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  • Etymology

    • Derived from “peri-” meaning around, and “lymphatic,” referring to the lymphatic vessels that drain lymph from the interstitial tissues.

    AKA and abbreviation

    • No commonly accepted abbreviation.

    What is it?

    • Perilymphatic distribution refers to the imaging pattern of abnormalities (e.g., nodules, thickening) that follow the lymphatic pathways within the lungs.
    • This pattern is seen in diseases affecting the interstitial lymphatic system, including granulomatous, lymphoid, and neoplastic conditions.
    • Pulmonary lymphoproliferative and immune-related disorders, such as MALT lymphoma, lymphoid interstitial pneumonia (LIP), lymphomatoid granulomatosis (LG), multicentric Castleman disease (MCD), primary effusion lymphoma (PEL), and nodular lymphoid hyperplasia (NLH), may exhibit a perilymphatic distribution.

    Characterized by

    • Imaging features:
      • Nodules, thickening, or other abnormalities distributed along lymphatic pathways:
        • Bronchovascular bundles: Central portions of the secondary pulmonary lobules.
        • Interlobular septa: Seen at the edges of lobules.
        • Subpleural regions: Involving the lung periphery.
        • Fissures: Along major and minor pleural boundaries.
      • Predominantly bilateral and symmetric distribution in most cases.
    • Associated features:
      • Lymphadenopathy in the hilar or mediastinal regions.
      • Potential calcifications (e.g., sarcoidosis).
      • Nodules may vary in size but are typically small (2-5 mm).
      • Involvement of pulmonary lymphoid structures, such as:
        • MALT lymphoma: Extranodal marginal zone lymphoma involving lymphoid tissue in the lung.
        • LIP: Diffuse lymphoid hyperplasia, often seen in autoimmune diseases like Sjögren syndrome or HIV.
        • LG: Angiocentric lymphoproliferative disorder.
        • MCD: Inflammatory lymphoproliferative disorder with systemic and pulmonary involvement.
        • PEL: HIV-associated lymphoma, often presenting with pleural effusions.
        • NLH: Reactive hyperplasia of lymphoid tissue.

    Anatomical Context

    • The perilymphatic route includes:
      • Bronchovascular lymphatics: Surrounding the airways and blood vessels.
      • Interlobular septal lymphatics: In the connective tissue separating secondary lobules.
      • Subpleural lymphatics: In the connective tissue beneath the visceral pleura.
      • Fissural lymphatics: Running along the pleural reflections.
      • BALT (Bronchus-Associated Lymphoid Tissue): Reactive or neoplastic proliferation along bronchial walls.
      • Pulmonary lymphoid structures: Sites of lymphoid hyperplasia or neoplastic infiltration, as seen in LIP, MALT lymphoma, or LG.

    Caused by

    Most common cause: Sarcoidosis.

    Other causes include:

    • Infections:
      • Tuberculosis with lymphatic involvement.
      • Viral infections (e.g., EBV) causing lymphatic inflammation.
    • Inflammatory/Immune:
      • Sarcoidosis: Non-caseating granulomas distributed along lymphatic pathways.
      • LIP: Associated with autoimmune diseases like Sjögren syndrome, HIV, or CVID.
      • BALT hyperplasia: Reactive lymphoid proliferation due to chronic inflammation or infection.
    • Lymphoproliferative Disorders:
      • MALT lymphoma: Extranodal lymphoma associated with chronic antigenic stimulation.
      • Lymphomatoid granulomatosis (LG): Angiocentric and necrotic lymphoproliferative disorder.
      • Multicentric Castleman disease (MCD): Inflammatory lymphoproliferative disorder with systemic involvement.
      • Primary effusion lymphoma (PEL): Rare HIV-associated lymphoma.
      • NLH: Reactive hyperplasia of lymphoid tissue.
    • Neoplasm:
      • Primary pulmonary lymphoma: Clonal lymphoproliferative disorder confined to the lungs.
      • Lymphangitic carcinomatosis: Malignant infiltration of lymphatics by tumor cells.

    Resulting in

    • Disruption of normal lung architecture.
    • Impaired lymphatic drainage and progression to fibrosis, malignancy, or lymphoid hyperplasia.

    Structural changes

    • Nodular or thickened lymphatic structures due to granulomatous inflammation, lymphoid proliferation, or malignant infiltration.

    Pathophysiology

    • Diseases with a perilymphatic distribution preferentially involve lymphatic pathways due to their location in the interstitial tissue.
    • Lymphoid hyperplasia (e.g., LIP or NLH) reflects a reactive immune response to chronic antigen exposure.
    • Granulomas form in sarcoidosis and infections, while neoplastic infiltration occurs in MALT lymphoma or lymphangitic carcinomatosis.

    Pathology

    • Granulomatous diseases: Non-caseating granulomas in sarcoidosis; caseating necrosis in tuberculosis.
    • Lymphoid hyperplasia: Reactive proliferation of lymphoid tissue in LIP or NLH.
    • Lymphoproliferative disorders: Malignant infiltration of pulmonary lymphoid tissue in MALT lymphoma, LG, or PEL.

    Diagnosis

    • Clinical correlation: Symptoms such as cough, dyspnea, fever, or systemic signs depend on the underlying condition.
    • Imaging:
      • CXR: Reticulonodular patterns along bronchovascular bundles, fissures, and subpleural regions.
      • HRCT: High-resolution images reveal nodules or thickening distributed along lymphatic pathways.
      • Biopsy: Essential for diagnosing granulomatous, lymphoproliferative, or neoplastic conditions.

    Clinical

    • Symptoms: Often asymptomatic in early stages; advanced disease may present with cough, dyspnea, or systemic symptoms like fever and weight loss.
    • Signs: Rales, crackles, or systemic features like lymphadenopathy or pleural effusions.

    Radiology Detail

    CXR:

    • Findings: Fine nodular opacities along lymphatic routes; lymphadenopathy.

    CT:

    • Parts: Bronchovascular bundles, interlobular septa, subpleural regions, fissures, and lymphoid structures.
    • Size: Nodules typically measure 2-5 mm.
    • Shape: Nodular, beaded, or diffuse thickening.
    • Position: Bilateral, symmetrical distribution.
    • Character:
      • Nodular or thickened lymphatic structures.
      • Calcifications in granulomatous diseases.
      • Ground-glass opacity or infiltration in lymphangitic carcinomatosis.

    Other relevant Imaging Modalities:

    • PET-CT: Evaluates metabolic activity in neoplastic or lymphoproliferative disorders.

    Pulmonary function tests (PFTs)

    • Normal in early disease; restrictive patterns may develop in advanced conditions.

    Recommendations

    • Imaging follow-up: Monitor progression in granulomatous, lymphoproliferative, or neoplastic conditions.
    • Biopsy: Required for definitive diagnosis in suspected malignancy or lymphoproliferative disorders.
    • Treatment: Tailored to the underlying condition (e.g., corticosteroids for sarcoidosis, chemotherapy for lymphomas).

    Key Points and Pearls

    • Perilymphatic distribution is a hallmark of granulomatous, lymphoproliferative, and neoplastic diseases.
    • Conditions such as MALT lymphoma, LIP, LG, and Castleman disease require biopsy and clinical correlation for diagnosis.
    • High-resolution CT is essential for identifying characteristic patterns and guiding management.