Kaposi sarcoma

Kaposi sarcoma is a low-to-intermediate grade mesenchymal tumour that involves the lymphovascular system. The tumour can involve the pulmonary, gastrointestinal, cutaneous and musculoskeletal systems.

Pathology

There are four recognised variants ¹:

• classic (chronic): multiple distal lower extremity predominant purple skin plaques and rarely involve visceral organs
• endemic (lymphadenopathic): common in equatorial Africa
• iatrogenic (organ transplant-related)
• AIDS-related (epidemic): usually requires the CD4 count to drop <200 cells/mm³; may develop in up to 35% of patients with AIDS ² and when developed it is considered an AIDS-defining illness

The latter two variants are much more common.

Aetiology

An aetiological association with human herpes virus type 8 (HHV8) has been postulated. The AIDS-related and post-transplant variants are also associated with immunosuppressive states states.

Histology

Histologically can comprise of sheets of plump spindle-shaped cells surrounding and lining slit-like vascular spaces.

Associations

• lymphoproliferative disorders (particularly with the classic form)

Radiographic features

There is a wide spectrum of imaging findings depending on which organ is involved. However, most features are non-specific ^1,2,4 but may assist in diagnosis if relevant clinical risk factors (e.g. background AIDS history) are evident. In 30% of cases, there is no concurrent cutaneous involvement ¹.

Plain radiograph

The following features may be seen on chest radiographs:

• parenchymal nodular or reticular opacities with a predilection towards perihilar mid to lower zones; has two major patterns
  1. linear interstitial nodules
  2. fluffy ill-defined nodules
• pleural effusion(s)
• mediastinal and/or hilar lymphadenopathy

CT

On HRCT of the chest:

• ill-defined (flame-shaped) nodular opacities with usually bilateral and roughly symmetrical perilymphatic and peribronchovascular distribution (1-2 mm)¹
• may have surrounding patchy ground glass changes
• interlobular septal thickening
• lymphadenopathy (may be present in up to 50%) ⁵
• lymphadenopathy is typically of high attenuation ⁶

On liver CT:

• ill-defined multifocal peripheral portal nodules with variable attenuation (commonest hepatic neoplasm in AIDS patients) ^1,4

Nuclear medicine

Scintigraphy may be useful if concurrent opportunistic infection or lymphoma is suspected:

• thallium-201: usually positive in both lymphoma and Kaposi sarcoma
• gallium-67: usually negative in Kaposi sarcoma but positive in lymphoma and infection

History and etymology

This condition was first described by Moritz Kaposi (1837-1902), an Austro-Hungarian dermatologist, in 1872.

Differential diagnosis

For thoracic involvement consider:

• lymphoma (AIDS-related lymphoma: ARL): appear more well defined
• atypical pneumonia (e.g. Pneumocystis jiroveci)
• fungal (e.g. angioinvasive aspergillosis) or mycobacterial infection
• bacillary angiomatosis: also has skeletal lesions