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Kaposi sarcoma

Kaposi sarcoma is a systemic angioproliferative disease of lymphatic and blood vessels driven by KSHV/HHV-8 infection, most commonly affecting immunocompromised patients with HIV/AIDS. Imaging is performed to evaluate extent of disease and guide diagnosis, with mortality often due to visceral involvement (lung and gastrointestinal tract).

Key Images

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Look For First
  • Bilateral, ill-defined, flame-shaped nodular opacities with perilymphatic and peribronchovascular distribution on chest CT
  • Hyperattenuating (high-density) lymphadenopathy relative to muscle, especially in the mediastinum and retroperitoneum
  • Multiple enhancing polypoid or nodular masses in the gastrointestinal tract with possible target/bull's-eye appearance
  • Lymphedema in lower extremities and face, often with concurrent skin and mucosal involvement on imaging
Key Image Findings
  • On chest CT, typical Kaposi sarcoma presents as ill-defined, flame-shaped nodular opacities greater than 1 cm in diameter with bilateral, roughly symmetrical perilymphatic and peribronchovascular distribution, often with lower zone predominance.
  • Nodules frequently show surrounding patchy ground glass changes and are associated with interlobular septal thickening, reflecting tumor growth through the peribronchovascular interstitium and interlobular septa.
  • Mediastinal and hilar lymphadenopathy is present in up to 50% of thoracic cases and is characteristically of high attenuation (hyperattenuating), which is highly suggestive of Kaposi sarcoma in the AIDS population.
  • On abdominal CT, Kaposi sarcoma manifests as enhancing polypoid or nodular masses in the gastrointestinal tract, often with concentric or eccentric bowel wall thickening and submucosal masses that may exhibit a target or bull's-eye appearance, particularly in the stomach and duodenum.
  • Hepatic and splenic involvement appears as low-attenuation nodules or masses; hyperattenuating lymphadenopathy is seen in up to 80% of cases with disseminated disease.
  • Plain chest radiographs show bilateral, ill-defined nodular opacities with perihilar and lower zone predominance, bronchial wall thickening, Kerley B lines, pleural effusions, and mediastinal lymphadenopathy.
  • On MRI, ocular disease (conjunctiva, eyelid, orbit, lacrimal gland) demonstrates circumscribed enhancing lesions with low T1 and high T2 signal intensity.
  • Skeletal involvement in AIDS-related KS shows lytic or mixed lytic-sclerotic lesions affecting the axial skeleton (vertebrae, ribs, pelvis), often with associated soft tissue masses.
Differential Diagnosis
  • AIDS-related lymphoma: presents with more well-defined masses compared to the ill-defined flame-shaped nodules of Kaposi sarcoma; positive thallium-201 in both but gallium-67 is positive only in lymphoma.
  • Atypical pneumonia (Pneumocystis jiroveci): causes more diffuse bilateral ground glass opacities with subpleural and perihilar predominance, lacking the nodular perilymphatic distribution of Kaposi sarcoma.
  • Angioinvasive aspergillosis: presents with larger, more consolidated masses often with halo sign; in immunocompromised patients but less common in AIDS.
  • Bacillary angiomatosis: vascular skin lesions in immunosuppressed patients with similar histologic appearance to KS; confirmed by Warthin-Starry stain or PCR for Bartonella species.
  • Acroangiodermatitis (pseudo-Kaposi sarcoma): benign angioproliferative disorder usually on lower extremities associated with chronic venous insufficiency; distinct on histopathology.
  • Pyogenic granuloma (lobular capillary hemangioma): rapidly growing, friable red papules or nodules often following trauma; lobular capillary proliferation distinguishes it on biopsy.
Discussion

Kaposi sarcoma is driven by KSHV/HHV-8 infection and behaves as a multicentric hyperproliferative process rather than a monoclonal neoplasm, though individual lesions in advanced disease may become monoclonal, suggesting progression to a more neoplastic phenotype.

The hyperattenuating lymphadenopathy (high attenuation relative to muscle) is a highly specific imaging feature for Kaposi sarcoma in the AIDS population, seen in up to 80% of disseminated disease and is key for distinguishing it from other malignancies.

Diagnosis requires tissue biopsy showing spindle cell proliferation, slit-like vascular spaces, and extravasated erythrocytes, confirmed by immunohistochemical staining for HHV-8 LANA; imaging findings alone are not sufficient for diagnosis.

In HIV-AIDS patients, antiretroviral therapy alone can induce regression in many cases with only skin or minimal mucosal involvement, but symptomatic or visceral disease requires ART combined with systemic chemotherapy.

Pulmonary and gastrointestinal tract involvement are major causes of morbidity and mortality, and in 30% of cases visceral disease occurs without concurrent cutaneous involvement, making imaging surveillance essential.

Long-term surveillance is indicated even after treatment response because KSHV persists and recurrence is common; immunosuppressed transplant patients require reduction of immunosuppression as the primary intervention.

Reporting Pearls

Report hyperattenuating lymphadenopathy (high density relative to muscle) in the mediastinum and retroperitoneum, and describe nodules using specific terms such as "bilateral, roughly symmetrical, perilymphatic and peribronchovascular, ill-defined, flame-shaped nodules" with precise location and assessment of surrounding ground glass changes, as these features are highly characteristic of Kaposi sarcoma in the immunocompromised population and aid clinician confidence in diagnosis.

Pitfalls
  • Mistaking the hyperattenuating lymphadenopathy of Kaposi sarcoma for benign reactive nodes or metastatic disease; remember that high attenuation relative to muscle is highly suggestive of KS in the AIDS population and should raise suspicion.
  • Underestimating visceral disease burden because 30% of cases present without cutaneous involvement; careful inspection of the chest, abdomen, and pelvis is essential even when skin lesions are inconspicuous.
  • Confusing the flame-shaped, ill-defined nodular pattern with typical pneumonia or other infections; the key distinguishing feature is the bilateral symmetry and perilymphatic distribution rather than random consolidation.
  • Failing to recognize that biopsy may be hazardous due to high bleeding risk, particularly for endobronchial or percutaneous lung biopsy; imaging features and clinical context often support diagnosis without tissue confirmation.
Source: Reference source

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