Histopathology reveals a dense, nodular or diffuse infiltrate of small, medium and large pleomorphic cells confined to the subcutaneous fat (Figs. 5.4 & 5.5). Perivascular aggregates of

Fig. 5.4 Subcutaneous T-cell lymphoma. Dense infiltrate showing prominent involvement of the subcutaneous fat, mimicking the histopathological picture of a lobular panniculitis.
Fig. 5.5 Subcutaneous T-cell lymphoma. Infiltration of subcutaneous fat by small- to medium-sized pleomorphic lymphocytes.

non-neoplastic cells may be located within the reticular dermis, but clusters of neoplastic T lymphocytes are almost never situated outside the subcutaneous tissues. The epidermis is spared as a rule. Neoplastic cells within the subcutaneous fat are arranged in small clusters or as solitary units around the single adipocytes (so-called 'rimming' of the adipocytes) (Fig. 5.6). Necrosis is often a prominent feature,

Fig. 5.6 Subcutaneous T-cell lymphoma. Note 'rimming' of an adipocyte by neoplastic lymphocytes. (Reprinted with permission from The American Journal of Surgical Pathology, in press.)
Fig. 5.7 Subcutaneous T-cell lymphoma. Prominent necrosis with several atypical lymphocytes left within the infiltrate.

and may completely mask the specific histopathological features (Fig. 5.7). A histiocytic infiltrate, often with the formation of granulomas, is also common [50,51]. In addition, reactive small lymphocytes can be admixed with the neoplastic cells but plasma cells and eosinophils are rare. Mem-branocystic (lipomembranous) lesions have been described in some cases [52,53].

In some lesions, the specific findings are confined to a small portion of the subcutaneous fat, thus rendering the examination of small biopsies (punch biopsies) problematic or even impossible (Fig. 5.8). In this context, it must be underlined that a diagnosis of subcutaneous T-cell lymphoma can only be made when large deep biopsies are available.

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