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HRCT LUNGS-RANDOMLY DISTRIBUTED NODULES

Nodules as small as 1-2 mm in diameter can be detected by HRCT. Nodules can be classified according to their appearance such as well-defined (likely interstitial) or ill-defined (likely air-space) or classified according to their distribution in relation to other lung structures (i.e. perilymphatic, random, or centrilobular).

Random nodules are usually well-defined and appear diffuse, but uniform in distribution.

HRCT LUNGS-PERILYMPHATIC NODULE

Nodules as small as 1-2 mm in diameter can be detected by HRCT. Nodules can be classified according to their appearance such as well-defined (likely interstitial) or ill-defined (likely air-space) or classified according to their distribution in relation to other lung structures (i.e. perilymphatic, random, or centrilobular).

Perilymphatic nodules are usually well-defined and occur in relation to the lymphatics. They often affect the pleural surfaces and the peribronchovascular, interlobular septa, and centrilobular interstitial components.

HRCT LUNGS-SEPTAL THICKENING

Interlobular septal thickening is commonly seen in patients with interstitial lung disease. On HRCT, numerous clearly visible septal lines usually indicates the presence of some interstitial abnormality. Septal thickening can be definied as being either smooth, nodular or irregular and each likely represents a different pathologic process.

HRCT LUNGS-LYMPHADENOPATHY

Enlargement of hilar or mediastinal lymph nodes can be symmetric or asymmetric. Lymphadenopathy can represent hematogenous metastasis, a primary carcinoma, or other pathology.

HRCT LUNGS-MOSAIC ATTENUATION

Mosaic perfusion refers to areas of decreased attenuation which results from regional differences in lung perfusion secondary to airway disease or pulmonary vascular disease. Distribution is often patch, hence the designation "mosaic." Often with mosaic perfusion, the pulmonary arteries will be reduced in size in the lucent lung fields thus allowing mosaic perfusion to be distinguished from ground-glass opacities.

HRCT LUNGS-HONEYCOMBING

Honeycombing suggests extensive lung fibrosis with alveolar destruction and can result in a cystic appearance on gross pathology. Honeycombing can be diagnosed via HRCT by the presence of thich-walled, air-filled cysts, usually between the size of 3mm to 1cm in diameter.

HRCT LUNGS-GROUND GLASS OPACITY

Ground-glass opacity is a non-specific term that refers to the presence of increased hazy opacity within the lungs that is not associated with obscured underlying vessels (obscured underlying vessels is known as consolidation). It can reflect minimal thickening of the septal or alveolar interstitium, thickening of alveolar walls, or the presense of cells or fluid filling the alveolar spaces. In an acute setting, it can represent active disease such as pulmonary edema, pneumonia, or diffuse alveolar damage.

HRCT LUNGS-PLEURAL EFFUSION

Transudative pleural effusions are formed when normal hydrostatic and oncotic pressures are disrupted. Exudative pleural effusions occur when pleural membranes or vasculature are damaged or disrupted therefore leading to increased capillary permeability or decreased lymphatic drainage.

HRCT LUNGS-PLEURAL EFFUSION

Transudative pleural effusions are formed when normal hydrostatic and oncotic pressures are disrupted. Exudative pleural effusions occur when pleural membranes or vasculature are damaged or disrupted therefore leading to increased capillary permeability or decreased lymphatic drainage.

HRCT LUNGS-BRONCHIECTASIS

Traction bronchiectasis refers to bronchial dilation that occurs in patients with lung fibrosis or distorted lung architecture. Traction on the bronchial walls due to fibrous tissue reults in irregular bronchial dilation (bronchiectasis). Usually segmental and subsegmental bronchi are involved, but small periperhal bronchi or bronchioles may also be affected. Commonly associated with honeycombing.

HRCT-AIR TRAPPING

Air trapping refers to the abnormal retention of gas within the lung following expiration. On HRCT, the lung parencyhma remains lucent on expiration, while normal lung areas show increased attenuation. Inspiration scans can be completely normal in air trapping. Air trapping therefore cannot be diagnosed on inspiration scans; lung inhomogeneity during inspiration scans can be interpreted as mosaic perfusion.