CT Chest

Differential diagnosis

• infectious processes (opportunistic vs non-opportunistic)

• chronic interstitial diseases

• acute alveolar diseases

• other causes

Radiopaedia

Often due to air trapping. 

Other DD at Radiopaedia

1. air trapping: refers to regions of the lung which following expiration do not show the normal increase in attenuation, or show little change in cross-sectional area

2. the presence of air trapping suggests airway disease

Honeycombing consists of enlarged air spaces with thick fibrotic walls lined by bronchiolar epithelium and often filled with mucin and inflammatory cells.

They represent an irreversible finding commonly seen in diffuse pulmonary fibrosis (usual interstitial pneumonia (UIP)). 

Radiopaedia

Subpleural reticulation is a type of reticular interstitial pattern where the changes are typically in a peripheral subpleural distribution (i.e. adjacent to costal pleural surfaces, located ≤1 cm from the pleura according to some publications

Pathology

Radiopaedia

Paraseptal emphysema is usually limited in extent occurring most commonly along the dorsal surface of the upper lung, and is often associated with fibrosis 4 and may coexist with other types of emphysema.

Any larger than 10 mm are referred to as subpleural blebs or subpleural bullae.

Radiopaediia

The head cheese sign (more recently termed the three-density pattern refers to a juxtaposition of regions with three (or sometimes more) different densities/regions of different attenuation within the lungs:

• ground-glass opacities, mosaic attenuation pattern, normal lung tissue 

• Highly specific for hypersensitivity pneumonitis, although it can also be seen in other mixed infiltrative and obstructive processes (e.g. sarcoidosis and atypical infections associated with bronchiolitis (e.g. mycoplasma pneumonia) .

Radiopaedia

Crazy paving refers to the appearance of ground-glass opacities with superimposed interlobular septal thickening and intralobular septal thickening, seen on chest HRCT or standard CT chest. It is a non-specific finding that can be seen in a number of conditions

Etiology

Radiopaedia

Tree-in-bud sign or pattern describes the CT appearance of multiple areas of centrilobular nodules with a linear branching pattern. Although initially described in patients with endobronchial tuberculosis, it is now recognized in a large number of conditions.

Differential Diagnosis

Radiopaedia

Pulmonary sequestration, also called accessory lung, refers to the aberrant formation of segmental lung tissue that has no connection with the bronchial tree or pulmonary arteries. It is a bronchopulmonary foregut malformation (BPFM).

Radiopaedia