Pelvic lymph nodes - Structure, Location, Function

Pelvic lymph nodes are a network of interconnected lymphatic structures located within the pelvic cavity. They serve as critical filtering stations for lymph drained from pelvic organs, perineum, lower abdominal wall, and parts of the lower limb. The major groups include the external iliac, internal iliac, sacral, and inguinal lymph nodes. These nodes are essential in immune surveillance and play a key role in the spread and staging of pelvic malignancies.

Structure

Pelvic lymph nodes are clusters of small, oval-shaped lymphatic tissues. Each node receives afferent lymphatic vessels, filters lymph through cortical and medullary sinuses, and sends efferent vessels to larger lymphatic trunks. The nodes are surrounded by a capsule and consist of lymphoid follicles containing B and T lymphocytes.

Major Groups

External iliac nodes – Along the external iliac vessels
Internal iliac nodes – Around the internal iliac artery and its branches
Sacral nodes – Over the sacrum near the median sacral vessels
Inguinal nodes – Located inferiorly in the femoral triangle (superficial and deep)

Location

The pelvic lymph nodes are embedded in the connective tissue of the pelvic cavity, often surrounding major arteries and veins. They form chains that follow vascular structures and drain into higher-order lymphatic trunks such as the common iliac and para-aortic nodes.

Node Group	Anatomical Location
External iliac nodes	Along external iliac vessels, anterior and lateral to pelvic brim
Internal iliac nodes	Medial to external nodes, surrounding branches of internal iliac artery
Sacral nodes	Posterior pelvic wall, along sacral vessels and anterior to sacrum
Inguinal nodes	In the femoral triangle, superficial and deep to the fascia lata

Function

Lymphatic drainage: Filter lymph from pelvic organs, perineum, genitalia, lower abdominal wall, and lower limbs
Immune defense: Act as sites of lymphocyte activation and antigen presentation
Cancer surveillance: First-line nodes for metastasis from pelvic malignancies (e.g., cervical, prostate, bladder cancers)

Drainage Patterns

Pelvic organs: Primarily to internal and external iliac nodes
Perineum and lower vagina: To superficial inguinal nodes
Glans penis/clitoris: To deep inguinal and external iliac nodes
Uterine fundus (via round ligament): To superficial inguinal nodes

Clinical Significance

Lymphadenopathy: Enlargement may indicate infection, inflammation, or malignancy
Sentinel nodes: First nodes involved in metastasis; often biopsied in cancer staging
Surgical landmarks: Identified and often dissected during oncologic pelvic surgeries