higher lesions may be accompanied by broader structural abnormalities, potentially improving prognostic assessment when interpreted in a comprehensive fetal imaging framework.
Key Findings
The main finding was that discordance between anatomy and function was the rule rather than the exception. In 85.0% of fetuses, the motor level was more caudal than the anatomical level. Put differently, the fetus often demonstrated preserved motor activity below the bony level of the lesion, indicating that the anatomical defect alone underestimated the functional neurologic level.
The median difference was two vertebral segments, although the observed range was broad, from -3 to +15. This wide spread is clinically meaningful. A negative value indicates that, in some fetuses, the motor level was actually more cranial than the anatomical level, while a very large positive difference suggests that preserved motor activity extended well below the defect. Such variability highlights why prenatal counseling based on lesion level alone can be misleading.
Lesion type emerged as an important determinant of discrepancy. Myeloschisis, compared with myelomeningocele, was associated with a greater anatomical-motor difference, with an adjusted coefficient of 0.78 and a highly significant p value of less than 0.001. Clinically, this suggests that more severe-appearing open lesions do not always translate into proportionally worse prenatal motor findings, at least as assessed by ultrasound.
By contrast, bilateral talipes and kyphosis were linked to smaller discrepancies. These associated findings likely reflect more advanced neuromuscular compromise and spinal deformity, narrowing the gap between visible anatomy and measurable motor function. In other words, when orthopedic abnormalities are already prominent, the motor level may more closely approximate the anatomical defect.
The study also found that higher anatomical levels were significantly associated with ventriculomegaly and vertebral anomalies. This is biologically and clinically plausible. Higher spinal lesions often occur within a broader spectrum of neural tube and vertebral developmental disruption, and ventriculomegaly may reflect associated central nervous system involvement, including hindbrain changes and cerebrospinal fluid dynamics alterations.
From a practical standpoint, these associations support a comprehensive fetal survey when open spinal dysraphism is detected. The spinal lesion should not be interpreted in isolation; the cranial vault, ventricular size, posterior fossa, vertebral alignment, lower-limb posture, and limb movements all contribute to a more complete prenatal phenotype.
Clinical Interpretation and Expert Commentary
This study reinforces a long-standing principle in fetal medicine: structural severity and functional severity are related but not identical. In open spinal dysraphism, prenatal ultrasound can identify the lesion and estimate neurologic involvement, but the anatomical level should not be treated as a surrogate for postnatal motor prognosis.
The finding that motor levels were more caudal than anatomical levels in the vast majority of cases is especially relevant to counseling. Families may understandably interpret the presence of a higher spinal opening as implying severe paralysis below that point. The current data suggest that this assumption would overestimate impairment in many fetuses. A more nuanced discussion is therefore warranted, emphasizing that residual lower-limb function may extend beyond the vertebral defect seen on ultrasound.
At the same time, the study does not imply that prenatal motor assessment is a perfect predictor of postnatal function. Fetal movement on ultrasound is influenced by many factors, including gestational age, fetal position, examiner experience, maternal habitus, and the limitations of visualizing subtle distal movements. Moreover, prenatal motor activity does not fully capture postnatal ambulation potential, orthopedic complications, bladder and bowel dysfunction, or the impact of Chiari II malformation and hydrocephalus.
The association between myeloschisis and greater discrepancy deserves careful interpretation. Myeloschisis is generally considered a more severe form of open dysraphism with exposed neural tissue, and one might expect a closer relationship between structural and functional deficits. The opposite pattern observed here likely reflects the complexity of fetal neurologic development and the fact that preserved movement below the lesion can still be present despite severe anatomical disruption. This underscores the value of direct dynamic assessment rather than reliance on lesion morphology alone.
The links between higher anatomical level, ventriculomegaly, and vertebral anomalies also have counseling implications. These findings may help teams identify fetuses at greater risk of broader developmental involvement and may support more detailed preoperative evaluation, especially when fetal repair is being considered. In centers offering fetal surgery, such information can assist in refining case selection and in setting realistic expectations regarding neurologic benefit.
Practical Implications for Prenatal Counseling and Fetal Care Planning
For clinicians counseling expectant parents, the central message is straightforward: the anatomical lesion level on prenatal ultrasound should not be used alone to predict motor outcome. A dynamic assessment of fetal lower-limb movement adds clinically important information and may better approximate functional severity.
In practice, this study supports a multicomponent prenatal assessment strategy:
First, define the anatomical lesion as precisely as possible, including the highest non-closed vertebral level.
Second, perform systematic dynamic evaluation of fetal lower-extremity motion to estimate the motor level.
Third, assess for associated findings such as bilateral talipes, kyphosis, ventriculomegaly, and vertebral anomalies, which may refine prognostic stratification.
Fourth, integrate these results into multidisciplinary counseling involving maternal-fetal medicine, pediatric neurosurgery, neonatology, genetics, and, when appropriate, fetal surgery teams.
Finally, counsel families with explicit acknowledgment of uncertainty. Prenatal findings inform risk but cannot determine individual postnatal functional outcome with precision.
Limitations and Future Research
As with all retrospective single-center studies, external validity is limited. Referral bias is likely, since tertiary centers often evaluate more complex or severe cases, which may influence both lesion spectrum and observed discrepancy patterns. The study also depends on the quality and consistency of ultrasound assessment over a long time period, during which imaging protocols and operator experience may have evolved.
Another important limitation is that prenatal motor level was based on ultrasound-detected movement rather than postnatal neurologic examination. While this is appropriate for a prenatal study, the clinical value of the observed discrepancy would be strengthened by direct correlation with neonatal and long-term functional outcomes, including ambulation, need for orthopedic intervention, and bladder function.
Future work should ideally be prospective, multicenter, and standardized, with uniform imaging protocols and postnatal follow-up. Such studies could determine whether specific prenatal motor findings improve prediction of later motor and urologic outcomes, and whether they meaningfully refine selection criteria for fetal repair.
Conclusion
This 12-year retrospective study provides important evidence that, in prenatal open spinal dysraphism, the motor level assessed by ultrasound is usually more caudal than the anatomical lesion level. The discrepancy is common, clinically relevant, and influenced by lesion type and lesion height. Myeloschisis and higher anatomical lesions are associated with larger differences, while bilateral talipes and kyphosis are associated with smaller ones. Higher lesions also correlate with ventriculomegaly and vertebral anomalies.
For clinicians, the take-home message is that prenatal counseling should not equate anatomical defect level with functional impairment. Dynamic motor assessment and comprehensive fetal ultrasound evaluation offer a more nuanced and clinically useful framework for prognosis, planning, and family counseling.
References
Arévalo S, Moreno E, Meléndez M, Giné C, Rodó C, Casellas A, Farràs A, Mendoza M, Maiz N. Anatomical-Motor Level Discrepancy in Prenatal Diagnosis of Open Spinal Dysraphism: A 12-Year Retrospective Observational Study. BJOG : an international journal of obstetrics and gynaecology. 2026-06-16. PMID: 42303947.
Adzick NS, Thom EA, Spong CY, et al. A randomized trial of prenatal versus postnatal repair of myelomeningocele. N Engl J Med. 2011;364(11):993-1004.
American Institute of Ultrasound in Medicine practice parameters and contemporary fetal anomaly imaging guidance for evaluation of the fetal spine and neural tube defects.
Funding and Trial Registration
The abstract provided does not report funding details or clinical trial registration. This was a retrospective observational study, and no trial registration number was provided.