Intrapulmonary lymph nodes

Last revised by Liz Silverstone on 29 Jan 2024

Intrapulmonary lymph nodes, or pulmonary lymph nodes, are normal lymph nodes found within the lung parenchyma itself.

Intrapulmonary lymph nodes may be perifissural (lying along a fissure) or juxtapleural 2 (within 15mm of visceral pleura).

The term excludes mediastinal, hilar and peribronchial lymph nodes. The latter occur at bronchial bifurcations up to and including the third branch.

They are commonly found during the assessment of CTs of the chest and are sometimes difficult to distinguish from pulmonary nodules with certainty.

Some publications suggest at they may represent 24–44% of noncalcified nodules in a "lung cancer screening setting" 7 and may represent up to 66% of all nodules on CT scans.

Thin sections and evaluation in two or three orthogonal planes underpin accurate evaluation. Intrapulmonary lymph nodes are characterized by:

  • location: middle and lower lobe predominant, inferior to the carina 4

  • pleura-adjacent or juxtapleural (within 15mm of a visceral pleural surface)

  • no effect on pleura

  • solid soft-tissue attenuation with no fat or calcification

  • sharply marginated with a smooth outline

  • 3 -15 mm diameter, usually less than 12 mm 7

  • elongated with an aspect ratio often > 1.78

  • lenticular, ovoid, semicircular, triangular, trapezoidal, polygonal, faceted

  • lymph nodes located at the junction of interlobular septa may show a discrete thin line extending to the pleura which may be due to interlobular septum, venule or lymphatics

  • may grow or shrink over time

  • no arterial attachment

In contrast, small peripheral cancers such as adenocarcinomas may show:

  • arterial attachment

  • indistinct or irregular margin, spiculation or microlobulation

  • as a round nodule which may touch a pleural surface

  • signs of visceral pleural invasion 9 such as:

    • large area of contact for pleural attached nodules

    • pleural thickening

    • tags to multiple pleural surfaces

    • jellyfish sign (multiple pleural tags from the margins of a pleura-attached nodule)

85% of cancers misdiagnosed as intrapulmonary lymph nodes were in the upper lobes and this was particularly common if the features were ‘atypical’ for intrapulmonary lymph nodes 8. Upper lobe nodules should trigger extra vigilance.

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Cases and figures

  • Case 1: perifissural
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  • Case 2: perifissural
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