S9C25aP16aGA



S9C25aP16a-1: In this early stage of fibrolysis in a lesion of granuloma annulare, mucinous deposits among collagen bundles are associated with fibrin deposits. Some of the patterns to the right of the center of the field are compatible with lysis and unbundling of collagen fibers of the reticular dermis. Both fibrocytes and histiocytes may be involved in the lytic process.

S9C25aP16a-2: This pattern is a rare feature of the granulomatous collagenosis of granuloma annulare. A collagen bundle and a smaller fragment (or perhaps two collagen bundles) are sequestered in a space (green arrows). Histiocytes are arranged in palisades around the bundles; the pattern might be characterized as histiocytic ring-binding of collagen bundles. In areas such as this, it is tempting to propose that an antigen is localized in the bundle and that the histiocytes recognize the respective bundle as foreign. The interstitium among clustered, activated histiocytes characteristically is mucinous, as is the interstitium in this field (alcian blue stain).

S9C25aP16a-3: An area such as this might be characterized as sclerotic granuloma annulare with the implication that the lesion is in a reparative phase. Histiocytes, however, are arranged in traceries among the coarsened collagen bundles. Green arrows identify altered, thin, and interrupted, elastic fibers. Near the green arrow in the center of the field, the thin elastic fiber appears to have a thin yellow sheath (pre-elastin); pre-elastin in this pattern has fibrinoid qualities with the Verhoeff-van Giesen stain. Currently, a demonstration of “pre-elastin” seems to be uncommon; I suspect the quality of the dye has been altered.

S9C25aP16a-4: Some lesions of granuloma annulare show a central area of necrosis; the acidophilic, structureless zone to the right of the green arrows is necrotic (it is structureless, acidophilic, and inflamed; in additon, some of the loosely spaced neutrophils in this area show fragmentation of their nuclei [leukocytoclasia]). In such areas, it is sometimes possible to identify necrotic (i.e., acellular structural components with fibrin thrombi) vessels in ghost outlines. In addition, it is sometimes possible to find vessels in the adjacent dermis that show fibrinoid necrosis and thrombosis. The vasculitic changes probably are secondary. The area of necrosis in this lesion has the qualities of a small infarct (it is “gummatous”). At the blue arrow, a collagen bundle courses into the lesion. The red arrows identify elastic fibers.

S9C25aP16a-5: Superficial lesions of granuloma annulare may extend to the dermal-epidermal interface. The zone of necrosis then induces a variable epidermal response in the nature of mild pseudoepitheliomatous hyperplasia. In this sequence, some of the necrotic tissue will be entrapped by the epithelium and carried to the surface in a pattern of so-called trans-epidermal elimination ( perforating granuloma annulare) (acid-fast stain & methylene blue counterstain).

S9C25aP16a-6: This lesion of the scalp from deep in the files (long ago and faraway) was coded as “Miescher’s granuloma.” It is a palisaded granuloma with giant cells. The central area is hyalinized with zones of fibrinoid necrosis. Miescher’s granuloma is a poorly defined category. In more recent times, some of these cases have been interpreted as examples of actinic granuloma. Necrobiosis lipoidica diabeticorum might also be considered in the differential diagnosis. Something characterized as atypical necrobiosis lipoidica has also been compared to Miescher’s granuloma.

S9C25aP16a-7: This is another example of an infarct-like, palisaded granuloma in the setting of granuloma annulare. The tissue is coagulated centrally with ghost outlines of both cells and fibers. In the area outlined by blue arrows, a vessel is represented in ghost outlines with extravasated red blood cells in its wall on the left. The lumen contains a fibrin and platelet thrombus. This is an uncommon feature of lesions of granuloma annulare.

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