Interstitial Pneumonias

Giant cell interstitial pneumonia

Here, the interstitial pneumonia is patchy with fibrosis and chronic inflammatory cells. The many multinucleated alveolar macrophages signify hard metal disease. The arrows indicate two macrophages that blend with the interstitium. This disease is a hypersensitivity reaction to cobalt, which is a component of hard metal.

Langerhans' cell histiocytosis (LCH) (Eosinophilic granuloma)

Features include:

There are no discrete granulomas. The Langerhans' cells and occasional multinucleated giant cells constitute a granulomatosis. The size of this lesion can be judged by the size of the alveolar spaces at the bottom.

Langerhans' cells have pink cytoplasm and grooved or lobulated nuclei (arrow). A positive immunoperoxidase stain for CD1a confirms that such cells are histiocytes of the Langerhans' type. A few eosinophils are present.

This electron micrograph shows a Birbeck pentalaminar body (arrow). The bilaminar outer membrane is derived from the cell membrane. A central unilaminar membrane makes the 5th layer. A terminal swelling gives a "tennis racquet" appearance.

The diagnosis of LCH is now usually confirmed by immunohistochemical stains (CD1a) and not by electron microscopy.

See also Case 19