Child sexual offenders show hypothalamic volume reduction
In
agreement with our first hypothesis of a reduction of hypothalamus
volume in CSO, we observed a hypothalamic reduction in persons with
pedophilia who committed CSO. The effect was evident in both
hypothalamic hemispheres in absolute volumes and after correction for
the two confounders ICV and age separately and simultaneously after
outlier exclusion. Following contrasts confirmed our hypotheses that the
effect was driven by the control as well as the P-CSO group. In our
study CSO is related to hypothalamic volume reduction in pedophilic men
and this effect is driven by the control group as well as the pedophilic
non-offender group.
Significance was initially lost after
simultaneous correction for ICV and age in the global univariate group
comparisons of hypothalamus volumes and reemerged after excluding the
statistical outliers. This suggests suppression effects due to
multicollinearity and a sensitivity of the parametric models to
non-normal outliers. The statistical outliers could not be explained by
variations in clinical characteristics, measurement, or sampling. To
account for the known sensitivity of parametric tests to outliers, we
reported results before and after excluding statistical outliers for the
purpose of transparency and reliability.
Since one contrast of
volume reduction was not significant in the right hypothalamus, we may
expect that the effect is more prominent on the left side. This would be
consistent with the findings of a volume reduction of the right
amygdala [24] and a functional connectivity between the right amygdala and the left hypothalamus in pedophilic offenders [65]. Blinding the rates to the hemispheres minimized the likelihood that the algorithm was applied differently.
Pedophilic
participants both with and without histories of committed CSO consumed
material depicting child sexual abuse, indicating the alteration in
hypothalamic structure appears to be associated with implementation of
CSO at the behavioral level. Our findings corroborate studies
highlighting the hypothalamus and its subsequent cascades and regulatory
mechanisms in violence [13,14,15,16,17].
Furthermore, our results are consistent with previous studies that
focused on sexual violence against children and showed an activity
reduction in the hypothalamus in pedophilic offenders [27] and acquired pedophilia and CSO after hypothalamic damages [18,19,20].
More precisely our findings possibly confirm our initial assumption
that a reduced hypothalamic volume may indicate a reduced HPA axis
activity. The deficit of glucocorticoids, induced by the hypofunction of
this axis, may be related to aggression and CSO through epigenetic
changes in the prefrontal cortex [31, 32]. In our sample Kruger et al. [37]
found no cortisol reduction in CSO, but it is not unlikely that this
may be due to methodological limitations, such as measuring at different
times, despite cortisol levels fluctuating throughout the day.
Voxel-based morphometry studies are less sensitive for small structures, such as the hypothalamus [66]. For this reason, this analyses of this area [23,24,25,26] may not have yielded results. Additionally, except for Schiffer et al. [25], the field strengths of the MRIs were lower in the mentioned studies and the sample sizes were smaller.
No significant differences in non-offending people with pedophilia
In
contrast to the results regarding CSO, we found no significant
difference in exploratory comparisons of left or right hypothalamic
volumes between non-offending pedophilic men and the control group. This
was in line with our expectations. Differences remained non-significant
even with correction for ICV and/or age. This suggests an unchanged
hypothalamic macrostructure in non-offending people with pedophilia.
Interestingly, there was no gradually progressive increase in
hypothalamic volume between the groups (e.g.
P + CSO < P-CSO < controls), not even descriptively. Thus, the
P-CSO group does not appear to be an intermediate stage between
pedophilic offenders and the control group. Contrary to our conclusions
previous studies attributed structural changes of the hypothalamus or
other brain regions to pedophilia [22, 23, 26]. It can be speculated that their results were influenced by sexual offenders.
General assessments of the observed hypothalamus volumes
The bilateral hypothalamus volumes measured in vivo with a total mean of 1543 mm3 (SD = 146.6 mm3) are slightly higher than the volumes previously measured with the same method (1427 mm3 to 1478 mm3) [52].
However, this was to be expected, as our sample consisted exclusively
of men and a sexual dimorphism of the hypothalamus, postulated to be
larger in men, has been shown before [67,68,69,70,71]. Furthermore, the correlations of hypothalamic volume with age and ICV are consistent with previous reports [66, 67, 72, 73].
The P + CSO group also had the lowest ICV. This finding has to be
questioned in future studies by exploring several distinct brain regions
involved in control of behaviour and sexual functioning.
Strengths and limitations
Probably
one of the greatest strengths of this study is the distinction between
offenders and non-offenders and thus also the fundamental distinction
between offenders and people with pedophilia. A disadvantage is that the
classification regarding the offender status was necessarily dependent
on the self-reporting of the participants, which risks a probability of
false statements in, theoretically, both directions. Attempts have been
made to mitigate this by ensuring anonymity. Balancing too many or too
few exclusion criteria is difficult as excluding individuals with
specific diagnoses or medications increases homogeneity at the cost of
generalizability. The distribution of lifetime mental and personality
disorder diagnoses was significantly different between all groups and
the hypothalamic volume may be affected by these. Violent crimes other
than CSO, which were not exclusion criteria, may have influenced the
results. Even though the sample size is large compared to previous
studies in the subject area, it is not sufficient to calculate an
equivalence test [64]
between the hypothalamus volumes of pedophilic non-offenders and the
control group. Since the study is designed cross-sectionally, no
conclusions about cause and effect can be drawn. Unbalanced sample
distribution among different locations and thus scanner models may have
an effect on the GM-TPMs. The evaluated 3-Tesla MR images provided a
strong basis for measurements of the brain structures, but a higher
field strength would reduce the partial volume effect. Manual
segmentation at submillimeter resolution is the most accurate method for
this, which is unfortunately hardly feasible for higher case numbers
such as in our study due to high time expenditure.
Our large-scale
multicenter sample consisted of only men; therefore we can only draw
conclusions about males. However, men are most relevant for the research
on sexual violence against children, as they are the major group of
offenders [74].
To answer whether the results are not only valid for people with
pedophilia who committed CSO, but also for CSO in general, exploring
non-pedophilic CSO subjects is needed. The structural analysis was based
on group comparisons and cannot serve as a basis for a diagnostic
criterion or to draw reliable conclusions about individuals.
To
our knowledge, no other study has accurately investigated the structure
of the hypothalamus in pedophilia with or without CSO. In addition to
theoretical considerations about understanding of the neurobiological
underpinnings of CSO in pedophilia, the study may add to additional
impact in the future, as trait markers of risk factors for committing
CSO are needed to stimulate early in the clinical course specific sexual
therapeutic treatment which covers more than general psychotherapeutic
intervention. The present results need to be replicated in further
studies and assessed in relation to, for example, endocrinological and
behavioral functions before practical implication can be raised.
Implementing an equivalence test would be an important challenge for
future studies to discuss the hypothesis of similar brain structures in
pedophilic non-offenders and subjects of a control group. However, the
required sample sizes for the populations of interest are difficult to
realize. Further studies are warranted using functional brain imaging to
investigate emotional processing according to the development of
pedophilia or CSO over the lifespan. Another interesting question to
examine is whether the hypothalamic volume reduction can also be found
in a (large) non-pedophilic CSO group to clarify whether our results
apply explicitly to the P + CSO group or are valid for CSO exclusively.
The
topics of pedophilia and CSO are undeniably emotionally charged.
Research such as ours not only provides a better understanding of neural
mechanisms underlying pedophilia and CSO, but also contributes to
education and public discussion about these matters, rather than
reinforcing threats to child welfare with silence and stigmatization.