Disseminated Invasive Aspergillosis

Joshua Lee Rosebrook, MD - Case Coordinator
Sidney Uttam Jain, MD - Radiology Discussion
Gerald P Bailey, MD, PhD - Pathology Discussion
Paul Whiston Spirn, MD - Attending Radiologist
Pablo R Ros, MD, MPH - Attending Radiologist

August 12, 2002

Presentation

Imaging Findings

Contrast-enhanced computed tomography (CT) images of the chest demonstrate relatively thick-walled cavitary lesions in the left lung (air-fluid levels). A moderate-sized left pleural effusion and trace right pleural effusion are also visible. A large, vaguely defined lesion can also be discerned in the posterior aspect of the right lower lobe. This wedge-shaped opacity at the base of the right lung may represent associated pulmonary infarct, although it may simply be related to the effusion. In addition, the esophagus appears to be dilated.

Differential Diagnosis

Diagnosis

Discussion

At autopsy, the lungs were found to be enlarged (~800 g) and to have multiple cavitary lesions. On cross-section, a fibrotic rim is seen to surround the cavitary rim of the lesion. It is also apparent that the lesions were in communication. On slides prepared with hematoxylin and eosin, hyphal forms and abscesses are apparent. The suspected diagnosis was confirmed with silver stain: the image shows fungal forms as well as the characteristic hyphal forms with 45-degree branching.

Radiology Discussion

The four different forms of aspergillosis correspond directly with a patient’s immune status.

Allergic bronchopulmonary aspergillosis (ABPA) occurs in patients with Type 1 hypersensitivity to Aspergillus (almost exclusively associated with asthma and, occasionally, cystic fibrosis). This type of infection initially causes bronchospasm, bronchial wall edema, and mucoid impaction, and progresses to cause bronchial wall damage, bronchiectasis, and pulmonary fibrosis in the adjacent lung. It is treated with oral prednisone. Radiological features of ABPA include fleeting pulmonary alveolar opacities; central bronchiectasis, often saccular and upper lobe; mucus plugging ("finger in glove appearance"); and bronchial wall thickening. Chronic disease may lead to upper lobe fibrosis.

An aspergilloma, also known as mycetoma or fungus ball, consists of fungal elements, mucus, and inflammatory cells. It occurs in patients with normal immune status, but requires a pre-existing cystic lung space in which to grow. In the U.S. these spaces are usually due to emphysema or sarcoidosis. Elsewhere, the cavities are most often the result of tuberculosis. Aspergilloma, particularly if responsible for hemoptysis, is generally treated by surgical resection or intracavitary amphotericin. Images typically show a mobile, focal intracavitary mass (3-6 cm) in an upper lobe space. Air surrounding the mass creates the "Monod sign". The appearance may mimic the cavitation produced by more invasive forms of aspergillus infection. Subjacent consolidation and pleural thickening are common.

Invasive aspergillosis occurs in severely immune-compromised patients and is associated with high mortality (70-90%). This infection progresses from endobronchial fungal infection to vascular invasion to thrombosis and infarction (so-called "angioinvasive infection"). Sites commonly involved (outside of the lungs) include the brain, liver, kidneys, and gastrointestinal tract. This aggressive infection is generally treated with a systemic antibiotic. Radiological features include multiple, irregularly shaped pulmonary nodules surrounded by ground glass halos due to hemorrhage; More advanced disease is associated with cavitary lesions (50% of nodules cavitate within 2 weeks). An air crescent sign is characteristic of the recovery phase with increased granulocyte activity. It is important that this finding not be confused with Monod sign. It is key to recognize the clinical history of compromised immunity. Peribronchial opacities and focal areas of consolidation are also commonly seen.

Semi-invasive aspergillosis occurs in areas of damaged lung in otherwise healthy patients or in patients with mildly compromised immunity. The pathophysiology is similar to invasive aspergillosis, but the disease progresses over the course of months rather than weeks. Correspondingly, the mortality rate is much lower (30%). Risk factors for this infection include diabetes, alcoholism, pneumoconioses, malnutrition, COPD and radiation lung injury. It is treated with systemic or intracavitary amphotericin. The radiological appearance is similar to the invasive form, but cavitation generally occurs approximately six months after initial infection.

References

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