Miliary opacities (lungs)

The term miliary opacities refers to innumerable, small 1-4 mm pulmonary nodules scattered throughout the lungs. It is useful to divide these patients into those who are febrile and those who are not.

Additionally, some miliary opacities are very dense, narrowing the differential - see multiple small hyperdense pulmonary nodules.

Pathology

Etiology

The causes can be broadly subgrouped dependent on whether or not the patient is febrile.

Afebrile

• infection
  • tuberculosis (often febrile but may be afebrile)
    • miliary tuberculosis
  • fungal (often febrile)
    • immunocompromised or elderly patients may be afebrile
  • healed varicella pneumonia
• miliary metastases
  • thyroid carcinoma
  • renal cell carcinoma
  • breast carcinoma
  • malignant melanoma
  • pancreatic neoplasms
  • osteosarcoma
  • trophoblastic disease
• others
  • sarcoidosis: miliary sarcoidosis ⁸
  • pneumoconioses
    • silicosis
    • coal workers pneumoconiosis
  • pulmonary hemosiderosis
  • BCGosis
  • hypersensitivity pneumonitis
  • Langerhans cell histiocytosis (LCH)
  • multifocal micronodular pneumocyte hyperplasia (MMPH)
  • diffuse pulmonary meningotheliomatosis ⁹
  • pulmonary alveolar proteinosis
    • small acinar opacities can mimic a miliary pattern ⁶

Febrile

• infection
  • tuberculosis
  • fungal
  • viral pneumonitis
  • nocardiosis
  • salmonella
  • melioidosis - occasionally described although not in radiology literature ¹⁰
• hypersensitivity pneumonitis (mild fever if any)

History and etymology

The term miliary is derived from the millet seed, a term used to describe a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder ⁵.

See also

• diffuse pulmonary nodules
• miliary lung nodules (mnemonic)