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Kaposi’s Disease
Kaposi’s Disease presents in various patterns. An individual lesion might be characterized as a fibrotic variant (S13C17P15-1-7), an angiomatous variant (S13C15P13-1-3), or a solid variant (S13C14aP12a-1-6). Minor variations, in the expression of vascular patterns in the fibrotic form,
might be characterized as angioendotheliomatous variant. At one time, the solid variant
would have been appropriately characterized as the classic form. Subsequent to the disease becoming common, particularly in the setting of HIV infection, the fibrotic variant is most frequently encountered. In the solid variant, the lesion is a nodular tumor, often one that is relatively confined to an inflamed, widened papillary dermis. It projects above the skin surface (S13C14aP12a-1-6). In the skin, Kaposi’s disease often is relatively confined to the reticular
dermis, sparing the subcutaneous fat. The nodule of a solid variant is composed of closely aggregated spindle cells (i.e., the scanty inter-cellular matrix has the characteristics of a reticulum). The
spindle cells have amphophilic, or pale cytoplasm (the cytoplasm of some of the cells is clear without a sharply defined vacuole) and an elongated, or round nucleus with uniform nuclear characteristics. Nucleoli are
variable. Slit-like spaces among the spindle cells are a variable feature; they contain red blood cells, and often are emphasized as an aid in the diagnosis of Kaposi’s disease. Spindle cells, in cross-section,
often appear to have clear cytoplasm in the vicinity of the nucleus. Scattered spindle cells contain pale, acidophilic rounded bodies (generally smaller, more variable in size, and with less acidophilia than
neighboring erythrocytes) in their cytoplasm. These bodies vary in size; they are an aid in the histologic diagnosis of Kaposi’s disease (S13C14aP12a-5). At the periphery of a nodule, clusters of tumor cells may be found projecting into
the lumen of a dilated, thin-walled vessels. Hemosiderin deposits are a regular feature (in contrast to the relative absence of hemosiderin in a lesion of pyogenic granuloma) (S13C14bP12b-1). The stroma of a solid variant of Kaposi’s disease is a frame-work of reticular
fibers; they are structured in tube-like fashion that is most suggestive of the reticular frame-work of a vascular neoplasm (S13C14bP12b-2). In classic Kaposi’s disease, as seen in the elderly, vessels adjacent to the
nodules are cuffed by infiltrates of chronic inflammatory cells, including plasma cells. Infiltrates of inflammatory cells are less common in the AIDS-related form. The patterns in the solid and angiomatous variants
are to be distinguished from the angioplastic nodules of newly formed vessels in acral angiodermatitis (S13P14bP12b-3)
Angiomatous Variant
Kaposi’s disease has become common; it is common in the setting of acquired immunodeficiency. In the classic form, three basic histologic patterns were recognized: 1.) fibrotic
variant, 2.) angiomatous variant, and 3.) solid variant. These three variants are represented in the setting of HIV infection, but the fibrotic variant seems to be the most common. In the fibrotic category, a
variant is characterized by a prominence of anastomosing vascular spaces among collagen bundles; the pattern has angioendotheliomatous qualities. This variation might be characterized as lymphangioendotheliomatous
variant. In the setting of HIV infection, inflammatory infiltrates often are minimal and generally are milder than those seen in the category of classic disease. Herpes virus, type 8, has been implicated in the
setting of AIDS-associated Kaposi’s disease.
In the angiomatous variant, the lesions are nodular (lobular); they are rounded and expansile. The patterns are dominated by clusters of dilated, symmetrically rounded spaces that
contain red blood cells. A spindle cell component in the background may be inconspicuous; such lesions may be easily dismissed as an angioma. Often, the clinical setting will be an aid in placing the patterns in a
proper perspective. The angiomatous pattern may be found as a minor component in fibrotic, or solid variants (S13C14aP12a-3).
Kaposi’s Disease
Fibrotic Variant
In the setting of HIV infection, the most commonly encountered form of Kaposi’s disease is the fibrotic variant. It is localized in the reticular dermis. It is biphasic with one
component consisting of peripheral loci of angioplasia (promontories) and a second component that is interstitial (S13C17P15-1-7).
In the interstitial component, spindle cells are increased in number among altered collagen bundles of the reticular dermis. The spindle cells often cling to a collagen bundle along one margin and abut upon a clear
space along the opposite margin; the clear space is slit-like. This pattern may be a recapitulation of the open-ended character of dermal lymphatics. In this approach, the spindle cells are “neoplastic”
lymphangioendothelial cells. The angioplastic loci are composed of loosely spaced, small vessels with a variable component of pale spindle cells in the adventitia of the vessels. If the adventitial spindle cell
component is prominent, the resulting patterns focally take on the character of the diffuse patterns encountered in the solid variant.
Kaposi’s Disease-like Angiosarcoma
Patterns resembling those of Kaposi’s disease may be encountered in the setting of localized lesions of the skin and soft tissue. The site may be unusual (one not commonly involved in
classic Kaposi’s disease) and the neoplasm may evolve in the pattern of a low-grade angiosarcoma (Kaposi’s disease-like angiosarcoma) (S13C16P14-1-6).
Tappero JW, et al: Kaposi’s sarcoma: epidemiology, pathogenesis, histology, clinical spectrum, staging criteria, and therapy. J Am Acad Dermatol 1993;28:371-95.
Orlow SJ, et al: AIDS-associated Kaposi’s sarcoma in Romanian children. J Am Acad Dermatol 1993;28: 449-53.
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