Pneumomediastinum Masquerading As Superior Vena Cava Obstruction in a Patient With Metastatic Colorectal Cancer: A Diagnostic Challenge.

Pneumomediastinum refers to the presence of free air within the mediastinum and is most commonly associated with trauma, instrumentation, or barotrauma, but may rarely occur spontaneously. In patients with thoracic malignancy, pneumomediastinum can mimic other oncologic emergencies such as superior vena cava obstruction (SVCO), creating diagnostic uncertainty. We present the case of a 57-year-old woman with metastatic recurrent colorectal carcinoma receiving palliative FOLFIRI (folinic acid, fluorouracil, and irinotecan) and panitumumab who was admitted with recurrent respiratory infections. During a subsequent hospitalization, she developed acute cervicofacial swelling with dysphagia and visible collateral chest wall veins, prompting empirical high-dose steroids and anticoagulation for suspected SVCO. Contrast-enhanced CT performed the same day demonstrated extensive pneumomediastinum with cervicofacial subcutaneous emphysema, but no venous obstruction or tumor progression. The leading etiologies considered included barotrauma and the Macklin effect associated with cough and asthma exacerbation; iatrogenic causes such as port-a-cath leak were excluded. She improved with conservative management (oxygen, bronchodilators, steroid taper, and antibiotics as indicated) and was discharged. Due to persistent hilar disease and recurrent respiratory compromise, the thoracic multidisciplinary team later proposed palliative surgical debulking. This case highlights the importance of prompt imaging and multidisciplinary assessment in differentiating pneumomediastinum from SVCO to avoid unnecessary invasive interventions.