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Popliteal lymph nodes

The popliteal lymph nodes are a group of deep lymph nodes located within the popliteal fossa, posterior to the knee joint. They receive lymph from the superficial and deep tissues of the leg and foot and serve as an important intermediate station before lymph drains to the deep inguinal lymph nodes. Though small and often clinically silent, they become important in infections, inflammatory conditions, and malignancies of the lower limb.

Synonyms

  • Lymph nodes of the popliteal fossa

  • Subpatellar lymph nodes

  • Knee lymph nodes

Location and Groups

  • Typically 4–6 nodes within the popliteal fossa

  • Classified into:

    • Superficial popliteal nodes: Associated with the small saphenous vein

    • Deep popliteal nodes: Located around the popliteal artery and vein

Relations

  • Anteriorly: Posterior surface of the knee joint capsule and femur/tibia

  • Posteriorly: Skin and fascia of the popliteal fossa

  • Laterally: Biceps femoris tendon and fibular nerve

  • Medially: Semimembranosus and semitendinosus tendons

  • Superiorly: Adductor hiatus and femoral vessels (continuity with inguinal nodes)

  • Inferiorly: Calf muscles (gastrocnemius, soleus) and tibial vessels

Drainage

  • Afferent drainage:

    • Superficial tissues of the posterolateral leg and foot (via the small saphenous vein)

    • Deep lymphatics from the knee joint, leg, and foot

  • Efferent drainage:

    • Drains into the deep inguinal lymph nodes via lymphatic channels accompanying the femoral vessels

Function

  • Filter lymph from the leg, foot, and knee joint

  • Trap infectious agents, tumor cells, and debris before lymph reaches inguinal nodes

  • Participate in immune surveillance via lymphocytes and macrophages

Clinical Significance

  • Enlargement may indicate infection of foot/leg, inflammatory arthritis, or malignancy

  • Important in staging for melanoma, sarcoma, or carcinoma of the lower limb

  • May mimic soft tissue masses in the popliteal fossa

  • Target for biopsy or sentinel node mapping in oncology

MRI Appearance

T1-weighted images:

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

  • Central fatty hilum, if present, shows bright signal

T2-weighted images:

  • Nodes appear with intermediate to high signal intensity

  • Reactive or inflamed nodes appear more hyperintense

  • Hilum appears relatively darker if preserved

STIR (Short Tau Inversion Recovery):

  • Nodes show intermediate to bright signal

  • Pathological nodes (infection, tumor) appear markedly bright

  • Fat suppression makes hilum less conspicuous

Proton Density Fat-Saturated (PD FS):

  • Nodes show intermediate baseline signal

  • Abnormal nodes (edema, tumor, abscess) appear with bright signal

T1 Fat-Sat Post-Contrast:

  • Normal nodes enhance mildly and uniformly

  • Malignant nodes: heterogeneous or irregular enhancement

  • Abscessed/necrotic nodes: rim enhancement with central non-enhancing necrosis

CT Appearance

Non-Contrast CT:

  • Nodes appear as soft tissue density nodules in the popliteal fossa

  • Central fatty hilum may appear as a small low-attenuation focus

  • Enlarged nodes become solid soft tissue masses without visible hilum

Post-Contrast CT:

  • Normal nodes show mild homogeneous enhancement

  • Reactive nodes: uniform but stronger enhancement

  • Malignant nodes: heterogeneous enhancement, loss of fatty hilum

  • Necrotic or abscessed nodes: rim enhancement with central low attenuation

  • Surrounding fat may show stranding if inflammation is present

MRI image

Popliteal lymph nodes coornal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

MRI image

Popliteal lymph nodes SAGITTAL cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

CT image

Popliteal lymph nodes ct axial

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Popliteal lymph nodes CT sagittal image