Pericardial cyst is a developmental anomaly of the pericardium, a benign cystic lesion lined by mesothelial cells. It accounts for approximately 6-7% of all mediastinal masses and is most commonly located at the right cardiophrenic angle (70%). It arises congenitally when embryonic pericardial recesses (lacunae) fail to coalesce, and may or may not communicate with the pericardial cavity. It is usually asymptomatic and discovered incidentally on chest radiography or thoracic CT. Typically diagnosed between ages 30-50, with no significant gender predilection. The cyst contents are clear, serous fluid, hence it appears as water density (0-20 HU) on CT, T1 hypointense and markedly T2 hyperintense on MRI. It shows no enhancement, which is critical for diagnosis. Large cysts may rarely cause compressive symptoms (dyspnea, chest pain). Treatment is usually unnecessary; percutaneous aspiration or surgical excision may be performed for symptomatic cases.
Age Range
25-60
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Pericardial cyst arises from a developmental defect during embryonic pericardial formation. Normally, ventral mesenchymal lacunae coalesce to form the pericardial sac; when one or more of these lacunae become sequestered from the rest of the pericardial sac, they develop as isolated cystic structures. The cyst wall has the same histological structure as the pericardial membrane, lined by a single layer of mesothelial cells with an underlying layer of fibrous connective tissue. The cyst contents consist of clear serous transudate with low protein content — hence the name 'spring water cyst.' This water-like fluid content explains the water density on CT (0-20 HU), low signal on T1 and very bright signal on T2 on MRI; contrast agent is not retained because there are no internal septa or solid components. Cyst growth is slow and dependent on osmotic gradient; hemorrhagic transformation or infection may rarely develop, which alters density/signal characteristics. It is more common on the right side (70%) because the right pleuropericardial canal closes later than the left.
A thin-walled cystic lesion at the right cardiophrenic angle with 0-20 HU water density and no enhancement is diagnostic for pericardial cyst. This location-density combination is extremely specific.
On non-contrast CT, homogeneous, well-circumscribed, round or oval cystic lesion at the right cardiophrenic angle with water density (0-20 HU). The wall is thin (<2 mm) and smooth. No internal septa, calcification, or solid components. There is usually no compressive relationship with surrounding structures. Density measurement is the most important diagnostic parameter — 0-20 HU range represents simple fluid. Size usually ranges 3-8 cm. In contact with pericardium and diaphragm.
Report Sentence
Well-circumscribed, homogeneous cystic lesion with water density (__ HU) at the right cardiophrenic angle, consistent with a pericardial cyst.
On contrast-enhanced CT, the lesion shows no enhancement. The cyst wall and internal structure demonstrate no increase in density in arterial and portal venous phases. The density difference between pre-contrast and post-contrast images remains below 10 HU. This feature proves the cyst is avascular and contains no solid components. Absence of enhancement is critical for differentiation from solid mediastinal masses such as thymoma, lymphoma, and neurogenic tumors. Very minimal wall enhancement may be seen — reflecting the minimal vascularity of the mesothelial wall.
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No significant enhancement is observed in the lesion on contrast-enhanced series; this finding supports the avascular nature of the cyst.
On T1-weighted images, the cyst is homogeneously hypointense (lower signal than muscle and liver). This low signal reflects the long T1 relaxation time of the serous fluid within the cyst. The cyst wall is usually not visible or appears as a very thin line. Homogeneous hypointensity is the most important T1 finding of an uncomplicated cyst. If T1 hyperintensity is present, proteinaceous or hemorrhagic content should be considered — this suggests a complicated pericardial cyst or an alternative diagnosis.
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The lesion demonstrates homogeneous hypointense signal on T1-weighted sequences, consistent with simple fluid content.
On T2-weighted images, the cyst is markedly hyperintense — showing signal intensity similar to CSF or urine. The signal is homogeneous without internal septa or solid components. This T2 hyperintensity confirms the cyst content as free water (simple serous fluid). The cyst wall may be visible as a thin hypointense line on T2. Contrast with surrounding mediastinal fat and cardiac structures is clearly delineated.
Report Sentence
The lesion demonstrates markedly hyperintense signal on T2-weighted sequences, isointense to CSF, consistent with simple cyst content.
On DWI, the cyst shows low signal (mild high signal may be seen due to T2 shine-through effect) but high ADC values on ADC map — there is NO true diffusion restriction. This indicates free water molecules within the cyst can move freely. Absence of diffusion restriction differentiates pericardial cyst from abscess and dense proteinaceous collections.
Report Sentence
No true diffusion restriction is observed in the lesion on diffusion-weighted sequences with high ADC values; abscess or solid component is excluded.
On echocardiography, pericardial cyst appears as an anechoic cystic lesion adjacent to the heart with posterior acoustic enhancement. Best evaluated at the right cardiophrenic angle. Wall is thin and smooth with no internal echoes. Must be differentiated from pericardial effusion — cyst is localized, effusion is diffuse. Transthoracic echocardiography (TTE) is usually sufficient but transesophageal echocardiography (TEE) may provide additional information for large cysts.
Report Sentence
An anechoic cystic lesion with posterior acoustic enhancement at the right cardiophrenic angle is seen on echocardiography, consistent with pericardial cyst.
Criteria
Communicates with pericardial cavity; may show periodic size changes
Distinct Features
May show size change with positional changes; spontaneous regression may rarely occur. Connection with pericardium may be visible as a thin channel on CT/MRI. Pericardial effusion may accompany.
Criteria
Completely separate from pericardial cavity; most common type
Distinct Features
Size is usually stable; attached to pericardium but no communication between lumens. If no size change on follow-up, no additional workup needed.
Criteria
Complicated by hemorrhage, infection, or high protein content; atypical imaging findings
Distinct Features
May show >20 HU density on CT, T1 hyperintensity, septation or wall thickening may develop. Complicated cyst can mimic solid lesions on imaging — MRI and clinical correlation are critical.
Criteria
Wide-based connection with pericardial cavity; actually a diverticulum, not a true cyst
Distinct Features
Size changes with heartbeat (pulsatile); opens to pericardium via wide neck. Pericardial effusion may accompany. Shows synchronous movement with pericardial cavity on cine MRI.
Distinguishing Feature
Bronchogenic cyst is usually subcarinal or paraesophageal in location (not at cardiophrenic angle); density may be variable (>20 HU due to proteinaceous content, sometimes hyperdense). Pericardial cyst is at the cardiophrenic angle and always water density.
Distinguishing Feature
Thymoma is a solid mass in the anterior mediastinum; soft tissue density (30-60 HU), shows enhancement. Pericardial cyst has water density and does not enhance. Thymoma is usually located more superiorly in the anterior mediastinum.
Distinguishing Feature
Thymic cyst is located in the anterior mediastinum at the thymic bed (not at cardiophrenic angle); variable size, may be multilocular. May show mild T1 hyperintensity on MRI due to proteinaceous content. Pericardial cyst is at the cardiophrenic angle, unilocular, and T1 hypointense.
Distinguishing Feature
Lipoma has fat density (-50 to -120 HU). Pericardial cyst has water density (0-20 HU). ROI measurement provides definitive differentiation — both lesions do not enhance but density values are completely different.
Urgency
surveillanceManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upPericardial cyst is a benign lesion with no malignant transformation. When typical imaging findings are present (cardiophrenic angle, water density, no enhancement), the diagnosis is definitive and biopsy is not needed. No treatment or follow-up is required for asymptomatic cases — follow-up can be discontinued after confirming no change at 6-12 months. For large or symptomatic cysts (compressive symptoms, cosmetic reasons), percutaneous aspiration or video-assisted thoracoscopic surgery (VATS) excision may be performed. Recurrence rate after aspiration can be up to 33%; surgical excision is definitive treatment. Complications (infection, hemorrhage, cardiac tamponade) are extremely rare.
Pericardial cyst is a benign lesion that generally requires no treatment. In rare cases, it may enlarge and cause cardiac compression. Size stability can be confirmed with follow-up CT or MRI. Percutaneous aspiration may be performed in symptomatic cases.