Variation in echogenicity of the basal ganglia: Anisotropic effect

We observed that the fetal brain demonstrates relatively increased echogeni city of the basal ganglia compared with the thalami and cortical brain pare nchyma, which we did not observe on neonatal sonograms. We hypothesized tha t the difference in relative echogenicity was due to differences in imaging techniques and anisotropic effects for prenatal and postnatal brain images . Ln 18 consecutive neonates, we obtained coronal images of the basal gangl ia and thalami through the anterior fontanelle and axial images through the anterolateral fontanelle with both 5 and 7.5 MHz transducers. Two observer s determined whether increased echogenicity or conspicuity of the basal gan glia was present, comparing the axial and coronal planes. We observed relat ively increased echogenicity of the basal ganglia in the axial plane in 11 of the 16 examinations in this series. Of these II, the increased echogenic ity effect was manifest only in the axial plane in seven neonates. In the f our instances in which the increased basal ganglia echogenicity was seen in both the coronal and axial planes, the effect was better shown in axial pl ane 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 II exami nations. 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 th e 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.