• • What is it:
    • Fissural nodules are small, localized opacities occurring along or adjacent to the pleural fissures of the lungs.
    • These nodules may represent
      • pleural-based processes,
      • lymphatic spread of disease, or
      • conditions involving the visceral pleura.
  • fissural nodules most commonly relate to
    • lymphoid disease or involvement,
      • This is due to the anatomical location of lymphatic channels that run along the pleural surfaces and fissures.

Key Points Supporting Lymphoid Involvement:

1. Lymphatic Anatomy of the Lung:
   • Lymphatic vessels are abundant along the pleural surfaces, including the fissures, and are common sites of disease spread in conditions involving lymphatic obstruction or inflammation.
2. Perilymphatic Nodules:
   • Diseases like sarcoidosis, which prominently involve lymphatic channels, frequently present with nodules along pleural fissures, making lymphoid involvement a significant cause.
3. Lymphatic Spread of Disease:
   • Malignancies (e.g., lymphangitic carcinomatosis): Tumor cells often spread along lymphatic channels, leading to nodules along fissures.
   • Granulomatous Diseases (e.g., tuberculosis or fungal infections): These may also spread via lymphatics to the fissures.
4. Primary Lymphoid Diseases:
   • Diseases like lymphoma can involve lymphatic structures along fissures, appearing as fissural nodules.

Exceptions:

While lymphoid involvement is the most common cause, other etiologies can also lead to fissural nodules, such as:

• Direct pleural involvement: Seen in infections or metastatic cancers.
• Subpleural inflammation: Conditions like cryptogenic organizing pneumonia (COP) may mimic lymphoid involvement.

Clinical Implication:

When fissural nodules are seen, lymphoid disease or lymphatic involvement should be high on the differential diagnosis, but other causes should also be considered based on the clinical context and associated imaging findings.

• • Etymology:
    • “Fissural” originates from the Latin word fissura, meaning “a cleft or groove,” referring to the pleural fissures.
    • “Nodule” derives from the Latin nodulus, meaning “small knot.”
  • AKA:
    • Pleural nodules (when associated with pleural surfaces).
  • Abbreviation:
    • FN (Fissural Nodules).
  • How does it appear on each relevant imaging modality:
    • Chest CT (preferred):
      • Parts: Discrete nodules seen along or within the pleural fissures.
      • Size: Typically small (<1 cm), but larger nodules may be present depending on the underlying cause.
      • Shape: Round or oval, occasionally irregular; may appear confluent in cases of lymphatic spread.
      • Position: Localized along the major or minor fissures of the lungs.
      • Character:
        • Calcifications may be seen in benign or treated lesions.
        • May exhibit contrast enhancement in malignancy or inflammation.
    • Chest X-ray:
      • Nodules along the fissures may appear as thickened or irregular fissural margins but are often challenging to detect.
    • PET-CT:
      • Increased metabolic activity (high SUV) suggests malignancy.
      • Low SUV is more consistent with benign conditions.
  • Differential diagnosis (starting with the most likely causes):
    • Infection:
      • Tuberculosis: Nodules along the fissures due to pleural or lymphatic involvement.
      • Fungal infections: Nodular infiltration of the pleural or subpleural regions (e.g., aspergillosis).
    • Inflammation:
      • Sarcoidosis: Perilymphatic nodules involving pleural fissures.
      • Rheumatoid nodules: Occasionally seen along fissures due to pleural involvement.
    • Neoplasm:
      • Primary lung cancer: Tumor spread along pleural surfaces or lymphatics.
      • Metastases: Often present as nodules along the pleura or fissures (e.g., breast, ovarian, or gastrointestinal cancer).
    • Idiopathic:
      • Cryptogenic organizing pneumonia (COP): Subpleural nodules involving fissures.
  • Recommendations:
    • Further evaluation:
      • Contrast-enhanced CT for detailed characterization of nodules and fissural involvement.
      • PET-CT for metabolic activity if malignancy is suspected.
      • Biopsy or pleural sampling (e.g., via thoracoscopy) for indeterminate nodules.
    • Surveillance:
      • Follow-up imaging based on risk factors and clinical suspicion (e.g., Fleischner Society guidelines for nodules).
  • Key considerations and pearls:
    • Fissural nodules are often associated with pleural or lymphatic processes, such as metastases, sarcoidosis, or infection.
    • The presence of calcifications often suggests a benign process or prior granulomatous infection.
    • Concomitant pleural effusion or thickening may point to malignancy or active inflammation.
    • Clinical history, including prior malignancy or exposure to infectious agents, is crucial for narrowing the differential diagnosis.
  • Fissural refers to anything related to or associated with the fissures
    of the lungs. The lungs have major fissures (the oblique fissures in
    both lungs and the horizontal fissure in the right lung) that separate
    the lobes and help define their structure. Fissural abnormalities,
    such as fissural thickening, displacement, or effusion (Etesami)
• • sarcoidosis (classic association)
  • amyloidosis – nodular form
  • lymphocytic interstitial pneumonia (LIP)
  • lymphangitic carcinomatosis:
  • silicosis
  • coal worker’s pneumoconiosis:

Sarcoidosis

Amyloidosis

TB