MRI of Fetal CNS Abnormalities
Overview
Magnetic resonance (MR) imaging is a valuable complement to ultrasound when additional information is needed to make treatment decisions during pregnancy. In the past studies were limited by fetal motion. Due to fast imaging techniques now available, images can be obtained in less than 1/2 a second. This means that neither the mother nor the fetus needs to be sedated.
One area where MR imaging has proven to be especially beneficial is in evaluation of the fetal CNS . Multiplanar views can be difficult to obtain with sonography due to fetal position or advanced gestational age. MR imaging can be used to obtain multiplanar views. In addition, MR imaging allows for direct visualization of the brain parenchyma and thus allows for detailed evaluation of the CNS anatomy in a manner not possible with sonography.
There is no known risk to fetal MRI, but due to theoretic concerns, we avoid scanning in the first trimester.
Word to Date
In an ongoing study, we are evaluating fetal CNS abnormalities with ultrasound and MR imaging. In many cases, the information provided by MR imaging is of the type which warrants changes in patient counseling or management.
Encephalocele
Sagittal view of a posterior encephalocele in a 32 week gestational age
fetus. Only a small portion of posterior cortex is tented toward the
defect. At surgery, the encephalocele was removed and a small portion
of cortex was pushed back into the cranial vault without difficulty.
Reproduced with permission from AJR 1999;172:813-818.
Agenesis of the corpus callosum
Agenesis of the corpus callosum in a 32 week fetus, incorrectly diagnosed as holoprosencephaly by ultrasound.
Oblique axial fetal MR with HASTE (half Fourier acquisition single shot
turbo spin echo) demonstrates unfused thalami (t), a falx anteriorly
and vertical configuration of the frontal horns consistent with
agenesis of the corpus callosum.
Sagittal MR shows a dorsal cyst and a cleft lip. Agenesis of the corpus
callosum can be difficult to diagnosis with ultrasound. Reproduced with
permission from Radiology 1997;204:635-642.
Porencephaly - Destruction of brain tissue
Moderate ventriculomegaly with porencephaly in a 38 week gestational
age fetus. Sonogram showed only moderate ventriculomegaly. Coronal MR
demonstrates porencephaly (destruction of brain tissue). Reproduced
with permission from Radiology 1997;204:635-642.
Partial absence of the septi pellucidi
Partial absence of the septi pellucidi in a 32 weeks gestational age
fetus. Axial, coronal and sagittal MR images demonstrates that only the
inferior portions of the septi pellucidi are visualized The sagittal MR
shows a normal corpus callosum. Reproduced with permission from
Radiology 1997;204:635-642.
Indications:
When a fetus has an anomaly that is not well visualized by ultrasound, an MRI may be helpful. Your obstetrician can order the study. We also have a NIH study for fetuses with enlarged cerebral ventricles in which the cost of the MR examination is paid for by an NIH grant, NIBIB 01998.
Contacts
To schedule an examination or for questions about the study: Contact D. Levine, MD at 617-667-8901.
