Limited Dorsal Myeloschisis: A Diagnostic Pitfall in the Prenatal Ultrasound of Fetal Dysraphism.

Objective: To determine the ultrasonographic characteristics of limited dorsal myeloschisis (LDM) at prenatal ultrasound (US) and to highlight the main features that may help differentiate LDM and myelomeningocele (MMC). Methods: In a tertiary reference center in fetal medicine, we prospectively collected the medical data and ultrasonographic characteristics of all patients referred for in utero prenatal repair of MMC between November 1, 2013 and April 30, 2015. Results: Among the 29 patients assessed, the diagnosis of MMC was revised in 7 cases. In 6 cases, the diagnosis of LDM was established. On US scan, LDM was characterized by a spinal saccular lesion with a thick peripheral lining in continuity with the adjacent skin. Within the saccular lesion, a thick hyperechoic well-delineated structure was present in continuity with the spinal cord. Cerebral structures were normal except for 2 cases showing a cisterna magna slightly decreased in size. In the remaining 22 cases MMC was confirmed, with cerebral anomalies present in 21/22 cases (95.5%). Conclusion: LDM is a form of closed dysraphism accessible to prenatal diagnosis by US that may mimic MMC. Considering the major difference in prognosis between these two entities, physicians should be aware of the existence and ultrasonographic characteristics of LDM.