I was reading over this subject again, looking at a number of papers (item quoted below in blue is just a general reference to the subject), and notice that the stated parameters always speak of (male) transexualism (TS) with some subgroups as early or later onset, and attracted to (either) men or women.
It seems to me that crossdressing, although often linked with transexualism, it is significantly different. Of the subgroups mentioned, the TS with female orientation seems to fit best, but is not the most accurate description of a significant proportion of the CD/TG/TS.
Now, since we are all conceived as and initially develop as females, somehow the hormones in the fetus beginning at about 8 weeks are not as complete, thus failing to masculinize ( androgenize(?) ) the BSTc region, but most everything else.
I wonder if the BST-c is different for crossdressers rather than transsexuals, as sort of an incomplete or half-way?
A possible explanation, but least likely: The Zhou/Kruijver results might reflect the chance selection of a sample of MtF transsexual brains with unrepresentative BSTc volumes and neuron numbers
Examination of the Zhou/Kruijver data reveals considerable variability in BSTc volume and neuron number within each of the groups they studied (i.e., MtF transsexuals, heterosexual men, homosexual men, and women). Could it be that there is really no difference in average BSTc volume and neuron number between nontranssexual men and MtF transsexuals and that the differences found in the Zhou/Kruijver studies merely reflected the chance selection of a highly unrepresentative group of MtF transsexuals?
Statistical testing provides an estimate of the likelihood of such an occurrence. In the case of BSTc volume, the observed difference in mean values between the MtF transsexual group and the heterosexual male group would be expected to occur by chance less than one time in 200 (p < .005; Zhou et al., 1995, p. 69). In the case of BSTc neuron number, the probability is greater, but still less than one time in 25 (p < .04; Kruijver et al., 2000, p. 2036). <<http://www.annelawrence.com/twr/brain-sex_critique.html>>