Head cheese sign (lungs)

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The head cheese sign refers to a juxtaposition of regions with three (or sometimes more) different densities/regions of different attenuation within the lungs:

A mixed infiltrative (ground-glass opacity) and obstructive (mosaic attenuation) disease process can give rise to the head cheese sign. Less frequently, superposition of a separate infiltrative and obstructive process causes this pattern. As the mosaic attenuation pattern is caused by airway narrowing/air trapping, these low attenuation areas may only be apparent on expiratory scans.

The head cheese sign is considered to be highly specific for hypersensitivity pneumonitis, although it can also be seen in other mixed infiltrative and obstructive processes (e.g. sarcoidosis and atypical infections associated with bronchiolitis (e.g. mycoplasma pneumonia) .

Head cheese, believe it or not, is not cheese and is often not made of the head. It is, in fact, a type of terrine, with bits of meat scavenged from various parts of various animals (including the head) usually from a calf or pig. The appearance of the cut surface of this dubious delicacy has been likened to the previously described pattern.