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  • Etymology

    • Derived from the Greek word ?mykes,? meaning fungus, and ?oma,? meaning mass or tumor.

    AKA and abbreviation

    • Also known as fungal ball or aspergilloma (in cases caused by Aspergillus species).

    What is it?

    • Mycetoma refers to a mass of fungal hyphae, inflammatory cells, fibrin, and necrotic debris that forms within a pre-existing lung cavity.
    • Most commonly caused by Aspergillus fumigatus but may also result from other fungi such as Candida, Zygomycetes, or Fusarium species.
    • Represents a non-invasive form of fungal infection in immunocompetent individuals but may cause significant symptoms or complications.

    Characterized by

    • Pathologic features:
      • Colonization of a pre-formed lung cavity by fungal elements without tissue invasion.
      • Formation of a round or oval mass within the cavity, often mobile.
    • Imaging features:
      • CXR: Round or oval opacity within a cavity, often with a crescent of air around it (Monod sign).
      • CT: Fungus ball with air crescent sign or dependent layering of fungal debris.
    • Clinical findings:
      • Hemoptysis (common and sometimes massive).
      • Cough, dyspnea, or asymptomatic in some cases.

    Anatomical Context

    • Typically found within pre-existing lung cavities, such as those resulting from:
      • Tuberculosis (most common underlying cause).
      • Sarcoidosis.
      • Cavitary lung cancer.
      • Pulmonary infarcts.
      • Pneumatoceles from trauma or infection.

    Caused by

    Most common cause: Colonization by Aspergillus fumigatus in pre-existing pulmonary cavities.

    Other causes include:

    • Infections:
      • Fungal species: Candida, Zygomycetes, Fusarium, Histoplasma, Coccidioides.
      • Bacterial infections predisposing to cavities.
    • Structural abnormalities:
      • Tuberculosis, sarcoidosis, and bronchiectasis leading to cavitation.
      • Pneumatoceles or bullae from trauma or infections.
    • Neoplasm:
      • Cavitary lung cancer or metastatic tumors.

    Resulting in

    • Chronic colonization of lung cavities by fungi.
    • Symptoms such as chronic cough, recurrent hemoptysis, or asymptomatic radiographic findings.
    • Risk of life-threatening massive hemoptysis.

    Structural changes

    • Formation of a mobile fungal ball within a cavity.
    • Surrounding cavity wall thickening or fibrosis due to chronic inflammation.
    • Potential erosion into blood vessels leading to hemoptysis.

    Pathophysiology

    • Pre-existing cavity provides a non-vascularized space for fungal colonization.
    • Hyphae grow in a dependent position within the cavity, forming a dense fungal ball.
    • Chronic inflammation and fungal metabolites may damage adjacent tissue, increasing the risk of vascular erosion and hemoptysis.

    Pathology

    • Dense fungal hyphae and necrotic debris in a non-invasive pattern.
    • No tissue invasion unless complicated by invasive fungal disease in immunocompromised patients.

    Diagnosis

    • Clinical correlation: Symptoms such as hemoptysis, cough, or dyspnea.
    • Imaging:
      • CXR and CT are diagnostic, revealing a fungal ball with an air crescent sign in a cavity.
      • Dynamic imaging may demonstrate movement of the mass within the cavity.
    • Laboratory studies:
      • Serum IgG antibodies to Aspergillus species.
      • Sputum or bronchoalveolar lavage for fungal culture.

    Clinical

    • Symptoms:
      • Chronic cough and hemoptysis (mild to severe).
      • Dyspnea, fatigue, or asymptomatic presentation in some cases.
    • Signs:
      • Crackles or localized findings on chest auscultation.
      • Signs of underlying conditions (e.g., tuberculosis).

    Radiology Detail

    CXR:

    • Findings: Cavity containing a round or oval opacity with air crescent (Monod sign).

    CT:

    • Parts: Located within pre-existing cavities.
    • Size: Varies depending on the cavity size.
    • Shape: Round or oval fungal ball.
    • Position: Fungus ball may move within the cavity in dependent positions.
    • Character:
      • Air crescent sign.
      • Thickened or fibrotic cavity walls.
    • Associated Findings: Adjacent lung fibrosis, bronchiectasis, or pleural thickening.

    Other relevant Imaging Modalities:

    • MRI: Limited utility in evaluating fungal balls.
    • PET-CT: May help distinguish fungal balls from malignancy in cavitary lesions.

    Pulmonary function tests (PFTs)

    • May be normal or show mild restrictive changes due to underlying lung disease.

    Recommendations

    • Evaluate underlying conditions that predisposed to cavity formation (e.g., tuberculosis).
    • Monitor for progression or complications like massive hemoptysis.
    • Consider surgical resection for localized disease with recurrent hemoptysis.

    Management

    • Conservative: Observation for asymptomatic cases.
    • Medical: Antifungal therapy is usually ineffective due to lack of tissue invasion but may be used in complicated cases.
    • Surgical: Lobectomy or wedge resection for persistent hemoptysis or large symptomatic mycetomas.

    Key Points and Pearls

    • Mycetoma in the lung is most commonly caused by Aspergillus fumigatus and occurs in pre-existing cavities.
    • The air crescent sign (Monod sign) is a hallmark radiologic feature.
    • Hemoptysis, ranging from mild to life-threatening, is the most common clinical presentation.
    • Management typically involves monitoring, and surgery is reserved for severe or complicated cases.