The clinical significance of lack of hindbrain herniation in fetal myelomeningocele/myeloschisis patients.

Objective: Hindbrain herniation (HH) is a clinical prerequisite for prenatal repair of myelomeningocele/myeloschisis; however, a subset of patients lack HH on initial fetal imaging and may ultimately progress to exhibit herniation on subsequent prenatal or postnatal imaging. The authors sought to explore the cohort of patients without HH at the time of initial fetal consultation for myelomeningocele/myeloschisis repair to define their clinical characteristics and outcome.

Methods: From July 2016 to July 2022, patients evaluated at the Children's Hospital of Philadelphia Center for Fetal Diagnosis and Treatment for myelomeningocele/myeloschisis were classified into two cohorts: those with and those without HH. The diagnosis of HH was obtained from prenatal and postnatal MRI. The osseous lesion level, prenatal sac volume, and prenatal ventricular size was obtained from fetal ultrasound. The fronto-occipital horn ratio was measured on the first postnatal ultrasound. Ambulation status was obtained from postnatal evaluation in the spina bifida clinic.

Results: A total of 176 patients with prenatal HH had postnatal follow-up, of whom 95 (54%) had HH resolution and 81 (46%) had herniation persistence. Of 73 patients without prenatal HH, 9 (12%) had herniation on subsequent prenatal imaging while 64 (88%) had no herniation on prenatal imaging. Of these 64 patients, 11 (17%) had postnatal HH, 32 (50%) had no postnatal herniation, and 21 (33%) were lost to follow-up or the pregnancy was terminated. For patients without HH throughout, the sac volume was larger (9 cm3) than those who had herniation progression or initial herniation; however, the rate of talipes was not significantly different among the groups. The majority of patients were also ambulators (with assistive devices or independent), and the atrial diameter was also < 10 mm for most patients. Overall, 53% of those with initial HH compared with 35% with progression of herniation required CSF diversion, while only 25% of those without herniation required diversion.

Conclusions: This study demonstrates the natural history of HH in patients with a prenatal diagnosis of myelomeningocele/myeloschisis. The majority of patients without any herniation had larger sac sizes but not higher rates of talipes and smaller ventricles and were ambulatory. These findings improve the ability to guide families during prenatal consultation.