Lobar collapse: what radiologists need to know

Radiologists have to diagnose lobar collapse routinely, so they should be familiar with the direct and indirect signs of lobar atelectasis and with uncommon findings, for being able to make early diagnosis. Atelectasis can be caused by several mechanisms: by obstruction (due to neoplastic or non-neoplastic causes), by loss of negative pressure in the pleural space and/or by compression of lung parenchyma (e.g., pneumothorax, hydrothorax, and pleural effusion) or by an increase in alveolar surface tension (e.g., acute respiratory distress syndrome and neonatal respiratory distress syndrome). Collapses, moreover, can be observed in several ways. Lobar atelectasis occurs when entire pulmonary lobe is collapsed. Linear atelectasis (previously “plate like” or “band like”) is a local collapse with linear, plate-like or band-like shape which usually parallels the hemidiaphragms. Rounded atelectasis is a consequence of chronic or recurrent pleural effusion, which could be related to asbestos disease, chronic cardiac or renal failure, and thoracic malignancies. It occurs as a rounded mass abutting the pleura with adjacent pleural thickening. Collapsed lobes can assume quite limited forms and radiologists require familiarity with radiographic findings for helping clinical physician in the diagnostic process.