• Etymology:
  • The term “reticulonodular” combines “reticular,” derived from the Latin word “reticulum” meaning “net,” and “nodular,” from the Latin “nodulus” meaning “small node.”
• AKA:
  • None.
• What is it?
  • A reticulonodular pattern refers to the coexistence of a reticular (net-like) pattern and nodules (small, rounded opacities) within the lungs, often identified on imaging studies.
• Characterized by:
  • An interlacing network of linear opacities (reticular pattern).
  • Superimposed nodular opacities, typically 1-10 mm in size, giving a combined reticulonodular appearance.
• Anatomically affecting:
  • Pulmonary interstitium and alveolar spaces, including:
    • Axial Interstitium: Surrounding bronchovascular bundles.
    • Peripheral Interstitium: Near the pleura and fissures.
    • Septal Interstitium: Within the interlobular septa.
• Pathophysiology:
  • The reticulonodular pattern arises from processes that cause interstitial thickening (reticular) and deposition or proliferation of nodular structures within the lung parenchyma.
  • These changes may occur due to inflammation, fibrosis, cellular infiltration, malignant infiltration, and deposition of substances such as calcium and amyloid
• Causes include:
  • Most Common Causes:
    • Infection:
      • Tuberculosis.
      • Fungal infections (e.g., histoplasmosis, coccidioidomycosis).
    • Inflammation:
      • Sarcoidosis.
      • Hypersensitivity pneumonitis.
    • Circulatory:
      • Pulmonary edema with interstitial involvement.
  • Other Causes include:
    • Neoplasm:
      • Lymphangitic carcinomatosis.
    • Inhalational Diseases:
      • Pneumoconioses (e.g., silicosis, coal worker’s pneumoconiosis).
    • Autoimmune Diseases:
      • Rheumatoid arthritis-associated interstitial lung disease.
      • Systemic sclerosis.
    • Infiltrative Diseases:
      • Amyloidosis.
    • Inherited and Congenital:
      • Hermansky-Pudlak syndrome.
    • Iatrogenic:
      • Radiation-induced pulmonary changes.
    • Idiopathic:
      • Idiopathic pulmonary fibrosis (IPF).
• Histopathology:
  • Findings reflect both reticular and nodular changes:
    • Reticular:
      • Fibrosis and thickening of interlobular septa.
      • Proliferation of collagen and extracellular matrix.
    • Nodular:
      • Granulomatous inflammation (e.g., in sarcoidosis or hypersensitivity pneumonitis).
      • Nodular deposits of amyloid or neoplastic cells (e.g., lymphangitic spread of carcinoma).
    • Additional Findings:
      • Cellular infiltrates (lymphocytes, macrophages) in inflammatory processes.
      • Honeycombing and cystic changes in advanced fibrosis.
• Imaging:
  • Applied Anatomy:
    • Parts: Interstitial and alveolar components, including septal and axial interstitium.
    • Size: Nodules typically 1-10 mm; reticulations fine, medium, or coarse.
    • Shape: Network of linear structures superimposed with rounded nodules.
    • Position: Often diffuse but may show regional predominance (e.g., upper lobes in sarcoidosis, lower lobes in IPF).
    • Character: Nodules can be sharply defined or poorly demarcated; reticulations may appear hazy or well-organized.
    • Time: Can represent acute or chronic processes.
  • CXR:
    • Appears as a combination of linear (reticular) and nodular opacities.
    • Distribution can be diffuse or localized, depending on the underlying cause.
    • Often seen in sarcoidosis or pneumoconiosis.
  • CT:
    • High-resolution CT (HRCT) provides better differentiation of reticulations and nodules.
    • Findings include:
      • Reticular thickening of interlobular septa.
      • Nodules distributed perilymphatically (e.g., sarcoidosis) or randomly (e.g., hematogenous metastases).
      • Honeycombing in advanced fibrosis.
    • Provides detailed anatomical mapping of the pattern and aids in narrowing the differential diagnosis.
  • MRI:
    • Limited role in evaluating reticulonodular patterns but may help in assessing associated mediastinal or cardiac pathology.
  • PET-CT:
    • Can identify metabolically active nodules, aiding in distinguishing inflammatory from neoplastic processes.
    • Useful in staging malignancies associated with lymphangitic spread.
  • Other:
    • Ultrasound has limited utility but may detect pleural changes or associated effusions.
• Differential Diagnosis:
  • Infection:
    • Tuberculosis.
    • Fungal infections (e.g., histoplasmosis).
  • Inflammation:
    • Sarcoidosis.
    • Hypersensitivity pneumonitis.
  • Neoplasm:
    • Lymphangitic carcinomatosis.
  • Autoimmune:
    • Rheumatoid arthritis.
    • Systemic sclerosis.
  • Inhalational:
    • Silicosis.
    • Coal worker’s pneumoconiosis.
• Recommendations:
  • Correlate imaging findings with clinical history and laboratory results.
  • HRCT for better characterization of reticulonodular patterns.
  • Biopsy or bronchoalveolar lavage in unclear cases to identify specific etiologies.
  • Pulmonary function tests (PFTs) to assess restrictive lung disease.
• Key Points and Pearls:
  • A reticulonodular pattern represents a combination of interstitial thickening and nodular deposition.
  • Distribution patterns (e.g., perilymphatic vs. random) are crucial for narrowing the differential diagnosis.
  • HRCT is the modality of choice for detailed evaluation.
  • Early identification of the underlying cause is essential for targeted therapy.
• Integration with Human Endeavors
  • • Integration with Art and Architecture:
      The reticulonodular pattern’s intricate latticework echoes the complex geometric interplays found in Gothic architecture, such as the ribbed vaults of cathedrals.
    • Artists like M.C. Escher, renowned for his use of interlocking patterns and nodular-like tessellations, capture a similar aesthetic.
    • Music The repetitive nature of nodules and reticulations can also be likened to Baroque music’s contrapuntal layering, where individual lines (reticulations) intertwine with recurring themes (nodules).

A reticulonodular pattern is a radiological term used to describe a
combination of interlacing lines (reticular pattern) and small
nodules seen on chest X-rays or CT scans, creating a mesh-like or
net-like appearance with scattered small, round opacities. This
pattern indicates a mix of interstitial thickening and nodular
changes in the lungs, often due to fibrosis, inflammation, or
granulomatous disease. The pathogenesis involves processes like
fibrosis, inflammation, or the accumulation of infectious or
inflammatory cells, leading to changes in both the interstitial tissue
and the formation of nodules. Diagnosis relies on imaging, with high
resolution CT (HRCT) offering more detailed visualization of the
reticulonodular pattern and helping to determine the underlying
cause. Further evaluation, such as pulmonary function tests, blood
work, or biopsy, may be needed to confirm the diagnosis and guide
treatment