The internal iliac vein is a major venous structure that drains blood from the pelvic organs, pelvic walls, and the gluteal region. It is formed by the confluence of several smaller veins, including the superior and inferior gluteal veins, obturator vein, and others from the pelvic region. Located deep in the pelvis, the internal iliac vein runs parallel to the internal iliac artery and ascends to join the external iliac vein. Together, they form the common iliac vein, which subsequently drains into the inferior vena cava. The internal iliac vein is located posterior to the internal iliac artery and near the sacroiliac joint.
Structure and Anatomy
Origin
The internal iliac vein originates deep within the pelvis, forming from the convergence of several smaller veins that drain the pelvic organs, walls, and gluteal region. It begins at the level of the greater sciatic foramen and runs posterior to the internal iliac artery. The internal iliac vein usually forms from tributaries that include the gluteal veins, obturator veins, and other pelvic venous structures.
Course
The internal iliac vein ascends within the pelvis, running posterior to the internal iliac artery. As it ascends, it moves medially and posteriorly toward the sacroiliac joint, passing along the lateral wall of the pelvis. The vein courses through the region to eventually meet the external iliac vein near the pelvic brim. At this point, the internal and external iliac veins merge to form the common iliac vein, which then drains into the inferior vena cava.
Tributaries
The internal iliac vein receives blood from several key tributaries that drain various regions of the pelvis and lower extremity:
- Superior and Inferior Gluteal Veins: These veins drain the gluteal region, including the gluteus maximus, medius, and minimus muscles.
- Obturator Vein: This vein drains the medial thigh and the pelvic region associated with the obturator muscle.
- Internal Pudendal Vein: Drains the external genitalia, perineum, and associated structures.
- Lateral Sacral Veins: Drain blood from the sacrum and surrounding structures.
- Vesical Veins: Drain the urinary bladder.
- Rectal (Hemorrhoidal) Veins: Drain the rectum.
- Uterine and Vaginal Veins (in females): These veins drain the uterus and vagina, respectively.
- Prostatic Venous Plexus (in males): Drains the prostate and surrounding regions.
Relationship with Surrounding Structures
- Internal Iliac Artery: The internal iliac vein runs parallel and posterior to the internal iliac artery. This proximity is important for surgical procedures and anatomical reference in the pelvic region.
- Pelvic Organs: The internal iliac vein lies in close relation to several pelvic organs, including the bladder, rectum, and, in females, the uterus and vagina. These organs contribute tributary veins to the internal iliac vein.
- Sacroiliac Joint: As the vein ascends, it passes near the sacroiliac joint, where the pelvis connects with the sacrum. This relationship is important in understanding the venous drainage patterns of the posterior pelvic structures.
- Lumbosacral Plexus: The internal iliac vein lies near the lumbosacral plexus, a network of nerves that supplies the lower limbs and pelvis.
Termination
The internal iliac vein terminates when it merges with the external iliac vein at the pelvic brim. Together, they form the common iliac vein, which continues to ascend toward the heart. The common iliac veins from both sides of the body eventually converge to form the inferior vena cava, which transports deoxygenated blood back to the right atrium of the heart.
Variations
The internal iliac vein can exhibit some anatomical variations in terms of its size, number of tributaries, and exact path. In some individuals, the vein may divide into smaller branches before forming the common iliac vein, or additional veins may drain into it directly. There may also be variations in the venous plexuses associated with the pelvic organs, depending on individual anatomy or pathological conditions.
Function
The internal iliac vein plays a vital role in venous drainage from the pelvic organs, gluteal region, and parts of the lower limb. It serves as a major conduit for returning deoxygenated blood from these regions to the heart via the inferior vena cava. Below is a detailed explanation of the specific functions of the internal iliac vein.
Venous Drainage of the Pelvic Organs
One of the primary functions of the internal iliac vein is to drain blood from the pelvic organs. These include:
- Urinary Bladder: The vesical veins, which drain into the internal iliac vein, carry deoxygenated blood from the bladder. This ensures proper circulation of blood within the urinary system, helping maintain bladder function and health.
- Rectum: The rectal veins, also known as the hemorrhoidal veins, drain the blood from the rectum. The internal iliac vein helps transport this deoxygenated blood to the systemic circulation.
- Reproductive Organs:
- In females, the internal iliac vein collects blood from the uterus and vagina via the uterine and vaginal veins, ensuring efficient drainage from these reproductive structures.
- In males, the internal iliac vein receives blood from the prostatic venous plexus, draining the prostate gland, an essential function for maintaining male reproductive health.
Venous Drainage of the Gluteal Region
The internal iliac vein plays an important role in draining the buttocks and posterior hip region. It collects blood from:
- Superior and Inferior Gluteal Veins: These veins drain the gluteus maximus, medius, and minimus muscles, which are involved in movement and support of the hip. This ensures that deoxygenated blood is efficiently removed from the gluteal region during physical activities such as walking, running, and climbing.
- Superficial Tissues and Skin: The skin and subcutaneous tissues of the gluteal region are also drained by the superior and inferior gluteal veins, with their deoxygenated blood ultimately flowing into the internal iliac vein.
Venous Drainage of the Pelvic Walls and Fascia
The internal iliac vein also drains the blood from the pelvic walls and deep fascia, which form the supportive structures of the pelvis. This includes:
- Obturator Vein: This vein drains the medial thigh muscles and portions of the pelvis, contributing venous blood to the internal iliac vein. The drainage of the pelvic walls ensures proper circulation within the supportive structures of the pelvis, including the obturator internus and other deep pelvic muscles.
- Lateral Sacral Veins: These veins drain the blood from the sacrum and surrounding bony structures, with the internal iliac vein acting as a pathway for deoxygenated blood from the bony pelvis.
Venous Return to the Systemic Circulation
Once the internal iliac vein collects deoxygenated blood from the pelvic organs, gluteal region, and pelvic walls, it transports the blood toward the systemic circulation. The internal iliac vein converges with the external iliac vein to form the common iliac vein, which eventually drains into the inferior vena cava. The inferior vena cava then carries the deoxygenated blood to the heart’s right atrium, where it enters the pulmonary circulation for oxygenation.
Collateral Circulation
The internal iliac vein also plays a role in collateral circulation, providing an alternative pathway for blood to return to the heart if other venous pathways are blocked or restricted. This adaptability is particularly important in cases of venous thrombosis, compression, or surgery, where the internal iliac vein can serve as a backup route for venous return. This function ensures continuous blood flow from the pelvic region even in pathological conditions.
Regulation of Pelvic Venous Pressure
The internal iliac vein contributes to regulating venous pressure within the pelvis. During physical exertion or increased abdominal pressure (e.g., during lifting or childbirth), the internal iliac vein helps adjust venous return from the pelvic region, preventing excessive venous pressure that could lead to complications such as venous congestion or varicosities.
Clinical Significance
The internal iliac vein holds significant clinical importance due to its role in pelvic and lower body venous drainage. Any pathology involving this vein can have wide-ranging implications:
Deep Vein Thrombosis (DVT)
The internal iliac vein is susceptible to deep vein thrombosis, especially following surgery, prolonged immobility, or pelvic trauma. A thrombus (blood clot) in this vein can lead to pelvic congestion and, if dislodged, may result in a life-threatening pulmonary embolism.
Surgical Considerations
The internal iliac vein is often encountered in pelvic surgeries, such as hysterectomies, prostate surgeries, and procedures involving the gluteal region. Careful navigation is required to avoid injuring this vein, as it can cause significant bleeding or complications.
Pelvic Congestion Syndrome
In females, incompetence or dilatation of the internal iliac vein can contribute to pelvic congestion syndrome, characterized by chronic pelvic pain, often associated with varicosities in the pelvic region.
Compression Syndromes
The internal iliac vein can sometimes be compressed by neighboring structures, such as tumors, enlarged lymph nodes, or pelvic fractures. This may result in venous stasis, leading to symptoms like leg swelling, pelvic pain, or varicose veins in the lower extremities.
