S9C25aaP16aa-Granuloma Annulare



S9C25aaP16aa-1: Above the center of the field, histiocytes (and activated mesenchymal cells) infiltrate the dermis in traceries among collagen bundles. There are perivascular infiltrates of lymphoid cells. Some of the collagen bundles in the region of the histiocytic infiltrates are more brightly acidophilic. Below the center of the field, there is a zone that is hypocellular. In this zone, collagen bundles are reduced in size and are more widely spaced; they are pale. At the interface between the cellular zone and the hypocellular zone, histiocytes are arranged in palisades (granuloma annulare).

S9C25aaP16aa-2: This immunoreaction for the demonstration of lysozyme shows that most of the cells in the palisades, including the giant cells, are immunoreactive. Cell processes of the radially arranged histiocytes extend into the hypocellular zone. Note that the activated histiocytes are dendritic in outline.

S9C25aaP16aa-3: Similarly, with a reaction for the demonstration of KP-1 (CD-68), the radially arranged cells, as well as the giant cells, are immunoreactive.

S9C25aaP16aa-4: Histiocytes in the zone of radially arranged cells are immunoreactive for CD-68.

S9C25aaP16aa-5: With a reaction for the demonstration of Factor XIIIa, some cells at the periphery, but beyond the zone of the palisaded cells, are strongly reactive; the cells of the palisaded zone are faintly reactive.

S9C25aaP16aa-6: With a reaction for the demonstration of S-100 protein, a few cells in the perivascular spaces and the adventitia of a sweat gland are reactive.

S9C25aaP16aa-7:The collagen bundles of the reticular dermis are reduced in size; the number of bundles cut in cross-section appears to be increased. There is widening of spaces among the collagen bundles of the reticular dermis. The dermis is relatively free of inflammatory infiltrates (elastolysis; macular atrophy; anetoderma).

S9C25aaP16aa-8: At higher magnification, the collagen bundles are widely spaced. Some have a feathery margin along one side; some are fissured or pock-marked. Elastic fibers are not visible among the collagen bundles (elastolysis).

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