Reevaluating the vesicouterine pouch: histological evidence for optimal dissection planes in oncologic surgery

Abstract

During dissection of the vesicouterine pouch, entering from the uterine body side may lead to an inappropriate plane that scrapes the uterine body, whereas dissecting from the bladder side often facilitates smoother separation of the vesicouterine pouch. This suggests that multiple dissectible layers exist in the vesicouterine pouch. In this study, we aimed to investigate the midline structures, which are crucial in oncologic surgeries. Overall, six halves of three cadavers were used. They had no history of lower abdomen or pelvic condition. No fasciae or septum-like structures were observed between the bladder and uterine and vaginal walls. A magnified image revealed several layers of connective tissue that were irregularly interspersed between the muscular layer of the bladder and vagina. Histological analysis demonstrated that the vesicouterine pouch consists of multiple dissectible layers, differing from descriptions in traditional surgical textbooks. Specifically, the pubocervical fascia and vesicovaginal septum were absent in the mid-sagittal section. Instead, multiple layers of connective tissue were irregularly interspersed within the bladder’s muscular layer. This finding is particularly important in oncologic surgeries, as it highlights the risk of cancer exposure at the dissection margins in cases with deep muscular invasion or stromal invasion. Additionally, it suggests that initiating dissection from the bladder side facilitates entry into the correct dissectible plane, reducing the risk of exposing malignant tissue.

Dear Editor,

In surgeries for cervical and endometrial cancer, positive surgical margins are known risk factors for recurrence. However, most studies focus on vaginal margins [1,2,3]. In surgical practice, cases with deep stromal invasion often reveal pathological specimens with exposed cancer at the dissection margins. During dissection of the vesicouterine pouch, entering from the uterine body (cranial) side may lead to an inappropriate plane that scrapes the uterine body (Video S1), whereas dissecting from the bladder (caudal) side often facilitates smoother separation of the vesicouterine pouch (Video S2). In Video S2, the peritoneum is incised along the line just adjacent to the adipose tissue that belongs to the bladder. This peritoneum cut line allows entry into the correct dissection plane without shaving the uterus or the vagina. This suggests that multiple dissectible layers exist in the vesicouterine pouch (Videos S1 and S2).

The 2 anatomical terms—“pubocervical fascia” and “vesicovaginal septum”—are frequently encountered in pelvic organ prolapse (POP) surgery [4,5], particularly in procedures involving pelvic reconstruction or vaginal repair. In surgical textbooks, a cystocele is defined as a defect in the fasciae. However, the cause of cystoceles remains unknown, and anatomical studies on the fasciae in which these defects occur are limited [6,7,8]. Although a previous anatomical study has reported on the gross anatomy of these defects, no studies have examined their exact pathology. Several pathological studies about pubocervical fascia are available; however, only a few studies have focused on the fascia in a mid-sagittal section that dissects between the uterus and bladder, and only one study has examined the lateral tissue section, which is reported to join the levator ani muscle [9,10]. In this study, we aimed to investigate the midline structures, which are crucial in oncologic surgeries.

The study was approved by the appropriate Ethics Review Board (Board of Ethics, Tokyo Medical and Dental University, M2018-006-05), and all methods were performed following the relevant guidelines and regulations. A cadaver was fixed using 8% formalin via arterial perfusion and preserved in 30% alcohol to prevent fungal growth and maintain tissue softness. As this was a small study, three female cadaver was used. The pelvis was dissected from the medial aspect and cut into halves along the midsagittal line using a diamond-band pathology saw (EXAKT 312; EXAKT Advanced Technologies, Norderstedt, Germany) [11,12]. Histological analyses were subsequently performed. The pelvis was excised en bloc and sectioned along the sagittal plane. Next, the tissues obtained were embedded in paraffin, sectioned into 5-mm-thick specimens, and stained with hematoxylin and eosin. The bladder, uterus, vagina, and vesicovaginal fossa were observed in the sagittal sections of the pelvis during the histological analyses.

Overall, six halves of three cadavers were used. Their ages were 92, 99, and 104 years. They had no history of lower abdomen or pelvic condition. No fasciae or septum-like structures were observed between the bladder and uterine and vaginal walls. A magnified image revealed several layers of connective tissue that were irregularly interspersed between the muscular layer of the bladder and vagina (Fig. 1).

Fig. 1. Histological analyses of the BI, Ut, and V in the midsagittal plane.

(A) Magnified image revealing several layers of connective tissue between the BI and V, which are irregularly interspersed with the muscular layer of the BI. (B) Magnified view of the square frame in panel A. (C) Magnified view of the dashed square frame in panel B. (D) Magnified view of the dashed square frame in panel C.

Bl, bladder; Pu, pubis; Re, rectum; Ur, urethra; Ut, uterus; V, vagina.

Histological analysis demonstrated that the vesicouterine pouch consists of multiple dissectible layers, differing from descriptions in traditional surgical textbooks. Specifically, the pubocervical fascia and vesicovaginal septum were absent in the mid-sagittal section. Instead, multiple layers of connective tissue were irregularly interspersed within the bladder’s muscular layer. This finding is particularly important in oncologic surgeries, as it highlights the risk of cancer exposure at the dissection margins in cases with deep muscular invasion or stromal invasion. Additionally, it suggests that initiating dissection from the bladder side facilitates entry into the correct dissectible plane, reducing the risk of exposing malignant tissue.

Beyond cancer surgery, this observation is also relevant to POP surgery. This finding differs from that noted in traditional POP surgery textbooks. During the minimally invasive surgeries, a more defined anatomy was observed; however, we could not detect any fascia-like structures between the bladder and vagina as both organs were dissected in random layers [9]. Our study findings suggest variations in the dissectible layer between the bladder and uterus; therefore, in vaginal POP surgery, artifacts of these connective tissue fibers, which are clustered in blunt dissection, are usually recognized as fasciae [4,7,13]. Furthermore, these findings have implications for obstetric surgery. The interspersed muscular layer and several layers of connective tissue may be the reason for the higher rates of bladder injuries in total hysterectomies or placenta accreta after previous cesarean sections; these complication rates increase proportionally with an increasing number of previous cesarean sections [14,15]. This may be because each repeated dissection of the uterovesical pouch divides the intermingled layers of the bladder muscle, resulting in gradual thinning of the bladder.

This study had some limitations. First, we focused on basic histological properties rather than clinical features. Second, information regarding cadaver vaginal parity or obstetric history was unavailable due to limitations in donor records. In the future, we aim to study the relationships among the bladder, uterus, umbilical artery, and surrounding fascia (i.e., the vesicohypogastric fascia) using a larger sample size.

In conclusion, the anatomical structures termed the “pubocervical fascia” and “vesicovaginal septum”—were not apparent in the female cadaver examined in this study; instead, several dissectible layers of connective tissue were identified between the bladder and vagina. In cancer surgeries, starting the dissection of the vesicouterine pouch from the bladder side can help avoid cancer exposure when deep muscular invasion is present. Further, we hypothesize that artifacts of connective tissue fibers, which are clustered during blunt dissection, are recognized as fasciae during vaginal POP surgeries and cause of complications, such as bladder injuries and placenta accreta, after previous cesarean sections because of anatomical construction of vesicouterine pouch.

SUPPLEMENTARY MATERIALS

Video S1

Dissection of the vesicouterine pouch starting from the uterine side, resulting in the uterine wall being scraped.

Video S2

Dissection of the vesicouterine pouch starting from the bladder side, smoothly entering the easily dissectible layer between the bladder and uterus.