Iliac Lymph Nodes

1. Overview

The iliac lymph nodes are a series of deeply situated lymph nodes located along the iliac blood vessels in the pelvis. They form a major part of the deep lymphatic system of the abdomen and pelvis and are responsible for draining lymph from pelvic organs, lower abdominal wall, perineum, and parts of the lower limb. These nodes are critical in the context of gynecological, urological, and colorectal cancers, as they are common sites for metastatic spread.

2. Location

Iliac lymph nodes are distributed along the iliac arteries and veins and are categorized into three main groups based on their anatomical position:

• External iliac lymph nodes: Located along the external iliac vessels, medial and lateral to the external iliac vein and artery. They drain the lower abdominal wall, pelvic side wall, bladder, prostate, cervix, and upper vagina.

• Internal iliac lymph nodes (hypogastric): Situated around the internal iliac vessels. They receive lymph from the pelvic organs including the rectum, bladder, cervix, uterus, prostate, and vagina.

• Common iliac lymph nodes: Located along the common iliac vessels above the bifurcation of the aorta. These nodes receive drainage from both the external and internal iliac lymph nodes and channel it toward the lateral aortic (para-aortic) nodes.

3. Structure

Each iliac lymph node is a small, encapsulated, bean-shaped organ composed of lymphoid tissue. The structural organization includes:

• Cortex: Contains follicles primarily filled with B lymphocytes for humoral immune responses.

• Paracortex: A T cell-rich zone where antigen presentation and cell-mediated immunity occur.

• Medulla: Contains plasma cells and macrophages arranged in cords and sinuses.

Afferent lymphatic vessels bring lymph from pelvic structures into the node. After filtration, efferent vessels drain toward the common iliac or directly into para-aortic (lumbar) lymph nodes.

4. Function

The iliac lymph nodes play essential roles in immune defense and lymphatic drainage of deep pelvic and abdominal structures. Their primary functions include:

• Lymph filtration: They filter lymph to remove microorganisms, cancer cells, and cellular debris.

• Immune activation: Serve as sites for initiating immune responses by activating T and B cells in response to antigens.

• Drainage relay: Act as intermediate nodes in the lymphatic pathway from pelvic viscera to higher-level lumbar nodes.

5. Physiological Role(s)

The iliac lymph nodes contribute to several key physiological functions that support immune system activity and fluid balance:

• Defense of pelvic organs: Constantly monitor lymph from organs like the bladder, uterus, prostate, and rectum for signs of infection or malignancy.

• Support mucosal immunity: Help coordinate immune responses from mucosal tissues of the genitourinary and lower gastrointestinal tract.

• Facilitate lymphatic drainage: Ensure that excess interstitial fluid from pelvic and lower limb regions is efficiently returned to the systemic circulation.

6. Clinical Significance

Lymphadenopathy

Enlargement of the iliac lymph nodes may indicate underlying disease processes, though they are not typically palpable on physical examination due to their deep location. Causes include:

• Infections: Tuberculosis, sexually transmitted infections (e.g., chlamydia, syphilis), or pelvic inflammatory disease (PID).

• Inflammatory diseases: Autoimmune conditions such as Crohn’s disease or sarcoidosis.

• Malignancies: Most significantly, cancers of the cervix, prostate, bladder, rectum, uterus, and ovaries commonly metastasize to these nodes.

Cancer Staging and Metastasis

Iliac lymph nodes are frequently involved in staging of pelvic and lower abdominal cancers. Their involvement may influence prognosis and treatment decisions:

• In cervical and endometrial cancer: Spread to internal and external iliac nodes is a common route of metastasis.

• In prostate and bladder cancer: Iliac node involvement often signifies regional spread requiring lymph node dissection.

• In rectal cancer: Metastasis to internal iliac and mesorectal nodes is common, influencing surgical approach and adjuvant therapy.

Imaging and Biopsy

Because these nodes are not accessible through palpation, imaging techniques are vital:

• CT or MRI: Often used for identifying enlarged nodes in cancer staging or suspected infection.

• PET scan: Useful in detecting metabolically active nodes in oncologic patients.

• Needle biopsy: Performed under image guidance for diagnostic confirmation in suspicious cases.

Surgical Relevance

Iliac lymph nodes are commonly removed during radical pelvic surgeries such as radical hysterectomy, prostatectomy, or pelvic lymphadenectomy. This helps in staging, prognosis, and local disease control but may lead to postoperative complications like lymphocele or lower limb lymphedema.