Chronic necrotising pulmonary aspergillosis

Chronic necrotising aspergillosis (CNA) is, as the name suggests, a chronic localised and indolent form of invasive aspergillosis. It is also known as semi-invasive aspergillosis. 

Epidemiology

Chronic necrotising aspergillosis (CNA) typically occurs in patients with a depressed immune system, but not as profoundly immunocompromised as bone marrow patients who more frequently develop angioinvasive aspergillosis. Patients are typically middle aged. Risk factors therefore include ^1-3:

• corticosteroids : most common systemic immunodepressant ³
• diabetes mellitus
• alcoholism
• pre-existing pulmonary pathology : present in ~80% of patients ³
  
  • COPD : most common
  • neoplasm with prior radiation therapy
  • sarcoidosis or other granulomatous disease
  • pulmonary infarction
  • previous pulmonary tuberculosis
  • pulmonary fibrosis or previous surgery
  • pneumoconiosis ⁵
• advanced age

Clinical presentation

Typically patients present with progressive respiratory and constitutional symptoms including fever, weight loss, cough, sputum production and haemoptysis ^2-3.

Diagnosis is not always straight forward, as both bronchial washings and biopsy have a low diagnostic yield ³.

Pathology

Although the end result of chronic necrotising aspergillosis (CNA) is similar to an aspergilloma, it represents are different process. Rather than Aspergillus colonising a pre-existing cavity, in CNA a focally invasive aspergillosis occurs which eventually undergoes central necrosis and cavitation forming its own cavity. It is the finding of tissue invasion that allows this entity to be distinguished from the more common aspergilloma ^2,5.

Presence of calcium oxalate crystals suggests that Aspergillus niger is the causative agent ³.

Radiographic features

Radiographic appearance vary according to when the condition is imaged. Typically CNA involves the upper zones and begins as a pulmonary opacity. Eventually the central necrotic area separates away form the surrounding lung and thus forms an air crescent sign. This occurs of weeks to months, eventually resulting in a cavity with or without a central mycetoma ³. Appearances may then then are the same as an aspergilloma. Often there are multiple cavities, often thick walled ². Adjacent pleural thickening is often present ^2-3.

It is similar in appearance to tuberculosis, actinomycosis, and histoplasmosis ².

Treatment and prognosis

During initial phases of the disease anti-fungals are the mainstay of treatment. Intravenous and intracavitary amphoteracin B, 5-flucytosine (5-FC) and itraconazole have all been tried ³. 

Surgery is reserved for patients who do not respond to initial medical management and have adequate pulmonary reserve and acceptable operative risks ^3,5.

Once the disease has ceased progressing treatment is the same as that of an aspergilloma ¹.

Prognosis is largely dictated by underlying lung disease and co-morbidities with mortality ranging from < 10% to 39% depending on criteria for diagnosis and treatment administered ³.

Differential diagnoses

• angioinvasive aspergillosis : usually obviously different due to patient demographics
• aspergilloma
• other infections
  • pulmonary tuberculosis
  • pulmonary actinomycosis
  • pulmonary histoplasmosis
• maligancy
• non-infective granulomatous disease