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  • Etymology

    • Derived from the Latin “massa,” meaning a lump or aggregation. Refers to a radiologically evident, well-defined, or poorly defined lesion in the lung parenchyma.

    AKA and abbreviation

    • Solid lung nodule or pulmonary mass (no commonly accepted abbreviation).

    What is it?

    • Solid lung mass refers to a focal area of increased density in the lung parenchyma measuring greater than 3 cm in diameter.
    • A mass may be benign or malignant and requires further evaluation to determine its etiology.

    Characterized by

    • Radiologic definition:
      • A lesion >3 cm on imaging, typically more concerning for malignancy than smaller nodules (<3 cm).
    • Imaging characteristics:
      • Mass with calcification:
        • Central, laminated, or popcorn-like calcifications suggest a benign etiology (e.g., granuloma, hamartoma).
        • Psammommatous calcifications: Rarely observed in metastatic diseases like papillary thyroid carcinoma or mucinous adenocarcinoma.
        • Dystrophic calcification can be seen in Castleman disease or post-treatment fibrosis.
      • Mass with fat:
        • Typically indicative of benign hamartomas but may also occur in rare malignant conditions such as liposarcoma.
      • Mass with air bronchogram:
        • Suggests alveolar filling processes such as adenocarcinoma, lymphoma, amyloidosis, or infections.
      • Mass with amyloid deposition:
        • Amyloidosis may result in localized or diffuse deposits and can occasionally be associated with calcification and an air bronchogram.
    • Differentiating features:
      • Malignant masses: Spiculated margins, rapid growth, associated lymphadenopathy.
      • Benign masses: Smooth margins, central or popcorn-like calcification, slow growth.

    Anatomical Context

    • Can arise from any part of the lung parenchyma, including:
      • Central masses: Adjacent to bronchi, often associated with bronchial obstruction.
      • Peripheral masses: Located near the pleura.

    Caused by

    Most common cause: Malignancy (primary or metastatic).

    Other causes include:

    • Infections:
      • Fungal infections (Aspergillus, Histoplasma, Coccidioides).
      • Tuberculosis or nontuberculous mycobacteria (NTM).
      • Lung abscess.
    • Inflammatory/Immune:
      • Granulomatous diseases such as sarcoidosis or granulomatosis with polyangiitis (Wegener?s).
      • Rheumatoid nodules.
      • Amyloidosis: May present with calcification and/or air bronchograms.
    • Neoplasm:
      • Primary lung cancers (e.g., adenocarcinoma, squamous cell carcinoma, small cell carcinoma).
      • Benign neoplasms: Hamartoma (may contain fat and calcifications).
      • Metastatic cancers (e.g., papillary thyroid carcinoma with psammommatous calcifications, mucinous adenocarcinoma).
    • Mechanical trauma:
      • Hematoma or post-traumatic pseudotumor.
    • Metabolic:
      • Rarely, amyloid deposits in the lung.
    • Congenital:
      • Pulmonary sequestration or congenital pulmonary airway malformation (CPAM).
    • Other:
      • Castleman disease (may have dystrophic calcifications or mimic neoplastic processes).
      • Foreign body granulomas.

    Resulting in

    • Potential airway obstruction if centrally located.
    • Risk of malignancy if growth rate or imaging characteristics suggest invasive behavior.

    Structural changes

    • Focal consolidation or dense parenchymal lesion.
    • Possible cavitation, calcification (including psammommatous), fat deposition, or air bronchograms depending on etiology.

    Pathophysiology

    • Varies depending on etiology:
      • Neoplastic: Unregulated cellular proliferation forming a mass.
      • Infectious: Consolidation or abscess formation due to microbial invasion.
      • Granulomatous: Chronic immune response forming fibrotic or necrotizing nodules.
      • Amyloidosis: Deposition of abnormal proteinaceous material in the lung, potentially with calcifications.

    Pathology

    • Histologic appearance ranges from benign cellular infiltrates (e.g., inflammation, granulomas, amyloid deposits) to malignant invasive neoplastic cells.

    Diagnosis

    • Clinical correlation: Symptoms such as cough, hemoptysis, weight loss, or incidental radiographic finding.
    • Imaging:
      • CXR: Initial evaluation; may show a solitary or lobulated mass.
      • CT scan: Provides detailed characterization (size, margins, density, and associated findings).
      • PET-CT: Assesses metabolic activity and helps differentiate benign from malignant lesions.
    • Biopsy: Necessary for histological confirmation.

    Clinical

    • Symptoms:
      • Cough, hemoptysis, dyspnea.
      • Constitutional symptoms such as weight loss, fever, or night sweats.
    • Signs:
      • Wheezing or stridor if obstructing a central airway.
      • Signs of paraneoplastic syndromes in malignant cases.

    Radiology Detail

    CXR:

    • Findings: Round, oval, or lobulated opacity with variable density.

    CT:

    • Parts: Central or peripheral lung regions.
    • Size: Greater than 3 cm in diameter.
    • Shape: Round, oval, or irregular.
    • Position: May abut the pleura or involve the bronchovascular structures.
    • Character:
      • Mass with calcification: Popcorn-like (hamartoma), psammommatous (metastases), or dystrophic (Castleman disease).
      • Mass with fat: Suggests benign hamartoma; may be seen in liposarcoma.
      • Mass with air bronchogram: Suggests adenocarcinoma, lymphoma, or amyloidosis.
      • Margins: Smooth, lobulated, or spiculated.
      • Density: Homogeneous or heterogeneous.
      • Cavitation may be present in some cases.
    • Associated Findings: Mediastinal lymphadenopathy, pleural effusion, or satellite nodules.

    Other relevant Imaging Modalities:

    • PET-CT: Detects FDG uptake, suggesting metabolic activity.
    • MRI: Rarely used but can assess soft-tissue invasion.

    Pulmonary function tests (PFTs)

    • May show restrictive or obstructive patterns if the mass affects lung mechanics.

    Recommendations

    • Imaging follow-up: Monitor for changes in size or character on serial CT.
    • Biopsy: Indicated for lesions with suspicious imaging features or clinical findings.
    • Multidisciplinary evaluation: Involve pulmonologists, thoracic surgeons, and oncologists as needed.

    Management

    • Benign masses: Observation or surgical resection if symptomatic.
    • Malignant masses:
      • Surgical resection (lobectomy or pneumonectomy).
      • Chemotherapy or radiation therapy for unresectable or metastatic cases.
    • Infectious masses: Antimicrobial therapy tailored to the pathogen.

    Key Points and Pearls

    • Solid lung masses >3 cm are more likely to be malignant and require thorough evaluation.
    • Radiologic characteristics such as calcification (including psammommatous), fat, and air bronchograms provide important diagnostic clues.
    • Amyloidosis can rarely present as a mass with calcification and an air bronchogram.
    • PET-CT and histopathology are essential for distinguishing benign from malignant lesions.