Among the primary malignant tumours of the spleen, fibrous histiocytoma (MFH) is extremely rare and only six cases have been reported in the literature. A splenectomy was carried out in a 22-year-old woman presenting with an acute abdomen. Imaging procedures showed a 5 cm round, heterogeneous mass in the spleen. At light microscopy the infiltrating cell population was arranged in nests or bundles with a storiform pattern. At higher magnification, most neoplastic elements were medium-sized, round or spindle-shaped, with acidophilic cytoplasm and oval or round nucleus. Mitotic figures were numerous; reactive foamy macrophages could be seen. At immunohistochemistry, in paraffin sections, there was strong positivity with the reagents against CD45, CD68, alfa-1-antichymotrypsin and vimentin. In frozen sections there was a clear-cut positivity with the antibodies EBM11 (CD68), KP1 (CD68), Ber Mac 3, anti-lysozyme and anti-vimentin. The case reported revealed morphological and immunohistochemical features consistent with MFH, of the storiform-pleomorphic variant. The clear-cut positivity for macrophage-associated molecules and for leucocyte common antigen would seem to suggest a histiocytic origin. MFH is considered an aggressive tumour, with a frequent recurrence and metastasis but our patient is alive and free of disease three years from surgery.

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