Part 1: Lung Anatomy I

Structures in Normal Lung HRCT

This image of normal left lung shows central, branching pulmonary arteries and bronchi. The bronchovascular bundles are made up of these paired structures and their surrounding interstitium (connective tissue). In cross section, the bronchus is a thin-walled, white circle with central air (black), and the adjacent artery appears as a solid, white circle. Find paired pulmonary arteries and bronchi.

More peripherally, numerous small "dots" and a few branching lines represent small pulmonary arteries and veins. Throughout, arteries branch at acute angles, and veins branch at 90° angles. Find one of each.

The pleura of the major interlobar fissure is a thin, horizontal line traversing the lung. The peripheral pleural surface, which cannot be seen, is smooth.

 

Structures of Normal Lung Gross Specimen

Round, air-filled bronchi are seen in the central lung. A few are cut longitudinally. A bronchovascular bundle is best seen at the asterisk.

Normal interlobular septa are seen occasionally as subpleural, fine, linear structures forming polygons, 1 to 2.5 cm in diameter. These septa define the pulmonary lobule, which is also referred to as the secondary pulmonary lobule (arrows delimit one).

At the center of the pulmonary lobule are the terminal bronchiolovascular bundles, outlined here with black pigment, which was inhaled from the environment.

The terminal bronchiolovascular bundle contains a pulmonary artery and a bronchiole enclosed by centrilobular interstitium. The pulmonary veins run in the interlobular septa. Arteries and veins are connected by capillaries in the intervening alveolar parenchyma.

The pleura surrounding the lung (right) is imperceptible.

An understanding of this anatomy is important for interpreting HRCT.

Histology of Normal Lung

A portion of a pulmonary lobule is delineated by interlobular septa that contain pulmonary veins. Two bronchiolovascular bundles are seen within the lobule.

The interlobular septa and terminal bronchiolovascular bundles are near the limits of resolution of HRCT and are rarely seen normally, but may be accentuated by disease.

Alveolar detail is below the resolution of HRCT. Normal alveolar walls and air-filled spaces result in a homogeneous, dark grey appearance compared to air-filled bronchi, which appear black.

Identification of structures

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A = artery branching at an acute angle

B = vein branching at right angles

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The black line marks the interlobular septum with veins (V). The oval marks one bronchiolovascular bundle within the lobule. In a second bronchiolovascular bundle to the left, the artery (A) and bronchiole (B) are marked.

A terminal bronchiole (the last airway before the respiratory bronchiole with alveoli in its wall) and its branches and alveoli comprise an acinus. There are several acini in a lobule.

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