The focal nature of granulomatous inflammation is demonstrated in this microscopic section of lung in which there are scattered granulomas in the parenchyma. This is why the chest radiograph with tuberculosis or other granulomatous diseases is often described as "reticulonodular". A biopsy could miss such lesions from sampling error, too.
Mouseover (touch) the box to the right to view a granuloma forming. Note the pale pink central caseous necrosis, dark blue lymphocytes, elongated epithelioid cells, and multnucleated Langhans giant cells.