The missing hilum: Chronic lobar collapse.

Background: Chronic lobar collapse, or atelectasis, presents a diagnostic challenge due to the subtlety of radiographic findings, particularly when classic signs are absent. Case presentation: We present the case of a 62-year-old male with emphysema and progressive dyspnoea, whose chest radiographs revealed indirect signs of left lower lobe (LLL) collapse, including a reduced left hilar silhouette, elevated left hemidiaphragm, right lung herniation, and mediastinal shift. These findings were confirmed by CT imaging, which demonstrated retraction of the LLL along the spine, which is an appearance not easily detectable on standard radiographs. Discussion: Chronic LLL collapse may be obscured due to reduced lobe volume and compensatory changes in surrounding structures. However, displacement and the apparent absence of the left hilum, in the absence of consolidation, can be a secondary sign of chronic LLL collapse. As such it should be taken in conjunction with other secondary signs of lobar collapse to suggest a possible diagnosis and prompt further confirmatory imaging. Conclusion: Awareness of imaging patterns of lobar collapse, such as the apparent absence of a hilum, is essential for accurate interpretation, particularly in patients without prior lobectomy and when direct signs of consolidation are lacking.