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External iliac lymph nodes

The external iliac lymph nodes are a group of deep pelvic lymph nodes located along the external iliac vessels. They form an important part of the pelvic lymphatic chain, receiving drainage from pelvic organs, abdominal wall, and inguinal nodes. These nodes are crucial in the staging of cancers of the pelvis and lower abdomen and are commonly assessed in radiology, oncology, and surgery.

Synonyms

  • External iliac chain

  • External iliac nodal group

  • Pelvic external iliac nodes

Location and Groups

  • Situated along the external iliac artery and vein, extending from the bifurcation of the common iliac vessels to the inguinal ligament

  • Divided into three main groups:

    • Medial group: Located medial to the external iliac vessels, adjacent to the pelvic viscera

    • Intermediate group: Situated directly along the external iliac vessels

    • Lateral group: Found lateral to the external iliac vessels, close to the psoas major muscle

Relations

  • Anteriorly: Peritoneum of the pelvic sidewall

  • Posteriorly: Psoas major and iliacus muscles

  • Medially: Pelvic viscera (bladder, uterus, prostate depending on sex)

  • Laterally: Pelvic wall and obturator nerve as it courses to the thigh

Function

  • Drain lymph from the inguinal lymph nodes, lower abdominal wall, and perineum

  • Receive drainage from pelvic organs including the bladder, prostate, cervix, vagina, and uterus

  • Act as filtration centers for pathogens and tumor cells in the pelvic and inguinal lymphatic drainage pathway

  • Serve as major nodal stations in pelvic oncologic staging

Clinical Significance

  • Enlargement may indicate infection, pelvic inflammatory disease, or malignancy

  • Frequently involved in cancers of the bladder, cervix, uterus, prostate, rectum, and testis

  • Common targets for pelvic lymphadenectomy in gynecologic, urologic, and colorectal oncology

  • Nodes may mimic pelvic masses on imaging and can compress adjacent vessels when enlarged

  • Evaluation is essential for oncologic staging, treatment planning, and prognosis

MRI Appearance

T1-weighted images:

  • Nodes appear as round or oval structures with low-to-intermediate signal intensity

  • Central fatty hilum, when present, demonstrates bright signal

T2-weighted images:

  • Nodes display intermediate to high signal intensity

  • Malignant nodes may appear enlarged and more heterogeneously hyperintense

STIR (Short Tau Inversion Recovery):

  • Normal nodes appear as intermediate signal structures

  • Inflamed or malignant nodes become bright hyperintense, often with loss of fatty hilum

T1 Fat-Sat Post-Contrast:

  • Normal nodes show mild, uniform enhancement

  • Malignant nodes often enhance heterogeneously

  • Necrotic or suppurative nodes demonstrate rim enhancement with central non-enhancing necrosis

CT Appearance

Non-Contrast CT:

  • Nodes appear as soft tissue density along the external iliac vessels

  • Fatty hilum, if present, appears as central low attenuation

  • Enlarged nodes appear as rounded or oval soft tissue masses without visible hilum

Post-Contrast CT:

  • Normal nodes enhance mildly and homogeneously

  • Reactive nodes may enhance more vividly but remain homogeneous

  • Malignant or necrotic nodes often enhance heterogeneously or show rim enhancement with central low attenuation

MRI image

External iliac lymph nodes MRI axial anatomy image-img-00000-00000

MRI image

External iliac lymph nodes MRI axial anatomy image-img-00000-00000_00001

CT image

External iliac lymph nodes CT axial anatomy image-img-00000-00000

CT image

External iliac lymph nodes CT axial anatomy image-img-00000-00000_00001

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External iliac lymph nodes CT axial anatomy image-img-00000-00000_00002