There are several theoretical mechanisms of how testosterone alterations and estrogen exposure impair spermatogenesis. Compromise in integrity of blood-testis-barrier with increased vulnerability to cytotoxic and immune damage; impaired adhesion with premature detachment of spermatids from Sertoli cells, causing altered shaping in spermatids; germ cells phagocitation (Walker, et al., 2011).
All these mechanisms can lead to impaired semen quality observed in transgender women, with lower total sperm count (Rodriguez-Wallberg KA, et al., 2021). At the time of fertility preservation only 26.4% of the post-thawed samples showed adequate semen quality for intrauterine insemination (de Nie, et al., 2020). Samples revealed a high incidence of azoospermia, oligozoospermia and asthenozoospermia, despite known factors associated with decreased semen quality in the general population (smoking, BMI, others) (Rodriguez-Wallberg KA, et al., 2021). Lower dosages of ethinylestradiol (20 micrograms/day) were not associated with impaired motility or density, while 60 micrograms per day were, showing a dose dependent mechanism (Chiniara, et al., 2019).
However, some studies show that even before HT, transgender women already demonstrate altered sperm quality. Tucking, low masturbation frequency and wearing tight underwear are suggested explanations (de Nie, et al., 2020).
Testicular volume seems to predict spermatogenesis with a positive correlation, as seen in our results. Scneider et al., in 2015, associated a 25% reduction in volume of testis with depletion of germ cells. This decline in testis weight represents a valid readout of the efficiency of spermatogenic suppression (Scneider et al., 2015). This finding is seen in other studies (Rodriguez-Wallberg KA, et al., 2021, Jindarak, et al., 2018). However, we could not correlate testicular volume with fibrosis parameters, suggesting that spermatogenesis arrest may occur earlier than hyalinization and reduction in seminiferous tubular diameter. On the contrary, a higher basal membrane/tubular diameter ratio is associated with spermatogenesis arrest as seen in table 3.
Previous histological analyses of orchiectomies are described in literature. Maturation arrest was found in 36.4%, hypospermatogenesis in 26%, Sertoli cell-only syndrome in 20.2%, normal spermatogenesis in 11%, and seminiferous tubule hyalinization in 6.4% of the specimens (Jindarak, et al., 2018). Matoso et al. describe decreased diameter of seminiferous tubules and expansion of the interstitium, marked hypoplasia of germ cells, rare cytomegaly, hypoplasia or absence of Leydig cells, and epididymal hyperplasia (Matoso et al,2018). Testicular neoplasia was not found in any of case studies in more than 2500 trans women submitted to orquidectomy (Kent, et al., 2018).
Our results showed reduced tubular diameter and increased basal membrane length, pointing out towards a pattern of fibrosis and hyalinization of testis overtime regarding HT duration. Other studies could not find an association between HT duration and altered histological findings. Majority of these studies had a lower mean time duration of therapy and smaller samples (Matoso, et al., 2018, Vereecke, et al., 2021). A role of HT age of initiation is proposed, since complete spermatogenesis occurs in Tanner stage 3 and onwards (de Nie, et al., 2021). We could not find this association, but only a minority of our patients initiated HT in pre-pubertal stage. Regarding spermatogenesis, majority of patients still exhibited germ cells levels-spermatogonias or spermatids. Therefore, our data is in agreement in what is already known in literature: despite long-term hormone therapy, majority of transgender women have germ cells present in testicle. Spermatogenesis is preserved in approximately 40% of these individuals. However, spermatozoids were not seen in our samples and represent a final step of gametogenesis.
Regarding other HT parameters, such as dose, route of administration and medical compound prescribed, data are scarce and conflicting. Majority of studies use an estrogen only regimen and few describe anti androgen medications (de Nie, et al., 2021). We could not find differences between our groups, probably due to sample size. A trend towards increased lamina propria length/ reduced tubular diameter ratio and parenteral or mixed (oral and parenteral) administration of HT was seen.
BM/TD ratio is an interesting marker of germ cell presence and it has not been previously described. It was designed to minimize inter-tubule changing parameters upon observation. This ratio also provides an instrument of easier interpretation, since it represents the percentage of diameter of the tubule that is filled with basal membrane, and hence atrophic. It showed a strong negative correlation with germ cell presence and a positive correlation with HT duration.
Spermatogenesis arrest may be reversible with HT cessation, although data are conflicting in literature (Adeleye, et al., 2018). If premenopausal female hormone levels are targeted, complete suppression of spermatogenesis is expected (Vereecke, et al., 2021). If not, anticonception advice should be offered due to a theoretical risk of unplanned pregnancy. Interestingly, after fertility preservation techniques with surgically obtained spermatozoa pregnancy rate per cycle has been reported to be 22.8% and the live birth rate 22.3% (de Nie, et al., 2021).
We recognize some study limitations. A single center of a developing country was enrolled and population may differ from previous studies. It is a cross-section study with no matched controls. Specific estrogen regimens varied widely among patients and serum hormonal levels were not monitored. We emphasize that histologic examination of the testicle is only a preliminary avenue of study and its true outcome regarding fertility is theoretical. Nonetheless, since data are scarce in this subset of patients, we acknowledge the importance of our contribution in the better understanding of future perspectives and patient care in transgender health. To our knowledge, this is the first study that evaluated the influence of other HT parameters in testicular histology and proposed BM/TD ratio as a predictor of germ cell presence.