Medical School · Year 1 · Anatomy Pelvis Head Neck · includes a quiz and discussion video
Lecture 7: Pelvic Vasculature and Lymphatics
Unit 1.5: Human Gross Anatomy III - Pelvis and Head/Neck
Learning Objectives
By the end of this lecture, students will be able to:
- Describe the course and branches of the internal iliac artery
- Identify the major pelvic veins and venous plexuses
- Describe the lymphatic drainage of pelvic organs
- Explain collateral circulation pathways in the pelvis
- Describe the anatomical basis for vascular procedures
- Correlate anatomical features with clinical conditions
Overview of Pelvic Vasculature
The pelvis receives an abundant blood supply primarily through the internal iliac arteries, supplemented by contributions from the gonadal vessels, the median sacral artery, and the superior rectal artery. This rich arterial network supplies the pelvic viscera, pelvic walls, gluteal region, and perineum. The venous drainage pattern parallels the arterial supply but is characterized by extensive venous plexuses surrounding the pelvic organs, which communicate freely with the vertebral venous system.
The pelvic vascular anatomy is notable for its extensive anastomotic connections, which provide collateral pathways when primary vessels are occluded. This feature allows surgical ligation of the internal iliac artery for hemorrhage control without causing pelvic ischemia. The intimate relationship between pelvic vessels and pelvic organs makes understanding this anatomy essential for surgical procedures in the region.
<image>Panel A: Superior-anterior view showing aortic bifurcation at L4 dividing into common iliac arteries. Panel B: Division at pelvic brim into external iliac continuing to lower limb and internal iliac descending into pelvis. Panel C: Internal iliac artery branching to supply pelvic walls, viscera, gluteal region, and perineum. Panel D: Venous plexuses around bladder, prostate/uterus, and rectum connecting to internal iliac veins with gonadal vessels and median sacral artery illustrated.</image>
Common Iliac Arteries
The abdominal aorta bifurcates at the L4 vertebral level into the right and left common iliac arteries. Each common iliac artery descends along the medial border of the psoas muscle for approximately 5 centimeters before dividing at the pelvic brim (near the sacroiliac joint) into the external and internal iliac arteries.
The external iliac artery continues along the pelvic brim and passes beneath the inguinal ligament to become the femoral artery, providing the principal blood supply to the lower limb. Along its course, it gives off the inferior epigastric and deep circumflex iliac arteries.
The internal iliac artery (hypogastric artery) is the main arterial supply to the pelvis. It descends into the pelvic cavity, where it branches to supply the pelvic walls, viscera, gluteal region, and perineum.
Important relations of the common iliac arteries include: anteriorly, the peritoneum, ureters (crossing from lateral to medial), and gonadal vessels; posteriorly, the psoas muscle and sympathetic trunk. On the right, the common iliac vein lies posterior to the artery. On the left, the left common iliac vein crosses beneath the right common iliac artery to reach the IVC—this anatomical relationship explains why left lower limb deep vein thrombosis is more common due to compression (May-Thurner syndrome).
<image>Panel A: Common iliac arteries traced from aortic bifurcation at L4 to pelvic brim division. Panel B: External iliac continuing to lower limb and internal iliac descending into pelvis. Panel C: Ureters crossing anteriorly with common iliac veins posterior and left vein crossing beneath right artery. Panel D: Psoas muscle as posterior relation with May-Thurner venous compression location indicated.</image>
Internal Iliac Artery: Overview and Divisions
The internal iliac artery begins at the common iliac bifurcation at the pelvic brim and descends approximately 4 centimeters into the pelvis before dividing into anterior and posterior divisions. This division typically occurs at the level of the superior edge of the greater sciatic foramen.
The posterior division gives rise exclusively to parietal (body wall) branches that supply the posterior pelvic wall and gluteal region. The anterior division gives rise to both parietal branches (supplying the body wall and perineum) and visceral branches (supplying the pelvic organs).
Understanding the branching pattern of the internal iliac artery is essential for surgical procedures, interventional radiology, and trauma management in the pelvis.
<image>Panel A: Internal iliac artery descending from common iliac bifurcation into pelvis. Panel B: Division near superior greater sciatic foramen edge into posterior and anterior divisions. Panel C: Posterior division giving three parietal branches directed posterolaterally and anterior division giving parietal and visceral branches. Panel D: Schematic tree diagram summarizing internal iliac division and branching pattern.</image>
Posterior Division Branches
The posterior division of the internal iliac artery gives rise to three parietal branches that supply the posterior pelvic wall and gluteal region.
The iliolumbar artery ascends posterior to the psoas major and obturator nerve, dividing into an iliac branch (supplying the iliacus muscle and ilium) and a lumbar branch (supplying the psoas and quadratus lumborum muscles). The lumbar branch sends a spinal branch through the intervertebral foramen to supply the cauda equina. This vessel anastomoses with the deep circumflex iliac, lumbar, and obturator arteries.
The lateral sacral arteries (typically two, superior and inferior) descend on the anterior surface of the sacrum, sending spinal branches through the anterior sacral foramina to supply the sacral canal contents and posterior branches to supply the erector spinae muscles. They anastomose with the median sacral artery.
The superior gluteal artery is the largest branch of the internal iliac artery and the only artery to exit the pelvis above the piriformis muscle, passing through the greater sciatic foramen. This anatomical feature is diagnostically useful: all other structures exit below the piriformis. The superior gluteal artery supplies the gluteus maximus, medius, and minimus muscles, as well as the tensor fasciae latae, anastomosing with the inferior gluteal and lateral femoral circumflex arteries.
<image>Panel A: Iliolumbar artery ascending behind psoas to reach iliac fossa and lumbar region. Panel B: Lateral sacral arteries descending along sacrum with spinal branches entering sacral foramina. Panel C: Superior gluteal artery as largest branch exiting through greater sciatic foramen above piriformis muscle. Panel D: Anastomotic connections indicated with dashed lines between posterior division branches.</image>
Anterior Division: Parietal Branches
The anterior division gives rise to three parietal branches that supply the lateral pelvic wall, gluteal region, and perineum.
The obturator artery runs along the lateral pelvic wall, accompanied by the obturator nerve, and exits through the obturator canal to supply the medial thigh compartment. It divides into anterior and posterior branches in the thigh, with the posterior branch giving an acetabular branch to the hip joint. A clinically important variant is the aberrant obturator artery (present in 20-30% of individuals), which arises from the inferior epigastric or external iliac artery rather than the internal iliac. This aberrant vessel crosses the superior pubic ramus near the femoral ring and is vulnerable to injury during hernia surgery—a situation referred to as "corona mortis" (crown of death) due to the severe hemorrhage that may result.
The inferior gluteal artery exits the pelvis through the greater sciatic foramen below the piriformis muscle, along with the sciatic nerve, pudendal nerve, and internal pudendal artery. It supplies the gluteus maximus, hip rotators, and the sciatic nerve itself (through the artery of the sciatic nerve). It anastomoses with the superior gluteal, medial femoral circumflex, and first perforating arteries.
The internal pudendal artery is the principal blood supply to the perineum and external genitalia. It follows a distinctive course: exiting the pelvis through the greater sciatic foramen below the piriformis, crossing the posterior aspect of the ischial spine (where a pudendal nerve block can be performed), and re-entering the perineum through the lesser sciatic foramen. Within the perineum, it travels in the pudendal canal (Alcock's canal) on the lateral wall of the ischioanal fossa. Its branches include the inferior rectal artery (to the anal canal and sphincters), perineal artery (to the muscles and skin of the urogenital triangle), and terminal branches to the erectile tissues—the artery to the bulb, urethral artery, deep artery of the penis/clitoris, and dorsal artery of the penis/clitoris.
<image>Panel A: Obturator artery coursing along lateral pelvic wall exiting through obturator canal with corona mortis variant inset. Panel B: Inferior gluteal artery exiting below piriformis alongside sciatic nerve. Panel C: Internal pudendal artery course - exiting below piriformis, wrapping around ischial spine, entering lesser sciatic foramen. Panel D: Internal pudendal traveling in pudendal canal to supply perineum with sequential branches labeled.</image>
Anterior Division: Visceral Branches
The anterior division gives rise to visceral branches that supply the pelvic organs, with differences between males and females.
The umbilical artery represents the patent proximal portion of the fetal umbilical artery. After birth, its distal portion obliterates to form the medial umbilical ligament, but the proximal segment remains patent, giving rise to the superior vesical artery (or arteries), which supplies the superior bladder and upper ureter. In males, it may also give rise to the artery to the vas deferens.
The inferior vesical artery (in males) supplies the bladder base, prostate gland, and seminal vesicles. It also contributes to the lower ureter. In females, this vessel is replaced by the vaginal artery.
The vaginal artery (in females) is the homologue of the inferior vesical artery. It supplies the vagina and gives branches to the bladder base and rectum. Paired azygos arteries of the vagina, formed by anastomoses between vaginal and uterine arteries, run along the anterior and posterior vaginal walls.
The uterine artery, unique to females, is one of the most surgically important vessels in the pelvis. It runs in the base of the broad ligament (within the cardinal ligament) to reach the lateral cervix. A critical relationship is its crossing over the ureter approximately 2 centimeters lateral to the cervix—"water under the bridge" describes this anatomy where the uterine artery passes over the ureter. At the cervix, the uterine artery turns upward to ascend along the lateral uterine border in a tortuous course (accommodating uterine growth during pregnancy), giving cervical, corporeal, tubal, and ovarian branches. The ovarian branch anastomoses with the ovarian artery in the broad ligament, providing collateral circulation.
The middle rectal artery supplies the muscular wall of the lower rectum. It is variable in size and may be small or absent. It runs in the lateral ligament of the rectum, anastomosing with the superior rectal (from IMA) and inferior rectal (from internal pudendal) arteries.
<image>Panel A: Umbilical artery with patent superior vesical branch and obliterated medial umbilical ligament in both sexes. Panel B: Middle rectal artery to rectum with male inferior vesical artery to bladder base and prostate. Panel C: Female vaginal artery and uterine artery coursing in broad ligament. Panel D: Inset showing uterine artery crossing over ureter ("water under the bridge") approximately 2 cm lateral to cervix.</image>
Pelvic Veins and Venous Plexuses
The pelvic venous drainage is characterized by venous plexuses surrounding the pelvic organs, which eventually drain into the internal iliac veins. The internal iliac vein, formed by tributaries corresponding to the arterial branches, runs posterior to the internal iliac artery and joins the external iliac vein to form the common iliac vein.
The vesical venous plexus surrounds the bladder base and, in males, the prostate (where it is termed the prostatic venous plexus). The prostatic plexus receives the deep dorsal vein of the penis and drains via the vesical veins to the internal iliac veins. This plexus communicates freely with Batson's vertebral venous plexus.
The uterine venous plexus runs along the lateral uterus between the layers of the broad ligament, draining the uterus and upper vagina via the uterine veins to the internal iliac veins.
The vaginal venous plexus surrounds the vagina and communicates with the vesical, rectal, and uterine plexuses.
The rectal venous plexus includes the internal hemorrhoidal plexus (above the dentate line, draining via the superior rectal vein to the portal system) and the external hemorrhoidal plexus (below the dentate line, draining via the middle and inferior rectal veins to the systemic circulation). This represents a portosystemic anastomosis.
<image>Panel A: Coronal section showing vesical plexus surrounding bladder with prostatic plexus around prostate receiving deep dorsal vein of penis in males. Panel B: Uterine plexus running along lateral uterus in females. Panel C: Rectal plexus with internal plexus draining to portal system and external plexus to systemic circulation. Panel D: All plexuses connecting to internal iliac veins joining external iliac veins forming common iliac veins draining to IVC.</image>
Batson's Vertebral Venous Plexus
Batson's plexus is a valveless network of veins extending along the entire vertebral column, with internal (within the vertebral canal) and external (around the vertebral bodies) components. It communicates directly with the pelvic venous plexuses via connections through the sacral foramina and along the lateral sacral veins.
The clinical significance of this communication cannot be overstated. Because the vertebral venous system lacks valves, blood can flow in either direction depending on pressure gradients. When intra-abdominal or intrathoracic pressure increases (during coughing, straining, or Valsalva maneuver), blood is forced from the abdominal and pelvic veins into the vertebral system.
This mechanism explains the characteristic pattern of metastatic spread from pelvic cancers—particularly prostate cancer—directly to the vertebral column without first passing through the lungs. Prostate cancer commonly metastasizes to the lumbosacral spine, thoracic spine, and even skull through this route. Similarly, bladder and cervical cancers may spread to the vertebrae via this pathway.
<image>Panel A: Batson's plexus alongside vertebral column showing internal component within vertebral canal and external component around vertebral bodies. Panel B: Plexus extending from skull to sacrum with direct communications to pelvic venous plexuses through sacral foramina. Panel C: Arrows indicating bidirectional flow depending on intra-abdominal pressure changes. Panel D: Clinical correlation showing prostate cancer metastasizing to lumbar vertebrae via this route bypassing pulmonary circulation.</image>
Gonadal Vessels
The gonadal arteries (testicular in males, ovarian in females) arise directly from the abdominal aorta at the L2 vertebral level, reflecting the embryological origin of the gonads in the posterior abdominal wall. They descend retroperitoneally, crossing anterior to the ureter, to reach their respective organs.
In males, the testicular artery descends through the deep inguinal ring and inguinal canal within the spermatic cord to reach the testis. It anastomoses with the artery to the vas deferens (from the inferior vesical) and the cremasteric artery (from the inferior epigastric), providing collateral blood supply to the testis.
In females, the ovarian artery crosses the external iliac vessels at the pelvic brim, enters the suspensory ligament of the ovary, and reaches the ovary through the mesovarium. It anastomoses with the ovarian branch of the uterine artery in the broad ligament.
The gonadal veins follow a different pattern on each side. The right testicular/ovarian vein drains directly into the inferior vena cava. The left testicular/ovarian vein drains into the left renal vein (entering at a right angle, with higher resistance to drainage). This asymmetry explains why varicoceles occur predominantly on the left side.
<image>Panel A: Gonadal arteries arising from aorta at L2 descending retroperitoneally to reach gonads. Panel B: Asymmetric venous drainage with right to IVC directly and left to left renal vein. Panel C: Male testicular vessels entering spermatic cord through deep inguinal ring. Panel D: Female ovarian vessels crossing pelvic brim entering suspensory ligament with anastomoses to pelvic vessels indicated.</image>
Collateral Circulation
The pelvis possesses extensive collateral pathways that can maintain perfusion when primary vessels are compromised. These anastomoses explain why ligation of the internal iliac artery—commonly performed for severe pelvic hemorrhage in trauma or obstetric emergencies—typically does not cause pelvic ischemia.
The lumbar pathway connects the iliolumbar artery with the lumbar arteries and the deep circumflex iliac artery, providing collateral around an internal iliac occlusion.
The sacral pathway connects the lateral sacral arteries with the median sacral artery from the aorta.
The gluteal pathway connects the superior and inferior gluteal arteries with the lateral femoral circumflex and first perforating arteries from the profunda femoris, maintaining gluteal perfusion.
The obturator pathway connects the obturator artery with the medial femoral circumflex artery.
The rectal pathway connects the middle rectal artery with the superior rectal (from the IMA) and inferior rectal (from the internal pudendal) arteries, maintaining colorectal perfusion.
The uterine-ovarian anastomosis connects the uterine artery's ovarian branch with the ovarian artery in the broad ligament, maintaining ovarian viability if either vessel is ligated.
<image>Panel A: Pelvis with internal iliac artery ligated showing iliolumbar-lumbar and lateral sacral-median sacral collateral pathways. Panel B: Superior/inferior gluteal to profunda femoris pathway with arrows showing compensatory flow direction. Panel C: Obturator-medial circumflex pathway and rectal anastomoses between superior, middle, and inferior rectal arteries. Panel D: Uterine-ovarian anastomosis in female pelvis with color-coded interconnected network of collaterals.</image>
Lymphatic Drainage of the Pelvis
Pelvic lymph nodes are organized into groups that receive drainage from specific organs and regions, with important implications for cancer staging and treatment.
The external iliac nodes lie along the external iliac vessels. They receive lymph from the upper bladder, upper vagina (two-thirds), cervix, body of the uterus, deep inguinal nodes (thus indirectly from the lower limb), and anterior abdominal wall. They drain to the common iliac nodes.
The internal iliac nodes lie along the internal iliac vessels. They receive lymph from the lower pelvic viscera, including the bladder base and neck, prostate, lower rectum, cervix, vagina, and deep perineum. They drain to the common iliac nodes.
The sacral nodes lie along the median sacral vessels. They receive lymph from the rectum and posterior pelvic wall, draining to the common iliac nodes.
The common iliac nodes surround the common iliac vessels. They receive lymph from the external iliac, internal iliac, and sacral nodes, draining to the para-aortic (lumbar) nodes.
The para-aortic (lumbar) nodes lie alongside the abdominal aorta. They receive direct drainage from the ovaries and testes (following the gonadal vessels), the uterine fundus (following the round ligament or ovarian vessels), and indirect drainage from all pelvic nodes via the common iliac nodes. They drain to the cisterna chyli and thoracic duct.
<image>Panel A: Anterior view showing green external iliac nodes along external iliac vessels and blue internal iliac nodes along internal iliac vessels. Panel B: Purple sacral nodes in sacral hollow draining to orange common iliac nodes. Panel C: Common iliac nodes draining to red para-aortic nodes with afferent drainage arrows from organs. Panel D: Direct gonadal drainage from ovaries/testes to para-aortic nodes bypassing pelvic nodes emphasized.</image>
Organ-Specific Lymphatic Drainage
Understanding which lymph node groups drain each pelvic organ is essential for cancer staging and surgical lymphadenectomy planning.
The bladder demonstrates regional drainage patterns: the superior portion drains to external iliac nodes, the base drains to both external and internal iliac nodes, and the neck drains to internal iliac and sacral nodes.
The prostate drains primarily to internal iliac and sacral nodes, with some drainage to external iliac nodes. The obturator lymph nodes (part of the internal iliac group) are particularly important in prostate cancer staging.
The uterus shows complex drainage: the body drains primarily to external iliac nodes, while the fundus has a unique pathway along the ovarian vessels directly to para-aortic nodes (or along the round ligament to superficial inguinal nodes). The cervix drains to external iliac, internal iliac, and sacral nodes.
The ovaries and testes drain directly to para-aortic nodes at the L1-L2 level, reflecting their embryological origin—not to pelvic nodes. This has major implications for cancer staging and treatment: ovarian and testicular cancers spread to the retroperitoneum, not the pelvis.
The vagina has segmental drainage: the upper two-thirds drain to external and internal iliac nodes, while the lower third drains to superficial inguinal nodes (similar to the vulva).
The upper anal canal drains to internal iliac and inferior mesenteric nodes, while the lower anal canal drains to superficial inguinal nodes.
<image>Panel A: Bladder segmental lymphatic drainage - superior to external iliac, base to external/internal iliac, neck to internal iliac/sacral. Panel B: Uterus drainage - body to external iliac, fundus to para-aortic, cervix to multiple pelvic groups. Panel C: Ovaries and testes with direct drainage to para-aortic nodes bypassing pelvis and prostate to internal iliac/obturator nodes. Panel D: Vagina with upper drainage to pelvic nodes and lower to inguinal nodes with arrows indicating pathways.</image>
Clinical Correlations
Internal Iliac Artery Ligation
Ligation of the internal iliac artery is performed for control of severe pelvic hemorrhage, such as in obstetric emergencies (postpartum hemorrhage, placenta accreta) or pelvic trauma. The rich collateral circulation usually prevents pelvic ischemia, though bilateral ligation may compromise gluteal perfusion. Unilateral ligation is typically well tolerated.
Uterine Artery Embolization
Uterine artery embolization (UAE) is a minimally invasive treatment for symptomatic uterine fibroids. Interventional radiologists access the uterine artery via femoral artery catheterization and selectively occlude the vessels feeding the fibroids with embolic particles. This preserves the uterus while reducing fibroid blood supply and causing shrinkage. The procedure requires detailed knowledge of the uterine artery's course and branches.
Pelvic Fracture Hemorrhage
High-energy pelvic fractures can cause life-threatening hemorrhage from injury to the internal iliac branches, particularly the superior gluteal and pudendal arteries. Initial management includes pelvic binders to reduce pelvic volume and provide tamponade. Angioembolization of bleeding vessels may be required, necessitating knowledge of the vascular anatomy.
Corona Mortis
The aberrant obturator artery (present in 20-30% of individuals) crosses the superior pubic ramus near the femoral ring. Injury during hernia repair or pubic symphysis procedures can cause significant hemorrhage. Awareness of this variant and careful surgical technique are essential.
Prostate Cancer Metastasis
Prostate cancer characteristically metastasizes to the lumbosacral spine and pelvis via the valveless vertebral venous plexus (Batson's plexus). This direct venous communication bypasses the lungs, explaining why bone metastases may occur without pulmonary involvement. Osteoblastic (sclerotic) metastases are typical of prostate cancer.
Pelvic Lymphadenectomy
Radical lymphadenectomy is a standard component of surgery for pelvic malignancies. Extended lymphadenectomy includes external iliac, internal iliac, obturator, and common iliac nodes. For ovarian and testicular cancers, retroperitoneal (para-aortic) lymphadenectomy is required because these organs drain directly to para-aortic nodes.
<image>Panel A: Internal iliac artery ligation for obstetric hemorrhage with collateral pathways maintaining pelvic perfusion. Panel B: Uterine artery embolization showing catheter access via femoral artery with selective embolization of uterine branches. Panel C: Corona mortis showing aberrant obturator artery at risk during hernia surgery and prostate cancer metastasis to spine via Batson's plexus. Panel D: Pelvic lymphadenectomy extent for staging procedures showing external iliac, internal iliac, obturator, and common iliac node dissection.</image>
Summary
The internal iliac artery is the main blood supply to the pelvis, dividing into posterior (iliolumbar, lateral sacral, superior gluteal) and anterior divisions. The anterior division provides parietal branches (obturator, inferior gluteal, internal pudendal) and visceral branches (superior vesical from umbilical, inferior vesical/vaginal, uterine, middle rectal). The superior gluteal artery is the only branch exiting above the piriformis; all others exit below. The internal pudendal artery is the principal supply to the perineum. The uterine artery crosses over the ureter ("water under the bridge") approximately 2 cm lateral to the cervix. Pelvic venous plexuses around the bladder, prostate/uterus, and rectum communicate with Batson's vertebral venous plexus, providing a direct route for metastatic spread to the spine. Lymphatic drainage follows patterns based on organ and region: external iliac nodes receive from the upper bladder and uterine body, internal iliac nodes from the bladder base and prostate, and para-aortic nodes directly from the gonads. Rich collateral circulation allows internal iliac artery ligation without pelvic ischemia.
Key Terms
Internal iliac artery (hypogastric artery): The main arterial supply to the pelvis, dividing into posterior and anterior divisions that supply the pelvic walls, viscera, gluteal region, and perineum.
Superior gluteal artery: The largest branch of the internal iliac artery and the only branch that exits the pelvis above the piriformis muscle through the greater sciatic foramen.
Internal pudendal artery: The principal arterial supply to the perineum and external genitalia, following a distinctive course around the ischial spine and through the pudendal canal.
Corona mortis: The clinically significant aberrant obturator artery (present in 20-30%) arising from the inferior epigastric or external iliac artery and crossing the superior pubic ramus at risk during hernia surgery.
Batson's plexus (vertebral venous plexus): The valveless venous system along the vertebral column that communicates with pelvic venous plexuses, providing a direct route for pelvic cancer metastasis to the spine.
Para-aortic (lumbar) lymph nodes: The lymph nodes along the abdominal aorta that receive direct drainage from the gonads and indirect drainage from all pelvic nodes via the common iliac chain.
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