Pericardial Cyst

A pericardial cyst is a benign, thin walled, fluid filled cyst lined by mesothelium, usually unilocular, 2 to 5 cm in diameter (rarely over 15 cm). It is uncommon (about 1 in 100,000) but is the commonest benign cyst of the mediastinum.

The usual site is the right cardiophrenic angle (about 70%), then the left cardiophrenic angle (about 20%), and uncommonly the hilum, posterior or anterior mediastinum.

Most are congenital, from failure of fusion of the mesenchymal lacunae during pericardial development, and the cyst has no communication with the pericardial cavity (a communicating sac is a pericardial diverticulum).

Acquired cysts follow inflammation, tuberculosis, rheumatic pericarditis, cardiac surgery, trauma, or infection with Echinococcus (hydatid cyst), which is important in East and southern Africa, the Mediterranean, the Middle East and South America. About three quarters are asymptomatic and are found on chest imaging.

Complications are compression of the right atrium, right ventricle, vena cava or airway, arrhythmia, tamponade, haemorrhage into the cyst, infection and rupture, and all are rare.

Pathophysiology. The cyst grows slowly, and symptoms come from mass effect on adjacent structures. A hydatid cyst grows from larval Echinococcus granulosus in the pericardium or myocardium and carries a risk of rupture, anaphylaxis, tamponade and dissemination.

• Asymptomatic in most patients.
• Atypical chest pain, dyspnoea, persistent cough, palpitations, and a sense of pressure. Positional symptoms sometimes occur.
• Signs of compression with large cysts: dullness at the base, raised venous pressure, and arrhythmia.
• Hydatid cyst: urticaria, wheeze or anaphylaxis if rupture occurs, and hepatic or pulmonary involvement. Pericardial and myocardial hydatid cysts may cause conduction disease or embolisation.

• Chest X-ray. Smooth, round or oval, well defined opacity at the cardiophrenic angle, often changing shape with posture.
• Echocardiography. Echo free, thin walled structure next to the heart with no internal flow. Transoesophageal echocardiography clarifies relations.
• CT. Water density (0 to 20 Hounsfield units), thin non-enhancing wall, no septation, with possible wall calcification.
• MRI. Low signal on T1 and high signal on T2, with no enhancement. It separates simple from complex cysts.
• Hydatid workup. Echinococcus serology (ELISA and indirect haemagglutination), abdominal and chest imaging for other cysts, and eosinophil count. Do not aspirate a suspected hydatid cyst for diagnosis, because leakage causes anaphylaxis and seeding.

Differential diagnosis.

• Pericardial diverticulum
• Bronchogenic, thymic and oesophageal duplication cysts
• Hydatid cyst
• Epicardial fat pad and Morgagni hernia
• Lymphangioma, lymphoma, thymoma, teratoma and mesothelioma
• Cardiophrenic lymph nodes
• Left ventricular, coronary or aortic aneurysm
• Loculated pleural or pericardial effusion
• Lung mass and pulmonary sequestration

• Asymptomatic cyst with typical imaging: no treatment. Repeat imaging (echocardiography, CT or MRI) at 6 to 12 months, and if the cyst is stable, review only for new symptoms.
• Symptomatic, large or enlarging cyst, or atypical features: percutaneous aspiration under ultrasound or CT control, with or without alcohol sclerosis through the catheter, in an experienced centre. Recurrence after aspiration alone is common, and the technique is avoided if hydatid disease is possible. Thoracoscopic or open excision is definitive and is preferred for large cysts, recurrence, failed aspiration, or diagnostic doubt.
• Tamponade: urgent pericardiocentesis or surgery.
• Infected cyst: drainage and intravenous antibiotics chosen by culture.
• Hydatid cyst: surgical excision without spillage, in a specialist centre, with antiparasitic cover. Albendazole 400 mg orally twice daily with a fatty meal (under 60 kg: 15 mg/kg daily in two divided doses, maximum 800 mg daily), starting at least 4 days before surgery and continuing for 1 to 3 months after. Monitor full blood count and liver enzymes every 2 weeks while on treatment. Contraindicated in pregnancy. Reduce or stop in severe liver impairment or cytopenia. Ensure resuscitation facilities, because rupture can cause anaphylaxis.

Special groups. Pregnancy: observe, with surgery only for urgent indications and no albendazole. Children: symptomatic cysts are excised.

Monitoring. Imaging at 6 to 12 months, then as symptoms dictate. After aspiration, imaging at 1 and 6 months for recurrence. After hydatid surgery, serology and imaging at 6 and 12 months, then yearly for 2 to 3 years, with liver enzymes and full blood count on albendazole.

Referral and escalation. Refer to cardiothoracic surgery for any symptomatic, enlarging or atypical cyst, and to infectious diseases for hydatid disease. Urgent for tamponade, rupture, infection, or airway or vena cava compression.