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Xanthogranuloma: Tumorous infiltrates of histiocytes are to be characterized as either neoplasms, or as inflammation. Inflammatory processes, that are rich in histiocytes, usually are accompanied by admixtures of common inflammatory cells, including lymphocytes and plasma cells. By a very special relationship, histiocytes and eosinophils often are companions. For many tumorous histiocytic lesions, the distinctions between neoplasm and inflammation have remained a source of controversy. The availability of cell markers has impacted on the conceptualization of histiocytic infiltrates. We approach each lesion as if the identification of a cell marker is, in addition, an identification of a specific variant of disease. In assigning significance to cell markers, we are faced with two options: Either phenotype is a fixed attribute defining a line of distinctive cells (in this situation, the expression of phenotype is independent of local influences), or histiocytes are phenotypically diverse and expressions of different phenotypes are readily accessible (the expressions depend on the setting in which histiocytes finds themselves).
The designation, xanthogranuloma, has greatest utility in defining histiocytic tumors in infancy
and childhood, hence juvenile xanthogranuloma. Lesions in this category generally show mixtures of activated histiocytes and foamy histiocytes. Activated histiocytes in tumorous patterns provide a “granulomatous” quality. Foamy histiocytes provide a xanthomatous quality. In combination, a lesion, containing cells of both types, is a xanthogranuloma. In practice, some examples are mostly “granulomatous.” Rare examples are mostly xanthomatous. If too great an emphasis is placed on cell marker studies, the category becomes heterogeneous; the door to a confusing array of lesions of questionable biologic significance is opened.
For some histiocytic lesions, the distinctions between histiocytosis X
and xanthogranuloma are difficult to define. The confusion is not simply at the level of cell marker studies; it extends to include cytologic features. Is it appropriate to speak of an “atypical” histiocytoma or “atypical” xanthogranuloma? Distinctions between xanthogranuloma and reticulohistiocytoma also may be a problem. Does the “ground-glass” quality of the cytoplasm of histiocytes in a reticulohistiocytoma refer a basophilic granularity, or to some other quality?
The category of necrobiotic xanthogranuloma also may be heterogeneous.
Currently, the willingness of editors to publish descriptions of new examples of “histiocytomas” makes it convenient to exploit cell marker studies with no attention to the
practicality of defining an apparently limitless array of “histiocytomas.”
HistiocytoisX (with “granulomatoid” variant of liver as example)
The infiltrates of histiocytosisX in the skin generally are diffuse in the papillary dermis and in the upper portion of the reticular dermis. The cells tend to be plump and molded
against their neighbors. Nuclear characteristics - deeply grooved nuclei - are an aid in diagnosis. A variation in the patterns of the infiltrates of histiocytosisX has been documented in lesions of the liver. In
this variation, the infiltrates have a granulomatous quality. The distinctive histiocytes tend to cluster in rounded aggregates. This aggregation of distinctive cells is characterized as “granulomatoid” pattern (S15C2P7-1-7).
In occasional examples of granulomatoid patterns in skin lesions, cells are reactive for S-100 protein and CD1a (S15C2P8-1-4). The distribution of the infiltrates in these lesions may not be typical of those of classic histiocytosis
X but, perhaps, these lesions should be accepted as the granulomatoid variant of histiocytosis X. On the other hand, the so-called granulomatoid variant may be a distinct and separate disease. In the child with the hepatic disease, as represented in the photomicrographs, the lesions responded to treatment for histiocytosis X. Following a drug-induced remission, the liver showed a pattern of fibrosis.
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