Table 5.

Chest HRCT Scan Features of the Nonfibrotic HP Pattern

HRCT Pattern	Typical HP	Compatible with HP	Indeterminate for HP
Description	The “typical HP” pattern is suggestive of a diagnosis of HP. It requires a) at least one HRCT abnormality indicative of parenchymal infiltration and b) at least one HRCT abnormality indicative of small airway disease, both in a diffuse distribution	“Compatible-with-HP” patterns are nonspecific patterns that have been described in HP	N/A
Relevant radiological findings	HRCT abnormalities indicative of parenchymal infiltration:	Parenchymal abnormalities:	N/A
	• GGOs	• Uniform and subtle GGOs
	• Mosaic attenuation*	• Airspace consolidation
		• Lung cysts
	HRCT abnormalities indicative of small airway disease:
	• Ill-defined, centrilobular nodules	Distribution of parenchymal abnormalities:
	• Air trapping	• Craniocaudal: diffuse (variant: lower lobe predominance)
		• Axial: diffuse (variant: peribronchovascular)
	Distribution of parenchymal abnormalities:
	• Craniocaudal: diffuse (with or without some basal sparing)
	• Axial: diffuse

Definition of abbreviations: GGO = ground-glass opacity; HP = hypersensitivity pneumonitis; HRCT = high-resolution computed tomography; N/A = not applicable.

^*Mosaic attenuation corresponding to parenchymal infiltration is created by GGOs adjacent to normal-appearing lung.