Variation in echogenicity of the basal ganglia: anisotropic effect.

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.