The normal pericardial cavity usually contains 25‑35 ml of fluid, and the cardiac lymph vessels drain the pericardial fluid to the left subclavicular vein via the mediastinal lymph vessels, lymph nodes, and thoracic ducts[7]. Chylopericardium is characterized by the accumulation of triglyceride-rich celiac effusion within the pericardial cavity, can be categorized into primary and secondary chylopericardium. Primary chylopericardium is more common, accounting for approximately 56% of cases[3]. Primary chylopericardium can only be diagnosed when there is a secondary etiology such as cardiothoracic surgery, trauma, radiotherapy, infection, tuberculosis, cervical mediastinal lymphangioma, multiple osseous lymphangiomas, lymphomas, and other malignant tumors, venous obstruction, and acute necrotizing pancreatitis[8–10]. The etiology and pathogenesis of primary chylopericardium remain unclear. Akamatsu et al.[11] suggested that it was related to (1) functional impairment of the branch valves with abnormal transportation of the thoracic duct and pericardial lymphatics, (2) increased pressure in the thoracic duct caused by lymphatic dilatation, (3) the presence of an abnormal transportation between the lymphatic duct and the pericardial cavity. Chylopericardium due to lymphatic malformation is rare. The disease is mainly seen in young adults, with no gender difference. The progression of the disease is slow, and some patients are asymptomatic for several years or more than ten years, and the enlargement of the heart is often found on chest X-ray during physical examination[12]. Common initial symptoms include dyspnea and cough, with other manifestations such as palpitations, chest pain, gastrointestinal symptoms, syncope, fatigue, and edema[13, 14]. A small number of patients with chronic pericardial effusion may develop cardiac tamponade due to obstructed venous return and reduced cardiac output. Physical examination often reveals typical signs of pericardial effusion such as enlarged cardiac silhouette, distant heart sounds, and paradoxical pulse, with prolonged disease course leading to enlarged liver and spleen, distended neck veins, ascites, and edema. There are no definitive diagnostic criteria for this condition, but it can be qualitatively diagnosed based on clinical presentation, echocardiographic findings, the appearance of pericardial fluid, positive Rivalta test, and chylomicron presence. We summarize previous studies and propose diagnostic criteria[3, 5]: milky white, pale yellow chylous, pale red chylous, hemorrhagic chylous, and coffee-colored appearance, triglycerides > 1.25 mmol/L or pericardial effusion triglyceride levels exceeding simultaneous blood levels with lower total cholesterol, total protein, and albumin levels compared to blood, cholesterol/triglyceride ratio < 1, negative bacterial culture or predominantly mononuclear cells with a monocyte ratio > 85%. One point for each feature, greater than 2 points for a diagnosis of chylopericardium.
Chest X-ray, echocardiography, CT and MRI are important tools in primary chylopericardium. Chest X-ray may show an enlarged cardiac shadow, and echocardiography may clarify the amount and location of pericardial effusion and localize the puncture. CT and MRI imaging can help to clarify the relationship of the thoracic duct to pericardial effusion. Radionuclide lymphoscintigraphy and CTL are also effective diagnostic tools[15]. Radionuclide lymphoscintigraphy using 99Tcm-labeled human albumin can identify the location of pericardial effusion, assess cardiac size and shape, and differentiate between pericardial effusion, cardiac enlargement, and cysts. Both radionuclide lymphoscintigraphy and CTL can determine the presence of lymphatic reflux and abnormalities around the pericardium, mediastinum, and thoracic duct, and accurately diagnose the etiology of chylous pericardial effusion. 99Tcm-DX lymphoscintigraphy is a non-invasive method for the diagnosis of this disease and can dynamically display lymphatic reflux[16].
All the cases in our study were categorized into 3 types based on the abnormal presentation of 99Tcm-DX lymphoscintigraphy: Type I (abnormal concentration), Type II (ectopic drainage), and Type III (non-imaging or transient imaging). Abnormal tracer concentration in Types I and II may be related to: (1) thoracic duct terminal obstruction causing lymphatic reflux obstruction (2) increased jugular venous angle backflow pressure leading to chyle outflow obstruction (3) Lymphatic fluid production is excessive, chylous fluid into the blood mouth is relatively narrow. 99Tcm-DX lymphatic imaging type II showed continuous development of bilateral venous angles, suggesting malformation of the thoracic duct and the possibility of double venous angular drainage with outlet obstruction. Type III, characterized by no imaging or transient imaging at the left jugular venous angle during the examination, may be due to low resolution of 99Tcm-DX lymphoscintigraphy or tracer retention in the lower limbs or leakage into the thoracoabdominal cavity, preventing reach to the thoracic duct terminal. 99Tcm-DX lymphoscintigraphy is clinically significant for identifying chylopericardium, chylothorax, and chyloperitoneum caused by thoracic duct obstruction, though it has lower resolution and less accuracy in detailing lesions compared to CTL. The high-density resolution of CTL not only reveals abnormalities of the thoracic duct and its branches, but also clearly shows abnormalities of the surrounding tissue structures, such as the degree and extent of pericardial effusion.
The results showed that the combined application of 99Tcm-DX lymphatic imaging and CTL is of great significance in the diagnosis of the location, extent and degree of systemic lymphatic abnormality in primary chylopericardium. The incidence of abnormal contrast distribution in the cervical or subclavian areas showed statistically significant differences among the different types of 99Tcm-DX lymphoscintigraphy (P = 0.000). A two-by-two comparison revealed a statistically significant difference in the distribution of contrast abnormalities in the bicervical or subclavian region, which was greater in type II than in types I and III (P = 0.000). The study demonstrated the significant diagnostic value of combining 99Tcm-DX lymphoscintigraphy with CT lymphangiography (CTL) for identifying the location, extent, and severity of primary chylopericardium and its related lymphatic anomalies. The incidence of abnormal contrast distribution in the bilateral cervical or subclavian regions showed significant differences among the groups in the 99Tcm-DX lymphoscintigraphy (P = 0.000), with Type II exhibiting a greater incidence than Types I and III. 99Tcm-DX lymphatic imaging type II suggests the presence of a double thoracic duct or right-sided thoracic duct malformation, with an abnormal distribution of contrast in the double cervical or subclavian region suggesting concomitant right cervical and subclavian lymphatic reflux, and the thoracic duct may be double stemmed or right-sided thoracic duct variant, which is consistent with the 99Tcm-DX lymphatic imaging. This study found that 34.5% of primary chylopericardium were associated with double or right-sided thoracic duct variations. There was also a correlation between 99Tcm-DX lymphoscintigraphy and CTL findings, with significant differences in the distribution of contrast in the posterior mediastinum, suggesting that this might relate to abnormal reflux, dilation, or constriction of the thoracic duct. Abnormal contrast distributions around the pericardium and the main pulmonary artery window were more prevalent in Type I compared to Type III (P = 0.009 and P = 0.011, respectively), indicating that obstruction at the terminal part of the thoracic duct and associated lymphatic abnormalities near the pericardium and the main pulmonary artery window might play a role in the pathogenesis of primary chylopericardium.CTL was instrumental in visualizing the location and distribution of abnormal lymphatic vessels, contributing to the understanding of the disease mechanism and imaging characteristics of lymphatic anomalies in primary chylopericardium.
There are limitations of this study: (1) This study is retrospective and has a small sample size. (2) This study did not include other methods of imaging examination, such as DLG and MRI, etc. The next study can include DLG and MRI examination methods for comprehensive analysis.
In summary, 99Tcm-DX lymphoscintigraphy is non-invasive, simple and repeatable imaging method. CTL can clearly show the location, degree and surrounding tissue of systemic lymphatic vessel abnormality. The combined application of the two methods is of great value for the diagnosis and pathogenesis of primary chylopericardium.