205. Massa intermedia Measurements in Children with Prenatal or Postnatal Closed Myelomeningoceles

Authors: Paige Lundy, MD; Paige Lundy, MD; Paul Grabb, MD (Kansas City, KS)

Introduction:Enlargement of the massa intermedia is a known anatomic variant present in children born with open myelomeningocele and Chiari II malformations.  The MOMs study demonstrated improvement of hindbrain herniation and hydrocephalus with prenatal closure of myelomeingocele.  Whether other classic supratentorial findings are altered by prenatal closure has not yet been explored.   The massa intermedia does pose an operative obstacle when attempting endoscopic intervention.   Thus it would be of interest to understand if prenatal closure changes this anatomical finding. 

Methods:We have reviewed MRI images for children with history of myelomeningocele who have undergone either prenatal or postnatal closure as well as control non-myelomeningocele patients. We used axial T2 images for AP (anterior-posterior) measurement of the massa intermedia. The midline sagittal scan was used to measure and calculate the cross sectional area of the massa intermedia.

Results:We reviewed the MRI images of 8 patients from each subgroup (prenatal closure, postnatal closure, and non-myelomeningocelen). The average age of prenatal MRI was group was 8.25 months, postnatal MRI was 5.125, non-myelomeningocele was 9.5. The average A-P diameter of the massa intermedia per axial MRI was 0.38mm, 0.59mm, and 0.19mm in the pre, post, and non-myelo group respectively.  The respective average cross sectional area of the massa intermedia was 0.195cm3, 0.568cm3, and 0.139cm3. There was a significant difference in cross sectional area between the postnatal and control groups (p=0.022).  Pre vs post-natal was nearly significant (p=0.053).  

Conclusion:Prenatal closure of myelomeningocele results in improvement of posterior fossa abnormalities related to Chiari II malformations. Here we have observed that prenatal closure may also alter the development of supratentorial abnormalities.  Changes in supratentorial abnormalities may improve obstacles to hydrocephalus treatment as well as indicate improved supranational formation that could be related to neurocognitive outcomes.