Anatomical vs. Motor Levels in Open Spinal Dysraphism

Clinicians often face challenges when counseling parents about the future mobility of a fetus with open spinal dysraphism. Specifically, clinicians traditionally used the anatomical level of the spinal lesion to estimate future neurological function. However, recent evidence suggests that the motor level of the fetus provides a more accurate picture.

Understanding Open Spinal Dysraphism and Lesion Levels

A landmark retrospective observational study analyzed 187 fetuses diagnosed with this condition. The investigators defined the anatomical level as the highest non-closed vertebra seen on ultrasound. Consequently, they compared this to the motor level, which they determined by dynamically assessing active muscle groups. Surprisingly, eighty-five percent of the fetuses exhibited a motor level that was more caudal than their anatomical level. This finding indicates that actual motor function is often better than what the skeletal defect suggests. Furthermore, the median difference between these levels was two vertebral segments.

Clinical Factors Influencing the Level Discrepancy

Notably, the study evaluated how different fetal pathologies affect this anatomical-motor discrepancy. For example, myeloschisis was associated with significantly greater discrepancies than myelomeningocele. Therefore, the specific type of lesion plays a crucial role in clinical expectations. Additionally, understanding these discrepancies helps specialists provide more accurate prognostic advice to anxious families. Clinicians in India, where neural tube defects remain prevalent, must adopt these refined scanning protocols. Consequently, this shift in practice can significantly improve prenatal counseling outcomes.

Frequently Asked Questions

Q1: What is the main clinical takeaway of this study?

Specifically, eighty-five percent of fetuses show a motor level more caudal than the anatomical skeletal level. Consequently, the child may have better mobility than expected.

Q2: Why does myeloschisis show a greater discrepancy than myelomeningocele?

Typically, myeloschisis exhibits different neural preservation and tissue dynamics. Therefore, this leads to a larger discrepancy between the bony defect and the functioning nerve roots.

References

1. Arévalo S et al. Anatomical-Motor Level Discrepancy in Prenatal Diagnosis of Open Spinal Dysraphism: A 12-Year Retrospective Observational Study. BJOG. 2026 Jun 16. doi: 10.1111/1471-0528.70287. PMID: 42303947.
2. Maiz N, Arévalo S, García-Manau P, et al. Presurgery motor level assessment for prediction of motor level at birth in fetuses undergoing prenatal repair of open spina bifida: time to abandon anatomical level in counseling. Ultrasound Obstet Gynecol 2023; 61: 728–33.