Histologic Changes--Nodule Formation

A more advanced lesion is shown here. The proliferating capillaries collapse to form rounded nodules. Collections of hemosiderin-filled macrophages in surrounding alveoli indicate old bleeding. A narrowed muscular artery lies at the lower left and an interlobular septum near the upper right (arrow).

At the edge of the nodule shown above is an area of alveolar wall collapse with several dilated capillary lumens containing many RBCs across their diameters. Scattered lymphoid cells are present in the interstitium, and there is mild type II cell hyperplasia. Note the hemosiderin-filled macrophages in the alveolus at the lower left.

Measurement of the narrower diameter of 20 dilated capillaries and 20 normal capillaries in the same section showed a mean diameter of 21 µm in the former and 6 µm in the latter.

Still later, the nodules show dense collagenization, again with hemosiderin-laden macrophages in collapsed alveolar spaces. A narrowed muscular artery enters the nodule at the left. Arterial ischemia, as well as venous narrowing, probably contributes to these lesions.

Hemosiderin-filled macrophages were also scattered throughout the surrounding more normal parenchyma. They account for the brown parenchyma noted around the firm nodules. These nodules account for the finely granular texture of the normal-appearing lung.

Clinical summary Image 4

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