Journal of Ultrasound in Medicine, Vol 18, Issue 2 153-158, Copyright © 1999 by American Institute of Ultrasound in Medicine
Variation in echogenicity of the basal ganglia: anisotropic effect
V. S. Ashraf, V. A. Feldstein and R. A. Filly
Department of Radiology, University of California, San Francisco, 94143-0628, USA.
We observed that the fetal brain demonstrates relatively increased
echogenicity of the basal ganglia compared with the thalami and cortical
brain parenchyma, which we did not observe on neonatal sonograms. We
hypothesized that the difference in relative echogenicity was due to
differences in imaging techniques and anisotropic effects for prenatal and
postnatal brain images. In 18 consecutive neonates, we obtained coronal
images of the basal ganglia and thalami through the anterior fontanelle and
axial images through the anterolateral fontanelle with both 5 and 7.5 MHz
transducers. Two observers determined whether increased echogenicity or
conspicuity of the basal ganglia was present, comparing the axial and
coronal planes. We observed relatively increased echogenicity of the basal
ganglia in the axial plane in 11 of the 16 examinations in this series. Of
these 11, the increased echogenicity effect was manifest only in the axial
plane in seven neonates. In the four instances in which the increased basal
ganglia echogenicity was seen in both the coronal and axial planes, the
effect was better shown in axial plane in all four. We did not observe any
cases of increased echogenicity of the basal ganglia only in the coronal
plane. The increased echogenicity was more conspicuous with the lower
frequency transducer in 10 of the 11 examinations. We believe that the
change in echogenicity of the basal ganglia is predominantly an anisotropic
effect. Observing that increased echogenicity of the basal ganglia can
disappear or decrease when comparing images in the axial to the coronal
plane or be better demonstrated with lower frequency transducers might be a
means by which to distinguish this phenomenon from true pathologic
processes of the neonatal brain.
