Non-necrotizing and necrotizing granulomas
Non-necrotizing granulomas are illustrated in Figs. 1,2,3. Granulomas of this type are characterstic of sarcoidosis, beryllium disease, hypersensitivity pneumonitis, drug reactions, tuberculoid leprosy. Crohn's disease, and others. The  presence of non-necrotizing granulomas is generally indicative of a non-infectious etiology. However, non-necrotizing granulomas may occur along with necrotizing granulomas in infectious diseases such as tuberculosis (Fig. 3) and may be the only finding in small biopsy specimens. The finding of non-necrotizing granulomas does not exclude infectious etiology.
Necrotizing granulomas are illustrated in Figs.  4,5,6. Granulomas of this type are characterstic of infectious diseases such as tuberculosis and fungal infections as well as rheumatoid nodules, Wegener's granulomatosis, necrobiotic post-surgical granulomas and others. Necrosis, usually minimal and focal, may also be seen in the granulomas of sarcoidosis. The use of the terms "caseating" and "non-caseating"  to describe the microscopic appearance of granulomas, although prevalent, is inappropriate since the term "caseous" applies only to the grossly visible cheese-like appearance that may be associated with necrotizing granulomas, necrotic neoplasms and other types of necrotic lesions. There is no typical microscopic appearance that corresponds to the gross appearance of caseation.
Fig. 1. Non-necrotizing granuloma - sarcoidosis
Fig. 2. Non-necrotizing granuloma with giant cell - sarcoidosis
Fig. 3. Non-necrotizing granuloma with giant cells - tuberculosis
Fig. 4. Necrotizing granuloma - tuberculosis
Fig. 5. Necrotizing granuloma - tuberculosis
Fig. 6.  Granuloma(s) with massive necrosis - tuberculosis