Congestive Heart Failure (CHF): This condition is the most common cause of both bilateral pleural effusions and pericardial effusions due to the increased pressure and fluid buildup in the heart, leading to fluid leakage into the pleural and pericardial spaces.

Metastatic Cancer: Cancers such as lung, breast, and ovarian cancer can metastasize to the pleura and pericardium, causing effusions.
Tuberculosis: A common cause of pleural and pericardial effusions, especially in endemic areas, due to the spread of the infection to these areas.
Uremia: In patients with severe kidney disease, the buildup of toxins can lead to fluid accumulation in the pleural and pericardial spaces.
Hypothyroidism: Severe, untreated hypothyroidism can lead to the accumulation of fluid in various body compartments, including the pleural and pericardial spaces.

Cardiac Tamponade: Although not a cause of pleural effusion, it's crucial to identify and treat pericardial effusions promptly to prevent cardiac tamponade, a life-threatening condition.
Pulmonary Embolism: Can cause acute right heart failure leading to both pleural and pericardial effusions, and is a medical emergency.
Aortic Dissection: Although less common, can lead to pericardial effusion and potentially pleural effusion if there's involvement of the descending aorta.

Sarcoidosis: A systemic disease that can cause inflammation and fluid accumulation in various parts of the body, including the pleura and pericardium.
Eosinophilic Granuloma with Polyangiitis (Churg-Strauss Syndrome): A rare autoimmune condition that can cause vasculitis and lead to pleural and pericardial effusions.
Familial Mediterranean Fever: A genetic disorder that can cause recurrent episodes of fever and inflammation, sometimes leading to pleural and pericardial effusions.
Whipple's Disease: A rare bacterial infection that can cause systemic symptoms, including pleural and pericardial effusions, although this is exceedingly rare.