Bullous lesions in Kaposi's sarcoma: case report.

Bullous lesions have been only rarely described in Kaposi's sarcoma (KS), and their histopathologic features have never been described in detail. We report a case of bullous lesions of KS in an 82-year-old Italian woman. The patient had typical smooth pale reddish-grey slightly-raised KS plaques on the legs, present for at least 10 years. Several dull grayish-pink blisters (0.5 to 2 cm in diameter) affected both dorsa of her feet and ankles symmetrically. Two punch biopsies were taken, one from an infiltrated KS plaque on the right buttock and the other from a bullous lesion on the right foot. Histopathologically, the late KS plaque on the buttock showed typical features of KS, with an increased number of spindle cells arranged in short bundles and extravasation of erythrocytes. The bullous lesion on the foot showed a full-thickness vascular neoplasm involving the upper and lower dermis and the subcutaneous fat. The upper portion of the lesion contained many newly formed, highly-dilated blood vessels, touching the overlying epidermis and separated from it by a narrow band of collagen and endothelial cells; wide, empty spaces characterized the superficial dermis, in which preexisting venules and bands of collagen associated with nonatypical endothelial cells floated. All these findings would suggest a lymphangiomatous lesion, if the presence of specific diagnostic criteria of KS were not recognizable at a deeper level of the lesion. Various criteria actually suggest that the bullous lesion may be regarded as an epiphenomenon of a KS plaque lesion: (a) full-thickness involvement of the reticular dermis and, in this case, also of the subcutaneous fat; (b) dense and patchy lymphoplasmocytic infiltrate typical of plaque lesions and, much less frequently, of patch lesions; (c) presence of ectatic blood vessels, filled with plasma and erythrocytes (pseudoangiomatous findings), a nonpathognomonic but highly characteristic finding of the plaque lesion; and (d) as in the KS plaque lesions, in the bullous lesion as well the reticular dermis was characterized by an increased number of anastomosing bizarrely shaped vascular spaces lined by nonatypical endothelial cells. We hypothesize that the prevalence of lymphangiomatous differentiation in the upper dermis represents one of the many features of KS lesions. When present, it may correlate with the clinical feature of a blister.