Pelvic Cavity Anatomy
Although the pelvic cavity is in direct continuity with the abdominal cavity, the two regions are delineated by the pelvic inlet (pelvic brim). This lies at approximately 45° to the horizontal and comprises the sacral promontory posteriorly, the arcuate and pectineal lines laterally and the pubic crests and upper border of pubic symphysis anteriorly (Figs 5.1 & 5.26).
The bony walls of the pelvis give attachment to two pairs of muscles. The obturator internus and piriformis muscles arise within the pelvis but their tendons pass out into the gluteal region to reach the femur. The fascia covering the medial surface of obturator internus is dense and provides attachment for the pelvic floor. The piriformis muscles spring from the anterior surface of the sacrum and are partially covered by the large nerves comprising the sacral plexuses (Fig. 5.4).
In both sexes, the pelvic cavity contains the rectum and bladder along with the lower parts of the ureters and loops of small or large intestine. The remaining organs differ between the sexes. The male reproductive organs found within the pelvis (Fig. 5.5) are the prostate, seminal vesicles and ductus deferentes. Those of the female (Fig. 5.6) are the ovaries, uterine tubes, uterus and upper part of vagina.
Fig. 5.4 Pelvis and lower abdomen after removal of all the organs and most of the vessels to demonstrate the pelvic inlet (pink line) and cavity.
Peritoneum lines the lateral and posterior pelvic walls and covers most of the pelvic organs (Figs 5.5 & 5.6). In both sexes peritoneum passes from the anterior abdominal wall onto the upper surface of the bladder. In the male, it descends on the posterior surface of the bladder and then passes onto the rectum, forming a recess, the rectovesical pouch (Fig. 5.14). In the female, peritoneum is reflected from the bladder onto the anterior surface of the body of the uterus, forming the vesicouterine pouch (Fig. 5.6). It covers the fundus of the uterus and on each side passes over the uterine tube, forming the broad ligament. From the posterior surface of the uterus, peritoneum passes over the vault of the vagina onto the anterior wall of the rectum, forming the rectouterine pouch (of Douglas). Fluid may collect in the rectovesical pouch of the male or the rectouterine pouch of the female and, if infected, may form a pelvic abscess.
Between the peritoneum and the pelvic organs, and intervening between the organs, lies the extraperitoneal fat or pelvic fascia (Fig. 5.7 and p. 235). This tissue is important in the spread of infection.