Friday, February 4, 2011

Cystic Lung Lesions

Differential considerations for multiple cystic lung lesions (wall thickness < 2 mm):
  • Langerhans cell histiocytosis: Upper lobe predominance with sparing of the costophrenic angles. Multiple nodules with cysts later. Nodules progressively cavitate to become thick-walled cavitary nodules and then thin-walled cysts.

  • Lymphangioleiomyomatosis: Primarily affects women of childbearing age. Indistinguishable from pulmonary involvement in tuberous sclerosis. Increased lung volumes, well-defined, smooth, and regular cysts interspersed with normal intervening lung. Diffuse distribution is in contrast to Langerhans cell histiocytosis. Nodules typically absent. Lymphangioleiomyomatosis may be associated lymphadenopathy and renal angiomyolipomas.

  • Lymphoid Interstitial Pneumonia (LIP): Idiopathic form is rare. More commonly associated with AIDS, autoimmune disorders, and collagen–vascular diseases (especially Sjögren syndrome). Chest radiographs reveal a nonspecific fine linear or reticulonodular pattern. The dominant high-resolution CT feature is ground-glass attenuation, which when combined with thin-walled perivascular cysts in the mid lung zones is highly suggestive of lymphoid interstitial pneumonia. The cysts are usually less numerous than in lymphangioleiomyomatosis or Langerhans cell histiocytosis. Diffuse or multifocal ground-glass opacities can be seen early on, but cysts may be the only finding in more chronic cases and after therapy. Lymphoid interstitial pneumonia may be associated lymphadenopathy.

  • Metastases: While typically thick-walled, thin-walled cysts can occur with sarcoma, squamous cell carcinoma, transitional cell carcinoma of the bladder, melanoma, and less commonly with lymphoma. Cysts are usually of different sizes and have a basal predominance.

  • Pneumatoceles: Caused by infection (pneumococcus, Escherichia coli, Klebsiella, and Staphylococcus, Pneumocystis jiroveci, Coccidioidomycosis), trauma, or hydrocarbon fluid inhalation. Can be thick-walled in the acute phase. Spontaneous resolution is the rule with infectious pneumatoceles.

  • Tracheobronchial papillomatosis: Lung parenchymal involvement by tracheobronchial papillomatosis is rare, but shows up on board exams. Cysts typically have a posterior predominance. Look for papillomas of the airway on CT.

  • Neurofibromatosis Type 1: Multifocal lung cysts with an upper lobe predominance are a rare manifestation. Look for subcutaneous and intercostal neurofibromas, ribbonlike ribs, meningoceles, mediastinal masses, and pulmonary fibrosis.

  • Congenital pulmonary airway malformation: Rare.

  • Birt-Hogg-Dubé syndrome: Rare autosomal-dominant multiorgan disorder that affects the skin, kidneys, and lungs. Patients can present with characteristic skin lesions, solid renal tumors, and multiple lung cysts of variable size in a lower lobe distribution.
Note: The classic teaching is that cysts associated with pulmonary Langerhans cell histiocytosis are less uniform in appearance than those associated with lymphangioleiomyomatosis and that Langerhans cell histiocytosis is associated with nodules (especially early in the course of the disease), while lymphangioleiomyomatosis is not. However, more recent work (Koyama et al, 2003) suggests that there is considerable overlap between the appearance of lymphangioleiomyomatosis and Langerhans cell histiocytosis and that CT can't be reliably used to differentiate the two.


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