Cranial ultrasound is a relatively new neuroimaging technique that shows tissue echogenicity (intensity of reflected ultrasound waves in the brain) through a healthy skull, first identified by neurodegenerative disorders and psychiatry in many centers around the world that is probably the best evidence for the value of this method. A wider application of TCS is in early diagnosis, differential diagnosis and screening of ADHD children. Therefore, the current study aimed to evaluate and compare the size of substantia nigra and other basal nuclei on TCS in ADHD and healthy children.
The findings of this study showed that the echogenicity of substantia nigra and thalamic nuclei was higher in the ADHD children compared to the control group. There was no significant difference in the size and echogenicity of other brain nuclei between the control group and the ADHD children. According to the echogenicity findings of substantia nigra, the frequency of isoechoic cases was 27.6% and 72.4%, and the frequency of hyperechoic cases was 66.7% and 33.3% for both patient and healthy groups, respectively, showing a significant difference between the two groups. Based on the results obtained from the echogenicity of thalamic nuclei, the frequency of hypoechoic cases was 76.5% and 55.2% and the frequency of isoechoic cases was 23.5% and 6% in the patient and healthy groups, respectively, indicating a significant difference between the two groups.
Analysis on the family history of children revealed that the results of TCS for healthy children with a positive family history of ADHD are significantly similar to the results of TCS for patients with this disorder.
Limited knowledge is available about changes in the echogenicity of substantia nigra over a lifetime with age. On the other hand, the size of this nucleus does not change much with age, but the maturation of substantia nigra is delayed [18, 19], which can be in turn a factor in reducing its echogenicity slower and play a role in pathophysiology. However, previous studies have shown that the echogenicity of substantia nigra decreases with age in adults, and dopaminergic neurons are lost with age [20]. A study reported a gradual decrease in the echogenicity of substantia nigra in 109 children aged 0–192 months, indicating age-related changes occurring in the first decade of life [21]. However, no significant association between the echogenicity of substantia nigra and the age of children was found.
The hypothesis that there is a delay in brain development in ADHD children compared to healthy children justifies the differences and sizes between different brain nuclei [22, 23]. Examining the studies to determine the difference in echogenicity of substantia nigra and thalamic nuclei by TCS, displayed that only one study used a method similar to the present study to examine echogenicity of brain nuclei in children with ADHD. However, there are many studies that have found such results with MRI. Daniella Berg in 2011 examined the intensity of substantia nigra using MRI and found that the intensity of substantia nigra is higher in ADHD children, in line with current findings that the nucleus echogenicity is higher in ADHD children than in the healthy group [24].
Weise (2009) found that ADHD patients had a larger substantia nigra area than healthy controls, indicating their dopamine dysfunction. This finding is similar to the results observed in Parkinson’s disease [25]. Contrary to the studies, no significant difference in this regard was seen in the present study.
Bailey (2015) examined various brain components, and found abnormalities in the pulvinar region in ADHD patients; it is said that any part of the dopaminergic system, including the thalamus, can be disrupted by ADHD [26]. Findings about the difference in the echogenicity of thalamus between sick and healthy children are very limited, and this study, despite the small number of ADHD patients tested, cannot make a definite judgment about the echogenicity of thalamus in hyperactive patients. It is noteworthy that in the present study, by examining the echogenicity of thalamus in ADHD and healthy groups, the substantial finding was achieved that there is a significant difference in echogenicity between these two groups (P = 0.04).
Drepper C introduced TCS as a new diagnostic method for determining changes in the echogenicity of subcortical brain structures in children with various disorders, such as obsessive–compulsive disorder, autism spectrum disorder, schizophrenia, panic disorder, ADHD, bipolar disorder and depression. However, the physical characteristics responsible for brain tissue echogenicity on TCS are principally unknown [10].
One of the limitations of this study was the method of selecting patients, which was performed qualitatively and not quantitatively. In addition, the accuracy of the findings depended on the quality of the ultrasound system as well as the competence of the researcher. Furthermore, due to the nature of the control sample, the control group did not fully represent the population from which the patient sample was taken.