S11C7P2-3: The changes are those of a superficial, lymphohistiocytic vasculitis. In this approach, pure, perivenular infiltrates of lymphocytes and histiocytes are accepted as a variation of the patterns seen in the vasculitic disorders. To the left, histiocytes are prominent in the perivascular spaces. This pattern can be accommodated in the category of indeterminate leprosy, but the changes are subtle.

For lesion of leprosy, the variations in histologic patterns have been categorized. The categorizations provide for the recognition of stages along an axis defined at one pole by tuberculoid lesions and at the opposite extremity by lepromatous lesions. In this example, the patterns are basically indeterminate in character.

S11C7P2-4: Perivascular, lymphohistiocytic infiltrates involve a small nerve which is represented in cross section (red arrows). The vacuolated histiocytes provide a lepromatous quality, but this is an example of borderline pathology. Lymphocytes are few in number, a deficiency indicating a progression in the failure of cell-mediated immunity; the progressions are of a type that may lead to polar, lepromatous leprosy.

S11C7P2-5: The infiltrate of borderline leprosy is represented. The vacuolated cells provide a lepromatous quality. They contain numerous, uniformly stained, acid-fast bacilli. The bacilli are delicate. Lymphoid cells are inconspicuous.

S11C7P2-6: Centrally and to the right, the infiltrates of histiocytes are confined to expanded perivascular spaces. The pallor reflects the vacuolation of the cytoplasm of the closely clustered histiocytes. To the left, the infiltrates are confluent; they are not merely confined to expanded perivascular spaces. The rounded vacuoles in the area of the confluent infiltrates are Virchow cells . In active lesions, Virchow cells are rich in organisms. The pattern is that of lepromatous leprosy, polar extremity. Lymphoid infiltrates are not a prominent feature. Lepromatous leprosy is an expression of a failure of cell-mediated immunity.

S11C7P2-7: The infiltrates are purely histiocytic; all the cells are vacuolated. This is the classic infiltrate of lepromatous leprosy. With special stains, a lesion of this type would be expected to contain numerous organisms; the organisms often will be compactly clustered to form packets.