Uncategorized

  • Etymology

    • Derived from “low-density,” indicating areas of reduced attenuation on imaging, and “lymphadenopathy,” which refers to the enlargement of lymph nodes.

    AKA and abbreviation

    • No commonly accepted abbreviation.

    What is it?

    • Low-density lymphadenopathy describes lymph nodes with hypodense areas on imaging, typically identified on contrast-enhanced CT or MRI.
    • The reduced density within the nodes reflects structural changes such as necrosis, cystic transformation, or infiltration by abnormal substances (e.g., lipids, proteins, or tumors).

    Characterized by

    • Imaging appearance:
      • Hypodense (low attenuation) regions within lymph nodes on CT.
      • May exhibit rim enhancement in necrotic nodes.
      • Often heterogenous, with central necrosis, cystic changes, or infiltrative processes.
    • Associated features:
      • Enlarged lymph nodes (>10 mm short-axis diameter for most regions).
      • May be single or multiple nodes.
      • Surrounding inflammation, mass effect, or associated findings in adjacent tissues.
    • Causes of low density:
      • Necrosis: Common in infections (e.g., tuberculosis) and malignancies (e.g., metastatic carcinoma, lymphoma).
      • Cystic transformation: Seen in congenital cystic lesions or chronic inflammation.
      • Infiltrative processes: Includes lipid or amyloid deposits in conditions like Castleman disease or amyloidosis.

    Anatomical Context

    • Frequently involves lymph nodes in the:
      • Neck: Cervical and supraclavicular nodes.
      • Chest: Mediastinal, hilar, and intrapulmonary nodes.

    Caused by

    Most common cause: Infectious or malignant processes.

    Other causes include:

    • Infections:
      • Tuberculosis with caseating necrosis.
      • Fungal infections (e.g., histoplasmosis, coccidioidomycosis).
      • Bacterial abscesses or suppurative infections.
    • Neoplastic:
      • Primary malignancy: Lymphoma (Hodgkin’s or non-Hodgkin’s).
      • Metastatic disease: Squamous cell carcinoma, papillary thyroid carcinoma.
    • Inflammatory/Immune:
      • Sarcoidosis (rarely low density unless complicated by necrosis).
      • Castleman disease with vascular and lipid-rich infiltrates.
    • Other:
      • Cystic lymphangioma or chronic inflammation causing cystic transformation.
      • Amyloidosis with protein infiltration.

    Resulting in

    • Structural disorganization of lymph nodes.
    • Potential compression of adjacent structures (e.g., airways, vessels).
    • Systemic symptoms (e.g., fever, weight loss, night sweats) depending on the underlying cause.

    Structural changes

    • Necrosis: Breakdown of nodal tissue, often surrounded by reactive inflammation.
    • Cystic changes: Fluid-filled transformation of lymph node parenchyma.
    • Infiltration: Replacement of normal nodal architecture with abnormal deposits or tumor cells.

    Pathophysiology

    • Low density reflects loss of normal cellular architecture due to necrosis, fluid accumulation, or infiltration.
    • Necrotic nodes are commonly caused by hypoxic cell death in infections or malignancies.
    • Cystic changes may arise from chronic inflammation or congenital processes.

    Pathology

    • Necrotic nodes: Caseating necrosis (e.g., tuberculosis), liquefactive necrosis (e.g., malignancy or abscess).
    • Cystic nodes: Congenital or secondary to chronic inflammation.
    • Infiltrative nodes: Amyloidosis or lipid-rich material in Castleman disease.

    Diagnosis

    • Clinical correlation: Symptoms such as fever, weight loss, or localized pain.
    • Imaging:
      • CT: Hypodense regions within lymph nodes; rim enhancement suggests necrosis.
      • MRI: Useful for characterizing cystic versus solid components.
      • PET-CT: High FDG uptake suggests malignancy or active infection.
    • Biopsy: Essential for definitive diagnosis in suspected malignancy or granulomatous diseases.

    Clinical

    • Symptoms:
      • Localized swelling, tenderness, or compressive symptoms in the neck or chest.
      • Systemic symptoms in malignancy or infection (e.g., fever, night sweats).
    • Signs:
      • Palpable lymph nodes in the neck.
      • Associated pulmonary symptoms in thoracic lymphadenopathy.

    Radiology Detail

    CT:

    • Parts: Neck, mediastinum, hilar, and intrapulmonary nodes.
    • Size: Enlarged nodes >10 mm in short-axis diameter.
    • Shape: Rounded or lobulated.
    • Position: Cervical, supraclavicular, or intrathoracic regions.
    • Character:
      • Hypodense (low attenuation) center.
      • Rim enhancement in necrotic nodes.
      • Associated findings: lung consolidation, effusion, or soft-tissue masses.

    MRI:

    • Useful for delineating cystic from solid components and evaluating surrounding soft tissues.

    PET-CT:

    • Differentiates active malignancy or infection (high FDG uptake) from benign processes (low FDG uptake).

    Pulmonary function tests (PFTs)

    • Normal unless nodes are associated with significant airway compression or parenchymal changes.

    Recommendations

    • Imaging follow-up: Monitor size and density changes in low-density nodes.
    • Biopsy: Indicated for persistent, necrotic, or metabolically active nodes.
    • Treat underlying causes: Antimicrobial therapy for infections, chemotherapy for malignancy, or surgical intervention for cystic lesions.

    Key Points and Pearls

    • Low-density lymphadenopathy is most commonly caused by infections or malignancies.
    • Necrotic nodes often appear with rim enhancement on imaging, indicating infection or malignancy.
    • PET-CT is valuable for assessing metabolic activity in low-density lymph nodes.
    • Biopsy is critical for definitive diagnosis when imaging findings are ambiguous.
    • Always correlate imaging findings with clinical history and laboratory results.