Mycobacterial and fungal infections are the most common causes of granulomatous lung disease, states the Archives of Pathology and Laboratory Medicine. Non-infectious causes include sarcoidosis, Wegener granulomatosis, hypersensitivity pneumonitis, hot tub lung and aspiration pneumonia. Due to the frequency of infectious causes in granulomatous lung disease, doctors must rule out an infectious organism before proceeding to possible non-infectious diagnoses.
The majority of fungal organisms are visible through hematoxylin-eosin stains, according to the Archives of Pathology and Laboratory Medicine. This is the recommended initial step in identifying the source of a patient's granulomatous lung disease. Mycobacteria, such as the organism responsible for tuberculosis, do not appear through this process and require special stains for detection. The majority of non-infectious cases of granulomatous lung disease are due to sarcoidosis. The granulomas in sarcoidosis cases typically exhibit well-defined structure and a lack of necrosis, although trace amounts of pink necrosis sometimes apply.
Granulomas are collections of histiocytes, or immune cells, that appear most commonly on the skin, subcutaneous tissues, lungs and lymph nodes, explains the Archives of Pathology and Laboratory Medicine. When present in a granuloma, histiocytes have irregular cellular structure that includes indistinct cell borders and elongated nuclei. Granuloma lesions may also display necrosis, lymphocytes, plasma cells or multinucleated giant cells.