Table 4.
Radiological Terms for Heterogenous Lung Attenuation
| Terminology | Significance | Description |
|---|---|---|
| Mosaic attenuation* | • Generic term referring to a patchwork of regions of differing attenuation on inspiratory CT images | • Term only used for description of inspiratory CT images |
| • Can reflect the presence of vascular disease, airway abnormalities, or ground-glass interstitial or airspace infiltration | • Combination of areas of low and high attenuation that can correspond to two main situations: | |
| a. Areas of GGO (“high”) and normal lung (“low”) or | ||
| b. Areas of normal lung (“high”) and areas of decreased attenuation (“low”) | ||
| • Areas of GGO reflect an infiltrative lung disease | ||
| Air trapping* | • Abnormal retention of air distal to airway obstruction | • Term exclusively used for description of expiratory CT images |
| • Recognized as parenchymal areas that lack the normal increase in attenuation and the volume reduction of normally ventilated lung | • Air trapping appears as focal zones of hypoattenuation in the background of hyperattenuating normal lung on expiratory CT images | |
| • Mosaic attenuation and air trapping are not synonymous and cannot be used interchangeably | ||
| Mosaic perfusion† | • Regional differences in lung attenuation secondary to regional differences in lung perfusion | • Term used for description of inspiratory CT images |
| • May be seen in vascular (exclusive perfusion abnormalities) or airway (perfusion abnormalities resulting from abnormal regional lung ventilation) diseases | • Presence of decreased vascular sections within areas of low attenuation in comparison with areas of normal lung | |
| • Differential diagnosis facilitated by expiratory scans: | ||
| a. In case of vascular disease: same gradient of attenuation between areas of low and high attenuation | ||
| b. In case of airways disease: the attenuation differences are accentuated due to the additional depiction of air trapping | ||
| “Three-density pattern”‡ | • Term coined to replace the “headcheese” sign, as most individuals worldwide do not relate to the headcheese sign | • Combination of three attenuations on inspiratory CT images: |
| a. Normal-appearing lung | ||
| • Indicative of a mixed obstructive and infiltrative process: | b. High attenuation (GGO) | |
| a. The obstructive abnormality (seen in small airway disease) is manifested by areas of decreased attenuation and decreased vascularity | c. Lucent lung (i.e., regions of decreased attenuation and decreased vascular sections) | |
| b. The infiltrative disorder results in GGO surrounding preserved normal lobules | ||
| • Sharply demarcated from each other | ||
| • Highly specific for fibrotic HP; has not been shown to be specific for nonfibrotic HP |
Definition of abbreviations: CT = computed tomography; GGO = ground-glass opacity; HP = hypersensitivity pneumonitis.
See Reference 326.
See Reference 327.
The term “three-density pattern” was coined by this committee. This descriptive pattern was unanimously determined by the committee to be the preferred term. This pattern has been shown to differentiate fibrotic HP from idiopathic pulmonary fibrosis (123) and, thus, raises the index of suspicion for the diagnosis of fibrotic HP whenever present; however, it is unknown whether the pattern is also present in nonfibrotic HP. Some radiologists relate this pattern to the appearance of headcheese and, therefore, it has been referred to as the “headcheese sign” in the literature(328, 329). The guideline committee strongly discourages the use of the term “headcheese” to describe this pattern.