Fungal Infections of the Lung

Overview

Fungal infections of the lung are less common than bacterial or viral infections but pose diagnostic and management challenges, particularly in immunosuppressed and critically ill patients. A distinction is made between opportunistic pathogens (affecting compromised hosts) and endemic pathogens (affecting immunocompetent hosts in specific geographic regions).

Pulmonary aspergillosis

Aspergillus is ubiquitous — inhalation of conidia is universal, but disease develops only in susceptible hosts. The spectrum of disease reflects the immune status of the host and pre-existing lung pathology.

Aspergilloma

A fungus ball composed of Aspergillus hyphae, fibrin, mucus, and cellular debris within a pre-existing pulmonary cavity. Most commonly arises in healed fibrocavitary TB. The time from PTB diagnosis to fungal ball formation ranges from 2–20 years, with upper lobe predilection.

Clinical features: Haemoptysis in 50–90% — the most common and significant symptom. Haemoptysis is due to vessel erosion, false aneurysm, proteolytic enzymes, or superimposed infection. Severity is unpredictable and not related to cavity size or general condition.

Imaging: CXR shows a cavity with a mass lesion surrounded by crescent of air (Monod's sign). CT provides detail of surrounding parenchyma and can identify hypertrophied bronchial arteries for embolisation planning.

Surgery for aspergilloma

Surgical resection is the definitive treatment. Indications: moderate or massive haemoptysis; continued bleeding despite antifungal therapy; indeterminate lesion with suspicion of malignancy. Anatomical resection (lobectomy) is preferred — complete removal prevents recurrence. Wedge excision is reserved for small aspergillomas with good lung function. Pneumonectomy may be required for multiple aspergillomas with destroyed/diseased lung.

Bronchial artery embolisation (BAE): Useful as a temporising bridge for massive haemoptysis before definitive surgery. Long-term recurrence is high due to rich collateral supply. Surgery after BAE is more challenging due to loss of planes.

Cavernostomy (opening the cavity, evacuating contents, closing communicating bronchioles, obliterating the space with limited thoracoplasty) is reserved for poor-risk patients and bilateral disease. Associated with high morbidity and recurrence — largely disfavoured.

ABPA

Allergic bronchopulmonary aspergillosis — a complex hypersensitivity reaction in patients with asthma or cystic fibrosis. Defective mucociliary clearance allows fungal colonisation, triggering eosinophilia and elevated IgE (>1000 IU/dL). CT shows mucoid impaction with finger-in-glove sign, central bronchiectasis, and cavitation. Management is with oral corticosteroids and systemic antifungals — surgical role is minimal.

Chronic pulmonary aspergillosis (CPA)

Associated with diseased lung (PTB, NTM, COPD, bronchiectasis) and some degree of immunosuppression. Characterised by indolent course, positive serum precipitins to A. fumigatus, and progressive pulmonary and pleural fibrosis with or without an aspergilloma. Treatment is long-term antifungal therapy. Surgery is reserved for select patients with localised resectable disease who fail medical therapy — carries high risk of disseminated aspergillosis and BPF.

Invasive aspergillosis (IA)

Characteristically seen in severe immunosuppression — neutropenia, haematological malignancy, stem cell/solid organ transplant, chronic steroid therapy, and ICU patients. CT shows nodules, the halo sign (ground-glass opacity surrounding a nodule — represents pulmonary infarction with haemorrhage), and in late disease cavities. Definitive diagnosis requires demonstration of organism in tissue/BAL. Treatment is systemic voriconazole.

Mucormycosis

An uncommon but life-threatening opportunistic infection (Rhizopus, Mucor, Rhizomucor species) in neutropenia and other immunocompromised states. Pulmonary mucormycosis presents with fever, haemoptysis, and lung infarcts. CT shows consolidation, halo sign, and late cavities. Treatment: intravenous liposomal amphotericin B and surgical debridement of necrotic tissue. Early diagnosis improves outcomes significantly.

Endemic fungal pathogens

The three major endemic dimorphic fungi — Histoplasma capsulatum, Coccidioides immitis, and Blastomyces dermatitidis — exist in nature as mycelium bearing infectious spores and transform to a yeast phase in tissue. All require special staining and culture methods. Amphotericin B is primary therapy for all three.

Histoplasmosis

Histoplasma capsulatum is found in bird and bat droppings in endemic river valley regions. After inhalation, it transforms to yeast form, causing granulomas. Most primary infections are asymptomatic or flu-like. Progressive disease occurs in patients with pre-existing lung disease. Mediastinal involvement can cause fibrosing mediastinitis with SVC syndrome. Surgical indications: chronic cavitary disease persisting after antifungal treatment; fibrosing mediastinitis with middle lobe syndrome or SVC syndrome.

Coccidioidomycosis

Coccidioides immitis is endemic to arid regions (south-western USA, Mexico). Primary pulmonary infection is often asymptomatic or presents as pneumonia. Chronic cavitary disease may develop. Surgical management (resection) is indicated for persistent symptomatic cavities, haemoptysis, or empyema.

Blastomycosis

Blastomyces dermatitidis is found in soil in south-eastern USA and Great Lakes region. Pulmonary infection resembles pneumonia. Can disseminate to skin, bone, and CNS. Surgical resection may be required for cavitary or mass-like disease, or for diagnosis when malignancy cannot be excluded. Medical treatment with amphotericin B or itraconazole; refer to current guidelines for dosing and duration.