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A small ruminant’s lung presented the following aspect:

Areas of darkened reddish pulmonary parenchyma of widespread distribution throughout the organ.


What is your diagnosis? (75)


If we cut the parenchyma we can see how dark areas affect only the surface of the parenchyma, the rest presents a normal color. If we'd look at this tissue in the microscope, what we could see is that it is an atelectasis, that is a collapse of the pulmonary alveoli. The lack of air is the what gives the reddish and darkened color. Although the lungs collapse (they are emptied of air) when we take them out from the thoracic cavity there is always some air inside and usually they present a pink color. For some reason, probably mechanical, when removing these lungs the most superficial layer has collapsed giving this darker appearance. It is, thus, an artifact and not a lesion per se. Pneumonia also causes changes in the color of the parenchyma, but on section we will observe that the lesion involves deeper layers of the parenchyma. Another very common artifact to observe is the aspiration of blood during the sacrifice that yields images of hemorrhagic appearance, with a more intense coloration, almost blackish, than the one we observe in this case.
You can see a histological image, from a very similar case, in Case 4 from the previous post on  this blog: Any given day in a ruminant slaughterhouse (1/2).

When sectioning the lung, we see that the alteration only affects the superficial layer (subpleural) of the parenchyma.

Your answers are highlighted below.
Question 1
What is your diagnosis?
These are suppurative bronchopneumonia lesions. I'm sure if we put a piece of this lung in water, it will sink because the alveoli are full of pus.
It is not a lesion, it is just an aspiration of blood (accidental blood intake through the trachea during the sacrifice).
These are obviously lesions of interstitial pneumonia because of the widespread distribution that they present throughout the organ.
It is not a lesion but an atelectasis (alveolar collapse) of the most superficial layer of the lung.
These are lesions of pleuritis because the change in color affects almost all the pleura.
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