Pulmonary involvement in Kaposi sarcoma: correlation between imaging and pathology

Abstract

Kaposi sarcoma is a low-grade mesenchymal tumor involving blood and lymphatic vessels. There are four variants of this disease, each presenting a different clinical manifestation: classic or sporadic, African or endemic, organ transplant-related or iatrogenic, and AIDS-related or epidemic. Kaposi sarcoma is the most common tumor among patients with HIV infection, occurring predominantly in homosexual or bisexual men. The pulmonary involvement in Kaposi sarcoma occurs commonly in critically immunosupressed patients who commonly have had preceding mucocutaneous or digestive involvement.The etiology of Kaposi sarcoma is not precisely established; genetic, hormonal, and immune factors, as well as infectious agents, have all been implicated. There is evidence from epidemiologic, serologic, and molecular studies that Kaposi sarcoma is associated with human herpes virus type 8 infection. The disease starts as a reactive polyclonal angioproliferative response towards this virus, in which polyclonal cells change to form oligoclonal cell populations that expand and undergo malignant transformation.The diagnosis of pulmonary involvement in Kaposi sarcoma usually can be made by a combination of clinical, radiographic, and laboratory findings, together with the results of bronchoscopy and transbronchial biopsy. Chest high-resolution computed tomography scans commonly reveal peribronchovascular and interlobular septal thickening, bilateral and symmetric ill-defined nodules in a peribronchovascular distribution, fissural nodularity, mediastinal adenopathies, and pleural effusions. Correlation between the high-resolution computed tomography findings and the pathology revealed by histopathological analysis demonstrate that the areas of central peribronchovascular infiltration represent tumor growth involving the bronchovascular bundles, with nodules corresponding to proliferations of neoplastic cells into the pulmonary parenchyma. The interlobular septal thickening may represent edema or tumor infiltration, and areas of ground-glass attenuation correspond to edema and the filling of air spaces with blood. These findings are a result of the propensity of Kaposi sarcoma to grow in the peribronchial and perivascular axial interstitial spaces, often as continuous sheets of tumor tissue.In conclusion, radiological findings can play a major role in the diagnosis of pulmonary Kaposi sarcoma since characteristic patterns may be observed. The presence of these patterns in patients with AIDS is highly suggestive of Kaposi sarcoma.

Figure 1

A to C. Chest X-rays of three patients with pulmonary KS showing bilateral paracardiac infiltration. Confluent lesions are most evident in C.

Figure 2

A and B. High-resolution CT scans of two patients with pulmonary KS showing peribronchovascular thickening and irregular narrowing of the bronchial lumen.

Figure 3

High-resolution CT scan at the level of the main bronchi of a patient with pulmonary KS, showing diffuse ill-defined large nodules and paracardiac peribronchovascular thickening.

Figure 4

High-resolution CT scan of a patient with pulmonary KS at the level of the main bronchi shows ground-glass attenuation areas in the posterior regions of both lungs, which correspond to pulmonary hemorrhage. Peribronchovascular thickening is observed in the right lung, as well as bilateral pleural effusion.

Figure 5

CT scan (mediastinal window) at the level of the carina of a patient with pulmonary KS shows bilateral pleural effusion.

Figure 6

A to D. High-resolution CT scans (A and B) of two patients with pulmonary KS that demonstrate marked peribronchovascular and interlobular septal thickening and the presence of small parenchimal nodules. Photomicrographs of histologic specimen show tumor cells infiltrating the periarteriolar connective tissue (C), and a neoplastic parenchymal nodule with indistinct borders (D) (HE, ×40).

Figure 7

A and B. High-resolution CT scan at the level of the main bronchi (A) of a patient with pulmonary KS demonstrates irregularity of the pleural surfaces and nodularity of the oblique fissures bilaterally. Photomicrograph of histologic section (B) demonstrates a neoplastic nodule adjacent to the pleural surface (HE, ×40).

Figure 8

A to D. High-resolution CT scans at the level of the upper lobe (A) and the lower lobe (B), of two patients with pulmonary KS, show extensive interlobular septal and peribronchovascular thickening. Photomicrographs of histologic specimens (C and D) show thickening of interlobular septa due to edema and tumor cells infiltration (HE, ×40).

Figure 9

A and B. High-resolution CT scan (A) shows areas of ground-glass attenuation and interlobular septal thickening in the upper lobes. A crazy-paving pattern is observed in the right upper lobe. Photomicrograph of histologic section (B) demonstrates infiltration of the interlobular septa due to edema and neoplastic cells and also edema filling the alveolar airspace (HE, ×40).