Rectovaginal septum is a real location for deep endometriosis; comment on, ‘the myth of rectovaginal septum endometriosis’

The article by Leonardi et al. (2026) published in this journal attempts to show that rectovaginal septum (RVS) endometriosis may be a myth. RVS is an anatomical location, used also in the international terminology for endometriosis (Tomassetti et al. 2021). This loose connective tissue located inferior to the posterior vaginal fornix separates the posterior vaginal wall from the anterior wall of the rectum. RVS is together with the most aboral part of the rectum infraperitoneal. However, it is in close distance with the peritoneal lining of the rectouterine pouch. The pouch of Douglas, the deepest part of the abdominal cavity, is one of the predilection sites of endometriosis. Due to the retrograde menstruation, endometrial tissue commonly implant at this site.The authors show in Fig. 1 the ultrasound image of the rectouterine pouch where the probe is inserted in the posterior vaginal fornix. In fact, the hyperechoic white Y-shaped lining is the meeting point where the pouch of Douglas serosa, anterior rectal wall serosa and RVS meet. If endometriosis implants at this point progress anteriorly, they infiltrate the vagina and torus uterinus, and if they grow posteriorly, they affect the rectum. Lateral progression affects the uterosacral ligaments and lateral parametrium (cardinal ligaments). However, endometriosis may also grow inferiorly into the loose connective tissue – RVS.Therefore, RVS involvement in the progression of the deep endometriosis (DE) is a logical progress of the disease and not a myth. Not only direct infiltration, but endometriosis originating from Müllerian rests by metaplasia can occur in the RVS (Nisolle & Donnez 1997). Isolated RVS DE is in all probability an existent, but extremely rare condition. However, the presence of DE in the RVS together with other posterior or lateral pelvic compartment locations is not uncommon. A recent multicentre study found that DE in the RVS was present in 16.5% of 1,182 patients who underwent surgery for DE (Bafort et al. 2026).I agree with the conclusion of the authors that precise terminology and localisation are critical for improving diagnostic consistency in endometriosis. Nevertheless, in my opinion, RVS should not be omitted as a location of endometriosis.The author declares that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work reported.This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.