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Interlobar lymph nodes

The interlobar lymph nodes are part of the intrapulmonary group of thoracic lymph nodes, located within the interlobar fissures of the lungs. They are positioned along the branching of the lobar bronchi into segmental bronchi and are responsible for filtering lymphatic drainage from the pulmonary lobes before it is directed toward the hilar lymph nodes.

These nodes play an important role in the immune defense of the lungs and are clinically significant in conditions such as pulmonary infections, sarcoidosis, lymphoma, and metastatic spread of thoracic and extrathoracic malignancies. Interlobar lymphadenopathy is frequently assessed on CT and MRI of the chest and is a key component of lung cancer staging.

Synonyms

  • Intrapulmonary lymph nodes (interlobar group)

  • Bronchopulmonary interlobar lymph nodes

  • Interlobar hilar nodes

Function

  • Filter lymph from pulmonary lobes and segmental bronchi

  • Act as immune surveillance centers within the lung parenchyma

  • Play a role in containment and spread of thoracic infection and malignancy

  • Serve as critical landmarks in lung cancer staging and thoracic imaging

MRI Appearance

T1-weighted images:

  • Normal nodes: isointense to muscle, slightly hypointense to lung parenchyma

  • Enlarged nodes: appear as well-defined soft tissue masses, hypointense compared to surrounding fat

  • Necrotic or cystic nodes may appear heterogeneous

T2-weighted images (normal):

  • Normal nodes: isointense to mildly hyperintense compared to muscle

  • Enlarged/inflamed nodes: appear hyperintense, sometimes with central necrosis (bright signal)

T2 TRUFISP (cardiac/respiratory-gated):

  • Provides high-resolution, bright blood imaging to delineate node position relative to vessels and bronchi

  • Interlobar nodes appear as round or oval hypointense masses within bright mediastinal background

  • Useful in distinguishing nodes from adjacent vascular structures

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, making lymph nodes appear bright hyperintense in cases of inflammation, edema, or malignancy

  • Helps differentiate pathological nodes from surrounding tissue

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Normal nodes: mild homogeneous enhancement

  • Pathological nodes (metastatic, granulomatous, infectious): show intense, heterogeneous, or rim-like enhancement

  • Excellent for evaluating vascular invasion, necrosis, and extranodal spread

CT Appearance

Contrast-Enhanced CT (Chest CECT):

  • Normal nodes: small, oval soft tissue densities in interlobar fissures, typically <10 mm short-axis

  • Enlarged nodes: appear as round/oval soft tissue masses, sometimes confluent

  • Malignant nodes may show irregular margins, central necrosis, or heterogeneous enhancement

  • Essential for lung cancer staging, lymphoma assessment, sarcoidosis, and infection

CT Coronary/Thoracic Angiography:

  • Clearly delineates nodes relative to adjacent pulmonary vessels and bronchi

  • Useful for differentiating nodes from vascular structures

  • Enhances detection of node-vessel interface in tumor invasion

CT image

interlobar lymph nodes anatomy CT coronal image -img-00000-00000

MRI image

Interlobar lymph nodes anatomy MRI coronal image -img-00000-00000