Subacute hypersensitivity pneumonitis

Case contributed by Melbourne Uni Radiology Masters


Loss of weight, fevers, shortness of breath, heavy smoker.

Patient Data

Age: 43-year-old
Gender: Male

CT Chest


Small non calcified mediastinal nodes are present.

Both lungs show changes of diffuse centrilobular nodular infiltration in both lungs.

Also, there are more confluent areas of ground glass opacification present.

Features of mosaic attenuation are noted.

Normal pleural spaces and pericardium.


CT Chest (19 days after - patient on high dose of steroids)


Clinical notes: patient removed from birds and on high dose steroids. 

Non-contrast inspiratory helical scan with supplemental expiratory and prone scans.

Previously noted bilateral widespread airspace opacity has improved but not completely resolved.

Centrilobular nodules are still present in both lungs.

No new findings.

Case Discussion

Respiratory function tests were severely reduced as was his exercise tolerance.

Bronchoscopy and washing showed a lymphocytosis of 80%, the majority of the lymphocytes were T8, this is diagnostic of SAHP.

A follow-up CT after 19 days and a repeated lung function tests revealed a significant improvement.

The differential diagnosis here lies between:

The high lymphocyte count and a definite history of antigen exposure plus the response to removal from birds make SAHP the most likely diagnosis.

On HRCT, subacute hypersensitivity pneumonitis usually has the following features:

  • ground-glass opacity
  • centrilobular nodules
  • mosaic attenuation
  • expiratory air trapping 
  • mediastinal lymphadenopathy in about 50%

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