Viral Pericarditis: This is often considered the most common cause of pericardial effusion, especially in the absence of other underlying conditions. Viral infections can lead to inflammation of the pericardium, resulting in fluid accumulation.

Heart Failure: Conditions leading to heart failure, such as coronary artery disease, cardiomyopathy, or valvular heart disease, can cause pericardial effusion due to increased pressure and fluid overload.
Malignancy: Metastatic cancer (e.g., lung, breast, or melanoma) and primary cardiac tumors can infiltrate the pericardium, leading to effusion.
Uremia: Patients with end-stage renal disease can develop pericardial effusion due to the accumulation of toxins.
Tuberculosis: In areas where TB is prevalent, it is a significant cause of pericardial effusion, often presenting with chronic inflammation and fluid accumulation.

Cardiac Tamponade: Although not a cause of pericardial effusion per se, it is a life-threatening complication that can arise from significant effusion. Prompt recognition and treatment are crucial.
Aortic Dissection: A type of acute aortic syndrome that can lead to pericardial effusion if the dissection involves the ascending aorta, potentially causing cardiac tamponade.
Trauma: Both penetrating and blunt trauma to the chest can cause pericardial effusion, which may be hemorrhagic and life-threatening.

Autoimmune Disorders: Conditions like lupus, rheumatoid arthritis, and scleroderma can cause pericardial effusion, though they are less common causes.
Sarcoidosis: A systemic granulomatous disease that can affect the pericardium, leading to effusion.
Hypothyroidism: Severe, untreated hypothyroidism can lead to pericardial effusion, among other cardiac complications.
Drug-Induced Pericarditis: Certain medications, such as hydralazine, procainamide, and some anticoagulants, can cause pericarditis and subsequent effusion as a rare side effect.