Lung Anatomy II


Interstitium in the normal lung is mostly invisible on HRCT. To illustrate the distribution of the lung interstitium, we present an example of unilateral lymphangitic spread of tumor. The interstitium in all of its locations contains lymphatics, which in this case are distended by tumor, thereby serving as a visible marker for the interstitium.

Interstitial Compartments of the Lung

In the image compare the irregularly thickened interstitial compartments in the right lung to the normal, mostly invisible counterparts in the left lung (R = right lung; L = left lung)

Red text: Find, position the cursor over, and click on the structure that is requested in red text. Confirmation appears. Click on "return." The arrow changes to a hand over a marked structure. Not all representative structures are marked.


Find 2 examples of thickened bronchovascular interstitium in cross section with paired bronchus and artery.

Find an example of thickened bronchovascular interstitum in longitudinal section.

Find 2 examples of interlobular septa around a lobule.

Find 2 examples of thickened centrilobular interstitium in cross section.

Find a peripheral bronchiolovascular bundle extending into the center of a lobule.


The interlobar fissure is thickened compared to that on the left, and the peripheral pleura is irregularly thickened by tumor.

Gross Specimen Showing Delineation of the Interstitium by Lymphangitic Tumor

Note the numerous polygonal lobules outlined by thickened interlobular septa. In some cases, the thickened terminal bronchiolovascular bundle, representing tumor in the centrilobular interstitium, is seen at the center of the lobule (see black polygon).

A large airway at the upper right (B) shows thickening of its wall by tumor in the bronchovascular interstitium, and the black, hilar lymph nodes (L) are partially replaced by tumor.

Histologic Section Showing Interstitium with Tumor

A pulmonary lobule outlined by tumor-filled interlobular septa is at the upper left.

In its center is the tumor-filled centrilobular interstitium (surrounding the terminal bronchiolovascular bundle).

Pleural interstitium is also thickened by tumor.

Identification of structures

High-power View of the Image Above

This vein (V) is surrounded by tumor in lymphatics.

The thickened interstitium is evident by HRCT because the intervening, aerated alveolar parenchyma is normal.

If the surrounding alveoli were not filled with air, the interstitium and vessels would not be visible as separate structures (see consolidation).





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Interlobular septa surrounding a lobule, which is 1 to 2.5 cm in diameter





























Bronchovascular interstitium in cross section or longitudinal section



























Bronchiolovascular interstitium extending into lobule






























Thickened centrilobular interstitium in cross section

































The interlobular septa thickened by tumor are marked by the black line. The centrilobular bronchiolovascular bundle and interstitium are marked with an asterisk. A vein (V) in another interlobular septum is also surrounded by lymphangitic tumor.