Recesses of the pericardium

Imaging description The pericardium is composed of two layers: a tough fibrous outer layer, which attaches to the diaphragm, sternum, and costal cartilage, and a thin inner serous layer, which lies adjacent to the heart [1, 2]. The normal pericardium may contain 15 to 50 ml of fluid [1, 2]. On CT and MRI, the normal pericardium appears as a thin linear structure measuring less than 2 mm surrounding the heart but may not be visualized over the left ventricle, where it often becomes very thin [1, 2]. On MRI, it has low signal intensity on both T1- and T2-weighted images and is outlined by high signal intensity mediastinal and subepicardial fat [1, 2]. The pericardium extends superiorly about the main pulmonary artery, ascending aorta, and superior vena cava [3]. The serous layer of the pericardium can be divided into parietal and visceral layers [4]. As the visceral pericardium adheres to the heart and great vessels, the separation from the parietal pericardium creates recesses and sinuses that may be seen on CT or MRI [3, 4]. The transverse sinus is located just above the left atrium and posterior to the ascending aorta and main pulmonary artery (Figure 62.1) [1–3, 5]. The superior reflection of the transverse sinus is known as the superior aortic recess, which has anterior, posterior, and right lateral portions [1, 3]. On CT, the posterior portion lies directly posterior to the ascending aorta at the level of the left pulmonary artery, is of fluid attenuation, and usually has a crescent shape (Figure 62.2) [3, 5]. This recess may extend into the high right paratracheal region (Figure 62.3) [5, 6]. The oblique sinus is the posterior extension of the pericardium and lies posterior to the left atrium and anterior to the esophagus [1–3] (Figure 62.4). Recesses may also arise from the pericardial cavity proper [3]. In particular, recesses may extend along the pulmonary veins (Figure 62.5). There are also smaller pericardial recesses including posterolateral to the superior vena cava and between the inferior vena cava and coronary sinus [4].