What are the possible causes and treatments for mildly enlarged hypermetabolic mediastinal and hilar lymph nodes up to 1.2 cm in size, and how can reactive versus other causes be differentiated?

From the Guidelines

Mildly enlarged hypermetabolic mediastinal and hilar lymph nodes up to 1.2 cm in size are likely to be benign, with reactive inflammation being a common cause, and can be managed with a watchful waiting approach, according to the guidelines outlined by the ACR incidental findings committee 1. When evaluating these findings, it's essential to consider the size, texture, and fluorine-18-2-fluoro-2-deoxy-D-glucose (FDG) activity of the lymph nodes. The size threshold of 1.2 cm is crucial, as lymph nodes under 1 cm are generally considered normal, while those over 1 cm warrant closer attention, especially when hypermetabolic on PET imaging. Some possible causes of mildly enlarged hypermetabolic mediastinal and hilar lymph nodes include:

• Infections (such as pneumonia or other thoracic infections)
• Sarcoidosis
• Congestive heart failure
• Diffuse lung diseases
• Granulomatous diseases
• Metastatic disease from undiagnosed seminoma and nonseminomatous germ cell tumors (in young male subjects) To differentiate between reactive and other causes, clinicians should:
• Evaluate for associated symptoms like fever, weight loss, night sweats, or respiratory complaints
• Perform laboratory tests, including complete blood count, inflammatory markers, and specific tests for suspected conditions
• Consider FDG PET/CT imaging, especially in young male subjects with incidental enlarged mediastinal lymph nodes
• Monitor with repeat imaging in 3-6 months for stable, asymptomatic patients
• Consider tissue sampling via endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) or mediastinoscopy for concerning features or symptoms suggesting malignancy, as recommended by the ACR incidental findings committee 1. Treatment depends entirely on the underlying cause, and may include antibiotics, observation, corticosteroids, or appropriate oncologic therapy. It's also important to note that the presence of a fatty hilum, smooth and well-defined borders, and uniform attenuation are features of benign lymph nodes, whereas the lack of these features or the loss of them since the previous examination raises suspicion of a clinically significant condition, as described in the study by Munden et al 1.

From the Research

Possible Causes of Mildly Enlarged Hypermetabolic Mediastinal and Hilar Lymph Nodes

• Malignancy (lung cancer, lymphoma, and extrathoracic cancer) 2
• Granulomatous conditions (sarcoidosis and tuberculosis) 2
• Nontuberculous mycobacterial infection 3
• Metastasis from extrathoracic malignancies (head and neck, carcinoma breast, and genitourinary) 4

Differentiation of Reactive versus Other Causes

• Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) is a useful modality for differentiating between reactive and malignant lymph nodes 2, 4, 5, 6
• Positron emission tomography-computed tomography (PET/CT) can help identify hypermetabolic lymph nodes, but has low specificity and high false positive rate 5, 6
• SUVmax cutoff values can be used to differentiate between malignant and benign lymph nodes, with higher values indicating higher specificity but lower sensitivity 5, 6
• A SUVmax cutoff value of 2.5 may be used in routine practice, but higher cutoff values (e.g. 4.58,5.25, and 6.09) may provide better specificity and diagnostic accuracy 5, 6

Treatment Options

• Treatment options depend on the underlying cause of the lymph node enlargement, and may include:
  • Antituberculosis therapy for granulomatous conditions 3
  • Chemotherapy and/or radiation therapy for malignancies 2
  • Surgery for certain types of cancer or other conditions 2
• Accurate diagnosis is necessary for optimal management, and a multidisciplinary approach may be necessary to determine the best course of treatment 2