Monday, April 2, 2012

Pulmonary Tuberculosis Histology and Explanation

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Here is the gross appearance of a lung with tuberculosis. Scattered tangranulomas are present, mostly in the upper lung fields. Some of thelarger granulomas have central caseation. Granulomatous disease of thelung grossly appears as irregularly sized rounded nodules that are firmand tan. Larger nodules may have central necrosis known as caseation--aprocess of necrosis that includes elements of both liquefactive andcoagulative necrosis)

On closer inspection, the granulomas have areas of caseous necrosis. This is very extensive granulomatous disease. This pattern of multiplecaseating granulomas primarily in the upper lobes is most characteristicof secondary (reactivation) tuberculosis. However, fungal granulomas(histoplasmosis, cryptococcosis, coccidioidomycosis) can mimic thispattern as well.

Well-defined granulomas are seen here. They have rounded outlines. The one toward the center of the photograph contains several Langhansgiant cells. Granulomas are composed of transformed macrophages calledepithelioid cells along with lymphocytes, occasional PMN's, plasma cells,and fibroblasts. The localized, small appearance of these granulomassuggests that the immune response is fairly good.

The edge of a granuloma is shown here at high magnification. At theupper right is amorphous pink caseous material composed of the necroticelements of the granuloma as well as the infectious organisms. This areais ringed by the inflammatory component with epithelioid cells,lymphocytes, and fibroblasts.

At high magnification, the granuloma demonstrates that the epithelioidmacrophages are elongated with long, pale nuclei and pink cytoplasm. Themacrophages organize into committees called giant cells. The typicalgiant cell for infectious granulomas is called a Langhans giant cell andhas the nuclei lined up along one edge of the cell. The process ofgranulomatous inflammation takes place over months to years

In order to find the mycobacteria in a tissue section, a stain for acidfast bacilli is done (AFB stain). The mycobacteria stain as red rods, asseen here at high magnification

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