Life-long increase of substantia nigra hyperechogenicity in transcranial sonography

Transcranial ultrasound of the substantia nigra (SN) shows a distinct hyperechogenicity in the majority of patients with Parkinson's disease. Recent studies indicate a larger area of hyperechogenicity in elderly healthy adult subjects. The present study aimed to determine the size of the SN hyperechogenicity and of the mesencephalic brainstem in children and adults without evidence of movement disorders. The areas of echogenicity in the substantia nigra (aSN) and the area of the ipsilateral midbrain (aMid) were assessed in 121 healthy infants and children as well as in 64 healthy adults. Furthermore, the ratio of aSN and aMid was calculated (S/M ratio). We found a positive correlation between age and aSN and between age and the S/M ratio. The values for aSN and S/M ratio were smaller in infants and children compared to healthy adults (aSNmax 0.06±0.05cm² vs. 0.13±0.08cm²). The aSN and S/M ratio grew with increasing age in an almost linear progression. The increase of SN hyperechogenicity over time suggests that the biological process underlying this ultrasound finding may be more dynamic and possibly progressive than previously thought.