Boundaries and osteoligamentous framework of the pelvis
The pelvis is divided into the greater and lesser pelvis. The conventional boundary between them is the terminal line (linea terminalis), formed by the sacral promontory, the arcuate line of the ilium, the pubic crest, and the upper margin of the pubic symphysis. In topographical anatomy, the pelvis specifically refers to the lesser pelvis—the structures below the terminal line. The iliac wings form the bony framework of the lower abdominal and gluteal regions.
The pelvic walls are formed by the pubic, iliac, and ischial bones, the sacrum, and the coccyx. The pubic bones are joined by the pubic symphysis, reinforced by the superior and arcuate pubic ligaments. The sacroiliac joint is supplemented by two key ligaments:
- sacrospinous ligament — from the sacrum to the ischial spine;
- sacrotuberous ligament — from the sacrum to the ischial tuberosity.
These ligaments convert the greater and lesser sciatic notches into the corresponding foramina, which serve as pathways for neurovascular structures.
Pelvic diaphragms and the perineum
The pelvic floor is formed by the pelvic diaphragm and the urogenital diaphragm. Pelvic muscles are divided into parietal (walls) and visceral (pelvic diaphragm: levator ani and coccygeus muscles, as well as the external anal sphincter).
The perineum has a diamond shape. The line between the ischial tuberosities divides it into the urogenital triangle (anteriorly) and the anal triangle (posteriorly); the perineal body (central tendon of the perineum) projects in the center. The urogenital diaphragm is formed by the deep transverse perineal muscle and the external urethral sphincter.
Three levels of the lesser pelvic cavity
The lesser pelvic cavity is divided into three levels.
- Peritoneal (upper) level — between the parietal peritoneum and the organs covered by it. In men, the peritoneum covers the superior surface of the urinary bladder, forming the transverse vesical fold and paravesical fossae, and reflects onto the rectum to form the rectovesical pouch. In women, it forms the vesicouterine pouch and the rectouterine pouch (pouch of Douglas), which is the lowest point of the peritoneal cavity. When full, the urinary bladder elevates the peritoneum, a feature utilized in extraperitoneal approaches.
- Subperitoneal (middle) level — between the peritoneum and the fascia covering the levator ani muscle. Contains the extraperitoneal parts of the bladder and rectum, ureters, and in men — the prostate, seminal vesicles, and ductus deferens; in women — the cervix and the upper part of the vagina.
- Subcutaneous (perineal) level — between the pelvic diaphragm and the perineal skin. This level contains the ischiorectal fossa (fossa ischiorectalis) with the fat pad, internal pudendal artery and vein, and the pudendal nerve — a common site for the development of paraproctitis.
Fasciae and fascial spaces
The pelvic fascia is divided into parietal and visceral layers. The visceral fascia forms organ capsules; the most prominent are the capsule of Pirogov–Retzius around the prostate and the fascia of Amussat around the rectum. The Denonvilliers' fascia (rectovesical septum) lies between the rectum and the urogenital organs.
Visceral fascial spaces: paravesical, periprostatic, paravaginal, parametrial, and pararectal spaces.
Parietal fascial spaces: prevesical (retropubic), retrorectal, two lateral spaces, and additionally the retrovesical space in men.
Suppurative tracks spread along neurovascular bundles: via the obturator canal into the adductor compartment of the thigh, through the infrapiriform foramen into the gluteal region, along the pudendal bundle into the perineum, along the ureters and ovarian vessels into the retroperitoneal tissue, and along the round ligament of the uterus into the inguinal canal.
Organs of the male pelvis
The urinary bladder lies posterior to the pubic symphysis, with its base resting on the prostate. Posteriorly, it is related to the ampullae of the ductus deferens, seminal vesicles, and terminal ureters. The prostate gland is enclosed in the capsule of Pirogov–Retzius, fixed by the puboprostatic ligaments, and is palpable on digital rectal examination. The prostatic venous plexus is thin-walled and anastomoses with vertebral veins—a pathway for prostate cancer metastasis to the pelvic bones and spine.
The ureter has three physiological constrictions. At the level of the pelvic brim, the left ureter crosses the common iliac artery, and the right crosses the external iliac artery. The rectum consists of a supra-ampullary part and an ampulla; its lower third is subperitoneal and is separated from the bladder and prostate by Denonvilliers' fascia.
Organs of the female pelvis
The uterus and its appendages lie between the urinary bladder and the rectum. Suspensory apparatus: broad, round, cardinal, and uterosacral ligaments. The parametrium — the connective tissue on the sides of the cervix — contains the uterine vessels and lymph nodes; it is a common site for parametritis and diffuse pelvic phlegmon.
The ureter crosses the uterine artery twice: the first time superficially to the artery, and the second time at the base of the broad ligament, where the artery runs anteriorly and superiorly. This creates a risk of incorporating the ureter into the ligature during ligation of the uterine artery, particularly during supracervical hysterectomy; ligation is performed as close to the uterine wall as possible.
The uterine tube is located along the superior margin of the broad ligament and comprises the uterine part, isthmus, ampulla, and infundibulum with fimbriae (ovarian fimbria). During tubectomy for ectopic pregnancy, the clamp is placed above the attachment of the mesovarium to preserve the ovary. The ovary is fixed by the proper ovarian ligament and suspensory ligament of the ovary; it is supplied by the ovarian artery. The rectum is related to the sacral plexus (hence pain radiation along the sciatic nerve) and to the posterior vaginal wall via the rectovaginal septum.
Neurovascular structures
The main blood supply to the pelvic organs comes from the internal iliac artery (a. iliaca interna), which branches off the common iliac artery at the level of the sacroiliac joint. Its visceral branches run within sagittal fascial partitions extending from the pubic bones to the sacrum. The pudendal neurovascular bundle (internal pudendal artery and vein, pudendal nerve) exits through the greater sciatic foramen, hooks around the ischial spine, and enters the ischiorectal fossa through the lesser sciatic foramen beneath the sacrotuberous ligament.
Key points
- The pelvic brim separates the greater pelvis from the lesser pelvis; topographically, "pelvis" equals the lesser pelvis.
- The lesser pelvic cavity is divided into three levels: peritoneal, subperitoneal, and subcutaneous (perineal).
- The pouch of Douglas in women is the lowest point of the peritoneal cavity and a site for exudate accumulation; it can be aspirated via posterior colpocentesis (culdocentesis).
- Denonvilliers' fascia separates the rectum from the urogenital organs.
- Visceral fascia forms organ capsules; the most prominent are the capsules of Pirogov–Retzius (prostate) and Amussat (rectum).
- The ischiorectal fossa is the site of paraproctitis development and contains the pudendal neurovascular bundle.
- The ureter crosses the uterine artery twice, which is of critical importance in gynecological surgery.
- Prostatic venous plexuses anastomose with vertebral veins, facilitating bone metastasis.