The left upper lobe also demonstrates a large thick walled tuberculous cavity. These are not uncommon but in this case the cavity is large and contains a heterogeneous attenuation mass with mottled air within it. Superior to the intracavitary mass there is a lucency of air. This appearance is typical of a mycetoma, due to Aspergillus, synonymously termed an Aspergilloma.
Such Aspergillomas are typically due to Aspergillus fumigatus, a non-invasive form of pulmonary Aspergillosis. They occur in immune competent patients as a saprophytic secondary infection in areas of pulmonary destruction, chronic scarring or typically cavities. Tuberculous cavities, scarring from sarcoidosis or cystic bronchiectasis are the commonest substrates for the disease to form. The infection is often preceded by progressive pleural focal thickening. Subsequently a fungus ball of hyphae forms. This is free within the cavity and can be demonstrated to re-position on decubitus positioning at CXR or CT. Above the hyphal ball there is a lucency of air within the cavity. This is often referred to as “an air crescent”.
Confusingly this term of "air crescent" is also sometimes used in patients with invasive aspergillosis. However, in contradistinction invasive aspergillosis occurs in neutropenic immune compromised patients. In that instance the air-crescent develops in during the neutropenic recovery phase in areas of focal air-space opacity that have developed in areas of previously normal lung. Frank cavities can form later, but they are the sequela of an invasive form of the disease not a secondary manifestation within chronic cavities. The crescent of air in Aspergilloma is also occasionally referred to as the Monod or Monad sign by purists but most will never have heard of this terminology!
The mortality of Aspergilloma is variable but usually low even if medical therapy fails and surgery is required. The Aspergilloma contains hyphae, cellular debris and some granulation tissue. As a result of the chronic inflammation hypertrophy of the bronchial arteries can occur and result in haemoptysis, occasionally massive. This can be treated by selective angiographic embolization.
For completeness, the lung can of course be affected by two more variations of aspergillus. The semi-invasive form of Aspergillus occurs in patients with minimally reduced immunity (e.g. chronic poor nutrition, alcoholics etc). It results in chronic air-space opacities that can be difficult to differentiate from other causes of chronic infection or organising pneumonia. The allergic phenomenon of allergic bronchopulmonary aspergillosis is an exaggerated hyper-immune response to Aspergillus typically in patients with asthma. It results in central bronchiectasis with mucoid impactions, sometimes referred to as “finger in glove” when branching from the hilum.