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Pericardial Fat Pad Mimicking Cardiomegaly


 Pericardial Fat Pad Mimicking Cardiomegaly: Cause of Increased Cardiothoracic Ratio on Chest X-Ray


Introduction


An increased cardiothoracic ratio (CTR) on chest X-ray (CXR) is commonly interpreted as cardiomegaly. However, not all apparent cardiac enlargement reflects true cardiac pathology. One important and often overlooked cause is a pericardial fat pad, which can enlarge the cardiac silhouette without any increase in actual heart size. Recognizing this entity is essential to avoid misdiagnosis and unnecessary investigations.



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What Is a Pericardial Fat Pad?


Pericardial fat refers to adipose tissue located:


Epicardial fat: between the myocardium and visceral pericardium


Paracardial (mediastinal) fat: outside the parietal pericardium



When excessive, this fat can project over the cardiac borders on CXR, producing a falsely increased CTR.



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Why It Increases CTR on Chest X-Ray


CTR is calculated as the ratio of maximal transverse cardiac diameter to maximal thoracic diameter (normal ≤50% on PA view).


Pericardial fat pad increases CTR by:


Expanding the apparent cardiac borders


Creating smooth, symmetric enlargement of the cardiac silhouette


Mimicking global cardiomegaly despite normal chamber sizes



This is particularly misleading on:


AP films


Supine radiographs


Obese patients




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Typical Chest X-Ray Features


Smooth, globular cardiac outline


Symmetric enlargement


Clear lung fields


Normal pulmonary vasculature


No signs of heart failure (no congestion, no effusions)




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How to Differentiate From True Cardiomegaly


Feature Pericardial Fat Pad True Cardiomegaly


Cardiac chambers Normal Enlarged

Pulmonary congestion Absent Often present

Symptoms Usually asymptomatic Dyspnea, edema, fatigue

Echo findings Normal chamber size Dilated or hypertrophied chambers

CT/MRI Fat-density around heart Increased myocardial size




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Role of Echocardiography


Echocardiography is the key next step when CTR is increased:


Normal LV and RV dimensions


Normal systolic and diastolic function


Hypoechoic or echo-lucent space anteriorly (fat)


No pericardial effusion



A normal echocardiogram essentially rules out true cardiomegaly.



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CT and MRI: Definitive Diagnosis


CT chest: clearly identifies fat by low attenuation (−80 to −120 HU)


Cardiac MRI: fat appears hyperintense on T1-weighted images



These modalities confirm diagnosis when uncertainty persists.



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Common Clinical Associations


Obesity


Metabolic syndrome


Elderly patients


Chronic steroid use


Incidental finding during routine imaging



Pericardial fat volume also correlates with cardiometabolic risk, but isolated fat pad enlargement does not equal structural heart disease.



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Clinical Importance


Prevents mislabeling patients with heart disease


Avoids unnecessary cardiac medications


Reduces anxiety and downstream testing


Reinforces importance of correlating CXR with echocardiography




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Key Take-Home Points


Increased CTR on CXR is not synonymous with cardiomegaly


Pericardial fat pad is a common benign cause


Always correlate CXR findings with echocardiography


CT or MRI can confirm fat when diagnosis is unclear


Clinical context and imaging correlation are essential


🫀 Not All Cardiomegaly Is Real: Pericardial Fat Pad on Chest X-Ray


Hashtags:

#ChestXRay #Cardiomegaly #PericardialFat #Echocardiography #Cardiology #Radiology #MedicalEducation

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