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Figure 8a.   Lung nodule caused by Dirofilaria (canine heartworm) in an asymptomatic 70-year-old man. (a) Close-up CT scan of the right lung shows a peripheral, smoothly marginated, noncalcified lung nodule. (b) Photograph of a specimen obtained with wedge resection shows a well-circumscribed, 2-cm nodule with yellow areas of geographic necrosis. (c) High-power photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows intravascular Dirofilaria. Most infections manifest as lung nodules from embolic infarction caused by intravascular worms.