What causes a necrotic lymph node in the lung?

Causes of Necrotic Lymph Nodes in the Lung

Necrotic lymph nodes in the lung are most commonly caused by metastatic malignancy (particularly lung cancer with nodal metastases), tuberculosis, and other granulomatous infections, with the clinical context and additional pathologic features being essential to distinguish between these etiologies.

Malignant Causes

Lung Cancer with Nodal Metastases

• Metastatic lung cancer frequently demonstrates necrosis in involved lymph nodes, particularly when tumor growth outpaces vascular supply, leading to central ischemic necrosis 1, 2
• Necrotic lymph nodes in lung cancer show discrete irregular foci of necrosis, fibrosis, and/or inflammation, sometimes with chronic hemorrhage and foamy macrophages 1
• Squamous cell carcinoma can present with pus-like purulent material on aspiration due to extensive necrosis, which should not be mistaken for infection 2
• The presence of necrosis in lymph nodes after neoadjuvant therapy may represent treatment response rather than active disease 1

Other Malignancies

• Hodgkin lymphoma demonstrates necrotic mediastinal lymph nodes in approximately 21% of newly diagnosed cases, though this finding has no significant prognostic impact 3
• Metastatic disease from extrapulmonary primaries (breast, colon, head and neck) can cause necrotic lymph nodes in the thorax 4

Infectious Causes

Tuberculosis

• Tuberculosis is a classic cause of necrotic (caseating) lymph nodes in the mediastinum and hilar regions 5, 6
• TB-related necrotic lymph nodes are characterized by caseation with multiple granulomas showing extensive central necrosis 6
• Mediastinal and abdominal lymph node tuberculosis can present with necrotic lymphadenopathy on CT imaging 5
• Thymic tuberculosis, though rare, can present as a partially necrotic mediastinal mass with foci of caseation 6

Other Infections

• Fungal infections and other granulomatous diseases can cause necrotizing lymphadenopathy
• Bacterial abscesses may rarely involve mediastinal lymph nodes

Benign Non-Infectious Causes

Anthracosis and Environmental Exposures

• Anthracosis from chronic biomass fuel or wood smoke exposure can cause necrotic mediastinal lymph nodes with black anthracotic pigment 7
• Silicoanthracotic changes produce necrotic-appearing lymph nodes with prominent carbon pigment and polarizable silica-like particles 1
• These benign changes must be distinguished from treatment-related necrosis in cancer patients 1

Treatment-Related Necrosis

• Neoadjuvant chemotherapy, targeted therapy, or immunotherapy can cause extensive lymph node necrosis as a sign of treatment response 1
• Complete pathologic response in lymph nodes is recognized by well-defined scar and/or tumor necrosis without identifiable viable tumor cells 1
• Immunotherapy (nivolumab) can cause nodal immune flare with noncaseating granulomas rather than metastatic tumor 1

Critical Diagnostic Approach

Distinguishing Features

• Malignant necrosis: Discrete irregular foci with fibrosis, inflammation, chronic hemorrhage, and foamy macrophages 1
• Tuberculous necrosis: Caseating granulomas with acid-fast bacilli on special stains 5, 6
• Anthracotic changes: Histiocytes filled with carbon pigment and polarizable particles 1, 7
• Treatment response: Well-defined scar with necrosis but no viable tumor 1

Imaging Characteristics

• Hypoechoic areas on EBUS without blood flow suggest necrosis from infection or malignancy 2
• CT findings of low attenuation, complex, fluid-like areas within lymph nodes indicate necrosis 3
• Calcified mediastinal adenopathy on CT suggests benign anthracosis rather than malignancy 7

Common Pitfalls to Avoid

• Do not assume purulent-appearing aspirate indicates infection—rapidly growing malignancies can produce pus-like necrotic material 2
• Do not confuse burnt-out granulomas and silicoanthracotic changes with histiocytic reaction to lymph node metastases; look for carbon pigment and silica particles 1
• Do not overlook the possibility of treatment response in patients with known malignancy who have received neoadjuvant therapy 1
• Always obtain adequate tissue for culture, special stains (AFB, fungal), and immunohistochemistry to establish definitive diagnosis 8, 2