Abstract:
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Purpose: To define features of the Chiari II malformation and associated spinal defects with magnetic resonance (MR) imaging in the fetus and evaluate the effect of gestational age on ability to identify these features.
Methods and Materials: Retrospective review of the MR database was performed to identify patients with suspected Chiari II malformations. Images from SSFSE sequences were reviewed for the ability to demonstrate the presence or absence of a small posterior fossa, caudal displacement of the brainstem, ventricular enlargement, cervicomedullary kink, tectal beaking, callosal hypogenesis, and prominent massa intermedia. Features were assessed as able or unable to be identified, and if identified, whether findings were normal or abnormal. The type, location, and size of the spinal defects were also recorded. Chi-squared analysis was performed to evaluate the relationship of gestational age to features identified.
Results: In 24 Chiari II cases reviewed, 21 spinal defects and 2 cephaloceles were identified; 1 low sacral spinal defect measuring 1mm at delivery was not seen. Localization and measurements of the defect was possible in 22 of the 23 identified cases. Central nervous system findings of small posterior fossa size, caudal displacement of the brainstem, and ventricular size were identified in all 24 cases; in 19 cases the atrial width was greater than 10mm. Presence or absence of cervicomedullary kink could evaluated in 14 cases and was abnormal in 9. Tectal beaking could be evaluated in 9 and was present in 7. The region of the corpus callosum was seen in 7 and hypogenesis was suspected once. A prominent massa intermedia was seen in all 4 cases when this area was identified. There was a trend toward identification of more areas of the fetal brain with increasing gestation, but it was not significant in our small series (p=0.59). Identification of the cerebral findings in fetuses with Chiari II malformations was not significantly effected by size or location of the spinal defect or cephaolocele (p=0.22).
Conclusion: 1. Major features of the Chiari II malformation (small posterior fossa and caudal displacement of the brainstem) were identified with MR in all fetuses beyond 13 weeks gestation; atrial width measurement was possible in all 24 and abnormal in 19 cases. 2. All but one (1mm) spinal defects were identified beyond 13 weeks gestation. 3. There was a trend toward identification of the more subtle features of the Chiari II malformation with increasing gestational age, but this was not statistically significant in our small population.
Brandon MD, J,
Fetal Magnetic Resonance Imaging of Chiari II Malformations and Associated Spinal Defects: Does Gestational Age Effect Ability to Identify Features?. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3101640.html
