• Perilymphatic distribution refers to
  • a pattern of lung involvement in which pulmonary abnormalities, such as
    • lymphatic congestion
    • lymphatic infiltration
    • or nodules,
  • align with the lymphatic vessels surrounding specific regions of the lung.
  • This distribution pattern is often indicative of diseases that affect the lymphatic system.
• For the purpose of this definition, the
  • lymphatic distribution can be visualized in the following regions:
    • bronchovascular
    • interlobular septa of the secondary lobule
    • intralobular regions of the secondary lobule
    • pleura
    • fissures
    • pulmonary veins

AKA:

• Lymphangitic Distribution

Abbreviation:

• PLD (Perilymphatic Distribution)

How does it appear on each relevant imaging modality?:

Chest X-ray:

• Parts: The pattern may show up as
  • • fine, linear or reticular markings
    • nodular densities
  • along the
    • bronchovascular bundle
    • interlobular septa of the secondary lobule
    • intralobular regions of the secondary lobule
    • pleura
    • fissures
    • pulmonary veins

CT Scan:

With higher contrast resolution the CT scan is far better to identify the anatomic location of the lymphatic or peri lymphatic involvement and similarly

the pattern may as

• • • fine, linear or reticular markings
    • nodular densities
  • along the
    • bronchovascular bundle
    • interlobular septa of the secondary lobule
    • intralobular regions of the secondary lobule
    • pleura
    • fissures
    • pulmonary veins

MRI:

• Parts: MRI is not typically used for evaluating perilymphatic distribution .

PET-CT:

• Role: PET-CT is  not typically used for evaluating perilymphatic distribution .

Differential diagnosis:

Infection:

• Tuberculosis (TB):
  • Character: Perilymphatic distribution of nodules or infiltrates in the lungs, often with associated hilar lymphadenopathy.
  • Imaging Findings: Small nodules or linear opacities located in a lymphatic distribution, often in the upper lobes.
• Fungal Infections (e.g., Histoplasmosis, Coccidioidomycosis):
  • Character: Granulomatous infection causing nodules in a perilymphatic distribution, sometimes with calcification.
  • Imaging Findings: Nodular infiltrates, often with a fine reticular pattern along the bronchovascular structures.

Inflammation:

• Sarcoidosis:
  • Character: Granulomatous disease causing nodular infiltrates along the bronchovascular bundles.
  • Imaging Findings: Hilar and mediastinal lymphadenopathy with a perilymphatic pattern, often associated with fine reticular opacities.
• Rheumatoid Arthritis (RA):
  • Character: Perilymphatic involvement due to inflammation associated with interstitial lung disease in RA.
  • Imaging Findings: Reticular or nodular infiltrates in the subpleural regions of the lungs.

Neoplasm (Benign or Malignant):

• Lymphangitic Carcinomatosis:
  • Character: Malignant spread via the lymphatic vessels, leading to a perilymphatic distribution of nodular infiltrates.
  • Imaging Findings: Fine nodular patterns around the bronchovascular bundles, often with pleural effusions.
• Metastatic Disease:
  • Character: Malignant cells can spread through the lymphatic vessels, leading to a perilymphatic distribution.
  • Imaging Findings: Nodules along the bronchovascular structures or at the pleural surface, associated with mediastinal or hilar lymphadenopathy.

Metabolic:

• Pulmonary Langerhans Cell Histiocytosis (PLCH):
  • Character: A rare disease that may present with perilymphatic distribution of nodules or cysts.
  • Imaging Findings: Peripherally distributed nodules that may evolve into cystic changes over time.

Recommendations:

Next diagnostic steps:

• Further imaging with CT or MRI to evaluate the extent, distribution, and characteristics of the perilymphatic distribution.
• Biopsy or fine needle aspiration (FNA) may be necessary for histological examination if malignancy or infection is suspected.
• Laboratory testing: Blood tests to evaluate for infections (e.g., tuberculin skin test), autoimmune markers (e.g., sarcoidosis), or cancer screening.