What causes Head cheese sign in lungs on HRCT?
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Answer:
Head cheese sign represents a mixed infiltrative and obstructive lung process seen in chronic hypersensitivity pneumonitis, characterized by juxtaposition of normal lung, ground-glass opacities from infiltration, and mosaic attenuation from small airway obstruction with air trapping; other causes include sarcoidosis, bronchiolitis obliterans, atypical infections like mycoplasma pneumonia, and desquamative interstitial pneumonitis.
Why is it called so?
The sign is named for its resemblance to head cheese, a terrine made from meat scraps of varying colors and textures from different animal parts, mimicking the variegated patchwork of low, normal, and high attenuation regions on CT.
Pathophysiology
Infiltrative processes such as cellular interstitial inflammation cause ground-glass opacities in affected lobules; concurrent small airway disease leads to bronchiolitis, air trapping, and hypoxic vasoconstriction in other lobules, producing low-attenuation mosaic areas; this creates sharply demarcated secondary pulmonary lobules of three densities, best seen on inspiratory HRCT and accentuated on expiratory imaging.
Alternative names: Three density pattern, three attenuation pattern
Other associated named signs: None
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