Question 1
What is the hallmark feature of the halo sign on a chest CT?
A. Central ground-glass opacity surrounded by a nodule
B. Central nodule surrounded by ground-glass attenuation
C. Uniformly dense mass without surrounding changes
D. Linear interstitial thickening
Answer: B. Central nodule surrounded by ground-glass attenuation
Explanation: The halo sign consists of a central nodular opacity with surrounding ground-glass attenuation, indicating hemorrhage, inflammation, or infiltration.
Reference:
Radiopaedia: Halo Sign. “The halo sign is characterized by a nodule surrounded by ground-glass attenuation on CT.”
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Question 2
Which of the following conditions is most classically associated with the halo sign in immunocompromised patients?
A. Tuberculosis
B. Invasive pulmonary aspergillosis
C. Sarcoidosis
D. Pulmonary embolism
Answer: B. Invasive pulmonary aspergillosis
Explanation: The halo sign is highly suggestive of angioinvasive fungal infections like aspergillosis, especially in immunocompromised patients.
Reference:
PubMed: Imaging in Aspergillosis. “The halo sign is a hallmark of invasive aspergillosis in immunocompromised hosts.”
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Question 3
What does the ground-glass attenuation in the halo sign represent?
A. Alveolar hemorrhage
B. Tumor invasion
C. Pleural effusion
D. Atelectasis
Answer: A. Alveolar hemorrhage
Explanation: The ground-glass halo surrounding the central lesion reflects perilesional alveolar hemorrhage, inflammation, or edema.
Reference:
Radiology Key: Pathophysiology of the Halo Sign. “The ground-glass halo typically represents hemorrhage around the lesion.”
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Question 4
Which imaging modality is most sensitive for detecting the halo sign?
A. Chest X-ray
B. CT scan
C. MRI
D. Ultrasound
Answer: B. CT scan
Explanation: CT is the most sensitive imaging modality for identifying the halo sign, as chest X-ray may not reveal it due to poor resolution.
Reference:
Radiopaedia: Halo Sign Imaging. “CT is superior for detecting the halo sign and associated features.”
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Question 5
Which of the following neoplasms can present with a halo sign on imaging?
A. Adenocarcinoma of the lung
B. Choriocarcinoma metastases
C. Squamous cell carcinoma
D. Small cell lung cancer
Answer: B. Choriocarcinoma metastases
Explanation: Hemorrhagic metastases, such as those from choriocarcinoma or angiosarcoma, can cause a halo sign due to surrounding hemorrhage.
Reference:
Radiographics: Halo Sign in Neoplasms. “Hemorrhagic metastases can produce a halo sign on CT.”
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Question 6
In which patient population is the halo sign most commonly observed?
A. Immunocompromised patients
B. Smokers with COPD
C. Children with asthma
D. Patients with pulmonary fibrosis
Answer: A. Immunocompromised patients
Explanation: The halo sign is most commonly seen in immunocompromised patients with invasive fungal infections or hematologic malignancies.
Reference:
PubMed: Halo Sign in Immunocompromised Hosts. “The halo sign is frequently observed in immunocompromised individuals.”
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Question 7
Which of the following infections is unlikely to cause a halo sign?
A. Invasive aspergillosis
B. Mucormycosis
C. Bacterial pneumonia
D. Tuberculosis
Answer: C. Bacterial pneumonia
Explanation: Bacterial pneumonia typically does not produce a halo sign. It is more associated with fungal infections or hemorrhagic processes.
Reference:
Radiopaedia: Infectious Causes of the Halo Sign. “The halo sign is not a common feature of bacterial pneumonia.”
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Question 8
What is the primary treatment for invasive pulmonary aspergillosis presenting with the halo sign?
A. Broad-spectrum antibiotics
B. Antifungal therapy
C. Corticosteroids
D. Immunosuppressive therapy
Answer: B. Antifungal therapy
Explanation: Invasive pulmonary aspergillosis is treated with antifungal agents such as voriconazole.
Reference:
ATS Guidelines: Treatment of Aspergillosis. “Antifungal therapy is the mainstay of treatment for invasive aspergillosis.”
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Question 9
Which of the following differentiates the halo sign from the air crescent sign on imaging?
A. Halo sign is seen early, air crescent sign is seen late
B. Air crescent sign indicates hemorrhage
C. Halo sign lacks ground-glass attenuation
D. Halo sign occurs in healed infections
Answer: A. Halo sign is seen early, air crescent sign is seen late
Explanation: The halo sign is an early finding indicating hemorrhage, while the air crescent sign is a late finding indicating resolution and necrosis.
Reference:
Radiology Key: Halo vs. Air Crescent Sign. “The halo sign appears early, while the air crescent sign is a late manifestation.”
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Question 10
Which vasculitis can present with the halo sign on chest imaging?
A. Granulomatosis with polyangiitis
B. Takayasu arteritis
C. Kawasaki disease
D. Polyarteritis nodosa
Answer: A. Granulomatosis with polyangiitis
Explanation: Granulomatosis with polyangiitis can cause nodules with surrounding ground-glass opacities due to alveolar hemorrhage, producing a halo sign.
Reference:
Radiopaedia: Halo Sign in Vasculitis. “The halo sign may occur in vasculitis, such as granulomatosis with polyangiitis.”
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