Aneurysmal ("angiomatoid") fibrous histiocytoma of the skin.

Seventeen cases are reported of a variety of cutaneous fibrous histiocytoma, which we have designated as aneurysmal ("angiomatoid") fibrous histiocytoma. These lesions differ from the classical cutaneous fibrous histiocytoma in both their clinical presentation and pathologic features. Clinically, they may be larger than the usual cutaneous fibrous histiocytoma, are blue, black, or dark red, and have a cystic consistency. They are most commonly located on the extremities and may be associated with symptoms of pain and rapid growth. The clinical diagnosis of fibrous histiocytoma is seldom considered in the differential diagnosis, which may include malignant melanoma, hemangioma, neurofibroma, and nonspecific cyst. Histologically, the lesions are characterized by the presence of large, blood-filled tissue spaces, which, at times, account for up to one half their size. These spaces lack an endothelial lining, being surrounded and lined by histiocytes, many of which contain hemosiderin pigment, fibroblasts, and foam cells. The solid portions of the tumor have the usual features of a cutaneous fibrous histiocytoma. This "angiomatoid" lesion is closely allied to what has been termed "hemosiderin histiocytoma," which appears to be a precursor stage in its formation. The presence of extravasated erythrocytes in combination with a spindle-cell stroma may lead to an erroneous diagnosis of Kaposi's sarcoma. This cutaneous tumor has architectural and cytologic similarities to its malignant soft tissue counterpart recently described as angiomatoid malignant fibrous histiocytoma. However, unlike the latter, the cutaneous lesion is benign and lacks the prominent inflammatory infiltrate, pleomorphic appearance, and systemic manifestations of its soft tissue counterpart. The distinctive clinical and pathologic features of the cutaneous lesion serve to separate it as a specific variant of the cutaneous fibrous histiocytomas.