GRANULOMA ANNULARE WITH FORMATION OF PALISADING GRANULOMATA
Palisading granulomata of the type seen in this case are illustrated in textbooks as being characteristic of granuloma annulare. Actually, such palisading granulomata are found in a minority of cases of granuloma annulare as it is encountered in day to day dermatopathology. The palisading granuloma consists of a central zone of altered collagen surrounded by cells having fibrohistiocytic morphology with the spindle cells focally radiating around the periphery. Many cases of granuloma annulare present with patchy collections of cells having fibrohistiocytic morphology associated with minimal alteration of the collagen and no palisading granulomata. There are many variants of granuloma annulare that are not illustrated here.

 
 
Scan showing palisading granuloma in the left side of the dermis. Perivascular lymphocytes are seen elsewhere.
Low power of a palisading granuloma in the left half of the picture with centrally altered collagen (so-called necrobiosis) surrounded by cells having fibrohistiocytic morphology.
High power showing some of the spindle cells radiating around the periphery of the zone of altered collagen (left of the infiltrate).

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