Histologic features: Several other features of the granulomas of HP are shown below. In A, the giant cells have empty slits that are believed to have harbored lipids before they were dissolved in the tissue processing. They are called "cholesterol clefts."

A

B. A giant cell in this granuloma has a dark, intracellular inclusion within a vacuole. Inclusions like this are composed of calcium and iron, and may be associated with small, birefringent crystals of calcium oxalate, several of which are shown by polarized light in image C (arrow marks one). Both the inclusions and the crystals are thought to be produced endogenously by the cell. As the inclusions enlarge, they become lamellated and are called conchoid (resembling sea shells) or Schaumann bodies. These structures develop intracellularly, but they may become extracellular. They are not specific for any disease and may be found in any type of granuloma, although they are most common in HP and sarcoidosis. (Giemsa stain)

C

D. This section shows an ill-defined granuloma (epithelioid cells and lymphocytes) that widens alveolar walls and fills alveoli. In this Giemsa stain, the mast cell, another inflammatory cell type in HP, can be recognized by its violet granules. Three are marked by arrows. Find 2 more. Mast cells are found scattered throughout the inflammatory infiltrate in this disease. They are also found more frequently compared to controls in transbronchial biopsies from patients with sarcoidosis, UIP, cryptogenic organizing pneumonia, and Langerhans' cell histiocytosis, and in resections from patients with plexogenic pulmonary angiopathy [1,2]. Their role in disease is not understood.

References

1. Pesci A, Bertorelli G, Gabrielli M, Olivieri D. Mast cells in fibrotic lung disorders. Chest 1993; 103:989-996.

2. Heath D, Yacoub M. Lung mast cells in plexogenic pulmonary arteriopathy. J Clin Pathol 1991; 44:1003-1006.

Clinical summary Discussion

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