C. Patent foramen ovale (PFO): Given the patient's recent history of pulmonary embolism and now a left cerebral infarction, a PFO is the most likely cause. A PFO could allow a clot to bypass the lungs and directly enter the systemic circulation, leading to a paradoxical embolism causing the cerebral infarction.

B. Carotid artery stenosis: Although less likely in a young patient without a history of atherosclerotic risk factors, carotid artery stenosis could be a cause of left cerebral infarction. The recent trauma and immobilization could potentially lead to carotid dissection or thrombosis.
A. Atrial fibrillation: This is a common cause of embolic strokes, but it would be unusual in a healthy 27-year-old without underlying heart disease. However, it cannot be ruled out without further investigation.

D. Hypertrophic cardiomyopathy: Although rare and less likely, hypertrophic cardiomyopathy could lead to atrial fibrillation or thrombi formation, increasing the risk of embolic events. It's a condition that could be deadly if missed due to its potential for sudden cardiac death.
Other cardiac sources of embolism: Conditions like cardiac tumors (e.g., myxoma), endocarditis, or other cardiomyopathies are rare but could be fatal if not diagnosed and treated promptly.

Other right-to-left shunts: Besides PFO, other congenital heart defects that allow right-to-left shunting could lead to paradoxical embolism, but these are less common and typically diagnosed earlier in life.
Vasculitis or other vasculopathies: Conditions like Takayasu arteritis or giant cell arteritis are rare and could cause cerebral infarction, but they would be unusual in this clinical context without other supporting symptoms or findings.
Coagulopathies: Underlying coagulation disorders could increase the risk of thromboembolic events, but these would typically present with a history of recurrent thromboses or other signs of coagulopathy.