Absence of the left pericardium: An incidental cause of leftward cardiac displacement to consider

Congenital absence of the pericardium is a rare condition with an estimated incidence of less than 1 in 10,000 and is often incidentally diagnosed when individuals undergo thoracic imaging for other reasons. ¹ , ² The condition is classified according to the location of the defect, and whether there is partial or complete absence of the pericardium. ² Although complete defects can be silent, individuals with partial defects can have symptoms such as dyspnoea when laying on one side but not the other [trepopnoea], or non‐exertional positional chest pain. ² , ³ , ⁴ Individuals may also be at risk of life‐threatening complications such as coronary artery compression or cardiac chamber herniation and strangulation, which influences their management. ² , ³ , ⁴ In addition, 30–50% of individuals with congenital absence of the pericardium have other cardiac and non‐cardiac congenital anomalies or syndromes. ² As the diagnosis can be difficult and often missed, radiologists should be aware of the condition. ⁴

Pericardial defects occur due to the failure of pleuropericardial membranes to fuse on one or both sides of the pericardium during embryological development. ² The most common defect is complete absence of the left pericardium (approximately 70% of cases), as right‐sided and bilateral defects are extremely rare. ² Direct visualisation of defects or the absence of the pericardial lining may require dedicated cardiac computed tomography (CT) or cardiac magnetic resonance imaging. However, the diagnosis can still be challenging to make, and therefore, the presence of indirect findings suggesting the absence of the pericardium should be considered. ⁴

The absence of the left pericardium can cause excessive displacement of the heart into the left hemithorax (levorotation of the heart), and in some cases, a cardiac apex that points laterally or even posteriorly. ² The chest radiograph may show flattening and elongation of the left border of the cardiac silhouette, which has been named the ‘Snoopy sign’. ⁵ Tracheal deviation does not occur despite cardiac rotation, and this finding should raise suspicion of the condition. ² Other features of complete absence of the left pericardium include interposition of lung tissue between the aortic root and the main pulmonary artery, or between the diaphragm and the base of the heart. ² , ⁴

Figure 1 demonstrates an example case of congenital absence of the left pericardium incidentally identified on contrast‐enhanced CT of the thorax, performed to rule out pulmonary embolism in an elderly male (patient A) with shortness of breath. Figures 2 and 3 demonstrate another example that was identified incidentally on contrast‐enhanced CT of the thorax, which was performed to investigate enlarged lymph nodes in a middle‐aged male (patient B). Due to leftward rotation of the heart, congenital absence of the left pericardium was suspected in both cases. This diagnosis was further supported by other associated features as described in the Figure legends. These cases highlight that awareness of the condition and its features is important, and that it should be considered when leftward cardiac displacement is seen.

Fig. 1.

Axial and sagittal contrast‐enhanced images from a CT pulmonary angiogram in an 88‐year‐old male (patient A) to rule out pulmonary embolism. The images demonstrate normal pericardium (green arrows) before an abrupt loss of the pericardium over the apical right ventricle and an absence of pericardium over the basal left ventricle (red arrows). [Colour figure can be viewed at wileyonlinelibrary.com]

Fig. 2.

AP chest radiograph of a 69‐year‐old male (patient B) demonstrating the classical ‘Snoopy sign’ due to cardiac levoposition, left heart border flattening and elongation (orange dotted line). The image also demonstrates other characteristic features such as a radiolucency separating the left ventricle and left hemidiaphragm (green arrow) and a radiolucency separating the pulmonary artery and aorta (red arrow). [Colour figure can be viewed at wileyonlinelibrary.com]

Fig. 3.

Axial and sagittal contrast‐enhanced non‐gated CT chest performed for investigation of mediastinal lymphadenopathy in a 69‐year‐old male (patient B). The images demonstrate leftward rotation of the heart into the left hemithorax, with interposition of lung parenchyma between the aorta and pulmonary artery (orange arrow, bottom right panel). In the bottom left panel, the leftward cardiac axis (red dotted arrow) is compared with the expected anatomical axis (green dotted arrow) using the axial steady‐state free‐precession cardiac magnetic resonance images. [Colour figure can be viewed at wileyonlinelibrary.com]

Data availability statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.