A 50-year-old immunocompromised patient presents with fever and dyspnea. Chest CT shows a 2 cm pulmonary nodule surrounded by a halo of ground-glass opacity. What is this finding called?
- A Air crescent sign
- B Reverse halo sign
- C Halo sign ✓
- D Feeding vessel sign
Correct answer: C. Halo sign
Explanation
The halo sign is a nodule or mass surrounded by a rim of ground-glass opacity, classically seen in invasive pulmonary aspergillosis in immunocompromised patients. The air crescent sign is a crescent of air within a cavitary lesion, seen in later stages of aspergilloma. The reverse halo sign (atoll sign) is a central ground-glass opacity surrounded by a ring of consolidation, seen in organizing pneumonia. The feeding vessel sign is associated with pulmonary infarcts.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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