Peripheral, pleura-based and perifissural nodules are located close to, or touching any pleural surface but do not arise from the pleura. Intrapulmonary lymph nodes are typically pleura-based, perifissural or peripheral in location ⁷ but must be distinguished from small peripheral lung cancers ⁸.

Terminology 

Perifissural lymph nodes have been well-described and may have specific appearances that allow a confident diagnosis of intraparenchymal lymph nodes. The same applies to lymph nodes along the costal, mediastinal and diaphragmatic pleura and the term juxtapleural was introduced to include these.

Unfortunately, the term juxtapleural does not have a consistent meaning in the radiology literature and the 2024 Fleischner glossary recommends using the following terms ¹¹:

• peripheral: close to the pleura

• pleura-based: in contact with the pleura but not derived from the pleura

• perifissural: in contact with fissural pleura but not derived from pleura

Radiographic features

CT

Intrapulmonary lymph nodes are characteristically:

• homogeneous, soft tissue attenuation and well-defined

• smooth outline

• lentiform, ovoid, semicircular, triangular or polygonal shape

• located on or within 15 mm of the visceral pleura ⁹

• contiguous with the pleura or they can lie at the junction of interlobular septa in which case a thin linear attachment to the pleural surface is often visible on thin high resolution CT ³

• predominantly located inferior to the carina in the middle or lower lobes

Features that are not typical for intrapulmonary lymph nodes include ⁶: 

• upper zone location, - a more common location for lung cancers

• spherical shape

• any surface irregularity e.g. indistinct, spiculated, microlobulated

• pleural distortion e.g. bowing, retraction, thickening, transgression (fissure)

• size >12 mm

• not completely solid ⁸

• intranodular fat or calcification

Peripheral lungs cancers are most commonly adenocarcinomas, followed by squamous carcinomas and carcinoid tumors. These are commonly round in shape. Carcinoids may have a smooth regular margin, but other tumors characteristically demonstrate surface irregularity and are less sharply marginated. Spiculation and microlobulation are the more obvious signs of malignancy. Signs of visceral pleural invasion may also be present in lung cancers ¹⁰:

• jellyfish sign: pleural-adjacent nodule with multiple pleural tags arising from the margins of the nodule

• pleural thickening

• large contact surface area for pleural-adjacent nodules

• multiple tags to different pleural surfaces

Treatment and prognosis

If peripheral nodules have all the typical features of intraparenchymal lymph nodes they are likely to be benign and follow-up at 1 year may be appropriate, however, lymph node size can change over time and they may grow ² or shrink over time.

Caution is advised for upper lobe nodules. Observer variation is well-documented ^ref, particularly so with inexperienced radiologists.