Kaposi Sarcoma (KS) is a low-grade angioproliferative tumour associated with human herpes virus 8 (HHV-8) [2] and is the most common AIDS defining malignancy worldwide [1]. Nonetheless, in the era of Highly Active Antiretroviral Therapy, the incidence of KS has declined.
At the time of diagnosis most patients with lung KS have previously treated cutaneous lesions or other visceral involvement. Nonetheless, cutaneous involvement is absent in 5–23% of patients with symptomatic pulmonary KS. Manifestations include parenchymal, tracheal, lymphatic, pleural and chest wall abnormalities. Common clinical symptoms include dry chronic cough, dyspnoea, fever, and hemoptysis.
The bronchoscopic appearance is considered characteristic to make a presumptive diagnosis (red or purplish stained lesions).
At radiography, AIDS-related KS may manifest as an isolated finding or in association with an opportunistic infection, further delaying and confusing the diagnosis. Radiography may demonstrate middle to lower lung zone reticular opacities and parenchymal nodules with a peribronchovascular distribution that may progress to consolidation, peribronchial cuffing, pleural effusions, and hilar or mediastinal adenopathies. When fever is present, sometimes it cannot be distinguished from superimposed infection at radiography.
CT scans have more specificity and sensitivity, and can demonstrate characteristic finding such as the presence of unilateral or bilateral ill-defined nodules, involving the peribronchovascular sheaths, often beginning in the peri-hilar regions and extending to the periphery, so called flame-shaped lesions [3]. Other findings include interlobular septal thickening, usually preserving the lobular architecture and simulating carcinomatous lymphangitis; large parenchymal nodules with irregular, poorly defined, and spiculated borders, some of them with a perinodular ground glass halo sign [2]. Other less common findings include asymmetrically distributed nodules and larger masses. Osseous and soft-tissue involvement such as lytic lesions of the sternum, ribs and the spine and soft-tissue masses are seen in up to 53% of cases.
The differential diagnosis includes lymphoma, bronchogenic carcinoma, infection, and bacillary angiomatosis. A diagnosis of mycobacterial or bacterial infection is favoured by the presence of a tree-in-bud pattern or subcentimeter nodules with a centrilobular distribution. P. jiroveci pneumonia does not usually manifest with hilar adenopathies or pleural effusion but may exhibit cavitation. Nodule size is not helpful in differentiating KS from lymphoma or bronchogenic carcinoma, and biopsy may be necessary. Bacillary angiomatosis may mimic AIDS-related KS, with violaceous plaques at bronchoscopy, solitary or multiple pulmonary nodules, and mediastinal lymphadenopathies that demonstrate intense enhancement at contrast-enhanced CT [3].