Question

Discuss the imaging features of pulmonary aspergillosis.

Hint:

HRCT chest is the most sensitive imaging modality for diagnosing pulmonary aspergillosis and is crucial for detecting early stages and complications of the disease.

Answer 1

Step 1: Introduction to Pulmonary Aspergillosis.
Pulmonary aspergillosis refers to a range of pulmonary infections caused by the fungus Aspergillus, most commonly Aspergillus fumigatus. It can present as a colonization, allergic reaction, or invasive infection. The most common form of pulmonary aspergillosis is allergic bronchopulmonary aspergillosis (ABP, followed by chronic pulmonary aspergillosis (CP and invasive pulmonary aspergillosis (IP. The imaging features can vary based on the type and severity of the disease.
Step 2: Imaging Features of Pulmonary Aspergillosis. (1) Chest X-ray:
- In ABPA, chest X-ray may show central bronchiectasis and airway changes. There may also be parenchymal infiltrates or nodules. However, chest X-ray is usually less sensitive than CT scan in detecting early changes.
- CPA may show cavitary lesions or fungal balls (also called aspergillomas), which are often seen in pre-existing lung cavities.
- In IPA, chest X-ray may reveal consolidation, cavitation, or multiple nodules. There may also be a ground-glass opacity pattern indicating infection or inflammation.
(2) High-Resolution CT (HRCT) Chest:
- ABPA: HRCT typically shows central bronchiectasis (which is often upper lobe predominant), tree-in-bud patterns, and mucus plugging. Parenchymal infiltrates may also be observed, particularly in the upper and middle lobes.
- CPA: HRCT is more sensitive for detecting aspergillomas within pre-existing cavities, and these typically appear as well-defined masses that move with the patient's position. The cavities may be surrounded by ground-glass opacities or nodular consolidations.
- IPA: Invasive aspergillosis often presents with nodular opacities that may coalesce to form consolidations or cavities. The lesions are often surrounded by a halo sign, which represents a ground-glass opacity surrounding a nodule. This sign is particularly seen in immunocompromised patients. Air crescent sign may appear later in the disease as the tissue necrosis progresses, with the formation of a cavity containing air.
- CT findings may also show pleural effusions in severe cases of aspergillosis, particularly in IPA.
(3) MRI:
- MRI is not typically used in routine diagnosis but may be helpful in cases of cavitary lesions or aspergillomas to assess the extent of the lesion or its effect on surrounding tissues. In cases of cerebral aspergillosis (brain involvement), MRI is the imaging modality of choice.
Step 3: Key Diagnostic Features of Imaging in Pulmonary Aspergillosis.
- Cavitary lesions are typical in CPA and IPA.
- Fungal balls or aspergillomas are often found in pre-existing cavities.
- Central bronchiectasis and mucus plugging are suggestive of ABPA.
- Halo sign and air crescent sign on CT are strongly associated with invasive pulmonary aspergillosis.