Disproportionate Mediastinal Shift From an Isolated Right Middle Lobe Collapse: A Case Report.

Mediastinal displacement toward the side of lung volume loss is a well-recognized radiographic feature of atelectasis. Significant mediastinal shift most commonly occurs when larger lung segments, such as the right upper or lower lobes, collapse. Because the right middle lobe (RML) contributes a relatively small proportion of total lung volume, isolated RML collapse typically produces minimal mediastinal deviation. The case in this report is of an 83-year-old woman with chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF), who presented with progressive dyspnea and increased oxygen requirements. Chest radiography demonstrated opacification of the right middle lobe with marked rightward displacement of the cardiac silhouette. Computed tomography (CT) of the chest confirmed isolated collapse of the right middle lobe with rightward mediastinal and cardiac displacement, without involvement of the right upper or lower lobes. Bronchoscopy revealed narrowing of the right middle lobe bronchus due to floppy cartilage consistent with bronchomalacia and no evidence of endobronchial mass or malignancy. The patient improved with conservative medical management, including diuresis, bronchodilators, and pulmonary hygiene. This case demonstrates that isolated RML collapse can produce significant mediastinal and cardiac displacement. Clinicians should recognize that even the collapse of relatively small lung segments may generate substantial radiographic shift, particularly in patients with underlying airway structural abnormalities or pulmonary hyperinflation.