This issue starts with an overview of what we know from
MRI neuroimaging of children and adolescents with
psychiatric disorders. As is often the case in child
psychopathology, accomplishments in adult psychiatry
serve as the model for the study of childhood conditions.
Thus Eliez and Reiss, in their clear overview of neuro-imaging studies, emphasise the results pertaining to
child/adolescent onset schizophrenia, with its main conclusion that childhood-onset schizophrenia is not distinct
from adult-onset schizophrenia from the standpoint of
neuroanatomical variation. The use of the new imaging
techniques in the search for neurobiological substrates of
the more common psychiatric disorders in children and
adolescents is still in its infancy. This can be concluded
from the fact that only a few studies are available on
children with ADHD, autism, or Tourette's disorder,
with no neuroimaging studies yet available on childhood
conditions such as depression, conduct disorder, anxiety
disorders, or pervasive developmental disorders other
than autism. A rather crude finding that stands out is the
relationship between total brain volume and intelligence.
The authors point out that studies that did not take IQ
into account erroneously interpreted differences between
groups of children to be specific for a certain condition,
whereas in fact the differences could have been explained
by differences between the groups in IQ. Reading this
annotation, one is struck by the many contradictory
findings of the neuroimaging studies that are reviewed.
These discrepancies may be due to variations in neuro-imaging methodology and variations in the definition
and measurement of neuroanatomical regions. Also, the
large etiological heterogeneity, as well as the lack of
precision with which we can define and measure behavioural phenotypes, will influence the variability in
findings. The authors give an example of how one MRI
study looked at children with ADHD without comorbid
conditions whereas another study looked at children with
ADHD of whom the majority had a comorbid diagnosis
of conduct disorder or oppositional defiant disorder. It is
not surprising, then, that neuroimaging studies on children with very different behavioural phenotypes, despite
claiming that they studied the same phenomenon, end up
with contradictory results. Instead of treating childhood
conditions such as ADHD as diagnostic categories that
are either present or absent, it may be advantageous for
MRI studies to retain more diagnostic information by
studying the covariation between brain morphology and
behavioural phenotypes as continuous measures. Now
that some experience with neuroimaging of child/adolescent psychiatric disorders is available, it is hoped
that studies using larger sample sizes, advanced techniques such as functional MRI, longitudinal designs,
and more precise diagnostic assessment techniques, will
shed light on the still somewhat inconsistent findings on
brain morphology of psychiatric conditions in children
and adolescents.