Diagnosis: Pulmonary Contusion
The diagnosis is D - pulmonary contusion, based on the classic presentation of blunt chest trauma with multiple rib fractures (3-7 left ribs), delayed onset of shortness of breath, and a well-demarcated lung infiltrate appearing on repeat chest X-ray hours after the initial injury 1, 2.
Clinical Reasoning
Why Pulmonary Contusion is the Correct Answer
Pulmonary contusion characteristically presents with alveolar hemorrhage and parenchymal destruction that manifests within the first 24 hours after blunt chest trauma, with the infiltrate appearing on imaging as the injury evolves 1, 2.
The delayed presentation of shortness of breath "a couple of hours later" is pathognomonic for pulmonary contusion, as respiratory distress typically develops within hours of injury and peaks at approximately 72 hours 1, 2.
The well-demarcated lung infiltrate on repeat chest X-ray represents the hemorrhage and edema within the lung parenchyma that defines pulmonary contusion 3, 1.
Multiple rib fractures (3-7 ribs) are the classic mechanism for pulmonary contusion in blunt chest trauma, as the force required to fracture multiple ribs is sufficient to cause underlying lung parenchymal injury 4, 2.
Why the Other Options Are Incorrect
Pulmonary Embolism (PE):
- PE would not produce a well-demarcated infiltrate on chest X-ray 5.
- The immediate temporal relationship to trauma and presence of multiple rib fractures makes traumatic lung injury far more likely than thromboembolic disease 4.
- PE typically presents days after trauma due to immobilization, not hours 4.
Flail Chest:
- Flail chest requires three or more consecutive ribs fractured in two or more places, creating a free-floating segment of chest wall 4.
- The question describes "3-7 left ribs fractures" without specifying multiple fracture sites per rib, making flail chest unlikely 4.
- Flail chest presents with paradoxical chest wall movement and immediate respiratory distress at the time of injury, not delayed onset 4.
- The well-demarcated lung infiltrate indicates parenchymal injury, not chest wall instability 5.
Cardiac Contusion:
- Cardiac contusion would not produce a lung infiltrate on chest X-ray 6.
- Chest radiographs have limited ability to identify direct findings of cardiac injury such as cardiac contusion, though they may show indirect findings like enlarged cardiac silhouette or hemopericardium 6.
- The patient's vital stability and isolated respiratory symptoms (shortness of breath only) argue against significant cardiac injury 6.
- Cardiac contusion typically requires sternal fracture or severe anterior chest trauma, not lateral rib fractures 6.
Clinical Pitfalls to Avoid
Do not dismiss the initial "normal" chest X-ray as excluding pulmonary contusion - chest radiographs miss approximately 50% of pulmonary contusions that are visible on CT, and the infiltrate may not appear until hours after injury 6, 1.
Recognize that pulmonary contusion is maximal during the first 24 hours and typically resolves within 7 days, so the patient requires close monitoring for respiratory deterioration over the next 72 hours 1, 2.
Be aware that pneumonia and acute respiratory distress syndrome are frequent complications of pulmonary contusion, occurring in a significant proportion of patients 1, 2.
The presence of multiple rib fractures significantly increases morbidity, particularly in patients over 65 years of age, and this 61-year-old patient approaches that high-risk threshold 7.
Management Implications
Management of pulmonary contusion is primarily supportive with oxygen supplementation, adequate pain control, and close respiratory monitoring 4, 2.
Consider chest CT if the patient's respiratory status deteriorates, as CT is highly sensitive for identifying the extent of pulmonary contusion and predicts the need for mechanical ventilation 1, 2.
Monitor for peak respiratory distress at 72 hours post-injury when hypoxemia and hypercarbia are typically greatest 1, 2.