Diagnosis & Discussion

Diagnosis

Spindle cell hemangioma.

Discussion

Classic KS, KS unrelated to Human Immunodeficiency Virus (HIV)-Acquired Immunodeficiency Syndrome (AIDS), is a disease of the elderly, with less than 10% of cases presenting in patients less than 50 years. It is especially common in elderly Mediterranean males. HHV8 infection is required for the development of both classical KS and AIDS-related KS. Patients present with purple or reddish macules, plaques and nodules of the legs and feet. Most patients with classical KS have an excellent prognosis. The histologic appearance of KS consists of a proliferation of bland spindle cells with vascular slit-like spaces and extravasated erythrocytes. Immunohistochemical staining for HHV8 detects the latent antigen within the spindle cells regardless of the HIV-status of the patient.

There are clinicopathologic mimics of KS including spindle cell hemangioma (SCH) and acroangiodermatitis. Spindle cell hemangioma classically presents in acral locations on young adults and may be multifocal; they may also present in the setting of Maffucci syndrome (extraosseous hemangiomas and multiple enchondromas). Histologically, SCH is a circumscribed dermal tumor composed of irregularly sized thin-walled vascular spaces, commonly with thrombi, and solid spindled areas. Another component is the presence of epithelioid cells with intracytoplasmic vacuoles. Compared with lesions of KS, the vessels in SCH are less slit-like and the spindle cell component is cytologically bland. Additionally, since SCH is a vascular proliferation, and thus composed of both endothelial cells and pericytes, SMA staining can be used to demonstrate retention of this pericyte population (as compared to KS which is an exclusively endothelial cell proliferation and negative for SMA). Finally, the spindle cells of SCH are negative for HHV8.

Another diagnostic consideration in the differential of KS is acroangiodermatitis, especially in a patient with history of venous insufficiency. Acroangiodermatitis, a reactive angiodyplasia of cutaneous vessels, shares a similar clinical presentation with KS with vascular red-purple papules plaques or nodules on the extensor surfaces of lower extremities. The histologic features of acroangiodermatitis are also similar to KS, with increased small vessels with a lobular architecture and intervening fibrous stroma and spindled cells surrounding vessels. Hemosiderin deposition and a lymphocytic infiltrate are often identified in the stroma. Similar to SCH, lesional cells are negative for HHV8 while positive for SMA. The prominent spindle cell component in the context of vascular spaces and some epithelioid cells with intracytoplasmic vacuoles supported a diagnosis of SCH rather than acroangiodermatitis.

Kaposi sarcoma mimics are a diagnostic dilemma that clinicians and pathologists alike should be aware of, as these mimics share several clinical and histologic features. Without caution, a patient with a benign condition could be mistakenly diagnosed with a low-grade malignancy. In cutaneous vascular lesions with a spindle cell component, a combination of HHV8 and SMA staining are useful in distinguishing benign lesions, such as SCH, from Kaposi sarcoma.

References

Billings, Steven D. Spindle Cell Hemangioma. Dermatopathology section. ExpertPath.

Coban I, Kokenek-Unal TD and Alper M. Spontaneous Acroangiodermatitis. Indian Journal of Dermatology 2015; 60(3); 2268-71

Kanner, William A, Stockman, David L. Kaposiform Angiodermatitis. Vascular Tumor section of Cardiology. ExpertPath.

Krown, Susan E and Singh, Jasmeet C. Classic Kaposi sarcom: Epidemiology, risk factors, pathology and molecular pathogenesis. Last reviewed Oct 2019. UpToDate.

Strutton G and Weedon D. Acro-angiodermatitis: A simulant of Kaposi’s sarcoma. American Journal of Dermatopathology 1987; 9(2): 85-9.

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