Saccular Limited Dorsal Myeloschisis: A Distinct Prenatal Entity.

Introduction: LDM is a distinct form of spinal dysraphism characterized by two important features: a focal "closed" midline defect and a fibroneural stalk that connects the skin lesion to the underlying cord. When a fluid-filled sac overlies the defect, it is classified as saccular LDM (s-LDM). The embryogenesis is incomplete disjunction between cutaneous and neural ectoderms - allowing persistence of a physical connection between the disjunction site and the dorsal neural tube. We aim to describe the prenatal features and perinatal outcomes of s-LDM.

Methods: This study is a review of case records from January 2018 to April 2024. A lesion was classified as s-LDM if the following criteria were met: (a) fluid-filled saccular lesion in the midline of the fetal back overlying dysraphic spine; (b) echogenic stalk connecting the saccular lesion to the cord. Presence or absence of posterior fossa abnormalities (Chiari II malformation) was not required for the diagnosis or exclusion.

Results: Twenty-three cases of LDM were identified - 5 cervical, 3 lumbosacral, 1 lumbar, and 14 sacral. A fibroneural stalk was identified in all. Perinatal outcome was available in all but one. Ten patients (1 cervical, 3 lumbosacral, 6 sacral) underwent surgery after birth, two awaiting surgery at the time of writing this paper. Ten pregnancies underwent termination, and one was lost to follow-up. Additional prenatal findings included obliteration of cisterna magna in two fetuses, frontal bone scalloping in three, bilateral ventriculomegaly in two, underlying intraspinal lipoma in one, Blake pouch cyst in two, and low-placed conus in twenty fetuses. Head circumference was normal in all cases.

Conclusion: s-LDM has unique sonographic features making it feasible for a definitive prenatal diagnosis. This is important since the postnatal surgical outcome is vastly different from myelomeningocele.