Invasive aspergillosis

Clinical History

An immunocompromised patient presenting with productive cough and dyspnoea.

Imaging Findings

A patient with a renal transplant presented with productive cough and dyspnoea. Plain films were obtained, followed by CT scans. The patient required a left pneumonectomy.

Discussion

Aspergillosis can be regarded as a spectrum of pathology with three major components:

1. mycetoma,
2. invasive and semi-invasive aspergillosis, and
3. allergic bronchopulmonary aspergillosis (ABPA).

There is overlap between these entities, and semi-invasive aspergillosis is known to occur in chronic cavities in patients with mild immunocompromise and lung damage. Bronchopulmonary aspergillosis is a relatively common association with asthma. The condition is usually seen in adults, although children are occasionally affected. ABPA, occurring almost exclusively in asthma patients, is characterised radiographically by fleeting pulmonary alveolar opacities caused by deposition of immune complexes and inflammatory cells within the lung parenchyma. Mucus plugging and bronchial wall thickening can be expected in time. Aspergilloma, occurring in patients with structural lung disease, typically appears radiographically as a focal intracavitary mass and is characterised initially by an increase in the wall thickness of a pre-existing cavity or cyst.

Invasive aspergillosis is virtually confined to immunocompromised patients, especially in patients with lymphoma and leukaemia. Invasive aspergillosis is characterised by mycotic vascular invasion, thrombosis, and infarction leading to necrosis and cavitation. The lungs may be seeded via the airways or via the bloodstream. The appearance on x-ray is variable. One-third of cases with symptoms will have a normal chest x-ray. A common pattern is one of rounded consolidations, which are randomly distributed in the lungs and have an indistinct margin. These represent foci of infarction resulting from vascular invasion. This results in central necrosis with a rim of haemorrhagic infarction and inflammation. These lesions may have irregular outlines and may contain air bronchogram. They may cavitate. Cavitation occurs with recovery from neutropenia. Cavitation is therefore a favourable sign, indicating a significant defence mechanism. Rarely a widespread miliary pattern is seen. CT may reveal a halo or ground-glass attenuation and is more accurate in the detection of early disease. This is the precursor of the crescent sign. Histologically this corresponds to surrounding haemorrhagic inflammation. Although this CT finding is not diagnostic, it is certainly suggestive. Thick-walled cavitary lesions are the most common radiological manifestation of invasive pulmonary aspergillosis in AIDS. The findings are more numerous and better defined on CT scans. Cavitation often develops with time and typically results in the air crescent sign. The single or multiple areas of consolidation slowly enlarge over 7 to 28 days. Hilar lymphadenopathy is not a feature. Pleural effusions are seen only if haemorrhagic infarction causes bleeding into the pleural space. Invasion of the chest wall is rare but has been documented. MRI has been used to diagnose invasive pulmonary aspergillosis. The majority of rounded consolidations have a target-like appearance, a hypointense centre and an isointense or hyperintense rim on T1-weighted images. Areas of central haemorrhage result in foci of hyperintensity within the low intensity central core. Enhancement is variable.

In semi-invasive aspergillosis, local invasion of the lung parenchyma is seen. This is seen in debilitated patients with pre-existing lung disease. The fungus may originate in a pre-existing cavity or may form its own cavity. This results in a thick-walled cavity in which a mycetoma may form. Semi-invasive aspergillosis is radiographically similar to the invasive form but differs in clinical course, being associated with mild immunosuppression or chronic illness and typically progressing over the course of months rather than weeks.

Differential Diagnosis List

Final Diagnosis

Invasive aspergillosis

URL:	https://www.eurorad.org/case/1618
DOI:	10.1594/EURORAD/CASE.1618
ISSN:	1563-4086