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Intermediate lacunar external iliac lymph nodes

The intermediate, lacunar, and external iliac lymph nodes form part of the pelvic and inguinal lymphatic system. They serve as important stations in the drainage of the lower limb, external genitalia, perineum, and pelvic organs. Their involvement in infections and malignancies makes them critical structures in oncology, radiology, and surgical planning.

Synonyms

  • Intermediate iliac nodes

  • Lacunar nodes of the femoral canal

  • External iliac nodal chain

Location and Groups

  • Intermediate lymph nodes:

    • Found along the external iliac vessels between the lateral and medial groups

    • Lie within the pelvic sidewall adjacent to the external iliac artery and vein

  • Lacunar lymph nodes:

    • Located in the femoral canal near the medial aspect of the femoral vein

    • Include the node of Cloquet (Rosenmüller’s node), considered the most superior deep inguinal node and transitional between inguinal and external iliac groups

  • External iliac lymph nodes:

    • Lie along the external iliac vessels, extending from the inguinal ligament to the common iliac bifurcation

    • Divided into lateral, medial, and intermediate subgroups

Relations

  • Anteriorly: Peritoneum of the pelvic wall

  • Posteriorly: Iliacus and psoas major muscles

  • Laterally: External iliac artery and vein

  • Medially: Urinary bladder and obturator nerve/vessels

Function

  • Drain lymph from the deep inguinal nodes, pelvic organs (bladder, prostate, cervix, upper vagina), anterior abdominal wall below the umbilicus, and external genitalia

  • Act as a filter against pathogens and tumor cells

  • Participate in immune surveillance through lymphocyte activity

Clinical Significance

  • Enlarged in pelvic and lower limb infections

  • Commonly involved in urologic, gynecologic, and colorectal cancers (prostate, bladder, cervical, endometrial, rectal malignancies)

  • Nodes are examined during oncologic staging (CT, MRI, PET) and surgical dissection

  • Cloquet’s node is biopsied as part of sentinel lymph node mapping

  • Pathology includes reactive lymphadenopathy, lymphoma, and metastatic disease

MRI Appearance

T1-weighted images:

  • Nodes show low-to-intermediate signal intensity

  • Fatty hilum, if present, appears bright

T2-weighted images:

  • Nodes show intermediate-to-high signal intensity

  • Reactive or inflamed nodes may show more intense bright signal

STIR (Short Tau Inversion Recovery):

  • Nodes appear intermediate-to-bright

  • Malignant nodes often show loss of fatty hilum and bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal nodes enhance mildly and uniformly

  • Malignant nodes show irregular or heterogeneous enhancement

  • Necrotic nodes demonstrate rim enhancement with non-enhancing center

CT Appearance

Non-Contrast CT:

  • Appear as soft tissue density structures along external iliac vessels or femoral canal

  • Fatty hilum may appear as a central low-density focus

  • Enlarged nodes appear solid and homogeneous or may lose hilum

Post-Contrast CT:

  • Normal nodes enhance mildly and evenly

  • Inflammatory nodes enhance more prominently

  • Malignant or necrotic nodes show heterogeneous enhancement or rim-enhancing low-attenuation centers

MRI image

Intermediate lacunar external iliac lymph nodes MRI axial anatomy image-img-00000-00000

MRI image

Intermediate lacunar external iliac lymph nodes MRI coronal anatomy image-img-00000-00000

CT image

Intermediate lacunar external iliac lymph nodes ct