Profusion Ratings on CT/HRCT Scans


Although the CDC/NIOSH has not come out with an official set of standard images showing interstitial profusion of small irregular opacities of asbestosis on CT or HRCT, there are many lectures, journal articles and peer-reviewed textbooks that show examples of normal lung tissue, mild interstitial lung disease, moderate interstitial lung disease and advanced or severe interstitial lung disease as examples.  These resources also differentiate different patterns and distributions of disease types.  The UIP (Usual Interstitial Pneumonia) pattern on CT and HRCT is the type occurring with asbestosis.  


Mild disease (equivalent to a 1/1 ILO chest x-ray profusion score) has subpleural parenchymal changes, often called Intralobular Interstitial Thickening (previously known as Core changes), which look like multi-locational, usually posterior subpleural (peripheral) hazy areas, if with (called reticular appearance) or without small dots or perpendicular small short lines, occurring bilaterally at the lung bases and best identified on Prone HRCT to alleviate dependent gravitational density as an etiology of posterior lung base densities.  


Moderate disease (equivalent to a 2/2 ILO chest x-ray profusion score) has similar findings to mild disease along with bronchiolectasis. It is often seen extending upward to involve the subpleural areas of the middle lung zones and may even extend into the upper lung zones where it can be posterior, lateral and anterior in location.  


Severe disease (equivalent to a 3/3 ILO chest x-ray profusion score) has similar findings to moderate disease, but involving all six lung zones, along with honeycombing and in some individuals, bronchiectasis and more centralized extension of diffuse density appearing as ground glass changes.  


Of course, there are circumstances in which the findings are in between these categories, such as a mild profusion study with limited bronchiolectasis or upward lateral subpleural creep (equivalent to a 1/2 ILO chest x-ray profusion score) or for instance, a moderate profusion study with limited honeycombing (equivalent to a 2/3 ILO chest x-ray profusion score). Also, note that the chest x-rays are not always identical to the findings on CT or HRCT as chest x-rays have overlapping densities and are not cross-sectional in nature.


The above article is provided as a public service by Daniel Powers, M.D.: B-Reader, Board-Certified Diagnostic Radiologist, Certified by the American Board of Radiology.


If you detect any errors, have additional information to point me to, use other useful terms or have comments, please do e-mail them to me at


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