Thoracic Sarcoidosis

Radiologic-Pathologic Correlation

Abstract Introduction Clinical Features Pathologic Features

Staging Radiologic Characteristics Complications Extrapulmonary Thoracic Manifestations

Differential Diagnosis Treatment and Prognosis Source Information References

Pathologic Features

Immunologic Mechanism

The etiology of sarcoidosis is unknown. It is currently viewed as a disorder of immune regulation, but the antigenic agent or agents responsible for the disease have not yet been identified (10,11). Cell-mediated immunity is stimulated in the lung, resulting in the formation of characteristic epithelioid cell granulomas.

Activated alveolar macrophages and T lymphocytes release a variety of biochemical mediators. Alveolar macrophages release interleukin-1 (a T-cell activator), fibronectin (fibroblast chemotactic factor), and alveolar macrophage derived growth factor (stimulates fibrosis). The activated T-lymphocyte population includes a higher proportion of T-helper cells than is seen in the normal lung. These activated T cells release interleukin-2 (stimulates growth of T-helper or cytolytic cells), monocyte chemotactic factor (attracts circulating monocytes), and immune interferon (a polyclonal B-cell activator) (6,11).

The above process may resolve spontaneously, or it may progress to form the histologic hallmark of sarcoidosis--the noncaseating granuloma (5,7,10). Progression of the granulomatous process to fibrosis may occur in a small percentage of patients (Figure 2).

Histologic Findings

The earliest pathologic manifestation of sarcoidosis is alveolitis, a nongranulomatous interstitial pneumonitis involving the alveolar walls. T lymphocytes recruit macrophages, which lose their motility and are transformed into epithelioid cells. Nodular collections of these epithelioid cells become interstitial granulomas. These noncaseating epithelioid granulomas are composed of lymphocytes, peripheral fibroblasts, and multinucleated giant cells (Figure 3). A fine network of reticular fibers is also present. If necrosis occurs, it is central and minimal (10).

In sarcoidosis, granulomas are widely distributed throughout numerous organs and tissues. They congregate in lymph nodes and in tissues with a rich lymphatic supply (Figure 4). In the lung, the granulomas are interstitial, located in the subpleural, septal, perivascular, and peribronchial spaces (3,7,10). In 10% 20% of patients with sarcoidosis, interstitial granulomas progress to pulmonary fibrosis (Figure 5).

Granulomas resulting from this nonspecific cell-mediated pathway are indistinguishable from those found in berylliosis, tuberculosis, leprosy, hypersensitivity pneumonitis, Crohn disease, primary biliary cirrhosis, fungal disease, and local "sarcoid reactions" seen in lymph nodes draining neoplasms and sites of chronic inflammation. For this reason, sarcoidosis is always a diagnosis of exclusion (3,10).

Abstract Introduction Clinical Features Pathologic Features

Staging Radiologic Characteristics Complications Extrapulmonary Thoracic Manifestations

Differential Diagnosis Treatment and Prognosis Source Information References