CTICasesAcute Hypersensitivity Pneumonitis (Head Cheese Sign)
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Imaging findings
A radiograph showed subtle ground-glass opacity or effacement of vessel margins. A subsequent CT revealed 'gray lungs' with central lobular nodules and areas of lobular hypoattenuation, forming a 'head cheese sign'.
Key takeaways
This case is another typical example of hypersensitivity pneumonitis, characterized by gray lungs, central lobular nodules, and the 'head cheese sign' (areas of lobular hypoattenuation). The presence of subpleural black lung and distinct bronchovascular bundles due to contrast from the abnormal lung parenchyma enhances visibility of these findings. This can be further distinguished from pure ground glass on thin sections by identifying the nodularity, making it a 'slam dunk' diagnosis, even necessitating a lung biopsy in this case. The concept of 'pointillism' versus 'watercolor' for differentiating nodular vs pure ground glass was also discussed.
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