Halo Sign

Robert B. Carr, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Halo sign refers to ring of ground-glass opacity surrounding pulmonary mass or nodule on CT
Ground-glass opacity usually represents alveolar hemorrhage

Helpful Clues for Common Diagnoses

Angioinvasive Aspergillosis
- Occurs in immunocompromised patients, especially AIDS, organ transplant, and chemotherapy
- Fungal invasion with occlusion of small-and medium-sized pulmonary arteries
- Results in tissue infarction, necrosis, and hemorrhage

Helpful Clues for Less Common Diagnoses

Pulmonary Metastasis
- Central nodule represents metastatic lesion
- Halo surrounding nodule represents hemorrhage
- May be seen uncommonly with numerous malignancies, including melanoma, choriocarcinoma, and angiosarcoma
Kaposi Sarcoma
- Usually occurs in patients with AIDS
- Commonly preceded by appearance of mucocutaneous lesions
- Ill-defined nodules in peribronchovascular distribution
- Some nodules produce halo sign due to surrounding hemorrhage
Wegener Granulomatosis
- Bilateral nodules and masses usually > 2 cm in size with no predilection for specific lung region
- Approximately 50% of cases show cavitation
- Look for associated tracheal involvement

Helpful Clues for Rare Diagnoses

Bronchioloalveolar Carcinoma
- Lepidic growth: Growth along alveolar and bronchiolar walls and septa without stromal invasion
- Halo sign is caused by infiltration of tumor cells growing in lepidic fashion
- May have internal bubbly lucencies referred to as pseudocavitation
Atypical Infection
- Has been described with tuberculosis, MAI, CMV, HSV, Mucor, candidiasis, coccidioidomycosis, pseudomonas