Teaching Case

A 22-year-old HIV-positive male patient was admitted in the context of a pneumonia with unspecific findings on chest CT. At physical examination a lobulated mass at the posteromedial aspect of the right upper leg was seen. The patient mentioned progressive growth for months.

Plain radiography showed a nonspecific soft tissue mass at the posteromedial aspect of the right upper leg.

Ultrasound with colour Doppler detected superficial soft tissue lesions, with well-defined borders. The lesions were hypoechoic with posterior acoustic enhancement and a strong hypervascularity.

CT and MR were able to define the extension of the lesions. No significant changes were detected in the bones. On gadolinium-enhanced T1 sequences there was an intense signal increase of the superficial mass of the posteromedial aspect of the leg and foci of hyperintensity were identified in the adjacent muscular planes.

Cutaneous biopsy was performed and the histopathological analysis showed Kaposi Sarcoma.

Background - Kaposi Sarcoma (KS), the most common tumour in patients with Acquired Immune Deficiency Syndrome (AIDS) [1], was first described in 1872 by Moritz Kaposi [2]. It is a low-grade malignancy associated with human herpes virus type 8 (HHV-8), that can also be responsible for non-Hodgkin´s lymphoma and Castleman’s disease. KS is generally multifocal and most commonly involves the skin and mucous membranes, although it can affect virtually every organ system. There is reactive polyclonal angioproliferative response in the connective tissue with malignant transformation, neoangiogenesis, inflammation and oedema.

Clinical Perspective - Four forms of this disease have been described [3, 4]: classic (rare, mostly found in the Mediterranean area) endemic (also known as African KS), epidemic (associated with Human Immunodeficiency Virus infection, with decreasing incidence since the widespread use of highly active antiretroviral therapy) and transplant-associated. Presenting symptoms and signs of KS are related to duration of the disease and the most affected organs [4].


Imaging Perspective: When cutaneous KS is suspected, imaging should be performed to characterize the lesions detected at physical examination. Primary musculoskeletal involvement is exceedingly rare. Usually skin lesions will extend to the deeper anatomical planes [2]. Plain radiography is often the first examination performed, depicting a non-specific superficial mass. At Doppler ultrasound cutaneous lesions are usually hypoechoic with posterior acoustic enhancement, have well-defined multilobulated borders and show hypervascularity, particularly in the AIDS-associated form [6]. Contrast-enhanced sectional imaging (Computed Tomography and Magnetic Resonance) allows a more accurate delineation of extent of the lesion and a better evaluation of bone and muscle involvement. CT can better demonstrate osseous lytic lesions with cortical destruction and periosteal reaction. MR is better at depicting bone marrow changes and soft tissue masses. On fluid sensitive sequences (FS T2-WI, STIR) there is increased signal in the superficial tissues in relation to oedema. The affected tissues (which in our case included muscles) show intense enhancement after intravenous administration of gadolinium contrast in concordance with the vascular nature of the lesions. The main differential diagnosis, bacillary angiomatosis, may present with similar clinical and imaging findings, although history of exposure to cats, positive serological tests and presence of lymph nodes may sometimes be useful. Osseous lesions are also more common [5]. However, biopsy is often required for definitive diagnosis [7].

Take Home Message: KS should be considered as a differential diagnosis when evaluating an HIV-patient with a soft tissue mass. Knowledge of the patient’s immunologic status is essential.