Pericardial Cyst

Etiology

Classically, a pericardial cyst is considered a congenital anomaly whereby incomplete fusion in embryogenesis leads to herniation or weakness in the pericardial sac, forming a diverticulum. This outpouching can persist as a pericardial diverticulum or form a pericardial cyst when the communication to the pericardial sac becomes obliterated. These cysts usually contain clear fluid.

Some retrospective data suggest the average diameter of these cysts is about 5.4 cm.[1] Less frequently, pericardial cysts are acquired, such as after cardiothoracic surgery, after an inflammatory process such as pericarditis or echinococcosis, post-trauma, or reportedly, in patients on chronic hemodialysis.[2][3][4] 

Epidemiology

Pericardial cysts are considered rare, with an approximate incidence of 1 in 100,000 persons and comprising an estimated 33% of all mediastinal cysts and 7% of mediastinal masses.[5] They are usually discovered as incidental findings on routine imaging and have been diagnosed in all ages, including antenatally and in patients up to 102 years of age.[6] 

Pathophysiology

Patients with pericardial cysts are mostly asymptomatic, with the discovery of reportedly up to 75% of pericardial cysts being incidentally.[1] Symptoms may occur via compression and mass effect in the remainder of patients when the cyst impinges upon or erodes into adjacent structures. This symptomatology can present with cardiac compression and subsequent retrosternal pain radiating to the shoulder, compression of the right side of the heart with a deviation of the septum, diastolic dysfunction, right ventricular outflow tract obstruction, pulmonary stenosis, mitral valve prolapse, or congestive heart failure.

Compression of the lung and hila can also occur with obstruction of the right mainstem bronchus and compression of the adjacent lobes of the lung.[7] This obstruction can cause repeated respiratory infections, cough, dyspnea, and cyanosis. In some instances, cyst infections can result in pericarditis. Rupture of the pericardial sac can also occur, causing pleuropericarditis and pneumonitis. Even more rarely, atrial fibrillation or erosion of the cyst into the SVC and right ventricular wall can occur, along with recurrent syncope.[7] There are rare reported cases of torsion at the neck of the diverticula or cyst, causing chest pain.[1] 

Histopathology

Histopathologically, a pericardial cyst has a relatively histologically simple wall of fibrous tissue lined by simple cuboidal mesothelial cells without specialized epithelium or smooth muscle cells.[8] 

History and Physical

As mentioned, patients with pericardial cysts are predominantly asymptomatic, with reportedly <25% of patients presenting with symptoms due to compression or erosion of adjacent structures. There have been reports of a large 11 x 11 cm pericardial cyst, causing substernal pain radiating to the bilateral shoulders after a long road trip, only discovered incidentally on imaging ordered to assess for pulmonary embolism.[9] 

Common symptoms are vague and can include chronic cough, chest pain, dyspnea, and retrosternal pressure. Rarely, dysrhythmias, syncope, and pneumonia can occur.[7] Exceedingly rare life-threatening complications such as pericardial tamponade have been reported, associated with pericardial cysts.[2] Physical examination typically yields no clues in the diagnosis of pericardial cysts. 

Evaluation

As mentioned earlier, clinicians diagnose most cases as incidental findings on chest radiographs, which can demonstrate a round, circumscribed mass adjacent to the heart, statistically most common at the right cardiogenic angle, with a reported incidence of 51% to 70%. They occur less commonly at the left cardiophrenic angle, with a reported incidence of 22% to 38%. Finally, mediastinal locations not adjacent to the diaphragm are approximately 8% to 11%.[10] 

Laboratory tests and electrocardiography are generally inconclusive in assessment for pericardial cysts.[1] Computerized tomography (CT) scan without contrast has been reported as the modality of choice for delineating the pericardial anatomy and subsequent diagnosis, as it can aid in precise localization and characterization. Findings typically include a single nonenhancing, thin-walled, ovoid homogenous mass without solid components. A disadvantage occurs if protein content increases (such as with bleeding), leading to errors in reporting.[7] 

Some authors suggest that echocardiography is a superior modality for delineating pericardial borders and characterizing the cyst from adjacent structures.[2] Other researchers indicate echocardiography is not a preferred method because of the narrow window for visualization, operator-dependent modality, and technical difficulties (ie, in the case of obesity). 

A cardiac MRI is recommended further to evaluate the possible compressive effects of the pericardial cysts, though this exam is costly and time-consuming. Additional errors in reporting can be seen in this modality, as well, if cyst protein content is high, thus altering signal characteristics. Pericardial cysts cannot enhance in contrast imaging of either a CT scan or MRI.[7] 

Treatment / Management

As the majority of patients are asymptomatic, treatment is usually conservative. Serial transthoracic echocardiography can assess for stability. If a patient remains asymptomatic and the cyst has not enlarged, continued surveillance and conservative management merit consideration.

If the patient becomes symptomatic or the cyst appears to be enlarging, the patient may become a candidate for surgery, mainly to prevent life-threatening emergencies and compressive effects. In the minority of those patients that become symptomatic, the patient can become a minimally invasive surgical candidate at the surgeon's discretion. These procedures can include percutaneous aspiration (recommended by the European Society of Cardiology) or ablation/ethanol sclerosis.[1]

The recurrence rate of pericardial cysts after aspiration is about 33%. There are no available data regarding adhesion formation or recurrence after alcohol sclerosis. Otherwise, surgical options include resection of the cyst via thoracotomy, sternotomy, VATS, or mediastinoscopy.[7] The recommendation for the treatment of pericardial cysts is based on observational data. As such, tailored management is necessary. 

Differential Diagnosis

Pericardial cysts may simulate pericardial fat or ventricular aneurysm on plain chest radiographs. Differential diagnoses would also include diaphragmatic tumors, such as teratoma, which one would expect to see both solid and cystic components. Lymphangioma can also be a consideration, as it would appear multilocular or multicystic. 

Morgagni hernia and eventration of the diaphragm could be additional considerations. Bronchial cysts are also possible, but one would expect to see bronchial epithelium lining the cyst on histology. Localized pericardial effusion is an additional differential in which one would expect to see fluid between the pericardium layers. Additionally, many different types of congenital cysts can be considered, such as esophageal duplication cysts or neurenteric cysts, but their typical location can sometimes differentiate these.[7][10][7]

Prognosis

The general prognosis is excellent for pericardial cysts, which is not unexpected considering that most patients are asymptomatic. Spontaneous resolution of lesions has even been reported.[11] Though exceedingly rare, life-threatening conditions can occur. In these cases, the prognosis varies and depends upon the tailored management of symptoms.

Complications

Complications from pericardial cysts are often due to compression of adjacent structures, including but not limited to the lung, esophagus, and heart. As such, symptoms are often vague and nonspecific. Rarely, complications can manifest as cyst infection, compression of the superior vena cava, and hemorrhage into the pericardial space, causing tamponade and death.[1]