Intrapulmonary lymph nodes
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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:
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
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.