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Pulmonary aspergillosis

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

Pulmonary apergillosis is a collective term used to refer to a number of conditions caused by infection with a fungus of the Aspergillus species (usually Aspergillus fumigatus).

There are a number of recognised pulmonary forms, the number depending on the author. ^1,3-4 Each form has specific clinical and radiological features and are discussed in separate articles:

aspergilloma (saprophytic / non invasive aspergillosis) : the most common form seen radiographically
allergic bronchopulmonary aspergillosis (ABPA)
invasive aspergillosis
- chronic necrotising aspergillosis (CNA) (or semi-invasive aspergillosis)
- airway invasive aspergillosis (or bronchopneumonic aspergillosis)
- angioinvasive aspergillosis
obstructive bronchopulmonary aspergillosis

The remainder of this article discusses general concepts pertaining to pulmonary aspergillosis.

Pathology

The various species of Aspergillus are ubiquitous and usually do not cause any human pathology provided the lungs are structurally normal and the host immunity is intact. If either of these is abnormal, then there is the possibility that this otherwise benign fungus may cause pathology.

Role of immunity in aspergillosis

In a patient with normal immunity, Aspergillus is unable to cause pulmonary pathology. Altered immunity, both heightened (hypersensitivity) or reduced (immunocompromised) predisposes to Aspergillus related lung disease.

Patients with hypersensitivity may develop allergic bronchopulmonary aspergillosis (ABPA), whereas immunocompromised patients can develop semi-invasive or invasive aspergillosis depending on the degree to which their immune system is depressed.

Role of pulmonary structure in aspergillosis

Aspergillus can colonise pre-existing pulmonary cavities, particularly those left behind by pulmonary tuberculosis. In this setting the fungus grows and as it is free to move within the cavity, typically takes on a spherical shape, and is known as an aspergilloma. Other cavities that can predispose to aspergilloma include bullae which may be secondary to emphysema.