Endometriosis is defined as chronic, incurable, ectopic growth of glandular tissue which is normally found within the uterus. The etiopathogenesis of the disease has not been completely unraveled, and various theories have attributed its development to the process of metaplasia and implantation of migrating endometrial cells with accompanying immune system malfunction. In the vast majority of cases, endometriosis is limited to the reproductive organs, however, on account of the immediate proximity of crucial organs of the lesser pelvis, and the pattern of endometrial spread, the disorder must often be addressed not only by a gynecologist, but also a surgeon, proctologist and urologist. The prevalence of endometriosis among women of reproductive age is estimated at approximately 10%, so they account for a significant proportion of both outpatients and inpatients treated by physicians of these specialties. However, because of ambiguous symptoms and difficulties associated with diagnostic imaging procedures, the disease is sometimes misdiagnosed and patients are referred back-and-forth between different medical specialists. Consequently, the period until the start of appropriate treatment may be as long as 7 years. One of the most severe forms of endometriosis is deep infiltrating endometriosis (DIE) involving the rectovaginal septum, which is discussed in detail below.

Deep infiltrating endometriosis is defined as subperitoneal invasion by endometriotic lesions exceeding 5 mm in depth. In view of differences in structure, form and function, in the 1990s endometrial lesions in the lesser pelvis were classified into three major categories: peritoneal, ovarian and deeply infiltrating ? in this case rectovaginal, with possible extension into the rectovaginal septum (RVS) (1, 2). The histopathological features of rectovaginal endometriosis which form the basis for the above division (among other factors) consist primarily of smooth muscle tissue and fibrous tissue, and to a lesser extent glandular tissue (3). This tissue composition is the underlying cause of the formation of hard, palpable nodules in this region. Differences can also be noted in the secretory activity of glandular epithelium, which ? in this location ? does not show typical changes associated with the second phase of the menstrual cycle, or the changes are incomplete. Based on these observations, the nodules were called adenomyosis of the rectovaginal septum (2, 4). Although the discussion on the origin and mechanisms underlying the development of these lesions is still ongoing, there is consensus that endometriosis involving this area is different from the peritoneal and ovarian types. The coexistence of these lesions is not necessary, so the clinical picture of endometriosis in the lesser pelvis may vary considerably. The prevalence of deep infiltrating lesions is estimated at approximately 1-2% (5). However, this value may be underestimated because of seemingly normal macroscopic features of some of the lesions (“tip of the iceberg” sign) (fig. 1) and the frequently coexisting extensive adhesion process (fig. 2), which often causes them to be “overlooked” during examinations of the peritoneal cavity.

The rectovaginal space extends from the bottom of the rectouterine pouch (also known as the pouch of Douglas) and reaches the perineal body, running between the posterior vaginal wall and the anterior rectal wall. In the sagittal plane, it can be divided into approximately 3 equal parts depending on the presence of its constituent structures including the connective tissue, nerves and blood vessels. According to a number of authors, by analogy to similar tissue found in men, an independent connective tissue structure, referred to as rectovaginal septum (RVS), is present in this area. Other authors challenge the existence of the structure, arguing that the connective tissue found in this location is a fragment of surrounding structures (rectum and vagina). The development of the tissue is sometimes attributed to high local tension (6). The rectovaginal septum consists of 2 thin elements. The upper one-third of the RVS, beginning in the peritoneal region of the rectouterine pouch, represents its thinnest part, predisposing to the development of enterocoele. Extending downwards, in the middle one-third, it has the greatest thickness and then becomes thinner again, merging into the tissue of the perineal body. The septum has no lateral boundaries, extending to the lateral vaginal wall in its anterior part, and to the rectum posteriorly. Its role and function also remain ambiguous. Since it has a relatively weak structure, especially outside the central part, the proposed function of maintaining vaginal and anal static strength is often questioned, and consequently its role is reduced to supporting vessels and nerves innervating the surrounding structures. From the point of view of endometriosis development, another important element is the presence of smooth muscle tissue within the septum. The presence of smooth muscle fibers has been confirmed immunohistochemically, though are also reports to the contrary (3, 7).

The development of endometriosis in the rectovaginal septum (RVS) may occur at one of its ends. Isolated infiltration of the septum is a rare occurrence, and usually the adjacent structures (i.e. the cervix, vagina, rectum as well as the sacrouterine ligament and the broad ligament of the uterus), are also affected. The invasion of the lower part of the septum occurs through damaged perineal and vaginal tissues. Most typically, perinatal trauma acts as a trigger, but there are also literature reports describing cases of invasion unrelated to childbirth (8). In addition to vaginal or rectal involvement, other possible findings in this area include infiltration of the anal sphincter as well as adjacent pelvic floor diaphragm muscles.

The presence and severity of symptoms associated with endometriosis of the rectovaginal septum depend significantly on the location, size and depth of infiltration. Occasionally, lesions in the same location may produce manifestations in some patients, while other patients remain unaffected by any symptoms. The coexistence of adenomyosis, peritoneal endometriosis as well as deep infiltrating endometriosis in another location (bladder, lateral wall of the lesser pelvis, intestine) increases the severity of pain. For the purpose of this publication, endometriosis of the rectovaginal septum can be divided into two types. Endometriosis of the lower part of the septum, in the region of anal sphincters and vaginal opening, manifests itself mainly as perineal pain in the episiotomy scar, pain during defecation and sexual intercourse (superficial dyspareunia), and the presence of a palpably tender nodule in the region of the episiotomy wound which may appear and disappear depending on the phase of the cycle. In addition to pain, symptoms include cyclic bleeding, sphincter dysfunction, and changes in stool. If endometriosis involves the upper part of the septum, the primary manifestations include deep dyspareunia, dyschezia and the presence of palpably tender nodules within the posterior vaginal vault, which may occupy its entire width, infiltrating the cervix and rectum. Depending on the degree of intestinal infiltration, symptoms of obstruction and gastrointestinal bleeding may appear. They are often accompanied by generalized irritable bowel symptoms. In each of the above cases, specific symptoms may be accompanied by other complaints. The most common manifestation is pain which occurs mostly during menstruation, but it may also persist during the entire menstrual cycle or grow in severity during the ovulation phase. Other major symptoms include abnormally heavy menstrual bleeding, infertility and coexisting ovarian cysts. In cases of bladder infiltration, possible manifestations include dysuria, hematuria or overactive bladder symptoms. Occasionally, symptoms of endometriosis of the lesser pelvis can impact adjacent structures, mimicking the dysfunction of other organs, as in the case of pain in the hip joint or in the lumbosacral region. Cyclical pain in the chest and lung apices may also indicate endometriosis in the pleura or diaphragm. In addition, there is a broad spectrum of pain symptoms not caused directly by the presence of lesions involving any given organ, but induced by the circulating mediators of inflammation and pain, or by the infiltration of nervous conduction pathways.