S1C28P18Collagenosis

S1C28P18-1: Focality is a quality of the granulomatous collagenosis of granuloma annulare. Blue arrows identify a well-developed, palisaded pattern of granulomatous inflammation at the periphery of a zone of altered connective tissue. In the central nidus, collagen bundles vary in size, and are widely spaced (mucinosis). In the nidus outlined by yellow arrows, histiocytes form traceries among, and have partially displaced, collagen bundles; in this nidus, the lesion might be characterized as “young;” the histiocytes have been recruited, but have not accomplished a significant digestion of the intervening collagen bundles.

S1C28P18-2: In this focus, histiocytes are focally aggregated and loosely clustered, especially in the zone outlined by yellow arrows. The histiocytes are stellate in outline; they have radially arranged cell processes. The morphologic accommodations are ideally suited for the insinuation of cytoplasmic processes among collagen fibrils of the collagen bundles. As a consequence, some of the collagen bundles are loosely fibrillated (they are in the process of being unbundled and digested).

S1C28P18-3: In this field, the digestion of collagen bundles is more advanced; the cytoplasmic processes of palisaded cells are prominent in the zone of collagenolysis above the center of the field.

S1C28P18-4: The sclerosing, or healing, phase of granuloma annulare is represented. Collagen bundles are compactly arranged, but many are loosely fibrillated. There is hyperplasia of fibrocytes and a reduction in the intensity of the histiocytic infiltrates. Patterns of this type are sometimes classified as interstitial variants, but all the patterns of granuloma annulare are interstitial; granuloma annulare is a disease of the dermal interstitium. For this example, the pattern probably represents a late stage in the evolution of a lesion of granuloma annulare.

S1C28P18-5: This is an area of edema in a lesion of morphea for comparison with the sclerosing granuloma annulare of S1C28P18-4. The interstitial spaces are widened, but not appreciably mucinous on this H&E stained section. Collagen bundles are fibrillated. There is a mild, loose interstitial infiltrate of lymphocytes and histiocytes. In a lesion of morphea, the alterations are more diffuse; they are not as focal in nature as in most example of granuloma annulare. Myxoid changes rarely are a prominent feature of the interstitium of the reticular dermis in a lesion of morphea.

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