Alveolar Pulmonary Pattern

There are different pulmonary radiographic patterns: Alveolar Pattern, Interstitial Pattern, Structured Interstitial (nodular) Pattern, Bronchial Pattern, Vascular Pattern and Mixed Pattern. 

The alveolar pattern occurs when fluid (such as exudate, hemorrhage, edema or rarely cells - neoplasic cells) filling up the pulmonary acini and displacing the air (consolidation) or not replaced at all (atelectasis). In either etiology, the lung is no longer aerated increasing the radiographic opacity of lung.

The alveolar pattern is identified by an increase in overall lung opacity that completely obscures the pulmonary vasculature in the opaque area. This pattern is characterized by  one or more of the following radiographic features (not all signs seen in every case): 

• Uniform opacity

• Air bronchogram (hallmark sign of an alveolar pattern) an air-filled bronchus traversing a region of abnormally opaque lung. Bronchial walls are not seen; only bronchial lumen.

• Lobar sign (the infiltrate extends to periphery) - opacified lobe border and adjacent normal radiolucent lobe. 

• Silhouette effect - loss of border visualization between heart and lung lobe. 

• Focal or multifocal distribution (depending the disease severity).

References:

• Donald E. Thrall. Textbook of Veterinary Diagnostic Radiology. 7th ed. Elsevier. 2018. 

• Ronald L. Burk. Alveolar Pulmonary Patterns. VIN Radiology Atlas. VIN.com

• Martha M. Larsen. Radiographic evaluation of Pulmonary Patterns and Disease (Proceedings). 2008. dvm360.com

DVM 360:

Radiographic evaluation of Pulmonary Patterns and Disease (Proceedings)