Three attenuation pattern

Last revised by Dr Muhammad Yousaf on 11 Mar 2024

The three attenuation pattern or three density pattern was formerly known as the head cheese sign and refers to the presence of well-defined areas of decreased, normal and increased attenuation on inspiratory CT 6.

The resultant mosaic is due to lobular air-trapping with reflex hypoperfusion, juxtaposed with areas of normal lung and areas of lobular inflammation. These areas are typically delineated by interlobular septa.

Although this pattern was initially thought to be specific for hypersensitivity pneumonitis, other diseases or disease combinations that cause small airway obstruction and lobular ground-glass opacity can cause a similar pattern.

The three attenuation pattern comprises well-defined areas of lobular air-trapping, normal lung and areas of ground-glass opacity. Air-trapping is accentuated on expiratory CT.

Head cheese is a type of terrine composed of pieces of meat scavenged from various parts of various animals. The term was meaningless to many people.

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